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108 Cards in this Set
- Front
- Back
what are the three levels of structure and function of the genome
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genome
chromosome gene |
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The sum total of genetic material of a cell
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genome
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describe a chromosome
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A discrete cellular structure composed of a neatly packed DNA molecule
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describe eukaryotic chromosomes
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DNA molecule tightly wound around histone proteins
Located in the nucleus Vary in number from a few to hundreds Can occur in pairs (diploid) or singles (haploid) Appear linear |
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describe bacterial chromosomes
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Condensed and secured by means of histone like proteins
Single, circular chromosome |
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what is A certain segment of DNA that contains the necessary code to make a protein or RNA molecule
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gene
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what kinds of genes code for proteins and RNA
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structural genes
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what do regulatory genes do?
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control gene expression
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sum of all types of gene expression
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genotype
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define phenotypes
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how the expression of the genotype looks
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do all of an orgs genes in their genotype manifest all the time?
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no
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what are the basic units of DNA
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nucleotides
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what are the three types of nucleotides
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Phosphate
Deoxyribose sugar Nitrogenous base |
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what types of bonds are formed between the deoxyribose sugar and phosphate?
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covalent
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each deoxyribose sugar attaches to _____ ______
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two phosphates
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where are the covalent bonds between the sugar and phospates on the deoxyribose?
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One bond is to the 5’ carbon on deoxyribose
The other is to the 3’ carbon |
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what do the nitrogenous bases consist of?
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purines and pyrimidines
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what do the nitrogenous bases bond to?
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the 1' position of the deoxyribose sugar and each other
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what kinds of bonds form between the nitrogenous base and the deoxyribose sugar?
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covalent bonds
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what kinds of bonds form between the complementary nitrogenous bases?
describe these bonds |
hydrogen bonds
Easily broken Allow the molecule to be “unzipped” |
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Adenine always pairs with _______
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thymine
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Guanine always pairs with _______
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cytosine
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describe Antiparallel Arrangement
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One side of the helix runs in the opposite direction of the other
One helix runs from 5’ to 3’ direction The other runs from 3’ to 5’ |
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describe The Overall DNA Replication Process
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Requires the actions of 30 different enzymes
Separate the strands Copy its template Produce two new daughter molecules |
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what is DNA Replication?
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DNA to DNA
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what is transcription?
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DNA to mRNA
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what is translation?
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mRNA to protein
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Synthesis of DNA proceeds ___’ to _____’ adding new bases to a free _____’ _______group.
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5' to 3'
3' OH groups |
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Each new DNA strand is made of :
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1 parent and 1 daughter strand (see slide 20)
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what unzips the DNA helix?
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helicase
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what synthesizes an RNA primer
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Primase
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what adds bases to the new DNA chain and proofreads the chain for mistakes/
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DNA polymerase III
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what removes the primer, closes gaps, and repairs mismatches?
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DNA polymerase I
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What is responsible for the final binding of nicks in DNA during synthesis repair
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Ligase
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what is responsible for supercoiling
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gyrase
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describe the origin of DNA replication
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Denotes the of DNA synthesis
Rich in A and T Held together by only two H bonds rather than three Less energy is required to separate the two strands |
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describe the action of helicases
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Helicases bind to the DNA at the origin
Untwist the helix Break the hydrogen bonds Results in two separate strands |
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what is the Enzyme responsible for for DNA synthesis in Prokaryotes
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DNA Plymerase III
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DNA polymerase Can only add a new base to an _____ _______
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existing 3’ OH
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what is the ability to “back up” and correct mistakes made during replication called?
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exonuclease activity
Greatly reduces mutation rate |
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what is responsible for making an RNA primer that provides the 3' OH group for DNA Polymerase III?
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RNA Primase
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what removes RNA primers and replaces them with DNA
Also has exonuclease (proofreading activity) |
DNA polymerase I
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when and what do DNA ligases act?
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When the forks come full circle and meet, DNA ligases move along the lagging strand
Anneal DNA fragments together into a continuos strand. Heavily involved in the continuous production of the lagging strand |
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what is the central dogma of DNA transcription and translation
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Genetic information flows from DNA to RNA to protein
Exceptions: RNA viruses and retroviruses |
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How does RNA differ from DNA?
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Single stranded molecule
Helical form Contains uracil instead of thymine The sugar is ribose instead of deoxyribose |
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what does RNA polymerase do?
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codes DNA into RNA
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what are The Major Participants in Transcription and Translation?
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mRNA
regulatory RNAs RNA Polymerase (Codes DNA into RNA) storehouse of raw materials |
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Only _______ is translated into a protein molecule
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mRNA
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what is the first stage of gene expression
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transcription
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A gene differs from another in its ______ __ _______
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composition of triplets
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what is a triplet?
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Three consecutive bases on the DNA strand
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Each triplet represents a code for what?
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a particular amino acid
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When the triplet code is transcribed and translated, it dictates the _________________in a polypeptide chain
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type and order of amino acids
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A protein’s primary structure determines its what?
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characteristic shape and function
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what ultimately determine phenotype?
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proteins
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DNA triplets are transcribed into a series of ________ by the ___________
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codons
messenger RNA |
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Describe how Amino acids are formed
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DNA triplets are copied into mRNA codons which code for the amino acids
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what is the message in messenger RNA?
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The mRNA codons and the amino acids they specify
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what is it called when a particular amino acid can be coded for by more than a single codon
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redundancy
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what is it called when only the first two nucleotides are required to encode the correct amino acid
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wobble
thought to permit some variation or mutation without altering the message |
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what is the start codon?
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AUG
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what are the three stop codons?
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UAA
UAG UGA |
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what is the second stage of gene expression?
where does it occurs |
translation - mRNA codes for amino acids broght together on the ribosmes
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what are the first three stages of translation?
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initiation, elongation, termination
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describe tRNA
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Also a copy of a specific region of DNA
It is uniform in length (75-95 nucleotides long) Cloverleaf shape Bottom loop of the cloverleaf exposes a triplet (the anticodon) that designates the specificity of the tRNA and complements mRNA’s codons |
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For each of the 20 amino acids there is at least one specialized type of ______to carry it
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tRNA
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describe the what happens after transcription
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after mRNA has been transcripted, it leaves the DNA transcription site
it is transported to the ribosomes in the cytoplasm ribosomal subunits have sites to hold the mRNA and tRNA |
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describe the steps of protein synthesis at the ribosome
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small subunit binds to the 5’ end of the mRNA
A sequence know as the Shine-Delgarno sequence in the mRNA binds the 16srRNA sequence - Large subunit docks with the small subunit, Start codon AUG initiates With the mRNA message in place on the ribosome, the tRNAs the enter with their amino acids The complementary tRNA carrying its corresponding amino acid, meets with the mRNA code, tRNA is released thru E site and leaves its amino acid |
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.
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describe simply the sequence of events from DNA to protein.
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DNA codes for mRNA
mRNA transferred to ribosome tRNA carries in amino acids and meets with complementary codes of mRNA tRNA leaves ribosome, leaving amino acid behind the amino acids are bound into a polypeptide chain which is released from the ribosome by release factors after the termination codon is reached (nonsense codons that don't code for a tRNA) |
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..
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..
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what enzyme is responsible for mRNA transcription?
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RNA polymerase
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Before it is released from the ribosome, the polypeptide chain starts to _____ _____ ____to achieve its biologically active ______ ______
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fold upon itself
tertiary conformation |
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polypeptide chains Join with other proteins to form ______ ______of structure
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quaternary levels
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what is an operon?
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Prokaryotes organize collections of genes into operons
Coordinated set of genes regulated as a single unit |
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what is an inducible operon?
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Inducible- the operon is turned on by the substrate of the enzyme for which the structural genes code
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what is a repressible operon?
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Repressible- contain genes coding for anabolic enzymes; several genes in a series are turned off by the product synthesized by the enzyme
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three things to know about protein synthesis
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ribosomes are the site of p.s.
tRNA brings in amino acids the anti codon on fRNA matches with an mRNA codon to determine which amino acid gets brought in. |
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what is the Best understood cell system for explaining control through genetic induction
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the Lactose operon
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three features of the lactose operon
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the regulator
the promoter the operator |
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describe the regulator
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a gene that codes for a protein capable of repressing the operon (a Repressor)
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describe the promotor
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recognized by RNA polymerase
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describe the operator
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a sequence that acts as an on/off switch for transcription
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what happens when there is no substrate (lactose)?
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the Repressor will grab on to the gene strand and prevent RNA polymerase from working (negative feedback)
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what happens when there is substrate
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the presence of lactose turns the operon on - the repressor is bound to the lactose inducer, allowing more lactase to be produced to digest the lactose. (positive feedback)
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the lactose operon is a model of ________ gene regulation
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inducible
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describe the repressible operon
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Normally the operon is in the “on” mode and will be turned “off” only when the nutrient is no longer required
The excess nutrient serves as a corepressor needed to block the action of the operon Example, arg operon (negative feedback) |
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describe the arg operon
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when you have enough arg. the arginine turns on the repressor - interacts with it to allow it to clamp onto the gene and stop the transcription
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define mutation
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when phenotypic changes are due to changes in the genotype
An alteration in the nitrogen base sequence of DNA |
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wild type
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Wild type: an organism that exhibits a natural, non-mutated characteristic
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mutant strain
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Mutant strain: when a microorganism bears a mutation
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what are the causes of mutations
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Spontaneous mutation: random change in the DNA arising from errors in replication
Induced mutation: results from exposure to known mutagens |
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what are point mutations?
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involve addition, deletion, or substitution of single bases
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what are the 4 types of point mutations?
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missense mutation
nonsense mutation silent mutation back-mutation |
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describe missense mutations
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Missense mutation: any change in the code that leads to placement of a different amino acid
Can create a faulty, nonfunctional protein Can produce a protein that functions in a different manner Can cause no significant alteration inI protein function |
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describe nonsense mutation
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changes a normal codon into a stop codon
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describe a silent mutation
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alters a base but does not change the amino acid and thus has no effect
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describe a back-mutation
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when a gene that has undergone mutation reverses to its original base composition
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describe frameshift mutations
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Frameshift mutations: mutations that occur when one or more bases are inserted into or deleted from a newly synthesized DNA strand
Changes the reading frame of the mRNA Nearly always result in a nonfunctional protein |
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what are the three means of genetic recombination in bacteria
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conjugation
transformation transduction |
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describe conjugation
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bacterial "sex"
requires cell to cell contact, usually through a pilus f+ donor cell donates genetic material (plasmid copy) into the f- recipient cell. |
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describe transformation
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living cell uptakes naked DNA from other dead cells
doesn't require cell to cell contact |
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describe trnsduction
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virally mediated horizontal DNA transfer
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