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Kaplan USMLE Review > DNA Replication and Repair > Flashcards

DNA Replication and Repair Flashcards

1
Q

What is semiconservative replication?

A

it is when each parental strand is used as a template for the replication of a new DNA strand

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2
Q

When are sister chromatids separated in eukaryotes?

A

mitosis

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3
Q

How many origin of replications do you find in prokaryotes when discussing DNA replication?

A

one

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4
Q

How does DNA polymerase initiate strand synthesis?

A

It can’t initiate strand synthesis on it’s own

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5
Q

What allow DNA polymerase to to prevent errors during DNA replication?

A

It has 3’ - 5’ exonuclease activity

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6
Q

What is the specific action of helicase?

A

It breaks the H-bonds holding the base pairs together

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7
Q

What is the reason for single strand binding proteins?(2 points)

A

they prevent reassociation of DNA and destruction of DNA from nucleases

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8
Q

What is the main DNA polymerase in the DNA replication process in prokaryotes

A

DNA polymerase III

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9
Q

What is the leading strand?

A

the newly synthesize strand during DNA replication. It is the strand which is usually synthesized towards the replication fork.

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10
Q

What is the lagging strand?

A

a strand of DNA that is synthesized discontinuously during DNA replication forming Okazaki fragments. These strands are synthesized away from the replication fork.

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11
Q

What is the direction of synthesis by DNA polymerase?

A

5’-3’

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12
Q

What removes the RNA primers during DNA replication in eukaryotes?

A

RNAaseH

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13
Q

What fills in the gaps during DNA replication?

A

DNA polymerase

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14
Q

What is the action of DNA polymerase I?(2 points)

A

It removes the primers having 5’ exonuclease activity and synthesizes at 5’ Okazaki fragments

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15
Q

What is the action of DNA ligase?

A

it seals the nick at Okazaki fragments

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16
Q

What is the action of DNA gyrase?

A

it introduces negative supercoils by nicking both strands of DNA to overcome the formation of the positive supercoils

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17
Q

In eukaryotes, what is the action of DNA polymerase α and δ?(2 points)

A

they work together synthesizing the leading and the lagging strand

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18
Q

What is the action of DNA polymerase γ in eukaryotes??

A

they synthesize mitochondrial DNA

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19
Q

What is the action of DNA polymerase β and ε in eukaryotes?

A

they participate primarily in DNA repair

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20
Q

What DNA polymerase can substitute for DNA polymerase δ in certain cases?

A

DNA ε

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21
Q

What is the action of DNA polymerase δ in eukaryotes?

A

works together with DNA polymerase α to synthesize both the leading and the lagging strands of DNA

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22
Q

What are receptive sequences at the end of liner DNA molecule?

A

telomeres

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23
Q

What DNA polymerase in eukaryotes can synthesize at the 5’ end?

A

none of them

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24
Q

How does replication of telomeres take place?

A

Telomerase

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25
What special type of activity does telomerase has?
hTRT or reverse transcriptase activity
26
Levofloxacin, Ciprofloxacin, Moxifloxacin are the most active against what specific type of bacteria?(2 points)
aerobic gram negative bacteria
27
What is the action of levoflxcin, ciprofloxacin and moxifloxacin?
they block the activity of topoisomerase II in prokaryotes or DNA gyrase in eukaryotes
28
How is AZT a good treatment for patients with HIV?
It impedes the activity of the reverse transcriptase found in HIV
29
What specific type of enzyme is reverse transcriptase?
It is an RNA dependent DNA polymerase
30
What direction is the movement of DNA polymerase α and δ during DNA synthesis?
towards the replication fork
31
What is the direction of lagging strand synthesis in DNA replication?
away from the replication fork
32
What gene encodes a protein that prevents a cell with damaged DNA from entering the S phase?
p53 gene
33
Inactivation or deletion of the p53 gene is associated with what syndrome?
Li Fraumen syndrome
34
What gene encodes a kinase essential for p53 activity?
ATM gene
35
How is ATM gene affected in ataxia telangiectasia?
It is inactivated
36
The inactivation of the ATM gene in ataxia telangiectasia has what characteristic features when it comes to the presentation of the patient?(2 points)
hypersensitivity to x-rays and predisposition to lymphomas
37
The mutation of the BRCA-1 gene is affected in what cancers?(3)
breast, prostate and ovarian cancer
38
The mutation of the BRCA-2 gene is affected in what cancer?
breast cancer
39
What is the role of the Rb gene?(3 points)
a negative regulator of the cell by its ability to bind to the EF transcription which prevents the transcription of genes needed for the S phase
40
What phase in the life cycle of a cell does most DNA repair take place?
G1 phase
41
What phase does mismatch repair take place?
G2 phase
42
UV radiation damage causing thymine dimers is repaired during what phase of the cell cycle most of the time?
G1
43
UV radiation causing thymine dimers is repaired by what repair enzymes using what activity?(3 points)
Excision endonuclease, DNA polymerase and DNA ligase
44
Mismatched base pairs during DNA replication are usually repaired in what phase of the cell cycle?
G2
45
Mismatched base pairs during DNA replication are usually repaired by what enzymes?(2 points)
DNA ligase and DNA polymerase
46
What is deficient in patients with Xeroderma pigmentosum?
excision endonuclease activity
47
What is deficient in patients who don't seem to have the ability to repair DNA mismatches?
A defective hMSH2 of hMSH1 gene
48
What is HNPCC?
Hereditary nonpolyposis colorectal cancer
49
Cytosine deamination as a result of spontaneous heat introduction is repaired during what phase of the cell cycle?
G1
50
Cytosine deamination as a result of spontaneous event/heat introduction is repaired by what enzymes using what type or recognition/excision enzyme?(3 points)
Repaired by DNA ligase and DNA polymerase. Uracil glyclylase AP endonuclease
51
UV light induces what type of DNA damage?
thymine dimers
52
How does the excision endonuclease remove the dimer?
It makes nicks in the phosphodiester backbone of the damaged strand on both sides of the thymine dimer and removes the defective oligonucleotide
53
Cytosine deamination due to a spontaneous event/heat introduction, is repaired during the G1 phase. What enzyme removes the uracil that forms after the removal of the amino group?
Uracil glycolyase enzyme removes the uracil
54
What enzyme subsequently removes the damaged sequences from the DNA after the uracil glycolyase removes the uracil group?
AP endonuclease
55
What enzymes synthesize the missing DNA stands after any DNA repair has taken place and seals the nick in the repaired strand?
DNA ligase and DNA polymerase
56
What important gene controls entry into the S-phase?(2 points)
p53 and Rb
57
Xeroderma pigmentosum patients are deficient in what enzyme?
exicision endonuclease enzyme
58
What type of genetic inheritance for Xeroderma pigmentosum patients?
autosomal recessive
59
How can Xeroderma pigmentosum be diagnosed?
measurement of the relevant excision endonucease enzyme in white blood cells
60
What genes are defected in patients with Hereditary Nonpolyposis Colorectal Cancer?
hMSH1 and hMSH2 gene are defective
61
HNPCC patients are known to have what characteristic feature doctors use a diagnostic tool when looking at the DNA base sequences in certain somatic cell expressing the defective gene?
microsatellite instability
62
What is micro satellite instability?
Short tandem repeats of sequences, di, tri and tetra nucleotide repeats dispersed throughout the DNA usually in noncoding regions.

Kaplan USMLE Review (5 decks)

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