Cell Communication & Receptor Families

Question 1

Cells in the body need to communicate with each other in order for:

Answer 1

• the body to function as a whole organism
• the body to sense to the environment
• the body to respond to the environment

Question 2

Why is it important to understand cell communication

Answer 2

Prevent and treat diseases from communication breakdowns.

Nervous system issues: motor neuron disease, multiple sclerosis, Parkinson’s disease.

Endocrine system issues: diabetes, metabolic disorders.

Question 3

Cell communication -What are the types of local signalling in cell communication?

Answer 3

Paracrine signalling: Cell releases a molecule affecting nearby cells (e.g., immune responses).

Synaptic signalling: Communication between neurons (e.g., thoughts and memories).

Question 4

Cell communication - long distance signalling - What is endocrine signalling

Answer 4

Hormone released into the bloodstream.
Hormone travels to target cells and initiates a response.
Enables communication between distant body parts.
Example: Insulin signals cells to take up glucose after a meal.

Question 5

Cell to cell communication overview: 3 stages of cell signalling

Answer 5

1. Reception
2. Transduction
3. Response

Question 6

Step 1: Reception

Answer 6

Receptors: Proteins that bind to signalling molecules (ligands/agonists) to trigger a cellular response.

Receptor and signalling molecule shapes must match.

Hydrophilic molecules: Receptors on the cell surface.
Hydrophobic molecules: Receptors inside the cell.

Question 7

Step 2 & 3: Transduction and response

Answer 7

Transduction pathway: Depends on the type of receptor the signalling molecule binds to.

Response: Depends on the type of receptor and the cell type. e.g.
Heart: Signal increases heartbeat.
Muscle: Signal causes contraction.

Question 8

Four families of receptors

Answer 8

-Ligand gated ion channels
-G protein coupled receptors
-Tyrosine kinase receptors
-Steroid receptors

Question 9

Cell surface receptors

Answer 9

1. Ligand-gated ion channels
   -neurotransmission, hormones
2. G protein coupled receptors
   -neurotransmission, hormones
3. Tyrosine kinase receptors
   -hormones

Question 10

Intracellular receptors

Answer 10

4. Steroid receptors
   -hormones

Question 11

Two main types of receptors involved in neurotransmission

Answer 11

1. Ligand-gated ion channels
   -Fast neurotransmission –> immediate effect
   -“Direct” neurotransmission
2. G protein coupled receptors
   -Slower neurotransmission
   -“Indirect” neurotransmission

Question 12

Ligated ion channels effect and impact

Answer 12

Effect: Opening allows ions to flow into or out of the cell.

Impact: Directly alters membrane voltage, triggering IPSPs (inhibitory) and EPSPs (excitatory) during synaptic transmission.

Question 13

G protein coupled receptors

Answer 13

Function: Vital in synaptic transmission and diverse cell signalling.

Examples: Sensing light, taste, hormone responses.

Interaction: Bind with G proteins associated with the receptor.

Effect: Activation triggers a cascade of intracellular effects.

Impact: Modifies depolarization or hyperpolarization but does not directly cause EPSPs or IPSPs

Question 14

Phosphorylation in protein regulation

Answer 14

Process: Kinases add phosphate groups, phosphatases remove them.

Effect: Activates or deactivates proteins.

Function: Acts as an on/off switch for cellular processes.

Pathways: G protein receptor pathways often activate kinases.

Question 15

G protein coupled receptors

Answer 15

1. Neurotransmitter binds to G protein-coupled receptor.
2. Activation of G protein.

3.This activates effector proteins (an enzyme)

4-5. This produces and activates second messengers

6. Second messengers activate kinases.
7. Kinases phosphorylate target proteins, modulating cellular response.

Example: Ion channel closure -> Gradual membrane potential change. Slower, indirect compared to ligand-gated channels.

Question 16

Signal amplification

Answer 16

• G protein-coupled receptors exhibit signal amplification.
• Occurs in G protein-coupled receptor signalling.
• Enables a small chemical messenger concentration to trigger a significant cellular response.

Question 17

Neurotransmitters

Answer 17

-Excitatory: Act on ligand-gated ion channels (EPSP); e.g., glutamate, acetylcholine.
-Inhibitory: Act on ligand-gated ion channels (IPSP); e.g., GABA.
-G protein-coupled receptors: Act on G protein-coupled receptors; e.g., acetylcholine, dopamine, noradrenaline.
-Multiple receptors: Can bind to G protein-coupled receptors or ligand-gated ion channels.
-Effect: Depends on postsynaptic cell’s receptor expression.

Question 18

Tyrosine kinase receptors

Answer 18

• Membrane receptors.
• Respond to hormones, not neurotransmitters.
• Key for slower processes like metabolism and growth.
  e.g. Insulin triggers glucose uptake into cells.
• Dysregulation leads to conditions like diabetes.

Question 19

Phosphorylation controls the activity of proteins

Answer 19

-Kinases phosphorylate proteins.
-Phosphorylated amino acids: Serine, Threonine, Tyrosine.
-Tyrosine kinase receptors: Enzyme-receptor combo.
-They self-phosphorylate at tyrosine residues.

Question 20

Tyrosine kinase receptors process

Answer 20

1. Initially exist as inactive monomers.
2. Signalling molecule binding induces monomer dimerization.
3. Each part phosphorylates the other at tyrosine sites, self-activating.
4. Activated receptors trigger downstream effects, like phosphorylation cascades.

Question 21

Phosphorylation cascade

Answer 21

A phosphorylation cascade is a series of kinase activations.
Step 1: One kinase phosphorylates and activates another.
Step 2: This process continues in a chain reaction.

Example: Tyrosine kinase receptor initiates the cascade.
Result: Signal is amplified and relayed downstream

Question 22

Many transduction pathways involve phosphorylation cascades

Answer 22

Result: Gene transcription, leading to:
-Protein synthesis.
-Cellular growth.
-Metabolic changes.
Slower process due to numerous biochemical steps.

Question 23

Steroid receptors

Answer 23

-Activating molecules: Hydrophobic
-Intracellular receptors for lipophilic hormones in cytoplasm
-Hormone binding triggers nuclear translocation
-Induces gene transcription and protein synthesis
-Slower due to multiple biochemical steps