Seminar 6: The cell cycle Flashcards
what is & func of histones, what do they produce
- extensively packed DNA
- their +ve charged r grps bind to -ve phosphate in backbone, forms ionic bonds
DNA-histone & histone-histone produces nucleosomes
what happens in each stage of interphase?
G1: cell growth, ensures enough nutrients for division
S: DNA replication
G2: spindle synthesis begins, prep for mitosis
what happens in prophase?
- spindle fibres form
- chromatin supercoil, becomes more condensed & packed
(chromosomes are more visible here)
stages of mitosis
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
what happens in prometaphase
- chromosome attach to spindle
- nuclear membrane break down
what happens in metaphase?
chromosomes align at centre of cell
what happens in anaphase
- each identical pair is split at centromere
- move to opposite poles of cell
what happens in telophase
- chromosomes decondense
- nuclear membrane reforms
what happens in cytokinesis
- cells separate
- cell wall/membrane forms
IN PLANTS: vesicles line up b/w cells, fuse to form a plate & secrete their contents, forms CELL PLATE/WALL
IN ANIMALS: cell membrane furrows, contractile ring forms (microfilaments of actin & myosin), forms contraction which pinches cell into 2
how is the cell cycle regulated?
- CDK (always present in cell) will bind w/ cyclin (conc fluctuates, formed when needed) = CDK-cyclin complex
- binds to proteins & ATP, phosphorylates the protein
- becuz of added Phosphate, protein shape changes, this either ACTIVATES/DEACTIVATES it to allow PROGRESSION/INHIBITION of cycle
how & when are chromosomes moved to opp poles of cell
IN ANAPHASE
1. kinetochores contain motor proteins (kinesin etc): use energy from hydrolysis of ATP to move chromosomes along microtubule
2. kinetochores shorten: brings chromosomes closer to kinetochore
3. causes centromere to move apart, aids in separation
what allows for segregation of sister chromatids
movement to opp sides of poles
how is APC inhibited if chromosome isn’t attached properly to spindle
occurs at spindle assembly checkpoint (@ end of metaphase)
1. M-phase CDK cyclin will NOT bind to APC & activate it
2. APC cannot bind to separase & activate it
3. Separase can’t remove remaining cohesin (sister chromatids won’t separate)
what makes up the spindle
microtubules b/w chromosomes & poles of cell
function of the spindle
- struc that chromosomes attach to
- keeps 2 poles apart (allows for segragation)
how do microtubules become more stable?
connect w/ kinetochores OR w/ other microtubules from other half of cell
what grps of microtubules are w/in the spindle
- POLAR: forms framework, run from 1 end to other
- KINETOCHORE MICROTUBULE: form ltr, attach to kinetochore on chromosome, ensures that sister chromatids MOVE TO OPP SIDES
why are indv chromatids visible during prophase?
because most of cohesin holding them have been removed, only helf by small amount @ centromere (kinetochore)
@ what stage do centrosome duplicate & separate
- S phase = duplicate
- start of prophase = separate
what is a centrosome
- organelle near the nucleus (non-membrane bound)
- when duplicated, move to opp sides & form the mitotic spindles
func of cohesin & condensin
- cohesin : hold sister chromatids together in G2
- condensin : coat DNA molecule & make them more compact
how do growth factors work?
- bind to specific receptors on target cell
- activate signal transduction pathways
- causes cyclin synthesis
- cyclin forms complex w/ CDK
- bind to RB & ATP
- RB is phosphorylated, changes its 3D shape, inactivating it
- RB not func, cell cycle can progress
How to regulate CDKs?
- regulate cyclin prod
- if cyclin is absent, CDK = inactive
Cyclin prod cyclically, @ specific times in cell cycle
what does the checkpoint @ each stage check for?
G1&G2: Cell damage
S: DNA rep incorrectly & DNA damage
M: chromosomes unattached to spindle
how to Cyclin-CDK complexes work?
- allosteric regulation
- by forming complex, CDK alters shape, exposes its active site, makes it FUNCTIONAL
what are growth factors?
- proteins made by cells that can travel to other cells or act on the cells that make them to stimulate cell division
-They bind to specific receptors on target cells, setting off cell signal transduction inside the cells - This can lead to gene expression of cyclins, which will bind to CDK & stimulate cell cycle progression.
what are the various levels of packing of genetic info contained in linear DNA
- During interphase, chromosomes are condensed by histone proteins into nucleosomes, these fold over one another to form chromatin fibres.
- In prophase, the fibres attach as loops to proteins, & these in turn loop extensively to form the chromosome
what happens if cohesin wasn’t functional?
- Cohesin proteins joins the chromatids together at their centromere
- non-functional cohesin protein would prevent chromatids from remaining bound from replication in S phase to metaphase in mitosis
- Therefore there would be no organisation for kinetochore attachment & thus ineffective segregation of 1 sister chromatid of each replicated chromosome into each daughter cell.
