lec 7 Flashcards
Why are there checkpoints in cell cycle
1) enerfy and resouces saved : if cell is not good, no reason to makea copy of it
2) Internal control: Allows for internal signals to be sent to areas where things did not go as planned so that if there is a possible fix, it could be fixed
3) External Control: growth factors, density dependent inhibition, tells cell to replicate if external problems, is environment favourable
Each checkpoint represents what
A control loop, the initiation of the next event is dependent on the outcome of the previous event
DNA integrity where is important
at the start of replication
as well the completion of dna replication IS IMPORTANT
Sucessful cell division requires 2 cycles to be coordinated…
1) Dna must replicate ONce and ONLY ONCE
-must not move on and try to divide cell without this being complete
2) Mass of cell must double to provide daughter cells with enough material
- must not start to replicate unless mass is suffecients
What is an exmaple of somethign that can caue cycle arrest
dna damage
Why is meiosis a fundemental problem
-we want to be diverse, it is of an organisms’s best interst to be unique/diverse/variable
(bc variability is important for survival if conditions change, this variability may help it survive compared to others)
So how can we preserve info while making it variable at the same time?
-Sexual reproduction using meiosis
-means that it produces special reproductive cells (gametes, 1n) and the fusion of two gametes (fertilization) leads to zygote (2n)
Three types of sexual life cycles
1) Animal: two gametes come together and make a zygote(during fertilzation), zygote becomes embryo, now becomes. ahuman, when they are older they produce their own gamete cells and these will be haploid
How does it go from 2n to n then in meiosis
Only one round of dna replication so we end up two XX, then two meitotic dividions occur
1) of the homologous chromosmes: two XX are seperated into one cell having one X other having other X (2n->n)
2) Seperation of sister chromatids: X -> I in one cell other I in next (n-> n)
Meiosis things allows for variability in what ways
1) Independent assortment of homologous chromosomes (meisosi 1)
-look at image slide 9 on lex 7
-think homologous chromosomes lie down next to eachother and are seperated (think sex u need to lie down next to eachother idk man he said it in lecture)
2)Crossing over during meiosis
-homologous chrmosomes are next to eachother so that means that they can interact with eachother and mix in order to create different combinations (exchanging genetic info with eachother, think about how the organism itself in sex is echanging genetic info with eachother so so is the chromosome, again idk he said it in lecture LOL)
Why is there no variation in mitosis
chromosomes are not lined next to eachother so no crossing over, each is just seperated
Number of possible combinations then from independent assortment?
2^n where n is equal to the haploid number of chromosomes for the species
Reductional vs equational division
reductional: 2n to n, happens in meiosis 1
equational n to n for meisosi 2 or 2n to 2n for mitosis
Chiasmata
when crossing over, the point that connects is the chiasmata
Gametophyte
haploid form of an organism, can grow thru mitotis
gametes undergo mitosis and form these things that are called gametophyotes
think a plant on its own undergoes meiosis, then mitosis, if u were to look atthe dna of a gametophyte, it would be half of the original dna of the plant
bidirectional
because one steand is 5’ to 3’ and the other is 3’ to 5’, and u have to transcribe dna in 5 to 3 direction, u can go either way id started in middle
Why is dna replication effieceint
it starts at a defined sequence (replication origin) and can happen very fast once it starts
Do bacteria have more than one replicator origin
no, they often only have one definded dna sequence that is needed
more complicated in euk genomes, there are multiple
what is a replicon
the region of dna that is replicated under that one origin (each region that is replicated from one origin is the replicon)
=a section of dna that replicated as a single unit
biodirectional confirmation tested
pulse chase experiment
puts tritium so that the dna first made wilol be labelled radioactive but then he swiches it out for ones without so the later ones are not radioactive (ones made away from the origin of replication will not be radioactive)
he uses this to see patterns,
if its unidirectional grwth pattern should be (radioactive, not radioactive, not)
if its bidirectiona l growth, it should be not, then radioactive, radioactive and not (because from the origin, it could move either way so thats why the radioactive parts are right next to eachother and the later ones are not)
dna have this radioactive tritium so all the ones that start making dna will make this kind of dna (first ones made radiactive ones other ones dont)
dna replication machinery
DnaA: initiaion
Single strand binding proteins: protection for hte dna since when dna is single stranded its exposed and more suceptible to degredation
Helicase (DnaB) and Primase (DnaG, RNA Polymerase)
Clamp loader (DnaC) Sliding clamp (ß clamp)
DNA polymerase III
DNA polymerase I & RNase H
DNA ligase
Topoisomerase
What is a replisome
combination of all the proteins that function at the replication fork and undertake the synthesis of dna
What are the three things of replication that make it so complicated
1) Dna polymerase cant break the interchain hydrogen bonds at the origin, so toher enzymes are needed to start replication and strand seperation
2) Dna cant start chains, it needs existing chain to add on new chain, so ne
3)
