DNA replication

Question 1

Semiconservative:

Answer 1

DNA replication uses each parental strand as a template for the daughter strands. Half
the parental DNA is conserved in each daughter strand.

Question 2

bidirectional:

Answer 2

replication begins at a site of origin and simultaneously moves out in both directions from this point

Question 3

Okasaki fragments:

Answer 3

the short fragments formed by the synthesis of the lagging strand begins from another
primer as the helix unwinds

Question 4

Origin

Answer 4

sites beginning replication (single on prokaryotes and multiple on eukaryotes)

Question 5

replication fork

Answer 5

sites where dan synthesis occurs

Question 6

Origin binding proteins

Answer 6

recognize and bind to origins of replication, which are AT rich sequences.
-Helicases: unwind the double helix

Question 7

Helicase

Answer 7

unwind the double helix

Question 8

single strand binding proteins (SSB):

Answer 8

bind to each single strand of DNA and hold it in a single stranded conformation

Question 9

Primase

Answer 9

DNA dependent RNA poly that cat. the rxn forming RNA primer (10 nucleotides) but copying the parental DNA strand

Question 10

-DNA polymerase I and III:

Answer 10

Prokaryotic DNA replication is carried out by two DNA polymerases: DNA Pol I and Pol
III.

Question 11

DNA poly III

Answer 11

DNA Pol III is the major replicative enzyme because it has a sliding clamp that keeps it attached to the DNA template over a long distance. Thus, DNA Pol III has much higher processivity than DNA Pol I.

Question 12

DNA poly I

Answer 12

DNA Pol I performs clean-up function during DNA replication and repair. DNA Pol I mediates replacement of RNA primers with DNA through its 5’-to-3’ exonuclease activity and 5’-to-3’ DNA polymerase activity.

Question 13

DNA ligase

Answer 13

an enzyme that catalyzes formation of phosphodiester bonds between a 3’-hydroxyl group and a 5’-phosphate group of two polynucleotide chains; join the Okazaki fragments

Question 14

Sliding clamp

Answer 14

keeps DNA poly 3 attached to DNA template over long distance

Question 15

topoisomerases

Answer 15

acts to prevent the extreme supercoiling of parental helix that would result as a consequence of unwinding at a replication fork

breaks and rejoins DNA chains

Question 16

DNA gyrase

Answer 16

a topoisomerase inhibited by quinolones, is found mostly in prokaryotes

Question 17

Telomerase

Answer 17

has a reverse transcriptase activity and carries its own RNA template, in order to restore the ends of chromosomes (telomeres) in human cancer and stem cells

Question 18

Reverse Transcriptase

Answer 18

catalyzes synthesis of DNA from an RNA template (Retroviruses contain RNA as their genetic material. The retroviral RNA serves as a template for synthesis of DNA by reverse transcriptase)

Question 19

leading strand

Answer 19

continuous

Question 20

lagging strand

Answer 20

discontinuous

Question 21

How does DNA Poly create phosphodiester bonds

during addition of dNTP

Answer 21

DNA polymerase catalyze nucleotide addition at the 3’ hydroxyl end of RNA primer and growing DNA chain . This means that new strands can only grow/elongate in the 5’ - 3’ direction

Question 22

DNA synthesis occurs in

Answer 22

3’ to 5’ direction

Question 23

errors during replication are corrected

Answer 23

3’ to 5’ exonuclease proofreading

Question 24

end replication problem

Answer 24

leading strand can be synthesized until the end, but the lagging strand cannot.
An RNA primer is needed to begin synthesis of each lagging strand, but there is nothing for this piece to attach to at the end of DNA. Therefore, the last section of the lagging strand cannot be synthesized and the telomeres get shorter as the cell replicates its genomes and divides. The cells eventually become so short that they signal for cell death (which is a normal process)

Question 25

Solution to end replication problem

Answer 25

Telomerase is RNA dependent DNA poly that maintains chromosomal ends by copying the telomeric repeat sequence from an RNA template. Telomerase activity is repressed in normal somatic cells.

Question 26

Replication origins are:

Answer 26

1. uniqueDNA segments with multiple short repeats
2. recognized by multimeric origin binding proteins
3. usually rich in A=T base pairs

Question 27

SSB in bacteria= ______ in humans

function?

Answer 27

RPA

protect the exposed single stranded DNA

Question 28

DNA Poly I has _____

Answer 28

5’ to 3’ endonuclease activity that removes the RNA primer

and then fills the gap by copying DNA 5’ to 3’

Question 29

distributive polymerase

Answer 29

dissociates from DNA easily

Question 30

Processive Polymerase

Answer 30

holds on to DNA via sliding clamp

Question 31

eukaryotic DNA Pol δ sliding clamp

Answer 31

PCNA

Question 32

______ is the sliding clamp of prokaryotic DNA Pol III

Answer 32

β-subunit

Question 33

Eukaryotic origin binding protein

Answer 33

ORC

Question 34

eukaryotic Helicase

Answer 34

MCM

Question 35

eukarytic single stranded DNA binding protein

Answer 35

RPA

Question 36

eukaryotic sliding clamp

Answer 36

PCNA

Question 37

eukaryotic clamp loader

Answer 37

RFC

Question 38

eukaryotic Polymerases

Answer 38

DNA Pol δ & Pol ε

DNA Pol α

Question 39

Eukaryotic primase

Answer 39

Pri-S

Pri L

Question 40

AZT targets

Answer 40

HIV reverse trasncriptase

Question 41

Acyclovir targets

Answer 41

Viral DNA polymerase
Herpes Simplex Virus
Varicella Zoster Virus

Question 42

Quinolones targets

Answer 42

bacterial DNA gyrase

Question 43

stem cells and cancer cells have

Answer 43

increased telomerase activity