DNA synthesis Flashcards
what are replication origins
replication origins are specific sites on a DNA where DNA replication is initiated
what are the features of a DNA helix?
two polynucleotide chains join to form a RH helix
the phosphate backbone nad sugars are on the outside of the helix while the bases are on the inside of the helix
the two strands are held together by hydrogen bonds between the bases, following the base pairing rule( adenine to thymine with double hydrogen bond AND guanine to cytosine with a triple hydrogen bond between them)
the helix has a diameter of 2nm with 10bp per turn.
the strands are antiparallel to each other. and two daughter duplexes can be formed during DNA replication
what are replication origins?
replication origins are specific sites on a DNA where DNA replication is initiated
what are replication origins recognised by?
an initiation complex.
what does DNA at the origin unwind to form?
A replication bubble.
when does DNA synthesis occur and what does it involve?
it occurs during the specific(S) phase of the cell cycle and it involves the complete unwinding of the parental DNA
how long does a bacterial cell cycle take and how many replication origins are involved?
20 to 30 mins
a single replication origin is involved.
how long does a human cell cycle take and how many replication origins are involved?
16 to 24 hour
multiple replication origins are involved.
what enzyme catalyses DNA replication?
DNA polymerase
mention the types of DNA polymerase bacterial cells have and their functions
I- repair
II- repair
III- replication
there are others whose function is to repair
mention the types of DNA polymerase human cells have and their functions
alpha-replication
beta-repair
gamma- mitochondrion
delta-replication
epsalom-replication
(plus repair & translesion polymerases)
what is the role of Telomerase
a reverse transcriptase expressed in stem and cancer cells, makes DNA at the telomere ends of chromosomes to offset DNA lost during normal replication due to the ‘end replication problem.
what are the key properties of DNA polymerase
acts in the 5’ to 3’ direction
has proofreading functions
it requires a DNA primer, DNA template, the four dNTP, and Mg2+ ions.
follows the A-T; C-G base pairing rule to make new DNA strands.
what is the role of magnesium ions in DNA replication
It plays important roles in the structure of nucleic acids and affects their interaction with proteins and other ligands.
what are building blocks for DNA
Deoxyribonucleoside triphosphate
what is the name of the fragments formed on the lagging strand by DNA polymerase
okazaki fragments
what enzyme closes the gaps between Okazaki fragments?
DNA ligase
what is the role topoisomerase
Topoisomerases remove +ve supercoils ahead of DNA replication forks-
solves the ‘DNA winding problem’
what is the role of DNA helicase
it unwinds the DNA and breaks the hydrogen bond between DNA strands for DNA replication to occur.
what is the role of primase
Primase catalyzes the synthesis of a short RNA (or DNA in some organisms) segment called a primer complementary to a DNA template.
what factors ensure that DNA replication proceeds with high fidelity
Base pairing in DNA, proof-reading by DNA
polymerase, and mismatch repair system
how many base pairs of DNA must human replicate
3x10^9
what is the error rate of replication in humans
approximately 1 in 10^8
what are examples of antibacterial drugs that inhibit replication
ciprofloxacin
levofloxacin
novobiocin
they are gyrase inhibitors
