dna structure and replication Flashcards
name the purines
A and G
name the pyrimidines
T and C
what makes up the nucleotides
base
phosphate
sugar
what direction does the DNA strand run in?
5 prime to 3 prime
what is at the 5 prime end?
a free phosphate group
what is at the 3 prime end?
an unlinked OH group
how many bonds do G and C form?
3
how many bonds do A and T form?
2
how many rings do the purines form?
2
how many rings do the pyrimidines form?
1
what is transcription?
DNA –> RNA
what is translation?
RNA -> protein
how does DNA form nucleosomes
DNA wraps around histones which form nucleosomes
what are the core histone proteins?
H2A, H2B, H3 and H4
what does topoisomerase do?
enzyme which prevents the supercoiling of DNA during replication
what do quinolones and fluoroquinolones do?
target topoisomerase which causes DNA to supercoil and break
what are the linker histones?
H1 and H5
what type of bacteria do quinolones target?
Aerobic gram positive and negative
some anaerobic gram negative
Tuberculosis
what does Trimethoprim-sulfamethoxazole target?
nucleotide synthesis
what type of bacteria does trimethoprim-sulfamethoxazole target?
Gram positive and negative
describe how low level mistakes in the DNA replication process are corrected
editing occurs in the 3-5’ direction as DNA is made by DNA polymerase in the 5’-3’ direction
mispaired nucleotide removed and correct one added
describe base excision repair?
- cytosine is deaminated to form a uracil
- a single mispaired base
enzyme comes and removes the base and breaks the sugar-phosphate backbone - DNA polymerase adds a new base and ligase seals it
explain nucleotide excision repair
pyrimidine dimer forms (caused by radiation)
forms adduct
either 12 (bacteria) or 20 (humans) nucleotides are removed from the strand either side using helicase and nuclease
DNA polyermase and ligase replace missing segment
explain how DNA mismatch repair works
error in the DNA forms
MutS and MutL binds
finds a break in the DNA and cuts it there and removes it
DNA repaired
describe non-homologous end joining
accidental break in the DNA and forms an overhang
enzymes break away at the overhang until the strands can join together
describe homologous end joining
loss of a segment of DNA
sequence completed by copying from a second chromosome
what is the phenotype of xeroderma pigmentosum
skin cancer
UV sensitivity
neurological abnormalities
what process is affected in xeroderma pigmentosum?
nucleotide excision repair
what is the phenotype of a mutation of MutS and MutL?
colon cancer
what process is affected in a mutation of MutS and MutL?
mismatch repair
what can a defect in BRCA2 cause?
breast and ovarian cancer
what process is affected in breast and ovarian cancer?
repair by homologous recombination
what is the function of linker histones?
locks DNA into place
allows it to be condensed into chromatin
what are okazaki fragments and why are they formed?
one DNA strand goes from 5 to 3 prime
DNA polymerase cant synthesise as its reading
this strand is the lagging strand and its synthesised discontinuously
RNA primers are added at the start of every segment so DNA polymerase adds bases here
these are okazaki fragments
