Lecture 23 Flashcards
4 important processes in DNA replication
Unwinding of strands, initiation of replication, elongation of DNA strands being replicated, termination of replication
Are there one or many origins of replication in eukaryotes
many, because of their size
A bubble of replication is made of
two replication forks
in DNA replication, you start with one helix and end with
two helixes,two daughter DNA molecules
DNA reads in which direction and synthesizes in which direction
it reads in the 3’ to 5’, but synthesizes in the 5’ to 3’
Fragments are how many nucleotides per piece?
100
when the DNA is continuous, it is called the
leading strand
when the DNA is in bits and pieces, it is called the
lagging strand (Okazaki fragment)
replication fork
y-shaped region of replicating DNA where parental DNA strands are unwound, and DNA replication takes place
origin of replication
part in the fork (region of DNA) that has specific sequence of nucleotides and where DNA replication begins
Helicases
unwind DNA; more they unwind, the tighter they become
Topoisomerases
cut DNA strands and rejoin in loops so that they become less tight
Single Strand Binding Proteins
stabilizers that bind to the unpaired DNA strands during replication, holding them while they serve as templates
Primase
RNA polymerase + RNA nucleotides that make the primer using parental DNA as a template
the RNA primer does what for the polymerase?
leaves the 3’ end free so it can act accordingly
dATP, dCTP, dGTP, dTTP
d = deoxyribose
a replication bubble is formed when
proteins attach and separate the DNA strands
DNA polymerase III
complex of enzymes at the end of polymerase which makes the new strand, copying it from the old strand
DNA polymerase III reads and elongates in which direction?
reads 3’ to 5’, elongates 5’ to 3’
DNA polymerase III is activated from
primase giving it a short sequence of ribonucleotides
DNA polymerase I
enzyme that removes and replaces the RNA primer
ligase
an enzyme that ligates (joins) ends of DNA molecules
DNA polymerase has a function of
proofreading
mismatched nucleotides evade proofreading or occur after DNA replication because of
exposure of cells to insults such as carcinogens and UV light
mismatched nucleotide problem is fixed by
enzymes in the cell that detect and repair the DNA (130 of them)
Nucleosomes contain
H2A, H2B, H3, H4
the histone H1 attaches
to the nucleosome
Histones can be modified either through
methylation or acethylation
methylation
condensation of DNA, prevents transcription of genes
acethylation
promotes de condensation of DNA and allow transcription of genes
Levels of chromatin packing
DNA, nucleosomes, chromatin fiber, looped domains, metaphase chromosome
chromatin
complex of DNA and protein that make up eukaryotic chromosome
euchromatin
less condensed form available for transcription
heterochromatin
highly compacted, generally, not transcribed
