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33 Cards in this Set
- Front
- Back
DNA contains many different genes that are transcribed into different:
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mRNAs, tRNAs, and rRNAs
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An RNA molecule is:
a double helix OR usually single-stranded |
usually single-stranded
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An mRNA molecule is produced by ________.
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transcription
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Each codon calls for a specific:
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amino acid
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Anticodons pair with ______.
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mRNA codons
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______ are base sequences that must be removed before a pre-mRNA molecule can be translated.
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introns
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_______ are the parts that are still in the mRNA when it has translated into protein.
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exons
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Transcription is initiated at a _________.
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promoter
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What three key respects makes transcription different from DNA replication?
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1. only ONE region of ONE DNA strand is used as a template.
2. instead of DNA polymerases, the type of enzyme known as RNA polymerase catalyzes nucleotide additions to a growing RNA strand. 3. at the end of transcription there is a single, free strand of RNA nucleotides, not a double helix |
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During gene transcription, adenine base-pairs with ______, and guanine with _______.
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uracil
cytosine |
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_______ are the only molecules that carry protein-building instructions from DNA into the cytoplasm.
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mRNAs
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Ribosomes are composed of what 2 things?
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rRNA and proteins
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Each kind of tRNA has a(n) _______ that is complementary to an mRNA _______.
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anticodon
codon |
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Enzymes, which can restrict bacteriophage growth in a host cell, are now called:
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restriction enzymes
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What is a genome?
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all of the DNA in a haploid number of chromosomes for a species
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Restriction enzymes cut DNA at a specific sequence.
What is the difference between blunt and sticky ends? |
*sticky: a restriction fragment's single-stranded tail can base-pair w/ a complementary tail of any other DNA fragment or molecule cut by the same restriction enzyme = this will form a recombinant DNA molecule sealed by DNA ligase
*blunt: ATGTCA TACAGT (nothing hanging off) |
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What is a plasmid?
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a very small circle of extra DNA that has just a few genes and that gets replicated along with the bacterial chromosome
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Explain the process to make a DNA clone.
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(before cell division, replication enzymes replicated the plasmid, so a cell can hold many identical copies of foreign DNA)
in research laboratories, foreign DNA typically is inserted into a plasmid for replication -the outcome is a DNA clone, b/c bacterial cells have made many identical, "cloned" copies of it |
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A DNA strand "copied" from a mature mRNA transcript is called:
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cDNA (complementary DNA)
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______________ catalyzes transcription in reverse.
Explain. |
Reverse transcriptase
-this enzyme from RNA viruses builds a complementary DNA strand on an mRNA transcript -then other enzymes remove the RNA from the mRNA-cDNA molecule and substitute a complementary DNA strand = the outcome is double-stranded cDNA |
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The polymerase chain reaction, widely known as PCR, is another way to _______ fragments of chromosomal DNA or cDNA
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amplify
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What are primers?
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*used in polymerase chain reaction
-synthetic, short nucleotide sequences, ten to 30 or so nucleotides long, that can base-pair w/ complementary sequences in DNA -DNA polymerases recognize them as START tags |
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Explain the PCR process. (amplifying DNA)
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*at the beginning of each temperature cycle, the 2 strands of all molecules of DNA in the mixture unwind from each other
*primers become positioned on exposed nucleotides at targeted sites according to base-pairing rules -DNA polymerases recognize the primers as START tags and assemble complementary sequences on the strands = this doubles the number of identical DNA fragments |
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PCR is far more rapid than ________ _________.
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cloning methods
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What do researchers use now to learn the sequence of cloned DNA or PCR-amplified DNA in only a few hours?
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automated DNA sequencing
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Standard nucleotides include dATP, dTTP, dCTP, and dGTP.
What is the importance of the modified versions of nucleotides in automated DNA sequencing? |
represented as T*, C*, A*, and G*
*ddNTP = dideoxydNTP = no 3'-OH which his required to have for DNA polymerase -each modified version is labeled with a molecule that fluoresces a certain color when it passes through a laser beam -every time one of these modified nucleotides get incorporated into a growing DNA strand, it arrests DNA synthesis |
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After the primer binds with its complementary sequence, DNA polymerase synthesizes a new DNA strand. Suppose the polymerase encounters a T in a DNA template strand. What 2 things might happen?
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-it will catalyze the base-pairing of either A or A* to it
*if A is added to the new strand, replication will continue *if A* is added to the new strand, replication will stop; the modified nucleotide will block addition of any more nucleotides to that strand |
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Because either a standard or a modified nucleotide could be added at every exposed base, the new strands end at _________ locations in the sequence.
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different
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What is the role of the automated DNA sequencer?
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*separates the sets of fragments by gel electrophoresis
-b/c the fragments all have a modified nucleotide at the 3' end, each set fluoresces a certain color as it passes through a laser beam -automated sequencer detects the color and indicates which nucleotide is on the end of the fragments in each set -it assembles the information from all nucleotides in the sample, and in this way it reveals the entire DNA sequence |
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A mixed collection of bacteria that contain different cloned DNA fragments is called:
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a gene library
-used when you want to isolate a gene from all others in a genome |
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What is a probe?
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a very short stretch of DNA labeled with a radioisotope so that it can be distinguished from other DNA molecules in a given sample
-part of the probe must be able to base-pair with some portion of the gene of interest |
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Any base-pairing that takes place between sequences of DNA (or RNA) from different sources is called:
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nucleic acid hybridization
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What are the 5 steps for the screening for genes?
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1.Grow the bacterial colonies on suitable medium in a petri plate.
2.Place a nylon filter over the colonies and lift some cells off. 3.Place the filter in a solution to disrupt the cells but leave DNA sticking to the filter. 4.Add a radioactively-labeled probe DNA to the filter where it will bind to the DNA fragments of complementary sequence. 5.Expose the filter to x-ray film to locate the gene of interest, which will be in the same location as the cells in the petri plate. |