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227 Cards in this Set
- Front
- Back
Describe components of DNA & explain its functional relationship to RNA & protein.
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consists of a strand of alternating sugars (deoxyribose) and phosphate groups with a nitrogenous base attached to each sugar. The bases are adenine, thymine, cytosine & guanine. DNA exists in a cell as two strands twisted together to form a double helix. The two strands are held together by hydrogen bonds between their nitrogenous bases. The bases are paired in a specific, C-G. The information held in the sequence of nucleotides in DNA is the basis for synthesis of RNA and proteins in a cell.
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A mutagen that is incorporated into DNA in place of a normal base.
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Nucleoside analog
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A mutagen that causes the formation of highly reactive ions.
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Ionizing radiation
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A mutagen that alters adenine so that it base-pairs with cytosine
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Base-pair mutagen
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A mutagen that causes insertions
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frameshift mutagen
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a mutagen that causes the formation of pyrimidine dimers
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nonionizing radiation
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Transfer of DNA from a donor to a recipient cell by a bacteriophage
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transduction
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Transfer of DNA from a donor to a recipient as naked DNA in solution
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transformation
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Feedback inhibition differs from repression because feedback inhibition
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stops the action of preexisting enzymes
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Bacteria can acquire antibiotic resistance by all of the following except
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snRNP's
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Suppose you inoculate three flasks of minimal salts broth with E. coli. Flask A contains glucose. Flask B contains glucose and lactose. Flask C contains lactose. After a few hours of incubation, you test the flasks for the presence of B-galactosidase. Which flask(s) do you predict will have this enzyme?
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C
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Plamids differ from transponsons because plasmids
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are self-replicated outside the chromosomes
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Mechanism by which the presence of glucose inhibits the lac operon
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catabolite repression
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The mechanism by which lactose controls the lac operon
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induction
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Two daughter cells are most likely to inherit which one of the following from the parent cell
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a change in a nucleotide in DNA
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Which of the following is not a method of horizontal gene transfer
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binary fission
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Genetics
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the study of what genes are, how they carry information, how their information is expressed, and how they are replicated and passed to subsequent generations or other organisms
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DNA in cells exists as double-stranded helix; held together by
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hydrogen bods between specific nitrogenous base pairs: AT & CG
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A Gene
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is a segment of DNA, a sequence of nucleotides, that codes for a functional product, usually a protein
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The DNA in a cell is duplicated before
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the cell divides, so each daughter cell receives the same genetic information
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Genotype
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is the genetic composition of an organism, its entire complement of DNA
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Phenotype
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is the expression of the genes; the proteins of the cell and the properties they confer on the organism
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The DNA in a chromosome exists as
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one long double helix associated with various proteins that regulate genetic activity
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Bacterial DNA is
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circular
the chromosome of E. coli, for example, contains about 4 million base pairs and is approximately 1000 timex longer than the cell |
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Genomics
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is the molecular characterization of genomes
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Information contained in the DNA is transcribed into
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RNA and translated into proteins
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During DNA replication
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the two strands of the double helix separate at the replication fork, and each strand is used as a template by DNA ploymerases to synthesize two new strands of DNA according to the rules of nitrogenous base pairing
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The result of DNA replication is two new strands of DNA, each having
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a base sequence complementary to one of the original strands.
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Because each double-stranded DNA molecule contains
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one original and one new strand, the replication process is called semiconservative.
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DNA is synthesized in one direction designated 5'--3'. At the replication fork,
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the leading strand is synthesized continuously and the lagging strand discontinuously
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DNA ploymerase proofreads new molecules of DNA and
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removes mismatched bases before continuing DNA synthesis
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Each daughter bacterium receives a chromosome that is
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virtually identical to the parent's
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During transcription, the enzyme RNA polymerase synthesizes
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a strand of RNA from one strand of double-stranded DNA, which serves as a template
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RNA is synthesized from
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nucleotides containing the bases A, C, G, and U, which pair with the bases of the DNA strand being transcribed
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RNA polymerase binds the promoter; transcription begins at AUG; the region of DNA that is end point of transcription is the
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terminator; RNA is synthesized in the 5'--3' direction
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Translation
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is the process in which the information in the nucleotide base sequence of mRNA is used to dictate the amino acid sequence of a protein
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the mRNA associates with ribosomes, which consists of
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rRNA and protein
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Three-base segments of mRNA that specify amino acids are called
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codons
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the genetic code refers to
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the relationship among the nucleotide base sequence of DNA, the corresponding codons of mRNA, and the amino acids for which the codons code.
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the gentic code is
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degenerate; that is, most amino acids are coded for by more than one codon.
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of the 64 codons, 61 are sense condons (which code for amino acids), and
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3 are nonsense codons (which do not code for amino acids and are stop signals for translation).
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the start codon
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AUG, codes for methionine
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specific amino acids are attached to
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molecules of tRNA. Another portion of the tRNA has a base triplet called an anticodon
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the base pairing of codon and anticodon at the ribosome results in
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specific amino acids being brought to the site of protein synthesis
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the ribosome moves along the mRNA strand, as amino acids are joined to form
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a growing polypeptide; mRNA is read in the 5'--3' direction
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Translation ends when
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the ribosome reaches a stop codon on the mRNA.
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Regulating protein synthesis at the gene level is energy-efficient because
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proteins are synthesized only as they are needed.
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Constitutive enzymes
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produce products at a fixed rate. Examples are genes for the enzymes in glycolysis.
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For these gene regulatory mechanisms, the control is
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aimed at mRNA synthesis
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Repression
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controls the synthesis of one or several (repressible) enzymes
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When cells are exposed to a particular end-product,
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the synthesis of enzymes related to that product decreases.
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In the presence of certain chemicals (inducers),
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cells synthesize more enzymes. This process is called induction.
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An example of induction
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is the production of B-galactosidase by E. coli in the presence of lactose; lactose can then be metabolized.
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The formation of enzymes is determined by
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structural genes.
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In bacteria, a group of coordinately regulate structural genes with related metabolic functions, plus
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the promoter and operator sites that control their transcription, are called an operon.
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In the operon model for an inducible system, a regulatory gene codes for
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the repressor protein.
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When the inducer is absent, the repressor binds to the
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operator, and no mRNA is synthesized.
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When the inducer is present, it bind to the
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repressor so that it cannot bind to the operator; thus, mRNA is made, and enzyme synthesis is induced.
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In repressible systems, the repressor requires
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a corepressor in order to bind to the operator site; thus, the corepressor controls enzyme synthesis.
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Transcription of structural genes for catabolic enzymes (such as B-galactosidase) is induced by the absence of
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glucose. Cyclic AMP and CRP must bind to a promoter in the presence of an alternative carbohydrate.
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The presence of glucose inhibits
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the metabolism of alternative carbon sources by catabolite repression.
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A mutation
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is a change in the nitrogenous base sequence of DNA; that change causes a change in the product coded for by the mutated gene.
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Many mutations are
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neutral, some are disadvantageous, and others are beneficial.
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Types of Mutation:
A base substitution occurs when |
one base pair in DNA is replaced with a different base pair.
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Alterations in DNA can result in
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missense mutations (which cause amino acid substitutions) or nonsense mutations (which create stop codons).
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In a frameshift mutation, one or a few base pairs are
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deleted or added to DNA.
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Mutagens are
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agents in the environment that cause permanent changes in DNA.
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Spontaneous mutations
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occur without the presence of any mutagen.
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Chemical mutagens include
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base-pair mutagens, nucleoside analogs, and frameshift mutagens.
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Ionizing radiation causes
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the formation of ions and free radicals that react with DNA; base substitutions or breakage of the sugar phosphate backbone results.
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Ultraviolet (UV) radiation
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is nonionizing; it causes bonding between adjacent thymines.
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Damage to DNA caused by UV radiation can be repaired by
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enzymes that cut out and replace the damaged portion of DNA.
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Light-repair enzymes repair
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thymine dimers in the presence of visible light.
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Frequency of Mutation:
Mutation Rate is |
the probability that a gene will mutate when a cell divides; the rate is expressed as 10 to a negative power.
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Mutations usually occur randomly along a
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chromosome.
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A low rate of spontaneous mutations is beneficial in
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providing the genetic diversity needed for evolution.
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Identifying Mutants:
Mutants can be detected by |
selecting or testing for an altered phenotype.
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Positive selection involves
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the selection of mutant cells and rejection of nonmutated cells.
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Replica planting
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is used for negative selection--to detect, for example, auxotrophs that have nutritional requirements not possessed by the parent (nonmutated) cell.
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Identifying Chemical Carcinogens:
The Ames test |
is a a relatively inexpensive and rapid test for identifying possible chemical carcinogens
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The test assumes
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that a mutant cell can revert to a normal cell in the presence of a mutagen and that may mutagens are carcinogens.
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Genetic Transfer & Recombination:
Genetic Recombination |
the rearrangement of genes from separate groups of genes, usually involves DNA from different organisms; it contributes to genetic diversity.
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In crossing over, genes from two chromosomes are
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recombined into one chromosome containing some genes from each original chromosome.
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Vertical gene transfer
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occurs during reproduction when genes are passed from an organism in its offspring.
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Horizontal gene transfer in bacteria
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involves a portion of the cell's DNA being transferred from donor to recipient.
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When some of the donor's DNA has been integrated into the recipient's DNA,
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the resultant cell is call a recombinant.
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Transformation in Bacteria:
During this process, genes are transferred from |
one bacterium to another as "naked" DNA in solution.
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This process occurs naturally among
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a few genera of bacteria.
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Conjugation in Bacteria:
This process requires |
contact between living cells.
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One type of genetic donor cell is an F+;
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recipient cells are F-. F cells contain plasmids called F factors; these are transferred to the F- cells during conjugation.
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When the plasmid becomes incorporated into the chromosome, the cell is called
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an Hfr (high frequency of recombination) cell.
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During conjugation,
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an Hfr cell can transfer chromosomal DNA to an F- cell. Usually, the Hfr chromosome breaks before it is fully transferred.
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Transduction in Bacteria:
In this process, DNA is passed |
from one bacterium to another in a bacteriophage and is then incorporated into the recipient's DNA.
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In generalized transduction, any bacterial genes can be
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transferred.
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Plasmids & Transposons:
Plasmids |
are self-replicating circular molecules of DNA carrying genes that are not usually essential for the cell's survival.
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There are several types of plasmids, including
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conjugative plasmids, dissimilation plasmids, plasmids carry genes for toxins or bacteriocins, and resistance factors.
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Transposons
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are small segments of DNA that can move from one region to another region of the same chromosome or to a different chromosome or a plasmid.
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Transposons are found
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in chromosomes, in plasmids, and in the genetic material of viruses. They vary from simple (insertion sequences) to complex.
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Complex transposons can carry
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any type of gene, including antibiotic-resistance genes and are thus a natural mechanism for moving genes from one chromosome to another
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Genes & Evolution:
Diversity is the |
precondition for evolution.
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Genetic mutation and recombination provide
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a diversity of organisms, and the process of natural selection allows the growth of those best adapted to a given environment.
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What must occur for an organism to pass its genetic information on to its offspring?
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The parent must copy its own DNA and provide a copy to its offspring.
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The process of copying DNA prior to cell replication is know as
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DNA replication
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What is meant by semiconservative replication?
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the new copies of DNA contain one original strand of DNA and one new strand of DNA
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What serves as the template fro DNA replication
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each of the original DNA strands
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What is the role of DNA helicase in DNA replication?
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DNA helicase uses the energy from ATP to break the hydrogen bonds between two DNA strands, thereby "unzipping" the molecule
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The replication fork
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is the point where DNA helicase is "unzipping" the double-stranded DNA molecule.
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What is the function of stabilizing proteins?
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The hold the separated strands apart and prevent their degredation.
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The replication fork moves
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ahead of the newly synthesized DNA
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Which enzyme can synthesize new strands of DNA?
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DNA polymerase
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Why is primase essential for DNA replication?
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It provides a 3' end of the newly synthesized strand, allowing DNA polyerase to begin copying DNA
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DNA synthesis occurs in which direction?
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From 5' to 3' on both the leading and lagging strands
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How does the DNA polymerase know which nucleotide triphosphate to add to the growing strand?
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It hydrogen-bonds the nucleotide to the parental strand, pairing adenines to thymines and guanines to cytosines
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What might happen if the cell does not have RNAse?
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The newly made chromosome would consist of DNA and RNA molecules
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Which of the following statements concerning DNA replication is true?
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The leading strand of DNA replication requires only one RNA primer. The lagging strand of DNA replications requires multiple RNA primers
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What is the function of the connector proteins?
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They link the leading strand DNA polymerase and the lagging strand DNA polymerase together
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Which of the following statements regarding Okazaki fragments are true?
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They are typically 1000 nucleotides in length. They are found on the lagging strand of DNA replication.
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Place the following events of lagging strand DNA synthesis in order
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Primase adds an RNA primer.
DNA polymerase synthesizes new DNA strand in the 5' - 3' direction. RNAse removes the RNA primer. Okazaki fragments are joined together. |
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Which mutation is the least likely to be harmful to a cell?
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silent mutation
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A mutation that results in the presence of a stop codon in the middle of the genetic code is a
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nonsense mutation
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What type of mutation can change all subsequent amino acids following it?
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frameshift mutation
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A chemical that can increase the rate of mutations is called a
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mutagen
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Base pair substitutions can result in what type of mutation?
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silent, nonsense, and missense
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How frequently does an error occur in DNA replication in the absence of a mutagen?
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one error for every one billion nucleotides copied
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What is a potential source of mutations from ionizing radiation?
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Ions and free radicals resulting from ionizing radiation can break chromosomes.
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Ethidium bromide can result in
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frameshift mutations via insertion or deletion of nucleotides
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x-rays would be considered which type of mutagen
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ionizing radiation
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which of the following is an example of a nucleoside analog?
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5-bromouracil
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Enzymes known a photolyases are involved in which type of repair?
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light-repair mechanism
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How can a mismatch repair enzyme detect which strand contains the correct DNA sequence?
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The original strand will likely have a methyl group attached, while the newly mutated strand will not.
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Which of the repair mechanism requires assistance from DNA polymerase to make the correction?
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excision-repair mechanism AND mismatch-repair mechanism
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Which of the following repair mechanism does not involve the removal of nucleotides
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light-repair mechanism
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Which of the following repair mechanisms might be involved in repairing a mutation that results from exposure to UV light?
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light-repair mechanism AND excision-repair mechanism
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which of the following is a product of transcription
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all of the above
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The role of transcription is
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to copy the information stored in DNA into RNA
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which of the following is used to make ribosomes
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rRNA
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which of the following is involved in bringing amino acids to the ribosomes
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tRNA
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which of the following is the copy of DNA sequence used to make protein
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mRNA
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in general, higher levels of transcription lead to
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higher amounts of protein
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how does protein-dependent termination differ from protein-independent termination
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protein-dependent termination involves the use of a protein to end transcription
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translation is
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the process of making protein from RNA
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which of the following is involved in translation
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all of the above
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ribosomes move along the mRNA in which direction
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5' to 3'
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how many codons code for the termination of transcription
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3
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AUG codes for
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methionine
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CAU codes for
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histidine
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which of the following codes for leucine
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all of the above
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according to the chart, how many amino acids are coded for by codons
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20
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what is the order of ribosomal sites that a charged tRNA molecule passes through
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A site, P site, E site
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the anticodon sequence is found on the
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tRNA
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an amino acid is considered charged
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when it is bound to its correct tRNA
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which of the following is not a part of the initiation complex
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mRNA
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release factors
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bind to the A site AND are coded by stop codons
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which of the following are genetic elements found in an operon
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all of the above
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which of the following statements regarding operons is true
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all of the above
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according to the animation, where does the activation and repression of an operon occur
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at the operator region
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what does the inducer bind to in the lac operon system
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repressor proteins
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which genetic element codes for the repressor protein
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the regulatory gene
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which of the following statements regarding the lac operon is true?
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the repressor proteins bind to the operator, preventing RNA polymerase from transcribing the structural genes
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when is the regulatory gene transcribed?
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it is always transcribed
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whch of the following statements regarding the trp operon is true
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the trp operon is always activated unless deactivated by a repressor
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what is the role of tryptophan in the trp operon
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it activates the repressor proteins
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which of the following are genetic elements found in an operon
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all of the above
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which of the following statements regarding operons is true
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all of the above
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according to the animation, where does the activation and repression of an operon occur
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at the operator region
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what does the inducer bind to in the lac operon system
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repressor proteins
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which genetic element codes for the repressor protein
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the regulatory gene
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which of the following statements regarding the lac operon is true?
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the repressor proteins bind to the operator, preventing RNA polymerase from transcribing the structural genes
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when is the regulatory gene transcribed?
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it is always transcribed
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whch of the following statements regarding the trp operon is true
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the trp operon is always activated unless deactivated by a repressor
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what is the role of tryptophan in the trp operon
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it activates the repressor proteins
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why is the transcription of structural genes of the trp operon turned off in the presence of tryptophan
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?
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what is the target of the activated repressor protein
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the operator region of the operon
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which of the following statements is false regarding the trp operon
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the structural genes of the trp operon are transcribed only in the presence of tryptophan
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would be an example of horizontal gene transfer
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the transfer of DNA from one bacterium to another
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is NOT a type of horizontal gene transfer
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transcription
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a cell that has incorporated new DNA as part of its own is termed a
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recombinant
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cells that are naturally able to take up DNA from their environment are said to be
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competent
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why do S strains escape killing by host phagocytes?
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?
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what reason most likely explains the recovery of S strain from a mouse injected with heat-killed S strain mixed with living R strain
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the R strain picked up the S-strain DNA, enabling it to produce capsules
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generalized transduction is initiated by
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the lytic cycle of viral replication
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transduction is
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the transfer of bacterial DNA from one host to another via a bacteriophage
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the process of generalized transduction
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all of the above
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fate of a bacterium infected by a generalized transducing bacteriophage
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integration of the packaged DNA into the host chromosome
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the following happens to initiate specialized phage transduction
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prophage integrates into the host genome AND bacteriophage enters lysogeny
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the following is packaged by the bacteriophage during
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the phage DNA with some of the host DNA
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the following terms could describe the newly infected host of a specialized transducing bacteriophage
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recipient cell
recombinant cell |
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the purpose of bacterial conjugation
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to transfer DNA between two living cells
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why is E. coli considered the model of bacterial conjugation
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the process of conjugation is best characterized in E. coli
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which statement about conjugation is true
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after conjugation, each cell involved has a copy of the shared DNA
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what is unique about the DNA transferred between two cells during conjugation
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it is transferred as a single strand
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conjugation order
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recipient cells together;
pulling of the donor; transfer of the DNA Fusion of the cell membranes |
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what characteristics do F+ and F- share
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they each contain a chromosome
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following conjugation between a donor and a recipient, what cell types are present
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two F+ cells
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the fertility factor is also known as
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an F plasmid
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what DNA molecule is transferred between cells during conjugation between an F+ and an F- cell
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a single-stranded F plasmid
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put the following events of conjugation in order
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attachment of the sex pilus;
pulling of donor and recipient cells together; fusion of the cell membranes; transfer of the F factor |
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how does an F+ cell become an Hfr cell
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by integrating the F plasmid into the chromosome
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what typically results from conjugation between an Hfr cell and an F- cell
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one Hfr cell and one F- cell
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what does Hfr stand for
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high frequency of recombination
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why are F- cells unable to spread the fertility factor
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F- cells rarely receive a complete copy of the fertility factor during conjugation
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how long does it take an Hfr strain of E. Coli to transfer its complete chromosome
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100 minutes
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approximately how long would it take for the serA gene to transfer
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62 minutes
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if conjugation was allowed to be carried out for 42 minutes, which genes would be transferred to the recipient strain?
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trp
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which gene would transfer quickest during conjugation for this Hfr strain?
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fertility factor
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if gen X transferred at 99 minutes, what conclusion could you make about gene X
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Gene X is close to the fertility factor on the Hfr chromosome, but it is near the end of the chromosome
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transposons are
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DNA fragments that can move from one location in the DNA to another
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which type of transposon would contain an antibiotic resistance gene
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complex transposons
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insertion sequences are composed of
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a transposase gene flanked by inverted repeats
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a region of DNA in which the sequence of nucleotides is identical to an inverted sequence on the complementary strand is known as a(n)
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inverted repeat
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what is the function of the enzyme transposase
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all of the above
? |
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how does replicative transposition differ from cut-and-paste transposition
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replicative transposition results in multiple copies of the transposon in DNA; cut and paste transposition has only one copy
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what is unique about complex transposons
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they have two simple transposons with another DNA sequence between them
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why is complex transposon containing an antibiotic resistance gene more likely to be copied than a simple insertion sequence when the host reproduces?
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they confer a survival advantage for the host
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PCR
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rapidly increases the number of copies of a piece of DNA
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what is/are the role of dNTPs in a PCR
|
both of the above answers apply
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which of the following is not a constituent of PCR
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dUTP
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what is unique about the DNA polymerase in PCR
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it can withstand the high temperatures needed for PCR
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place the following steps of PCR in order:
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separation of strands;
annealing of primers; synthesis of new DNA |
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the device used to achieve the varying temperatures required for PCR is called a(n)
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thermocycler
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why is a temperature of 94 degrees C required during PCR
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it allows for the strands of the target DNA to separate
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which of the following statements about PCR is true
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the number of DNA double after each cycle
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event order PCR
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denature at 94 C;
prime at 60 C; extend at 72 C; repeat 30+ times |
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what is the ultimate goal of recombinant DNA technology
|
to improve the organism
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which of the following cuts DNA at specific sequences
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restriction enzyme
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why must the recipient plasmid be cut with the same restriction enzyme
|
to allow for a site in the plasmid for the donor DNA to attach
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which of the following can result once the recombinant DNA molecule has been made?
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all of the above
? |