DNA replication Flashcards
How is the structure of the double helix described?
right handed helix
What is a nucleoside vs a nucleotide
nucleoside = base and the sugar
nucleotide = base, sugar and a phosphate
Name the 5 nucleotides (UCATG)
adenosine
cytidine
guanosine
thymidine
uridine
Name for base + ribose sugar
ribonucleic acid
what is an NTP
nucleotide triphosphate
what is a dNTP
deoxynucleotide triphosphate
what are the purines?
adenine and guanine
larger structure with two rings
what are the pyrimidines?
cytosine and thymine and uracil
how does the numbering of carbons work for the sugars
1 starts at the carbon attached to the base
how are DNA/RNA molecules polar?
5’ end is negative due to PO4^3-
3’ end has hydroxyl group where the O is delta negative and H is delta plus
how does polymerisation work
new base added to 3’ end of chain via phosphodiester bond
how are the bases arranged in the double helix
stacked up and pointing the same way
how is DNA replication initiated?
RNA primers (later replaced with DNA)
DNA cannot be synthesised de novo
DNA primase role
assembles as catalyses the synthesis of short RNA primers from NTPs on the DNA template
structure of incoming dNTP being added to newly synthesised strand
deoxyribonucleoside triphosphate
PPPi on 5’ carbon
how is DNA replication discontinuous
leading and lagging strands
lagging strand is synthesised discontinuously forming okazaki fragments that each start with an RNA primer
what are single stranded binding proteins
proteins that prevent ssDNA from base pairing with the other template strand
what is the sliding clamp
complex of proteins that keeps DNA polymerase from falling off the strand
it is assembled at the replication fork by a clamp-loader complex
it ensures efficient replication
which enzyme joins up discontinuities where RNA primers were
DNA ligase
why does DNA supercoiling occur
DNA is under tension as the replication form forms so it coils up in front of the fork
liable to break
how is DNA tension solved
supercoiling relieves some tension
topoisomerases relieve the tension by cutting the DNA and allowing it to unwind
allows DNA to rotate freely
2 types of topoisomerases
one makes a single strand cut
other makes a double strand cut
risk of double stranded cuts
chromosomal translocation
proof reading mechanism
proof reading function in the DNA polymerase
mismatch of nucleotides causes a discontinuity
in the active site where there is a base mismatch, the whole strand gets pushed from the polymerase domain into the proof reading domain where there is an exonuclease active site that snips off the last added nucleotide
strand flipped back to polymerase domain
