Seminar 6: The cell cycle

Question 1

what is & func of histones, what do they produce

Answer 1

• extensively packed DNA
• their +ve charged r grps bind to -ve phosphate in backbone, forms ionic bonds
  DNA-histone & histone-histone produces nucleosomes

Question 2

what happens in each stage of interphase?

Answer 2

G1: cell growth, ensures enough nutrients for division
S: DNA replication
G2: spindle synthesis begins, prep for mitosis

Question 3

what happens in prophase?

Answer 3

1. spindle fibres form
2. chromatin supercoil, becomes more condensed & packed
   (chromosomes are more visible here)

Question 4

stages of mitosis

Answer 4

1. prophase
2. prometaphase
3. metaphase
4. anaphase
5. telophase

Question 5

what happens in prometaphase

Answer 5

1. chromosome attach to spindle
2. nuclear membrane break down

Question 6

what happens in metaphase?

Answer 6

chromosomes align at centre of cell

Question 7

what happens in anaphase

Answer 7

1. each identical pair is split at centromere
2. move to opposite poles of cell

Question 8

what happens in telophase

Answer 8

1. chromosomes decondense
2. nuclear membrane reforms

Question 9

what happens in cytokinesis

Answer 9

1. cells separate
2. 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

Question 10

how is the cell cycle regulated?

Answer 10

• 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

Question 11

how & when are chromosomes moved to opp poles of cell

Answer 11

IN ANAPHASE
1. kinetochores contain motor proteins (kinesin etc): use energy from ATP to move
2. kinetochores are attached to microtubules, microtubules shorten
3. pull chromatids to opp poles

Question 12

what allows for segregation of sister chromatids

Answer 12

movement to opp sides of poles

Question 13

how is APC inhibited if chromosome isn’t attached properly to spindle

Answer 13

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)

Question 14

what makes up the spindle

Answer 14

microtubules b/w chromosomes & poles of cell

Question 15

function of the spindle

Answer 15

• struc that chromosomes attach to
• keeps 2 poles apart (allows for segragation)

Question 16

how do microtubules become more stable?

Answer 16

connect w/ kinetochores OR w/ other microtubules from other half of cell

Question 17

what grps of microtubules are w/in the spindle

Answer 17

1. POLAR: forms framework, run from 1 end to other
2. KINETOCHORE MICROTUBULE: form ltr, attach to centromere on chromosome, ensures that sister chromatids MOVE TO OPP SIDES

Question 18

why are indv chromatids visible during prophase?

Answer 18

because most of cohesin holding them have been removed, only helf by small amount @ centromere (kinetochore)

Question 19

what is a centrosome

Answer 19

1. organelle near the nucleus (non-membrane bound)
2. when duplicated, move to opp sides & form the mitotic spindles (during prophase)

Question 20

func of cohesin & condensin

Answer 20

1. cohesin : hold sister chromatids together in G2
2. condensin : coat DNA molecule & make them more compact

Question 21

how do growth factors work?

Answer 21

1. bind to specific receptors on target cell
2. activate signal transduction pathways
3. causes cyclin synthesis
4. cyclin forms complex w/ CDK
5. bind to RB & ATP
6. RB is phosphorylated, changes its 3D shape, inactivating it
7. RB not func, cell cycle can progress

Question 22

How to regulate CDKs?

Answer 22

1. regulate cyclin prod
2. if cyclin is absent, CDK = inactive
   Cyclin prod cyclically, @ specific times in cell cycle

Question 23

what does the checkpoint @ each stage check for?

Answer 23

G1&G2: Cell damage
S: DNA rep incorrectly & DNA damage
M: chromosomes unattached to spindle

Question 24

how to Cyclin-CDK complexes work?

Answer 24

• allosteric regulation
• by forming complex, CDK alters shape, exposes its active site, makes it FUNCTIONAL

Question 25

what are growth factors?

Answer 25

- 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.

Question 26

what are the various levels of packing of genetic info contained in linear DNA

Answer 26

- During interphase, chromosomes are condensed by histone proteins into nucleosomes, - multiple nucleosomes coiled together, stack on each other & form chromatin (fibres) - prophase: the fibres attach as loops to proteins, & then loop extensively to form the chromosome

Question 27

what happens if cohesin wasn't functional?

Answer 27

- 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.