molecular biology Flashcards
describe formation of chromatin
negatively charged DNA loops twice around positively charged histone octamer to form a nucleosome bead
what gives the histone octamer it’s positive charge?
arginine and lysine
which histones are present in the histone octamer?
2 x each: H2A, H2B, H3, H4
what is H1?
H1 is the only histone not in the octamer, it is responsible for tying beads together in a string
describe heterochromatin; transcription?
highly condensed form
transcriptionally inactive due to steric hindrance
describe euchromatin; transcription?
less condensed form
transcriptionally active
what is the consequence of DNA methylation? which bases are methylated?
parent/template strand is methylated during DNA replication allowing for mismatch repair enzymes to distinguish between old and new strands; cytosine and adenine can be methylated
role of histone methylation
inactivates DNA transcription
role of histone acetylation
allows for DNA uncoiling/transcription
Purines = # of rings
PUR Adenine and guanine
2 rings
pyrimidines = # of rings
PY Cytosine, uracil, thymine
1 ring
how do complementary DNA strands base pair?
A-T (2 H bonds)
C-G (3 H bonds)
DNA with higher ___ content will have a higher melting point
C-G
Amino acids required for purine synthesis
Glycine
Aspartate
Glutamate
nucleoside =
base + ribose sugar
nucleotide =
base + ribose sugar + phosphate
what type of bond links phosphate to sugar?
3’-5’ phosphodiester bond
Helicase
unwinds DNA template at replication fork by breaking H bonds
Single-Stranded binding proteins
stabilize strands to prevent reannealing and protect from degradation
DNA topoisomerase
creates “nicks” in the helix to relieve supercoiling during replication
drugs that inhibits prokaryotic DNA topoisomerase II (DNA gyrase)?
floroquinolones
drug that inhibits eukaryotic topoisomerase?
etopiside (cancer drug)
why must an RNA primer be added first?
RNA primer is required because DNA polymerase cannot initiate a strand, it can only add on and lengthen a strand
enzyme that adds primer
primase
DNA polymerases in prokaryotes
III and I
DNA polymerases in eukaryotes
alpha, delta
2 roles of DNA polymerase III
- synthesizes DNA 5’ - 3’
- exonuclease activity 3’-5’ allowing for proofreading
role of DNA polymerase I
same as pol III plus excises RNA primer with 5’ - 3’ exonuclease activity and fills in the gap
what removes primer in eukaryotes?
RNase H
what fills in the gap left by the primer in eukaryotes?
DNA pol
what enzyme is responsible for joining Okazaki fragments together?
DNA ligase
why do prokaryotes not require telomerase
circular DNA
why is proofreading important in DNA replication?
yields “high fidelity” DNA product
leading strand is synthesized ___, ___ the fork
continuously, toward
lagging strand is synthesized ___, ___ the fork
discontinuosuly, away from
nucleotide excision repair occurs during-
G1
steps in nucleotide excision repair (3)
1- endonucleases remove damaged bases
2- DNA polymerase fills in gap
3- ligase seals
common defect that uses nucleotide excision repair
thymine dimer formation secondary to UV light exposure