Protein Control of Cell Division

Question 1

What is the cytoskeleton?

Answer 1

Network of protein fibres that extend throughout the cytoplasm in all eukaryotic cells

Question 2

Function of the cytoskeleton

Answer 2

Gives mechanical support and shape to cells

Question 3

The cytoskeleton consists of…

Answer 3

Different proteins including microtubules

Question 4

What are microtubules?

Answer 4

Hollow cylinders composed of the protein tubulin
Radiate from the microtubule organising centre (MTOC) or centrosome

Question 5

Function of microtubules

Answer 5

Control the movement of membrane-bound organelles and chromosomes

Question 6

Cell division requires the…

Answer 6

Remodelling of the cytoskeleton

Question 7

What is the remodelling of the cytoskeleton?

Answer 7

Formation and breakdown of microtubules, involves polymerisation (growth) and depolymerisation (shrinkage) of tubulin

Question 8

Microtubules form…

Answer 8

Spindle fibres that are active during cell division

Question 9

What does the cell cycle regulate?

Answer 9

The growth and replacement of genetically identical cells throughout the life of the organism

Question 10

2 stages of cell cycle…

Answer 10

Interphase
Mitotic (M) Phase

Question 11

Interphase involves…

Answer 11

G1- a growth phase
S phase- DNA is replicated
G2- a further growth phase (of organelles and proteins)
(preparation for mitosis)

Question 12

Mitotic phase involves…

Answer 12

Mitosis- chromosomal material is separated by the spindle microtubules
Cytokinesis- cytoplasm is separated into 2 daughter cells

Question 13

4 stages of mitosis

Answer 13

Prophase
Metaphase
Anaphase
Telophase

Question 14

What happens during prophase?

Answer 14

DNA condenses into chromosomes (consist of 2 sister chromatids)
Nuclear membrane breaks down, spindle microtubules extend from MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region

Question 15

What happens during metaphase?

Answer 15

Chromosomes are aligned at the metaphase plate (equator of the spindle)

Question 16

What happens during anaphase?

Answer 16

As spindle microtubules shorten by depolymerisation, sister chromatids are separated and chromosomes are pulled to opposite poles

Question 17

What happens during telophase?

Answer 17

Chromosomes decondense and nuclear membranes are formed around them (each set of chromosomes)

Question 18

Progression through the cell cycle is controlled by…

Answer 18

Checkpoints

Question 19

What are checkpoints?

Answer 19

Mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met

Question 20

What are the 3 checkpoints?

Answer 20

G1 checkpoint
G2 checkpoint
Metaphase checkpoint

Question 21

G1 checkpoint…

Answer 21

Occurs towards end of G1
Sufficient cell growth must have occurred before cell can enter S phase

Question 22

G2 checkpoint…

Answer 22

Occurs towards end of G2
Success of DNA replication and any damage to DNA is assessed

Question 23

Metaphase checkpoint…

Answer 23

Occurs during metaphase and controls entry to anaphase
Progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules

Question 24

What does retinoblastoma protein (Rb) do?

Answer 24

Acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication

Question 25

What do cyclin proteins do?

Answer 25

Accumulate during cell growth and are involved in regulating the cell cycle Combine with and activate cyclin-dependent kinases (CDK's)

Question 26

Active cyclin-CDK complexes...

Answer 26

Phosphorylate proteins that regulate progression through the cycle, if sufficient phosphorylation is reached the progression occurs

Question 27

Phosphorylation by G1 cyclin-CDK...

Answer 27

Inhibits retinoblastoma protein allowing transcription of genes that code for proteins needed for DNA replication (therefore cells can progress from G1 to S phase)

Question 28

At G2 checkpoint, DNA damage triggers the activation of several proteins such as...

Answer 28

p53 which can... Stimulate DNA repair Arrest cell cycle Cause cell death (initiate apoptosis) if DNA damage is too severe

Question 29

What does an uncontrolled reduction of cell cycle rate lead to?

Answer 29

Degenerative disease e.g. Alzheimers

Question 30

What does an uncontrolled increase in cell cycle rate lead to?

Answer 30

Tumour formation (cancer)

Question 31

What is a photo-oncogene?

Answer 31

Normal gene usually involved in the control of cell growth or division Can mutate to form tumour promoting oncogene

Question 32

What triggers apoptosis?

Answer 32

Cell death signals

Question 33

Why must destruction of cells in multicellular organisms be carefully controlled?

Answer 33

Excessive apoptosis leads to degenerative conditions Inhibition of apoptosis leads to tumour formation

Question 34

Where do external cell death signals originate?

Answer 34

Out with cell

Question 35

Where do internal cell death signals originate?

Answer 35

Within cell

Question 36

Example of external cell death signal

Answer 36

Production of death signal molecules from lymphocytes

Question 37

External death signal molecules bind to...

Answer 37

A surface receptor protein, triggering a protein cascade within cytoplasms

Question 38

Example of internal cell death signal

Answer 38

DNA damage

Question 39

Internal death signal resulting from DNA damage results in...

Answer 39

Activation of p53 tumour-suppressor protein

Question 40

Both types of cell death signal result in...

Answer 40

Activation of caspases

Question 41

What are caspases?

Answer 41

Types of protease enzyme that cause destruction of cells

Question 42

When else might cells initiate apoptosis ?

Answer 42

In the absence of growth factors

Question 43

Apoptosis is essential during...

Answer 43

Development of am organism to remove cells no longer required as development progresses Metamorphosis (when an animal changes from after hatching/birth)