1.1 Cell-cell communication

Question 1

Describe the general principles of communication

Answer 1

Signalling cell → signalling molecules/transmitters (endogenous agonists) → target cell

Question 2

What is a contact dependant effect?

Answer 2

Local

Membrane bound signal on the signalling cell with a transmembrane receptor on the target cell

Question 3

What is a paracrine effect?

Answer 3

Local
Signalling cell releases soluble messengers to the transmembrane receptors on the target cells
- important in inflammation
- may recruit more local cells

Question 4

What is an autocrine effect?

Answer 4

Local
Signalling cell is also the target cell
- important in cells that are terminally differentiating into a specific cell type

Question 5

What is the endocrine effect?

Answer 5

Distant

Endocrine cell releases the hormone which is absorbed into the bloodstream and travels to the target cells

Question 6

What is the synaptic effect?

Answer 6

Distant
The impulse is expressed down the axon from the neurone cell body in which is ends up at the pre-synaptic membrane.
Once here neurotransmitter is released which travelles across the synapse to receptors on the target cell

Question 7

What are the basic functions of the nervous system?

Answer 7

Acquire information, transmit and integrate the input and bring about a response to a stimulus

Question 8

What is signal transmission?

Answer 8

Between nerves or between nerves and effectors occurs at a synapse (muscle)

Question 9

What is synaptic transmission?

Answer 9

Tends to be mediated by neurotransmitters

Question 10

What is a neuron?

Answer 10

Functional unit 
Dendrites receive inputs 
- > 1 dendrite per neurone 
Cell body/soma contains organelles 
Axon connect to the target 
- 1 axon per neurone

Question 11

Describe the polarity of a neurone?

Answer 11

Action potential pass along the axon from the soma to the synapse only
UNI-DIRECTIONAL

Question 12

How do transmitters achieve specificity?

Answer 12

Through activation of any target cell expressing the cognate receptor

Question 13

What are common transmitters?

Answer 13

Neurotransmitters

Hormones

Question 14

What are common receptors?

Answer 14

Ligand gated ion channel
G-protein couples receptors
Receptor tyrosine kinases
Transcription factors

Question 15

What are common cellular response pathways?

Answer 15

Depolarisation (neurones)
Depolarisation and electromechanic coupling (muscle)
Depolarisation and secretion (endocrine glands)
Transcriptional and translational effects (all cell types)

Question 16

What are hormone receptors?

Answer 16

Can be intracellular (transcription factors) or plasma membrane bound (e.g., G protein coupled receptors)

• steroids have intracellular receptors
• protein hormone usually have membrane receptors

Question 17

How does steroid binding allow gene expression?

Answer 17

1. Inhibitor protein is binded to the DNA binding region
2. Once steroid is added the DNA binding region becomes free and the inhibitor protein is dissociated
3. This means that gene expression can be activated as the activated receptor protein with an exposed DNA binding site with two zinc fingers is open.

Question 18

Describe the general structure of a hormone receptor

Answer 18

Three domains/regions
- N terminus is always on the extracellular domain
- C terminus is always on the intracellular domain
G proteins are important therapeutic targets

Question 19

How does an ion linked channel receptor work?

Answer 19

Ligand binds and channel opens, ions move in/out dependant on the concentration
- transient - quick to open/close

Question 20

How does an enzyme linked receptor work?

Answer 20

Ligand binds to receptor and activates the enzyme

Question 21

How does a G-protein coupled receptor work?

Answer 21

Receptor and G protein are linked and this in turn can active the effector

Question 22

What are G-protein linked receptors?

Answer 22

7-pass transmembrane proteins

Question 23

How do G-protein linked receptors work?

Answer 23

Trimeric G proteins relay the signal
GTP activates 𝛂 subunit
- which causes a dissociation between the 𝛂,𝛃,𝛄 subunits
- 𝛃 + 𝛄 subunits are activated, which can lead to the effect of the protein
Coupling the receptor to its target (enzyme or ion channel) generating second messengers like cAMP, IP3 or DAG

Question 24

What is the purpose of cAMP in signal transduction?

Answer 24

Stimulatory G-proteins (G𝛂s) signal via secondary messenger cyclic adenosine phosphate e.g., 𝛃-adrenergic receptor, glucagon receptor
Which allows free active G𝛂s to interact with the enzyme adenylyl cyclase at the membrane which generates cAMP from ATP

Question 25

What effect does cAMP have on G-protein linked receptors?

Answer 25

cAMP activates the regulatory serine-threonine protein kinase, PKA (cAMP dependant protein kinase), phosphorylates protein substrates to affect cells

• phosphorylate kinase - liver
• hormone sensitive lipase - adipocytes
• CREB - liver (transcription factor) = fasting response

Question 26

What controls GPCRs?

Answer 26

transmitters

nerves

Question 27

How does the body respond in so many different ways (sometimes contradictory) to a single stimulus?

Answer 27

Tissue-specific expression of different adrenergic receptors:

• a1 receptors - link to Gq which generates IP3 and DAG - expressed on smooth muscle of some arterioles
• 𝛃 receptors - link to Gs which generates cAMP - expressed on: cardiac muscle, smooth muscle of bronchi, smooth muscle of other arterioles