1.5 Protein Control of Cell Division

Question 1

What is the cytoskeleton?

Answer 1

-Network of protein fibres that extends throughout the cytoplasm.

• anchored to proteins in the plasma membrane
• is constantly breaking down and re-forming to allow the cell to change shape.

Question 2

What are the functions of the cytoskeleton?

Answer 2

• Providing mechanical support so that cell shape can be maintained
• Providing a method of anchoring the organelles of the cell (and some enzymes)
• It can enable the whole cell to move
• It can enable the organelles within a cell to move

Question 3

What is the cytoskeleton made up of?

Answer 3

Several types of protein including microtubules

Question 4

What are Microtubles?

Answer 4

Microtubules are around 25nm wide and are hollow, straight cylinders composed of proteins called tubulins.

Question 5

How is the length of microtubles controlled?

Answer 5

The addition or removal of tubulin at the ends of the microtubles

(polymerisation/ depolymerisation)

Question 6

What is the role of microtubles

Answer 6

Microtubules are responsible for the location and movement of the membrane-bound organelles and other cell components including chromosomes.

Question 7

Where do microtubles originate from?

Answer 7

The microtubule-organising centre (MTOC)

Or the centrosome which is located near the nucleus and contains centrioles, which are the site of microtubule synthesis.

Question 8

Describe the role of microtubles in Cell division

Answer 8

used in remodelling of the cell’s cytoskeleton.

also form the spindle fibres which are active during cell division.

Question 9

What is the purpose of cell division?

Answer 9

Cell division is a vial process that allows an organism to grow and develop, to replace dead cells and repair tissue.

Question 10

What are the two stages of cell division?

Answer 10

interphase and the mitotic phase

Question 11

During the interphase a cell is undergoing…….

Answer 11

a period of growth which involves

• protein synthesis
• creation of the organelles
• the replication of chromosomes

Question 12

What are the 3 stages of interphase?

Answer 12

G1
S phase
G2

Question 13

Describe G1

Answer 13

G1 is the first growth/gap phase, during this time proteins and organelles are synthesised

Question 14

What happens in the S phase

Answer 14

S phase involves the replication of DNA

Question 15

What happens in G2

Answer 15

G2 is the second growth/gap phase which also involves the synthesis of proteins and organelles.

Question 16

What are the stages of mitosis?

Answer 16

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 17

Describe the events occuring in prophase

Answer 17

• DNA condenses into chromosomes each consisting of two sister chromatids.
• The nuclear membrane breaks down
• spindle microtubules extend from the MTOC (by polymerisation) and attach to chromosomes via their kinetochores in the centromere region

Question 18

Describe the events occuring in Metaphase

Answer 18

chromosomes are aligned at the metaphase plate (equator of the cell/spindle)

Question 19

Describe the events occurring in Anaphase

Answer 19

As spindle microtubules shorted (by depolymerisation) sister chromatids are separated and the chromosomes are pulled to opposite poles

Question 20

Describe the events occurring in Telophase

Answer 20

the chromosomes decondense and the nuclear membranes are formed around them.

Question 21

What is the final part of the cell cycle?

Answer 21

Cytokinesis

Question 22

What happens during cytokinesis

Answer 22

Cytoplasm splits to form two daughter cells.

Question 23

Why must cell be produced at the correct rate and in the correct locations

Answer 23

to allow regulated growth and repair

Question 24

An uncontrolled reduction in the rate of the cell cycle will result in…..

Because……..

Answer 24

degenerative disease such as Alzheimer’s or Parkinson’s as insufficient replacement cells are being formed for normal tissue function

Question 25

An uncontrolled increase in the rate of the cell cycle may result in.....

Answer 25

the formation of tumours. Uncontrolled growth may be benign or may result in a malignant cancer

Question 26

What is a proto-oncogene?

Answer 26

A **proto-oncogene** is a normal gene that can **mutate to form a tumour-promoting oncogene**

Question 27

What is progression of the cell cycle controlled by?

Answer 27

Checkpoints

Question 28

What types of signalling is used to control the cell cycle

Answer 28

internal and external

Question 29

Which proteins accumulate during cell growth and what is their role?

Answer 29

**Cyclin proteins** that accumulate during cell growth are involved in **regulating the cell cycle**

Question 30

What do cyclins combine with and activate?

Answer 30

cyclin-dependent kinases (CDKs)

Question 31

What do Active cyclin-CDK complexes do?

Answer 31

phosphorylate proteins that regulate progression through the cycle

Question 32

The next stage of the cell cycle will occur if

Answer 32

sufficient phosphorylation is reached

Question 33

Describe What occurs at the G1 Checkpoint

Answer 33

This occurs towards the **end of G1**. At this checkpoint: - retinoblastoma protein **(Rb) acts as a tumour suppressor by inhibiting the transcription of genes** that code for proteins needed for DNA replication. - **Phosphorylation by G1 cyclin-CDK inhibits the Rb.** This allows transcription of the genes that code for proteins needed for DNA replication. The cell can then progress from G1 to S phase.

Question 34

Describe the G2 Checkpoint

Answer 34

Occurs at the end of G2, the **success of DNA replication and any damage to DNA is assessed**. - DNA **damage triggers** the activation of several proteins including **p53** that can stimulate DNA repair, arrest the cell cycle or cause cell death.

Question 35

Describe the M Checkpoint

Answer 35

- Occurs during metaphase - controls progression from metaphase to anaphase. - At this checkpoint, progression is **halted until the chromosomes are aligned correctly** on the metaphase plate and **attached to the spindle microtubules.**

Question 36

Apoptosis is triggered by.....

Answer 36

cell death signals that can be external or internal

Question 37

How are External death signals transmitted

Answer 37

- External death signal **molecules bind to a surface receptor** protein - **trigger a protein cascade** within the cytoplasm

Question 38

Describe Internal death signals

Answer 38

Internal death signal resulting from DNA damage causes **activation of p53 tumour suppressor protein**

Question 39

Death signals result in......

Answer 39

The **activation of caspases** (types of protease enzyme) that cause the **destruction of the cell**

Question 40

Why is Apoptosis important?

Answer 40

**Removes cells no longer required** as development progresses or during metamorphosis

Question 41

Cells may initiate apoptosis in the absence of....

Answer 41

Growth Factors