Cell signalling

Question 1

What are the key components of a cell signalling system?

Answer 1

Signal molecule, target cell, and response.

Question 2

What are essential properties of an effective signalling molecule?

Answer 2

It must reach its target, be rapidly modifiable, and be highly controllable.

Question 3

What is endocrine signalling?

Answer 3

Long-range signalling using hormones transported through the bloodstream.

Question 4

What are examples of endocrine hormones?

Answer 4

Adrenaline, cortisol, insulin, glucagon, oestradiol, testosterone.

Question 5

What is paracrine signalling?

Answer 5

Local signalling using growth factors, histamine, or nitric oxide.

Question 6

What is autocrine signalling?

Answer 6

A cell responds to signals it releases itself.

Question 7

What is neuronal signalling?

Answer 7

Fast, targeted signalling through neurotransmitters at synapses.

Question 8

What are examples of neurotransmitters?

Answer 8

Acetylcholine, dopamine, GABA.

Question 9

What is contact-dependent (juxtacrine) signalling?

Answer 9

Direct signalling via membrane-to-membrane contact.

Question 10

Give examples of contact-dependent signalling.

Answer 10

PD-L1/PD-1 in immune evasion, gap junctions, cadherins.

Question 11

What are the three main types of cell surface receptors?

Answer 11

Ion channel-coupled receptors, GPCRs, and enzyme-linked receptors.

Question 12

What do ion channel-coupled receptors do?

Answer 12

Convert chemical signals into electrical signals by allowing ion flow.

Question 13

Give examples of ion channel-coupled receptors.

Answer 13

nAChR, GABA-A, GluN, GlyR.

Question 14

What is the structure of GPCRs?

Answer 14

7 transmembrane domains.

Question 15

How are GPCRs activated?

Answer 15

Ligand binding causes GDP to be replaced by GTP on the G-protein, activating it.

Question 16

What second messengers are activated by GPCRs?

Answer 16

cAMP, IP₃, DAG.

Question 17

What are examples of GPCRs?

Answer 17

Muscarinic acetylcholine receptors, β-adrenoceptors.

Question 18

What is an enzyme-linked receptor?

Answer 18

A receptor that activates an intracellular kinase upon ligand binding.

Question 19

What is a common example of an enzyme-linked receptor?

Answer 19

Receptor Tyrosine Kinase (RTK), such as EGFR.

Question 20

Why are RTKs important in medicine?

Answer 20

They are slow-acting receptors often targeted in cancer therapy, e.g., by cetuximab.

Question 21

What are the main functions of intracellular signalling molecules?

Answer 21

To relay, amplify, integrate, and distribute the signal.

Question 22

Describe the cAMP pathway.

Answer 22

GPCR → adenylyl cyclase → ATP to cAMP → activates PKA → phosphorylates targets.

Question 23

Describe the IP₃/DAG pathway.

Answer 23

GPCR → phospholipase C → PIP₂ → IP₃ + DAG; IP₃ releases Ca²⁺ from ER, DAG activates PKC.

Question 24

Describe the MAPK pathway.

Answer 24

RTK → Ras (GTP) → Raf (MAPKKK) → MEK (MAPKK) → ERK (MAPK) → transcription factors → Myc → G1-CDK → phosphorylates Rb → releases E2F → S-phase gene transcription.

Question 25

How does phosphorylation regulate signalling?

Answer 25

Protein kinases add phosphate groups, phosphatases remove them.

Question 26

What are GTP-binding switches?

Answer 26

Proteins like Ras that are active when GTP-bound and inactive when GDP-bound.

Question 27

What proteins regulate GTP-binding switches?

Answer 27

GEFs activate (GDP to GTP); GAPs inactivate (stimulate GTP hydrolysis).

Question 28

What are intracellular receptors?

Answer 28

Receptors in the cytosol or nucleus that bind lipophilic signals like steroids.

Question 29

Describe the function of nuclear receptors.

Answer 29

Hormone binds → receptor dimerises → enters nucleus → regulates transcription.

Question 30

Give an example of a nuclear receptor.

Answer 30

Estrogen receptor (ER).

Question 31

What are agonists and antagonists of the estrogen receptor?

Answer 31

Agonist: 17β-estradiol; Antagonist: Raloxifene.

Question 32

What do transcription factors do?

Answer 32

Bind to DNA to activate or repress gene expression.

Question 33

Where do transcription factors bind?

Answer 33

Upstream of genes at promoters or enhancers.

Question 34

Give examples of transcription factors.

Answer 34

p53 (activates p21), NF-κB (inflammation/cancer), CREB (activated by cAMP/PKA).

Question 35

How does the MAPK pathway control the cell cycle?

Answer 35

Leads to Myc activation → G1-CDK → phosphorylates Rb → releases E2F → genes for S-phase are transcribed.

Question 36

What is the role of Rb protein?

Answer 36

Tumor suppressor that binds and inhibits E2F; phosphorylation by G1-CDK releases E2F.

Question 37

Why is the MAPK pathway important in cancer?

Answer 37

Its dysregulation (e.g., mutations in Ras, Myc, or Rb) causes uncontrolled cell division.

Question 38

What are the three types of receptors based on speed?

Answer 38

Ion channels (fast), GPCRs (medium), RTKs (slow).

Question 39

How do intracellular cascades contribute to signalling?

Answer 39

They amplify, integrate, and control complex responses.

Question 40

How do transcription factors contribute to long-term changes?

Answer 40

They alter gene expression in response to signalling.

Question 41

What is the central signalling pathway for growth and cancer?

Answer 41

The MAPK pathway.