DNA synthesis

Question 1

Describe replication origins.

Answer 1

→DNA replication is initiated at specific sites on DNA called replication origins.

→These origins are recognised by an initiation complex.

→DNA at the origin unwinds to form a replication bubble and allow access to the replication machinery.

Question 2

give an overview of the bacterial cell cycle

Answer 2

→ S phase
→ M phase
→ divides once every 20-30 minutes

Question 3

give an overview of the mammalian cell cycle

Answer 3

→ G1 phase 
pairing DNA 
replication of proteins
→ S phase
DNA replication
semi conservative
→ G2 phase
prepare for mitosis 
→ M phase

Question 4

what is the difference between the bacterial and mammalian cell cycle?

Answer 4

→ bacterial lasts 20-30 mins
→ mammalian is 16-24 hours long
→ bacterial only has one replication origin
→ mammalian has multiple replication origins

Question 5

what are the different types of polymerases?

Answer 5

BACTERIA
→ I,II,III that repair

EUKARYOTIC 
→ α replication 
→ β replication 
→ γ mitochondrion 
→ δ replication (causes elongation) 
→ ε replication (causes elongation)

Question 6

what are the properties of DNA polymerase?

Answer 6

→ acts in a 5’ to 3’ direction
→ utilizes A-T C-G pairing to make a new strand
→ has a proof reading function

Question 7

what does DNA polymerase require to function?

Answer 7

→ DNA template
→ primer
→ 4 dNTPs and Mg2+

Question 8

how does replication occur?

Answer 8

→DNA unwinds the helix by breaking the hydrogen bonds

→ when DNA unwinds the strand it creates negative supercoils

→topoisomerase II relieves the stress and tension created from the -ve supercoils by adding +ve supercoils

→single stranded binding proteins bind to the DNA which helps keep the strands apart so they don’t reanneal and helps protect them from degradation by nucleases

→a primer is laid down by RNA primase at the 5’ end of both strands

→The leading strand only needs one primer as the synthesis is continuous

→ the lagging strand needs more than one primer as the synthesis is discontinuous because it copies away from the replication fork as it opens

→ the okazaki fragments are joined by DNA ligase

Question 9

What are the enzymes involved in DNA synthesis and what do they do?

Answer 9

→ HELICASE - separates the base pairs producing single strands

→ TOPOISOMERASE - gets rid of coils in DNA that helicase caused

→ PRIMASE - lays down RNA so DNA polymerase knows where to start replicating

→ DNA BINDING PROTEINS - stabilize the single stranded DNA and prevent is reannealing

→ REPLICATIVE DNA POLYMERASE - copies the parental strand

→ REPAIR DNA POLYMERASE - repair the fragments and takes out the RNA so it will be a full DNA strand

→ DNA LIGASE - joins the okazaki fragments together

Question 10

Why is the error rate of DNA Polymerase so low?

Answer 10

→due to base pairing and proofreading/editing function of the enzyme

→due to the mismatch repair system, which corrects most of the polymerase errors.

Question 11

what is the error rate of DNA polymerase?

Answer 11

1 in 10 ^ 8

Question 12

why are DNA replication inhibitors important?

Answer 12

→ antibacterial,antitumor and antiviral agents

Question 13

list some antibacterials

Answer 13

→ ciprofloxacin

→novabiocin

Question 14

list antitumor drugs

Answer 14

→ doxorubicin

→mitoxantrone