L12- DNA review Flashcards
a replicate chromosome is what shape
x-shaped
- two chromatids
shot arms
p arms
long arms
q arms
telomere found
on the ends of chromosomes
how many diff types of chromosomes
4
name diff types of chromosomes
1) Metacentric
2) submetacentric
3) acrocentric
4) telocentric
metacentric
centromere in the middle of the p and q arms
submetacentric
centromere further up P arm
acrocentric
centromere even further up p arm
telocentric
centromere right at top of p arm
DNA helicase
unwinds and separates double stranded DNA as it moves along the DNA. It forms the replication fork by breaking hydrogen bonds between nucleotide pairs in DNA.
replication only progresses in
5’ to 3’ end
DNA polymerase has to add to
3’ end
primer binds to the
3’ end of the strand- acting as a starting point for replication by polymerase
primers are
oligonucleotides generated by DNA primase
once both continuous and discontinuous strands are formed exonucleases
remove all RNA primers from original strand- primers then replaced with appropriate bases
function of exonuclease domain in DNA polymerase
- RNA degradation (primers)
- DNA proofreading
o Work by scanning directly behind as DNA polymerase adds new nucleotides to the growing strand - Transcriptional regulation
exonuclease cleave…
nucleotides off one at a time from the end (exogenous) of the polynucleotide chain by hydrolysing phosphodiester bonds
exonuclease and cancer
- If exonucleases are mutated they will not perform their regular function of proofreading DNA and cleaving wrongly transcribed DNA
o E.g. a gene controlling cell division may be mutated and the exonuclease would not be able to recognise and correct it
E.g. tumour suppressor gen
DNA gyrase (topoisomerase)
unwinds and rewinds DNA strands to prevent the DNA from becoming tangled or supercoiled.
DNA ligase
- joins DNA fragments together by forming phosphodiester bonds between nucleotides.
DNA polymerases can only make DNA in the ……. why may this pose a problem
5’ to 3’ direction, and this poses a problem during replication.
A DNA double helix is always anti-parallel; in other words, one strand runs in the 5’ to 3’ direction, while the other runs in the 3’ to 5’ direction.
This makes it necessary for the two new strands, which are also antiparallel to their templates, to be made in slightly different ways.
leading strand
runs 5’ to 3’ towards the replication fork.
This strand is made continuously, because the DNA polymerase is moving in the same direction as the replication fork.
This continuously synthesized strand is called the leading strand.
DNA demythylation and histone acetylation
increases amount of active chromatin (euchromatin)
methylation of histone groups
decreases amount of active chromatin, increasing amount of heterochromatin
why do major and minor grooves exist in alpha helical structure
Two different types of grooves as sugar is asymmetrically bonded to base pair
- DNA- protein binding will bind to major groove- more space to binds
Question 2: Azidothymidine (AZT) is used to treat HIV and AIDS and has the structure shown below (the azido group is shaded). Suggest how the drug works.
AZT looks like a funny deoxyribonucleoside
- Therefore can be incorporated into a DNA strand
- Forms hydrogen bonds with other bases (similar shape to thymine)
- AZT lacks 3’OH therefore elongation by polymerase cannot occur after
a high does of AZT would
Would stop all DNA replication- including human. Therefore cells with a high turnover rate e.g. cells that line the gut will not be renewed
- Can cause digestive problems
