DNA synthesis Flashcards
Describe replication origins.
→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.
give an overview of the bacterial cell cycle
→ S phase
→ M phase
→ divides once every 20-30 minutes
give an overview of the mammalian cell cycle
→ G1 phase pairing DNA replication of proteins → S phase DNA replication semi conservative → G2 phase prepare for mitosis → M phase
what is the difference between the bacterial and mammalian cell cycle?
→ bacterial lasts 20-30 mins
→ mammalian is 16-24 hours long
→ bacterial only has one replication origin
→ mammalian has multiple replication origins
what are the different types of polymerases?
BACTERIA
→ I,II,III that repair
EUKARYOTIC → α replication → β replication → γ mitochondrion → δ replication (causes elongation) → ε replication (causes elongation)
what are the properties of DNA polymerase?
→ acts in a 5’ to 3’ direction
→ utilizes A-T C-G pairing to make a new strand
→ has a proof reading function
what does DNA polymerase require to function?
→ DNA template
→ primer
→ 4 dNTPs and Mg2+
how does replication occur?
→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
What are the enzymes involved in DNA synthesis and what do they do?
→ 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
Why is the error rate of DNA Polymerase so low?
→due to base pairing and proofreading/editing function of the enzyme
→due to the mismatch repair system, which corrects most of the polymerase errors.
what is the error rate of DNA polymerase?
1 in 10 ^ 8
why are DNA replication inhibitors important?
→ antibacterial,antitumor and antiviral agents
list some antibacterials
→ ciprofloxacin
→novabiocin
list antitumor drugs
→ doxorubicin
→mitoxantrone