dna replication - exam 1 Flashcards
nucleotide
phostphate gtoup, pentose sugar, nitrogenous base
5 nitrogenous bases – ACTUG
what the nucleotide is named after
deoxyribonucleic acid
dna
contains instructions used in development & functioning of all living organisms
ribonucleic acid
crucial for tkaing instructions in dna & making proteins that wn the cell
dna bases
ATGC
rna bases
AUGC
dna sugar
deoxyribose
rna sugar
ribose
dna # of strands
2, double helix
rna # of strands
1
dna location in cell
nucleus
rna location in cell
nucleus, cytosol
ATGGCTA
TACCGAT
dna
ACUGCA
UGACGU
rna
hydrogen bonds
2 bonds in TA
3 bonds in GC
genome
complete set of dna in an orgnaism
every cell in the body contains a complete set of the genome
contains all of the info needed for an organsim to develop & grow
no correlation between size of genome & complexity of organism
helicase
unwinds double helix at replication fork
single stranded binding protein
stabilize replication bubble
keep single strands from re pairing
topoisomerase
relieves supercoiling ahead of helicase
allows helicase to keep moving
dna polymerase III
makes dna strand complementary to template
but dna needs a 3’-OH to get started so it needs a primase
primase
makes a primer
now dna pol III can make dna complementary to template strand
the compl. strand is built in 5’ –> 3’ direction
dna can only build by adding nucleotides to 3’ end
primer
short strand of rna complementary to template
provides 3’-OH for dna pol III
dna polymerase I
removes primers
fills in gap w/ dna nucleotides
it cannot make the phosphdiester bond to connect dna fragments
dna ligase
makes phosphodiester bond to connect dna fragments
continous synthesis
leading strand
moving towards inside of fork
discontinous synthesis
lagging strand
moving towards open end of fork
has to keep making small strand as the fork opens up
why can’t dna syntehsis occur after primer is removed
no 3’ - OH available
what happens because the primer is removed
gap doesn’t get filled
cell hates single stranded dna
single stranded ends get chopped off
the chromosome gets shorter
telomeres
ends of chromosomes
stretches of repeated bases
do not contain genes
what happens when telomere repeats are gone
start losing genes
chromosomes fall apart (shoelace w/out aglet)
chromosomes fuse
cells die
hayflick limit
40-60 divisions before cell death
more than this & the cells start to mutate, can become harmful
telomerase
enzymes that can “fill in the gap” in cells that need to replicate over the hayflick limit
- embryo & stem cells
chromosomes maintain length upon each cell divsion
telomere & aging
telomere length correlates with age
longer telomere = longer life span
telomeres shorten w age
too much telomerase
overexpression of telomerase
expands lifespan
compromises fertility
did not lead to longer telomeres
mutations = cancer
3’ –> 5’ exonuclease activity
pol. adds incorrecct nt
pol. detects mispaired bases
uses 3’-5’ exonuclease to remove incorrect nt
nuclease
chops up nucleic acid
exonuclease
chops up nucleic acid starting at an end
3’-5’ exonuclease
chops up from 3’ end
mismatch repair system
remove/replace incorrectly pair nts, later
mismatch detacted
endonuclease cuts out mismatch
dna pol. fills in the correct nts
dna ligase makes the last phophodiester bond
endonuclease
chops up internal mistakes
excision repair system
similar to mismatch but works later
uv light can cause thymine dimer to become misshapen
endonuclease cuts out the damage
dna pol fills in the gap
ligase connects pieces
