Cell cycle & Mitiosis

Question 1

Why is cell division is important ?

Answer 1

• important in growth and repair of tissues in multicellular organism
• reproduction of all organisms

Question 2

What four events must occur for cell division ?

Answer 2

• a reproductive(intra/extracellular) signal initiates cell division
• replication of DNA
• Segregation :Distribution of DNA into 2 new cells
• Cytokinesis: separation of cellular material into 2 new cells

Question 3

How does binary fission occur ?

Answer 3

• Replication occurs as the DNA is threaded through ‘ Replication complex’ of proteins
  -Rapidly dividing prokaryotes the entire time is DNA replication between cell divisions

Question 4

Binary fission how 2?

Answer 4

When replication is complete the daughter DNA molecules are segregated at opposite ends
The ORI regions move towards opposite ends of cells aided by special protein

Question 5

3 binary fission ?

Answer 5

Cytokinesis begins by a pinching in of a plasma membrane ; protein fibres (mostly Ftsz) form ring
New Cell wall materials are synthesised resulting in a separation of 2 cells being formed

Question 6

Cell cycle in eukaryotes consist of ?

Answer 6

MITOSIS
CYTOKINESIS
INTERPHASE

Question 7

Interphase ?

Answer 7

nucleus is visible & cell functions,including DNA replication,occur
Begins after cytokinesis ends when mitosis starts

Question 8

Interphase subspaces ?

Answer 8

G1: (Gap 1) between cytokineses and S phase ;chromosomes are single , unreplicated structures
- Duration varies from minutes to years
Some cells enter resting phase (G0)

Question 9

Interphases 2 nd sub stage ?

Answer 9

G1 TO S transition the commitment is made to DNA replication and subsequent cell division .
Called Restriction (R )point

Question 10

Describe S phase & G2 Phase ?

Answer 10

S phase -(synthesis ) DNA replicates forming 2 sister chromatids stay together
G2 :(gap 2 ) cell prepares for mitosis
By synthesising structures to move the chromatids

Question 11

How do transitions occur from 1 stage to the next ?

Answer 11

Specific signals trigger this-add more

Question 12

What do these signals act through ?

Answer 12

through proteins called cyclin-dependant kinases (Cdk’s)
Kinase catalyse transfer of a phosphate group from ATP to a protein (Phosphorylation)
A Cdk must be activated by binding to a cyclin protein
Allosteric regulation altering the shape of Cdk thus exposing its active site to allow it to transfer a phosphate

Question 13

Is there 1 cyclin-CD-R complex ?

Answer 13

no there ar many. At diff stages
1.) G2 PHASE
2.) MITOSIS
3.)G1
4.) S PHASE

Question 14

What does the Cyclin Cdk do at the G1-S transition ?

Answer 14

Progress between the restriction point depends on Retinoblastoma protein (RB)
RB usually inhibits cell cycle BUT when phosphorylated by cyclin Cdk in a lot of places ,RB becomes inactive (changing 3D structure) and thus allows cell cycle

Question 15

What are cell cycle checkpoints ?

Answer 15

G1- DNA damage
S - incomplete replication or DNA damage
G2 - DNA damage
M - chromosomes unattached to spindle

Question 16

Mitosis

Answer 16

Newly replicated chromosomes-SISTER CHROMATIDS
-separates into 2 new nuclei
Sepeerating many large liner chromosomes would be diffifvutl

Question 17

How is DNA packed ?

Answer 17

Eukaryotic DNA molecule are “packed” and organised by histone proteins even uncondensed DNA is wound around histones to form nucleosomes.
When the chromosomes condense these Hilton’s begin to pack together

Question 18

The phases of mitosis ?
PROPHASE

Answer 18

The chromatin condenses and distinct chromatids become visible under a microscope

Question 19

PROMETAPHASE?

Answer 19

Nucleus envelope breaks down and chromosomes attach to the ‘spindle ‘ of microtubles

Question 20

ANAPHASE

Answer 20

The chromatids seperate and move to opposite poles by the spindle

Question 21

TELOPHASE

Answer 21

Nuclear envelope reforms,spindle disappears,chromosomes become less compact

Question 22

Interphase

Answer 22

• Orientation is determined but the centrosome an organelle near the nucleus

Question 23

Prophase in depth

Answer 23

Each centrosome can consist of 2 centrioles- hollow tubes formed by microtubules at right angles

The centrosome doubles during S phase ;during prophase they move to oppposite ends of the nuclear envelope

Question 24

PROMETAPHASE

Answer 24

Late in prophase ,the spindle attachment points called kinetochores develop on each chromatid

Microtubules form between the poles and the chromosomes to make up the spindle fibres
Nuclear envelope breaks down and chromosome attach to a spindle of microtubule

Question 25

METAPHASE

Answer 25

2 types of microtubules in the spindle
Chromosomes line up in the middle of/ equatorial plate

• polar microtubules form spindle framework; run from one pole to the other
• Kinetochore microtubules attach to kinetochores on the sister chromatids and to microtubules in opposite halves of the spindle

Question 26

ANAPHASE

Answer 26

After separation ,the chromatids are called daughter chromosomes

• chromatids share a centromere
• chromosomes have their own centromere
  During the separation of SC -controlled by M phase Cyclin-Cdk; it activates ANAPAHSE -PROMOTING COMPLEX(APC)

Cohesion that hold the chromatids together is hydrolysed by seperase.
Chromatids separate and move to opposite poles of spindle

Question 27

Anaphase 2

Answer 27

Kinetochores have motor proteins; energy from ATP moves chromosomes along the microtubules

Kinetochores microtubules also shorten ,drawing chromosomes towards pole

Question 28

Telophase

Answer 28

Nuclear envelope reforms spindle fibres disappear chromosomes become less compact

Question 29

Cytokineses

Answer 29

Division of the cytoplasm follows mitosis
In animal cells the plasma membrane pinches in between the nuclei
\

Question 30

Cytokinesis in plant cells

Answer 30

The membrane bound vesicles appear along the plane of cell division .
These fuse to form a new plasma membrane

Contents of vesicles form a cell plate -the beginnings of new cell wall.