Cell Communication

Question 1

What is a gap junction?

Answer 1

• Gap junctions allow flow of current from cell to cell - allows rapid transmission
• Electrical transmission
• Linked cells can act together as one unit - a syncytium

Question 2

What are the 3 modes of chemical transmission between cells?

Answer 2

1. Cell to cell -> synapse
2. Cell to several cells -> paracrine
3. Many cells to many cells -> endocrine

Question 3

What does the resulting effect depend on in cell to cell chemical transmission (i.e. at a chemical synapse)?

Answer 3

The type of neurotransmitter

The receptor the neurotransmitter acts on

Question 4

What is the sequence of events that occurs at a chemical synapse?

Answer 4

1. Impulse arrives at terminal of presynaptic cell
2. Transmitter released from storage vesicles
3. Transmitter diffuses in synaptic cleft
4. Transmitter binds to receptor on postsynaptic cell
5. Transmitter alters the postsynaptic cell: excitatory or inhibitory

Question 5

What is paracrine communication?

Answer 5

• One cell communicates with several cells locally
• Often used by defence cells
• Can be part of a ‘cascade’ of reactions

Question 6

What is autocrine communication?

Answer 6

• When chemical acts back on cell releasing it

Question 7

What is endocrine transmission?

Answer 7

• Chemical sent to all parts of the body via the bloodstream

- Hormone acts only on cells with the correct membrane receptor protein (target cells)

Question 8

What are the main differences between neural and hormonal communication?

Answer 8

Neural communication: actions often very specific and localised, quick impulse transmission (>100m/s), suitable for rapid transmission

Humoral communication (hormonal): can affect many cells in different parts of the body, co-ordinated body-wide actions, slow to act but effect persists

Question 9

What are some examples of neural communication?

Answer 9

• Control of voluntary muscle contractions
• Sensory systems
• Salivary gland responses
• Control of blood pressure

Question 10

What are some examples of endocrine communication?

Answer 10

• Gastro-intestinal gland responses
• Control of metabolism and growth
• Regulation of menstrual cycle

Question 11

What is the ‘first messenger’ in cell communication?

Answer 11

The first messenger is the chemical transmitter which acts on a receptor protein. Some can pass through the cell membrane and act on receptors within the cell. Others cannot enter the cell.

Question 12

What type of molecule are steroid hormones?

Answer 12

Lipids

Question 13

Which type of hormone can pass through the cell membrane?

Answer 13

Steroid hormones - they are lipids (lipophilic)

Question 14

Where are the receptors for steroid hormones located?

Answer 14

Inside the target cell

Question 15

Why can peptide transmitters not pass through the cell membrane?

Answer 15

They are not lipophilic

Question 16

Where are receptors for peptide transmitters located?

Answer 16

On the cell membrane

Question 17

What is cAMP?

Answer 17

Cyclic AMP - a 2nd messenger

Question 18

Describe the sequence of events in GPCR activation via receptor binding

Answer 18

GPCR = G-protein coupled receptor

1. The transmitter binds to the GPCR
2. G protein is activated by GTP
3. ATP is converted to cAMP by the enzyme adenyl cyclase
4. cAMP activates protein kinase
5. Protein kinase phosphorylates a specific enzyme (activates it) which catalyses a chemical reaction, resulting in the formation of a molecule (protein)

Question 19

Describe how calcium can act as a 2nd messenger

Answer 19

• Transmitter binds to a membrane receptor (GPCR)
• This activates a G protein, which activates an enzyme: phospholipase C
• This causes opening of Ca2+ channels, Ca2+ enters cell
• Ca2+ binds to protein in the cytosol (e.g. calmodulin)