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GN 421 Final > Quiz 12 > Flashcards

Quiz 12 Flashcards

(72 cards)

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1
Q

During the first step of translation elongation, an aminoacyl-tRNA dictated by the next codon in the mRNA binds to which site in the ribosome?

A

A site

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2
Q

What is required for the first step in translation elongation?

A

EF-Tu and GTP

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3
Q

What happens during the second elongation step of translation?

A

Peptide bond formation when the growing peptide chain is transferred from the tRNA in the P site to the new amino acid attached to its tRNA in the A site

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4
Q

What is required for the second step in translation elongation?

A

Peptidyl transferase

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5
Q

During the third step of translation elongation, what is translocated?

A

The mRNA with its peptidyl-tRNA attached in the A site moves one codons length to the P site

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6
Q

What is true for suppressor tRNAs regarding the relationship between the anticodon and a stop codon?

A

The anticodon is complementary to a stop codon

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7
Q

What binds to amber, opal, and ochre codons?

A

Release factors

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8
Q

What do the first and third steps of translation have in common with translation release factors and IF-2 dissociation from the translation initiation complex?

A

GTP

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9
Q

If your brain cells divided once in the last 3 months and one of your red blood cells divided 10 times, how many more mutations would you expect in your red blood cells?

A

27

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10
Q

DNA replication is:

A

Semi-conservative

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11
Q

Which DNA strand is synthesized discontinuously?

A

The lagging strand

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12
Q

During DNA replication, which bacterial polymerase removes RNA primers and replaces them with the appropriate DNA sequence?

A

DNA polymerase I

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13
Q

What is the function of the clamp loader of DNA polymerase III?

A

It loads the clamp onto the DNA and core polymerase

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14
Q

What are the 2 major activities of the primosome that functions during DNA replication?

A

Priming and Helicase

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15
Q

Which factor in E. Coli is most similar in function to eukaryotic PCNA?

A

The beta clamp

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16
Q

To coordinate DNA replication, the beta subunit of DNA polymerase III binds to:

A

The core complex and DNA

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17
Q

Which subunit of DNA polymerase III coordinates replication of the leading and lagging strands by keeping the two core polymerases together?

A

tau

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18
Q

What is the signal that stimulates the gamma complex to unload the beta clamp from the DNA during replication?

A

The polymerase bumps into an Okazaki fragment

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19
Q

Which type of cells have active telomerase?

A

Cancerous cells

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20
Q

What is the difference between DNA damage and mutation?

A

If repair works, DNA damage does not lead to mutation

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21
Q

What is the most difficult type of DNA damage to repair?

A

Double-stranded breaks

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22
Q

Which type of DNA repair utilizes DNA polymerase I?

A

Excision repair

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23
Q

Which enzymes and factors coordinate recombinational repair in cells?

A

Those that also carry out homologous recombination

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24
Q

Is recombination more useful in a rapidly changing environment or a stable environment?

A

Rapidly changing

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25
Which mechanism is most likely to introduce mutations in DNA?
Non-homologous end joining
26
Which results in greater genetic diversity: crossover recombination or non-crossover recombination?
Crossover recombination
27
Which factors are required for step 1 of translation elongation?
EF-Tu and GTP
28
Which factors are required for step 2 of translation elongation?
Peptidyl transferase
29
Which factors are required for step 3 of translation elongation?
EF-G and GTP
30
Which rRNA may be the peptidyl transferase?
23 rRNA
31
How does translation terminate?
Translation terminates when the ribosome encounters an amber, ochre or opal stop codon within the mRNA
32
What is "stop codon suppression"?
When a stop codon is interpreted as a sense codon during translation, overcoming termination signals
33
What is suppressor tRNA?
Mutant tRNA that functions at stop codons to allow translation to continue
34
What are the 3 prokaryotic release factors and their functions?
1. ) RF1: recognizes UAA or UAG 2. ) RF2: recognizes UGA or UAA 3. ) RF3: ribosome-dependent GTPase binds GTP and helps other 2 RFs binds to ribosome
35
What are the 2 eukaryotic release factors and their functions?
1. ) eRF-1: can recognize all 3 stop codons unlike either of 2 prokaryotic RFs which only recognize 2; performs same role as both RF1 and RF2 2. ) eRF-3: performs role of bacterial RF3
36
What is one of the most important activities of genes?
Replication
37
Name 4 factors that can contribute to DNA damage
1. ) Chemicals 2. ) Radiation from the environment 3. ) Thermal accidents 4. ) Reactive molecules
38
How are mutation rates measured in prokaryotes?
Measure the mutation rate of the gene required to utilize lactose
39
How are mutation rates measured in eukaryotes?
Compare the amino acid sequences of the same proteins in several species
40
What are the 4 properties of DNA replication?
1. ) Semiconservative 2. ) Half discontinuous 3. ) Requires RNA primers 4. ) Usually bidirectional
41
What is the role of helicase in DNA replication?
Unwinds DNA helix at replicating fork
42
What is the role of single stranded binding proteins in DNA replication?
Prevents reannealing, protects ssDNA from degradation by enzymes in the cell, and stimulates DNA polymerase
43
What is the role of the primosome during DNA replication?
Makes primers for a replicating DNA; repeatedly primes Okazaki fragment synthesis to build lagging strand
44
What are the 3 enzymatic activities of DNA polymerase I and how is each used?
1. ) DNA polymerization: adds nucleotides one by one to DNA strand 2. ) 3’ to 5’ exonuclease activity: proofreading 3. ) 5’ to 3’ exonuclease activity: DNA repair
45
What is the role of DNA polymerase I?
Removes primers and joins nascent DNA fragments to fill in gap
46
What is the role of DNA polymerase II?
Needed for replication
47
What are the 4 major subunits of DNA polymerase III and what are their functions?
1) Core: DNA polymerase, 3’-5’ exonuclease, stimulates epsilon exonuclease 2) Tau subunit: dimerizes core and binds gamma complex 3) Beta clamp: sliding clamp that hold enzyme onto template 4) Gamma complex (clamp loader): helps beta subunit join preinitiation complex
48
What is the speed of DNA replication in E. Coli?
750 nt/sec
49
What is the origin of replication?
DNA site at which DNA replication begins and is essential for proper replication to occur
50
What is the direction of helicase movement on the lagging strand template and its role?
Helicase moves in the 5’ to 3’ direction on the lagging strand template during replication (same direction as the replication fork) Anchors the primosome for priming Okazaki fragments
51
How do replication forks move?
Many replication forks move simultaneously to replicate a chromosome
52
How does the speed of replication in eukaryotes compare to prokaryotes?
Replication is slower in eukaryotes and it takes about 8 hours for DNA replication
53
Which type of chromatin is replicated first?
Open chromatin is replicated before highly condensed chromatin
54
What is the role of the alpha polymerase?
Priming of replication of both strands
55
What is the role of the delta polymerase?
Elongates both strands (most similar to DNA polymerase III)
56
What is the role of the beta and epsilon polymerases?
DNA repair
57
What is the role of the gamma polymerase?
Replicates the mitochondrial DNA
58
What makes polymerases more processive?
Association with PCNA (in eukaryotes) and the beta clamp (in prokaryotes) make polymerases more processive
59
What does the sliding beta clamp bind?
The sliding (beta) clamp binds both the core complex and DNA to make the polymerase processive
60
What is the role of the tau subunit in dimerization?
The tau subunit holds two polymerase subunits together, serving as a dimerizing agent for the core enzyme
61
What is the function of the clamp loader?
The clamp loader helps the beta subunit of the holoenzyme join the preinitiation complex (provided by the gamma complex) so that the sliding clamp can hold the enzyme onto the template
62
How do electrophiles damage DNA?
Electrophiles can attack negatively charged regions of DNA and damage it
63
What is excision repair?
Removing damaged bases and then filling in the correct bases
64
What are the functions of the RecA protein?
Involved in both recombination repair and error-prone SOS bypass Nick allows it to create a new tail that finds region of homology and pairs with the gap in the other DNA
65
What are the two ways that ds breaks are repaired in eukaryotes?
Homologous recombination and non-homologous end joining
66
What is the importance of homologous recombination?
Creates genetic variation for natural selection
67
What are the major steps of homologous recombination?
1. ) Pairing of 2 homologous DNAs 2. ) Breaking of 2 homologous DNA strands 3. ) Re-forming phosphodiester bonds to join homologous strands 4. ) Breaking the other 2 strands and joining them
68
What is the difference between noncrossover and crossover recombination?
Crossover: nick the opposite strands, exchange occurs a long way down the chromosome Noncrossover: nick the same strands, only a small amount is exchanged
69
When does a Holliday junction form?
After the 2 strands have exchange and DNA ligase has sealed new intermolecular phosphodiester bonds
70
What is the importance of dsDNA breaks?
They are processed as a first step in generating meiotic crossovers and stimulate homologous recombination of DNA
71
What is the importance of homologous recombination?
It has evolved into a broader mechanism that allows population of organisms to genetic adapt more quickly to their environment
72
How can ds break repair be used to manipulate the genome?
Certain researchers are exploiting DSB repair to engineer genomic changes in cells from bacteria to mammals

GN 421 Final (5 decks)

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