Lecture 8 (Ex.2) DNA Replication & Repair

Question 1

What three elements are required for the eukaryotic DNA replication?

Answer 1

Telomere, centromere, origin of replication

Question 2

Portions of the mitotic spindle attach to what part of the chromosome?

Answer 2

The centromere

Question 3

During which phase are chromosomes duplicated?

Answer 3

Interphase

Question 4

Telomeres

Answer 4

Form special caps at each chromosome end. They contain special nucleotide sequences that enable the chromosome ends to be replicated.

Question 5

What are the functions of the telomere?

Answer 5

• Prevent misrecognition as broken DNA

- Contribute to chromosome stability.

Question 6

What are the implications of chromosomal shortening?

Answer 6

Aging. Chromosomal instability, which leads to abnormal fusions/gene arrangements which can lead to cancer.

Question 7

DNA replication is _______

Answer 7

Semiconservative. One intact parent strand is passed onto each daughter cell. Errors in DNA replication are apparent as mismatches occur

Question 8

What did the Meselson-Stahl experiment show?

Answer 8

That DNA replication is not conservative. They attached heavy nitrogen isotopes to DNA. It was either dispersed or semi-conservative. It was later realized to be semi-conservative

Question 9

Who discovered that DNA replication is semiconservative?

Answer 9

Meselson and Stahl

Question 10

When does DNA replication occur in the cell cycle?

Answer 10

DNA replication occurs in S phase

Question 11

Replication Origins

Answer 11

Have regions rich in A-T sequences

Question 12

How many origins of replication do bacterial genomes have?

Answer 12

Only one

Question 13

How many origins of replication do eukaryotic cells have?

Answer 13

10,000 origins

Question 14

Core component of DNA replication machinery

Answer 14

DNA Polymerase

Question 15

To which end does DNA polymerase catalyze the new DNA strand

Answer 15

To the -OH group of the 3’ end. It catalyzes a phosphodiester bond

Question 16

In what state do the nucleotides come into the replication site?

Answer 16

They come as high energy nucleotide triphosphates. This provides energy for polymerization

Question 17

In what direction is DNA synthesized?

Answer 17

from 5’ to 3’

Question 18

How many errors does DNA polymerase commit?

Answer 18

DNA polymerase is self-correcting. It makes one error every 10^7 bps

Question 19

DNA polymerase and proofreading

Answer 19

DNA polymerase has proofreading activity in the 3’ to 5’ direction. Can correct mistake using a nuclease that cleaves the phosphodiester backbone. Occurs as DNA is being synthesized.

Question 20

True or false. DNA proofreading and polymerization are carried out by two different enzymes?

Answer 20

False. Polymerization and proofreading are carried out by ONE enzyme. These activities, however, occur at different domains of this enzyme

Question 21

Why does DNA have to be synthesized in the 5’ to 3’ direction?

Answer 21

Besides needing the -OH group to synthesize a phosphodiester bond with the incoming nucleotide triphosphate, proofreading corrections can only occur id DNA is synthesized from 5 to 3

Question 22

What happens in a hypothetical 3’ to 5’ strand growth?

Answer 22

Reaction does not proceed because no high energy bond would be cleaved

Question 23

Is the DNA replication fork symmetrical?

Answer 23

No.

Question 24

Who discovered telomerase and the mechanism by which telomeres protect the chromosomes

Answer 24

Elizabeth Blackburn, Carol Greider, Jack Szostak

Question 25

Where does the cell cycle begin?

Answer 25

At the S phase. S phase is when DNA is replicated

Question 26

Primase

Answer 26

RNA polymerase-an enzyme that makes RNA using a DNA template. RNA/DNA duplex is known as a heterodimer

Question 27

What removes the RNA primers? How is it able to recognize the sequence that must be removed?

Answer 27

Nuclease. It is able to recognize the DNA/RNA duplex

Question 28

What is the composition of telomerase?

Answer 28

Part protein and part RNA. It recognizes the repeats and adds more repeats every time the cell replicates

Question 29

How many base pairs does primase require to synthesize 10 base pair primer

Answer 29

~20

Question 30

Deamination

Answer 30

When a amino group is lost from cytosine and is thus converted to Uracil nitrogenous base

Question 31

True or False. For homologous recombination to take place, it is required that the sequence similarity be perfect.

Answer 31

False. Requires extensive stretches of sequence similarity, but it does not have to be perfect.