Signal Transduction and apoptosis

Question 1

Signal transduction

Answer 1

The conversion of the extra cellular signal to an intracellular signal in order to elicit a specific response

Question 2

Second messengers

Answer 2

Molecules which are activated by a membrane receptor and go on to activate other proteins.

Question 3

Signal Cascade

Answer 3

The activation of proteins activated by second messengers which go on to activate other proteins and so on until a response is elicited

Question 4

Signal amplification

Answer 4

The increased number of molecules activated due to signal reception.

Eg. receptor activates 10 second messengers which go on to activate 10 molecules each

Question 5

What determines whether the receptor is in the cell or on it?

Answer 5

Solubility in the cell membrane. If the signalling molecule hydrophilic (water soluble) then the receptor is on the outside, if hydrophobic ( water repelling) receptor is inside the cell

Question 6

Apoptosis

Answer 6

Programmed cell death leading to an orderly fragmentation and clearance of the cell

Question 7

Causes of apoptosis

Answer 7

• cellular injury (eg. Radiation or heat)
• Viral infection
• stimulation by signalling molecules (eg. Cells that aren’t needed anymore)

Question 8

Capases

Answer 8

Family of Enzymes that cleave protein molecules and carry out processes involved with apoptosis.

Question 9

How does the extrinsic pathway of apoptosis occur?

Answer 9

A signalling molecule binds to the death receptor on the cell which initiates caspases

Question 10

How does the intrinsic pathway of apoptosis occur?

Answer 10

the mitochondria (upon stimulation) releases a protein, cytochrome C into the cytosol which activate caspases.

Question 11

Steps of apoptosis
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Answer 11

• caspases break down the cytoskeleton of the cell
• other proteins in the cytoplasm and nucleus get broken down
• nuclear DNA is cut by DNAses
• blebs are formed on the surface of the cell as the cytoskeleton is broken down
• cell fragments turn into vesicles containing organelles and cytoplasmic material
• macrophages phagocytose these vesicles and “recycle” them

Question 12

Apoptosis and causes

Answer 12

programmed cell death leading to orderly fragmentation and clearance of the cell

caused by:

• cellular injury (heat or radiation)
• viral infection
• stimulation by signalling molecules( when cells aren’t needed)

Question 13

two paths of apoptosis

Answer 13

Extrinsic pathway (death receptor pathway)
Instrinsic pathway (mitochondrial pathway)

Question 14

how does the extrinsic pathway of apoptosis occur?

Answer 14

a signalling molecule binds to the death receptor on the cell, which initiates the activation of a series of enzymes called caspases.

Question 15

how does the intrinsic pathway of apoptosis occur

Answer 15

a protein called cytochrome C is released by the mitochondria into the cytosol which activate caspases

Question 16

caspase

Answer 16

a family of enzymes that are responsible for the procedures carried out in apoptosis such as cleaving the cytoskeleton

Question 17

steps of apoptosis

Answer 17

• cell shrinks
• cytoskeleton is broken down by caspases causing blebbing
• Other proteins and nucleus are broken down
• nuclear DNA cut by DNAses
• cell fragments into vesicles

Question 18

Explain what Cancer is

Answer 18

Due to mutations in the cell’s DNA, cells may continually divide due to inhibited apoptosis

Question 19

Metastasis

Answer 19

When cancer cells move from the tumour into the blood stream or lymph vessels and start dividing elsewhere in the body