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Flashcards in DNA Replication And Repair Deck (47):
1

What direction does DNA replication proceed?

5' to 3' direction

2

Leading strand

DNA is replicated in one smooth, continuous process

3

Lagging strand

DNA is replicated in small sections then fused together

4

Primers

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

5

Helicase

Separates the DNA strands. Requires ATP.

6

What reaction does DNA polymerase catalyze?

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

7

Primase

RNA polymerase that is required to initiate DNA synthsis

8

Okazaki Fragments

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

9

Replisome

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

10

Topoisomerases

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

11

Type I topoisomerase

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

12

Type II topoisomerases

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

13

Single Stranded binding protein

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

14

DNA polymerase I

Removes RNA primers (5' ā€“> 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

15

DNA polymerase III

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

16

DNA ligase

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

17

Types of DNA mutations

Point mutations, insertions, deletions

18

Point mutations

substitution of one base for another

19

Insertion

Adding one or more nucleotides within a DNA sequence

20

Deletions

Removal of one or more nucleotides with a DNA sequence

21

Steps of DNA repair

Removal, filling of the gap, ligation

22

Nucleotide excision repair

Removal of a group of nucleotides

23

Base excision repair

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

24

What serves as substrates in DNA synthesis?

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 Cā†’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