exam 3 Flashcards
nucleic acid
biopolymer made of monomer units called nucleotides
what are nucleotides?
- nitrogenous base derived from purine or pyrimidine
- contain: pentose sugar, ribose or deoxyribose, phosphoric acid
difference between dna and rna?
no U (uracil) in DNA, no T (thymine) in RNA
nucleotides are linked by what?
phosophodiester bond between phosphate group at C-5’ and the OH on the C-3’
T pairs to
A
G pairs to
C
how many h bonds between t and a?
2
how many h bonds between g and c?
3
double helix
two antiparallel strands are coiled in a right handed manner; structure is based on xray crystallography
histone
a protein particularly rich in basic AAs (lys and arg) found in eukaryotic dna
what is chromatin?
dna molecules wound around particles of histones in a beadlike structure
structure of chromatin
each bead is a nucleosome
each nucleosome consists of
DNA wrapped around histone core
RNA
pentose unit is ribose
- single stranded (can have double stranded regions)
- pyrimidine base uracil instead of thymine
prokaryotic replication (summarized)
separation of 2 original strands and synthesis of 2 new daughter strands using originals as templates
why is replication labelled as semiconservative?
b/c each daughter dna contains one template strand and one new one
dna replication steps
- dna unwinds at origin of replication
- new chains are synthesized in both directions from origin of replication (bidirectional)
- there are TWO replication forks
- 1 origin of replication and 2 replication forks in prokaryotes
in dna replication of euks, there are several…
origins of replication and two replication forks at each origin
dna polymerase functions have the following requirements:
dTTP, dATP, dGTP, dCTP (deoxyribonucleoside triphosphates)
- Mg2+ (cofactor)
- RNA primer
dna polymerase iii is responsible for
polymerization
dna polymerase i is responsible for
the removal of primer and replacing it with DNA
dna is synthesized in a
5’ to 3’ direction
leading strand is synthesized
continuously in a 5’ to 3’ direction
lagging strand is synthesized
discontinuously (okazaki fragments) in a 5’ to 3’ direction, AWAY from the replication fork