Lec 15 DNA Replication & Repair

Question 1

DNA replication
How does base pairing work

Answer 1

both strands used as templates
semiconservative

Question 2

DNA replication origins
the positions at which the double stranded DNA is first open for replication. what is its span?

Answer 2

100 base pairs

Question 3

DNA replication origins
the positions at which the double stranded DNA is first open for replication. what type of proteins do sequences attract?

Answer 3

initiator proteins

Question 4

DNA replication origins
the positions at which the double stranded DNA is first open for replication. What type of sequences do they prefer and why

Answer 4

sequences with fewer hydrogen bonds and easy to open

Question 5

DNA replication origins
the positions at which the double stranded DNA is first open for replication. at which base pairs?

Answer 5

often A-T rich stretches of DNA

Question 6

Does eukaryotes or prokaryotes have multiple replication origins and how many?

Answer 6

Multiple replication origins in eukaryotes
10,000 in human genomes but only one in bacteria

Question 7

Explain replication forks

Answer 7

two replication forks are formed at each replication origin
move in both directions

Question 8

how fast are replication forks

Answer 8

move at a rate of 1000 bp/sec in bacteria and 100 bp/sec in human

Question 9

Which strand grows continuously

Answer 9

leading strand

Question 10

which strand grows discontinuously and what is this called?

Answer 10

lagging strand
Okazaki fragments

Question 11

What does helicase do?

Answer 11

unzips the double helix ahead

Question 12

what does single strand DNA binding protein do

Answer 12

prevent DNA from re-forming base pairs

Question 13

what do DNA primase do and how long

Answer 13

make primers (10 bases long) for DNA replication

Question 14

what does DNA polymerase (3) do

Answer 14

adds nucleotides to the 3’ end of a growing DNA

Question 15

What direction does DNA synthesis go

Answer 15

goes unidirectionally (5’->3’)

Question 16

what does DNA polymerase 1 do

Answer 16

replaces the RNA primers with DNA

Question 17

what does DNA ligase do

Answer 17

joins the Okazaki fragments

Question 18

what are the ends of chromosomes called

Answer 18

telomeres

Question 19

Replication at chromosome ends
telomers contain what repetitive base pair?

Answer 19

contain repetitive 6 base pair DNA sequence which is TTAGGG

Question 20

how long are telomeres

Answer 20

10-15 kb long

Question 21

when do telomeres become shorter

Answer 21

after each DNA replication

Question 22

What do telomerase complex consist of and what do they do?

Answer 22

Telomerase complex consists of reverse transcriptase and telomere RNA which can add multiple copies of the repeats to the ends and slow down shortening of telomere

Question 23

If telomerase complex activity is low what does it result in?

Answer 23

aged cells

Question 24

If telomerase complex activity is high, what does it result in?

Answer 24

cancer cells

Question 25

If there is a replication mistake what repairs it?

Answer 25

repaired by the 3’->5’ exonuclease activity of DNA polymerase (3)

Question 26

what does un-repaired mutations cause

Answer 26

can cause disease ex: sickle cell anemia

Question 27

What are the consequences of DNA damage caused by chemical reactions

Answer 27

deamination- point mutation
depurination- deletion

Question 28

What is the T-T dimer caused by UV radiation

Answer 28

T-T dimer: covalent bond between two thymine’s

Question 29

explain Replication Process 5 steps

Answer 29

open DNA double helix
build primers which are RNA
assemble complementary strand (DNA synthesis)
replace RNA primers with DNA nucleotides
Join Okazaki fragments (200 bp long)

Question 30

What is this and how does it work?

Answer 30

This is replication origin

Question 31

what is depurination

Answer 31

purine is removed
purine is 2 ring with N base (A&G)
entire genomic nitrogenous base is gone
water req

Question 32

how many base pair on chromosome

Answer 32

5 cm/0.34 nm/bp= 15X10^7 bp