DNA Replication

Question 1

DNA of different molecular weights are separated using the following method?

Answer 1

Cesium chloride density gradient centrifugation

Question 2

What model of DNA is the correct model?

Answer 2

Semi-conservative model. Each daughter contains one parental and one daughter strand

Question 3

Which enzyme catalyzes the formation of a phosphodiester bond between the 3’ hydroxyl group or one nucleotide and the 5’ phosphate of an adjacent one?

Answer 3

DNA-dependent DNA-polymerase

Question 4

In the nucleotide addition reaction by DNA polymerase, the 2’-hydroxyl attacks the alpha phosphate from the adjacent nucleotide. T/F?

Answer 4

False

Question 5

What direction are chains synthesized?

Answer 5

5’ –> 3’

Question 6

Where does DNA copying start?

Answer 6

At origin of replication

Question 7

Does DNA replication start in more than one place?

Answer 7

In bacterial cells no, in eukaryotic cells YES (10,000+ in humans). Starts at replication origins. Ends at terminus of replication.

Question 8

Does DNA replication go in one direction or in two directions?

Answer 8

Bidirectional so 2

Question 9

Does bidirectional DNA replication proceed continuously?

Answer 9

One strand is continuous (leading), the other is discontinuous (lagging). The lagging strands are OKAZAKI fragments.

Question 10

What are autonomously replicating sequences (ARS)?

Answer 10

Multiple origins of replications. Multiple origins means less characterized (eukaryotes).

Question 11

What enzymes are involved in bacteria replication?

Answer 11

DnaA- binds 9-mer sequences, bends DNA, breaks hydrogen bonds

DnaB- helicase that uses ATP to break hydrogen bonds of complementary bases to separate strands and unwind helix

DnaC- carries DnaB to helix

Question 12

What enzymes are required only for initiation of bacterial replication?

Answer 12

DnaA and DnaC

Question 13

What enzyme is required throughout process of replication?

Answer 13

DnaB, SSB, and topoisomerases

Question 14

What else is needed for DNA replication?

Answer 14

A primer created by PRIMASE an RNA polymerase

Question 15

DNA dependent DNA polymerase I function

Answer 15

Repairs enzymes and excise and replace mismatch nucleotides (fill gaps).

Question 16

DNA dependent DNA polymerase II function

Answer 16

Repairs enzymes

Question 17

DNA dependent DNA polymerase III function

Answer 17

Major DNA replicase involved in replicating bacterial genome

Question 18

DNA dependent DNA polymerase IV and V

Answer 18

Primarily repair functions in SOS response (major DNA damage)

Question 19

What is a holoenzyme?

Answer 19

Multiprotein complex in which a core enzyme is associated with the additional components needed for full function

Question 20

How many copies of DNA Pol III are in the replisome?

Answer 20

2 (sometimes 3) at each replication fork. 1 copy elongates in same progression as fork progression (leading strand) and one elongates discontinuously in opposing direction (lagging strand).

Question 21

Activities of DNA polymerase I?

Answer 21

1. 5’-3’ exonuclease activity that removes RNA primers.
2. 5’-3’ polymerase activity that adds DNA nucleotides to 3’ end of DNA segment

Question 22

What enzyme seals the gap between DNA segments?

Answer 22

DNA ligase

Question 23

How many protein subunits are included in DNA polymerase III holoenzyme?

Answer 23

11 including 2 Pol III core polymerases

Question 24

What is DNA proofreading?

Answer 24

Correct occasional errors that occur because tautomers pair with the wrong patterns.

Question 25

What are tautomers?

Answer 25

DNA nucleotide bases that convert to alternative structures. Different base pairing preferences. MOST COMMON FORM OF REPLICATION ERROR

Question 26

What happens to a mismatched base pair on a daughter strand?

Answer 26

Displaced into the 3'-to-5' exonuclease site of the enzyme. 3' end returns to polymerase active site and incorporation of new nucleotides resumes.

Question 27

Steps:

Answer 27

1. separate strands 2. add RNA primers 3. polymerize DNA from RNA 4. remove RNA primers 5. Fill in the gaps by extending DNA from 5' ends

Question 28

What are telomeres?

Answer 28

Repetitive sequences at the end of chromosomes that ensure incomplete chromosome replication does not affect vital genes. Synthesized by telomerase.

Question 29

Telomerase parts

Answer 29

1. RNA= template for copying to synthesize the DNA telomere sequences 2. Protein part

Question 30

What kind of polymerase is telomerase?

Answer 30

RNA-directed DNA-polymerase

Question 31

Steps of telomerase:

Answer 31

1. uses it's RNA component to synthesize complementary DNA in short bursts 2. DNA polymerase completes the lagging strand

Question 32

What is the relationship between telomeres, aging and cancer?

Answer 32

Chromosome stability, cell longevity, and reproductive success. active in germ-line cells and some stem cells

Question 33

What happens to reactivation of telomerase?

Answer 33

Lead to aging cells that continue to proliferate

Question 34

During DNA replication, the following strands are synthesized/extended in the 5' to 3' direction?

Answer 34

Both leading and lagging

Question 35

Which activity of the DNA pol I is used for RNA primer removal in prokaryotes?

Answer 35

5'-3' exonuclease