week 8 Flashcards
Nitrogenous base linked by
phosphodiester bond
GC forms __ H bonds -Slightly ___ base pairing
AT forms __ H bonds
3
stronger
2
Always read nucleotides
from 5’ to 3’
minor grooves are ___ together
Major grooves ___ apart -Enough space for a ___ to get access to ___
minor grooves are closer together
Major grooves further apart
Enough space for a protein to get access to nucleotide
most bacterial chromosomes are
circular
Bacteria doesn’t have ____ to wrap dna, uses ____ instead
Bacteria doesn’t have histones to wrap dna, uses supercoiling instead
DNA gyrase (2)
topoisomerase
makes supercoiled DNA
supercoiling needs what and why
Requires E from atp
Makes it essentially impossible to pull apart
In most bacteria DNA is _____ supercoiled
Coiled to the ____ direction of helical shape
In most bacteria DNA is negatively supercoiled (under-wound)
Coiled to the opposite direction of helical shape
Back reaction
does it need E
releases supercoiled (requires no extra E)
each strand serves as a ____ for the new daughter strand
Each strand is the reverse ____ of the other
____ replication
each strand serves as a template for the new daughter strand
Each strand is the reverse complement of the other
Semiconservative replication
DNA polymerase
catalyze synthesis of complementary strand of DNA
dna synthesized in what direction and forms what bonds
Synthesized in 5’-3’ direction only forming phosphodiester bonds
Enzymes require (3)
Template - direct synthesis of complementary strand
Primer. DNA or RNA
dNTP (dATP, dTTP, dCTP, dGTP) - deoxynucleotide triphosphates
Why does DNA polymerase need a primer
Can elongate nucleic acid but not form it from nowhere
Replication fork
____ replication from single ori
is where DNA is unwound and strands are separated
Bidirectional replication from single ori
DnaA binds to ___
causes what?
bind to oriC (origin of repl) causing bending and separation of strands
DnaB does what?
does it need E
helicases like DnaB separate strands
Form the replication fork
Requires atp
Single stranded binding proteins bind
ssDNA to prevent strands from annealing/coming together
primase synthesizes
RNA primer
Lagging and leading strand is synthesized by
DNA polymerase III
Okazaki fragments
does it need new primers for every sequence
are short pieces of DNA synthesizes on the lagging strand
yes
e.coli has how many polymerase
which one plays more role in rep
e.coli has 5 DNA polymerase with polymerase III playing the major role in replication
DNA polymerase holoenzyme
complex of 10 proteins
Contains proofreading function
dnaQ (3)
proofreading
subunit of DNA polymerase III
Removal of mismatched base from 3’ end of growing strand by exonuclease activity of enzyme
is proofreading 100% effective?
Activity isn’t 100% effective
Mutation rates are 10^-8 to 10^-11
Depends on rate of cell replication or type of cell
one reason why mutations occur
nucleotides have other/rare forms
DNA polymerase I
removes RNA primers, fill gaps with DNA
Okazaki fragments are joined by
DNA ligase
dna ligase forms a _____ bond between 3’-___ of the ____ strand with the 5’-____ of an Okazaki fragment
dna ligase forms a phosphodiester bond between 3’-OH of the growing strand with the 5’-phosphate of an Okazaki fragment
____ proteins binds ___ sequence and prevents further replication
tus proteins binds ter sequence and prevents further replication
Topoisomerases
liberate chromosomes
Cleave DNA, thread strand through, relegate DNA
