DNA Replication And Repair Flashcards

(47 cards)

1
Q

What direction does DNA replication proceed?

A

5’ to 3’ direction

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2
Q

Leading strand

A

DNA is replicated in one smooth, continuous process

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3
Q

Lagging strand

A

DNA is replicated in small sections then fused together

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4
Q

Primers

A

Short section of RNA which is complementary to the template strand and contains free 3’ OH group

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5
Q

Helicase

A

Separates the DNA strands. Requires ATP.

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6
Q

What reaction does DNA polymerase catalyze?

A

Hydrolysis of PPi to 2Pi that allows the incoming nucleotide to be bound to the strand.

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7
Q

Primase

A

RNA polymerase that is required to initiate DNA synthsis

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8
Q

Okazaki Fragments

A

Short sections of primer RNA plus DNA that form on the lagging strand. Will be joined together later.

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9
Q

Replisome

A

Total proteins and enzymes required for DNA synthesis at a replication fork

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10
Q

Topoisomerases

A

Acts to prevent the extreme supercoiling of the parental helix by breaking and rejoining DNA chains. Relieves the tension ahead of the replication fork.

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11
Q

Type I topoisomerase

A

Makes a break/nick in a strand of DNA helix, passes the other strand thru the break to relax the coil. Removes 1 supercoil

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12
Q

Type II topoisomerases

A

Requires ATP. AKA DNA gyrase in E. Coli Produce break in BOTH strands of DNA. 2 supercoils are removed in one step

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13
Q

Single Stranded binding protein

A

Keeps the separated strands as single strands. Are displaced and reused as DNA is replicated

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14
Q

DNA polymerase I

A

Removes RNA primers (5’ –> 3’ exonuclease activity) and fills in gaps with dNTP that matches the exposed DNA template. Edits/proofreads the strand (3’->5’ exonuclease activity), cleaving off any unpaired 3’ terminal nucleotide

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15
Q

DNA polymerase III

A

Major replicative enzyme. Stays on the DNA molecule for long stretches of processing

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16
Q

DNA ligase

A

Enzyme that catalyzes formation of phosphodiester bond b/t 2 Okazaki fragments

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17
Q

Types of DNA mutations

A

Point mutations, insertions, deletions

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18
Q

Point mutations

A

substitution of one base for another

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19
Q

Insertion

A

Adding one or more nucleotides within a DNA sequence

20
Q

Deletions

A

Removal of one or more nucleotides with a DNA sequence

21
Q

Steps of DNA repair

A

Removal, filling of the gap, ligation

22
Q

Nucleotide excision repair

A

Removal of a group of nucleotides

23
Q

Base excision repair

A

Specific glysosylase that removes a damaged base by hydrolyzing an N-glycosidic bond

24
Q

What serves as substrates in DNA synthesis?

A

Deoxyribonucleotide triphosphates

25
What do DNA polymerases require for activity?
Primer and template
26
Ciprofloxin
Works on both Gram - and + bacteria. Effects the supercoiling of bacterial DNA gyrase
27
Replisome
All factors required for DNA synthesis
28
What 4 classes of DNA polymerase are found in the nucleus?
Alpha, beta, delt, sigma
29
Where is gamma DNA polymerase found?
mitochondria
30
What 2 classes of DNA polymerase are involved in DNA repair?
beta and sigma
31
What two chemical reactions are used to disassociate histones from DNA?
Acetylation and phosphorylation
32
What proteins dictate the phase of replication that the cell is in?
Cyclins (A and E involved in DNA synthesis)
33
What two types of agents cause DNA damage?
physical and chemical
34
What causes thymine dimers to form?
UV rays
35
Why does a thymine dimer cause disfunction in DNA?
Distorts the helix, so the DNA cannot be replicated without error
36
What is deamination?
Cytosine converts to uracil, ultimately leading to a C→T mutation
37
Single Strand break
The phosphodiester bond is broken on a single strand of DNA, is easily repaired.
38
Double strand break
2 single strand breaks occur near each other on opposite sides of the DNA. Is very hard to repair, and usually results in cell death
39
When is excision repair used?
Used to repair bulky damages to DNA
40
When is base excision repair used?
Small modifications to DNA bases
41
Postreplication repair
is known as the SOS repair, error prone repair which occurs as a last ditch effort where a random nucleotide is inserted
42
Xeroderma pigmentosum
Excision repair proteins have lost activity, so cannot repair damages, particularly those done by UV. Can have eye photosensitivity
43
Ataxia Telangiectasia
Gamma irradiation sensitivity. Usually have lymphomas, Signs: ataxia, dilation of blood vessels in the skin, chromosomal aberrations
44
Fanconi's Anemia
Have a sensitivity to cross linking. Causes leukemias. Signs: hypoplastic pancytopenia, congenital abnormalities
45
Bloom's Syndrome
Sensitivity to UV. Causes leukemias. Signs: skin photosensitivity, usually a butterfly shaped rash on the face
46
Cockayne's Syndrome
Have a sensitivity to UV. Causes various tumor cancers. Signs: neurological defects, dwarfism
47
10% of colorectal cancers are cased by what defect?
Mismatch repair is defective