CH 6 Flashcards
In Eukaryotes, DNA is stored in the
nucleus
Chromatin
Complex of DNA and proteins, keeps it from getting tangled
Chromosome
Chromatin stored in condensed shapes
The ends of Eurkaryotic chromosomes are…
Telomeres - caps that protect them
TTAGGG repeats
Replication origin
where replication begins
Centromere
area where microtubules attach during cell division
Bacterial Chromosomes
-Circular
-located in nucleoid
-single replication origin
Plasmids
-smaller circular pieces of DNA
-can encode useful traits like anti-biotic
resistance
*distinct from chromosomal DNA
What holds bases in DNA together
hydrogen bonds
Base Pair
set of two complimentary nucleotide bases
-purines (A, G) pair with pyrimidines (C, T, U)
Nucleotide composition
One phosphate group, Nitrogen base, 5 Carbon sugar
Nucleoside di and triphosphates do…
carry energy in their bonds
di and triphosphates combine w other groups to form
coenzymes
can also be used as small intracellular signaling molecules
key difference between RNA and DNA
RNA has an extra OH on 5C sugar
what bonds form nucleic acid polymers
phosphodiester bonds
synthesis of DNA or RNA is driven by
ATP hydroylsis
Specific sequences where initiator proteins bind…
break hydrogen bonds between strands
DNA polymerase function
synthesizes DNA using parent strand as a template
Growth direction
5’ –> 3’
what attaches a base pair
nucleoside triphosphate pairs with base in the template strand, DNA polymerase catalyzes the covalent linkage
DNA Primers are made of
short lengths of RNA
Primer
short sequence of nucleotides
Primase
RNA polymerase that binds to DNA in replication fork to synthesize a primer
Sequence of replication
Primase makes RNA primer
DNA poly binds to RNA/DNA double strand
DNA poly extends RNA primer w/ DNA
Nicks are sealed by…
Ligase
DNA polymerase is self correcting…
Proofreading allows a mispaired nucleotide to be removed
For proofreading to occur, DNA must…
be copied in 5’ - 3’ direction because there is not high energy bonds on the 3’ end
Hydrolysis of what drives the overall reaction of polynucleotide synthesis
pyrophosphate
- hydrolysis is highly favorable
Clamp Loader function
allows the same DNA poly to polymerize all of the Okazaki fragments
uses ATP to lock sliding clamp to DNA
DNA helicase
uses energy of ATP hydrolysis to pry apart DNA double helix ahead of the fork
Single-strand DNA binding protein
Binds to exposed DNA strands preventing base pairs from reforming
Topoisomerase
Produces transient breaks in one strand of double helix to relive tension caused by unwind of DNA
Sliding Clamp
Keeps DNA polymerase attached to template allowing the enzyme to slide
Ligase
uses ATP hydrolysis to join Okazaki fragments made on lagging strand
DNA relives torsional stress by…
Supercoiling with topoisomerase
-DNA freely rotates around broken single bond
-breaks backbone
Telomerase
replicates end of eukaryotic chromosomes
adds bases 5’ to 3’ on the lagging TEMPLATE strand
*allows replication proteins to replicate lagging strand without it shrinking with each division
3 steps of DNA repair
1) excision
Damage is recognized and cut out by one of a series of nucleases
2) Resynthesis
orginal sequence is restored by REPAIR DNA POLYMERASE
3)Ligation
DNA Ligase seal the break left in the backbone
DNA mismatch repair system
removes replication errors that escape proofreading
Double strand DNA breaks require different strategy…
Non-Homologous end joining
Homologous recombination
preferred restoration of sequence
-Requires shortly after replication w homologous DNA copy nearby
-no loss of nucleotides at repair site
-complimentary base pairing
Non-Homologous end joining
loss of nucleotides at repair site
“quick and dirty”
One single nucleotide change can cause
disease like sickle cell
Homologous recombination is found in virtually all cells on Earth
Shared by many organisms because they are so critical
