Lecture 2 Flashcards
Where are covalent bonds in DNA
Sugar-Phosphate
Which H bonds are easiest to break in dna
A-T, double bonded, G-C are triple bonded
What do h bonds hold together in DNA
2 strands of DNA
What differs on the 2’ carbon of Deoxyribose and ribose
Deoxyribose has Hydrogen on 2’carbon
Ribose has Hydroxyl group on 2’ carbon
Are purines and pyrimidies double or single ringed
Purines: Double (A/G)
Pyrimidines: Single (C/T)
Nucleoside vs nucleotide
Nucleoside: sugar and base
Nucleotide: Sugar, base, phosphate
Features of DNA
5’–>3’
Right handed
Complementary
Antiparallel
What happens in gap phase
growing and getting ready for what’s next- make proteins and get ready to split to 2 cells
What happens in S phase
SECOND (S) copy- DNA replication
What happens in G0 phase
Cells have stopped dividing
What happens in M phase
Mitosis
What phase is where chromosomes condense so you can see them clearly
Metaphase
Phases of mitosis
IPMAT
What is different about meiosis from mitosis
one round of replication, 2 rounds of division, total of 4 haploid cells
Where do sister chromatids get seperated
metaphase 2
What kind of cell do you start with for both mitosis and meiosis
a diploid cell
Which phase results in recombinant chromosomes
Prophase- crossing over in prophase leads to recombinent chromosomes
How many chromosomes in gametes
23- haploid
What do you end up with Mitosis vs meiosis
Mitosis: 2 identical daughter/sister cells
Meiosis: 4 haploid daughter cells
What unzips the 2 strands of dna
helicase
What starts Transcirption
primase
Which direction can DNA bases be added
5’–>3’
How is DNA replicated in terms of new and old strands
semi-conservative- keep 1 strand as base
What direction can replication occur in
5’–>3’
Why can dna only replicate 5’–>3’
Have to have OH group to replicate
Can only add to Hydroxyl
What does DNA ligase do
seal two strands of DNA together where there were bubbles
How many replication sites can be going at one time?
MANY- can do it in many places at the same time
What does Topoisomerase do
unwind supercoils on DNA
What do cancer drugs commonly inhibit
topoisomerase- they inhibit DNA replication
Which strand (leading/lagging) can be synthesized continuously
leading
What are okazaki fragments associated with
lagging strand
What polymerase helps add on to RNA primer (adds DNA on to RNA primer)
DNA polymerase 3- adds in DNA
What polymrease recognizes a mutation and takes it out/corrects it
exopolymerase
What does DNA polymerase 1 do
remove RNA, put in DNA
What does DNA ligase do
Seals nick after last nucleotide of RNA primer with phosphodiester bond bewtween 5’ P group and 3’ OH group
What are telomeres
DNA at end of chromosomes
is telomere shortening in gametes or somatic cells
somatic cells
What does telomerase
prevent telomeres from shorteining in every single round (has RNA so DNA can add onto it, gives artificial template)
Which enzyme aids with coiling and uncoiling in the tertiary structure
Topoisomerases
What is a nucleosome
repeating unit of DNA that wraps around a protein and makes up chromatin
What charge are histones and how does this compare to DNA
histones are positive, attracts DNA, which is negative
Why do we visualize DNA in metaphase
It is highly wound together and easily visible, most condensed
What does DNA repair prevent
- Delay senescence
- prevent apoptosis
- prevent uncontrolled cell division
What does nucleotide excision repair do
remove many DNA pairs (24 ish).
Seen in the case of skin cancer from sun
What does double strand break repair fix
non-homologous end joining/homologous recombination
Most detremental
What is mismatch repiar
take out mismatch, put in right strand, seal with ligase
What is lynch syndrome
-Autosomal dominant, mismatch repair gene not functioning
- Tied to colon cancer.
-A different mismatch repair gene not functioning causes breast cancer
What is exroderma pigmentosum
- Something in nucleotide exision repair is not working, early and frequent skin cancers, cannot fix mistakes on cells
What is homologous recombination associated with
breast cancer - BRCA1/2
Born with this is problematic
DNA polymerase 1 vs polymerase 3
1: removes and replaces primers
3. elongates DNA
