2.9 Cell Signaling

Question 1

What are the four reasons we need cell signalling?

Answer 1

1. Process sensory stimuli
2. Self preservation (e.g. spinal reflexes)
3. Voluntary movement
4. Homeostasis (e.g. thermoregulation, glucose homeostasis)

Question 2

What is meant by self-preservation?

Answer 2

The activation of the reflex arc to protect ourself from danger

Question 3

What are the two systems which provide the main lines of communication?

Answer 3

Nerve fibers of the central and peripheral nervous system

Blood vessels of the cardiovascular system

Question 4

What line of communication is used for a rapid, instantaneous response?

Answer 4

The nerve fibres of the CNS and PNS

Question 5

What line of communication is slower and more versatile?

Answer 5

The blood vessel system

Question 6

What is meant by intercellular signalling?

Answer 6

Signalling between cells

Question 7

What is meant by intracellular signalling?

Answer 7

Signalling within a cell

Question 8

What are the four methods of signalling?

Answer 8

1. Autocrine
2. Endocrine
3. Paracrine
4. Communication between membrane attached proteins

Question 9

What is meant by endocrine communication?

Answer 9

When the hormone travels in the blood vessel and acts on a distant target cell

Question 10

How does glucagon act as an example of endocrine signalling?

Answer 10

Glucagon is released by the alpha cells of the Islets of Langerhans, and then transported in the blood to act on the liver

This stimulates gluconeogenesis and glycogenolysis

Question 11

How does insulin provide an example of endocrine communication?

Answer 11

Insulin produced by the pancreas acts on muscle and adipose tissue

Question 12

How does adrenaline provide an example of endocrine communication?

Answer 12

Produced by the adrenal glands and travels in the blood to act on many body systems like the lungs and trachea

Question 13

What type of communication is shown in response to hypoglycaemia?

Answer 13

Endocrine

Question 14

What types of communication is shown in response to hyperglycemia and why?

Answer 14

Paracrine – beta cells release insulin which inhibits glucagon secretion from adjacent alpha cells

Endocrine – reduces glycogenolysis and gluconeogenesis in liver

Question 15

What is meant by paracrine communication?

Answer 15

When the hormone that is released acts on the adjacent cell

Question 16

How does the pancreas show paracrine communication?

Answer 16

Insulin produced by the beta cells acts on the adjacent alpha cells inhibit glucagon production

Question 17

Describe how nitric oxide acts in a paracrine manner

Answer 17

Nitric oxide is produced by endothelial cells in blood vessels and causes vasodilation

Question 18

Describe how osteoclast activating factors work in a paracrine manner

Answer 18

They are produced by adjacent osteoblasts

Question 19

What is meant by membrane attached protein comunication?

Answer 19

When plasma proteins in the membrane of two different cells interact

Question 20

Describe an immunological example of membrane-attached protein communication

Answer 20

APC detects a bloodborne virus
APC digests the pathogen and expresses MHC II on surface
Circulating T cell interacts with MHC II via T cell receptors

Question 21

Give 2 other examples of signalling between membrane attached proteins

Answer 21

HIV GP120 glycoprotein binds to CD4 receptors on T lymphocytes

Bacterial cell wall components bind toll-like receptors on haematopoietic cells

Question 22

What is meant by autocrine communicaiton?

Answer 22

When a hormone acts on the same cell that produced it

Question 23

How do T cells display autocrine forms of communication?

Answer 23

When T cells become activated they express IL-2 receptors and also release IL-2 which mediates cytokine release and binds to the receptor on the same cell

Question 24

How does ACh display autocrine signalling?

Answer 24

ACh binds to presynaptic M2 muscarinic receptors

Question 25

How do growth factors show autocrine communication?

Answer 25

Growth factors from tumour cells can bind to and act on tumour cells to cause mitogenesis

Question 26

Describe how neurotransmission occurs?

Answer 26

1. Acton potential arrives at the synapse due to an influx of sodium ions into the pre-synaptic bouton 2. This triggers the opening of voltage gated calcium channels, allowing an influx of Ca2+ into the neurone 3. Ca2+ binds to vesicles containing NT 4. The NT vesicles then move to the cell membrane and are released into the synapse through exocytosis 5. They then bind to receptors on the post-synaptic neurone

Question 27

What are the four distinct categories of receptors which exist?

Answer 27

1. Ligand gated ion channel receptors 2. G protein coupled receptors 3. Enzyme-linked receptors 4. Intracellular receptors

Question 28

How do ligand-gated ion channel (ionotrophic) receptors work?

Answer 28

Ligand binds to receptor protein Conformational change in the protein opens a pore This allows the flow of ions in or out of the cell

Question 29

How is the direction of the movement of ions through ionotrophic receptors determined?

Answer 29

Through concentration gradients

Question 30

What is an example of an ionotrophic receptor?

Answer 30

Acetylcholine binds to **nicotinic ACh receptors** on skeletal muscle resulting in muscle contraction

Question 31

What is the ligand for NMDA receptors?

Answer 31

Glutamate

Question 32

What is the ligand for GABA alpha receptors?

Answer 32

GABA

Question 33

What are G-coupled receptors also known as and why?

Answer 33

7-transmembrane receptors as the channel protein crosses the membrane 7 times

Question 34

In resting state what does the G protein complex consist of?

Answer 34

Alpha subunit, beta-gamma subunit, and an associated GDP molecule

Question 35

Describe how G coupled receptors work?

Answer 35

1. **G protein complex** binds to **G coupled receptor** which is embedded in the cell membrane 2. The GDP is phosphorylated and swapped with GTP 3. The G protein complex dissociates into **alpha** and **beta-gamma** subunits with **alpha** binding to a **target protein** 4. GTP is dephosphorlyated to GDP, thus the **alpha** subunit dissociates from the target protein and binds **beta-gamma** again

Question 36

What is stimulated to convert ATP to cAMP?

Answer 36

AC - adenyl cyclase

Question 37

What is cAMP?

Answer 37

Cyclic adenosine monophosphate

Question 38

What does cAMP activate?

Answer 38

Protein kinase A

Question 39

Which G protein linked receptor activates adenylyl cyclase?

Answer 39

**Gs** protein linked receptor

Question 40

Which G protein linked receptor inactivates adenylyl cyclase?

Answer 40

**Gi** protein linked receptor

Question 41

What is an example of a G protein linked receptor which stimulates adenylyl cyclase?

Answer 41

Beta 1-adrenergic receptor

Question 42

What is an example of a G protein linked receptor which inacitaves adenylyl cyclase?

Answer 42

M2 muscarinic receptor

Question 43

What is the downstream effect of Gq protein linked receptors?

Answer 43

Activates **AT-1 angiotensin receptor** due to protein kinase C being activated

Question 44

How do enzyme linked receptors work?

Answer 44

1. Ligand binds and receptors cluster 2. Enzymes **phosphorylate the receptor**, causing binding of **signalling proteins** to the receptor's **cytoplasmic domain** 3. The signalling proteins recruit other ones, generating a signal in the cell 4. Signal terminates when phosphatase **dephosphorylates** the receptor

Question 45

What enzyme is activated when insulin binds to the insulin receptor?

Answer 45

Tyrosine kinase

Question 46

What enzyme is activated when ANP and BNP bind to the NPR1 receptor?

Answer 46

Guanylyl cyclase

Question 47

What enzyme is activated when TGF beta binds to TGF B receptors?

Answer 47

Serine/threonine kinase

Question 48

What is the physiological effect of serine/threonine kinase activation?

Answer 48

Apoptosis

Question 49

What is the physiological effect of activation of tyrosine kinase?

Answer 49

Glucose uptake and lipid metabolism

Question 50

What is the physiological effect of activation of guanylyl cyclase?

Answer 50

Vasodilation and reduction in blood pressure

Question 51

Where are type 1 intracellular receptors located?

Answer 51

Within the cytosolic compartment

Question 52

Where are type 2 intracellular receptors located?

Answer 52

In the nucleus

Question 53

What chaperone molecules are type 1 intracellular receptors normally associated with?

Answer 53

Heat shock proteins

Question 54

How do type 1 intracellular receptors work?

Answer 54

1. Hormone enters through membrane 2. Binds to receptor, heat shock protein dissociates 3. 2 hormone bound receptors form a **homodimer** 4. Homodimer translocates to the nucleus and binds to DNA

Question 55

How do type 2 intracellular receptors work?

Answer 55

The hormone ligand binds straight to the DNA in the nucleus

Question 56

What is an example of a type 1 intracellular receptor?

Answer 56

Glucocorticoid receptor

Question 57

What ligands binds to the glucocorticoid receptor?

Answer 57

Cortisol and corticosterone

Question 58

Physiological effect of cortisol binding to glucocorticoid receptor?

Answer 58

Reduced immune response and increased gluconeogenesis

Question 59

What is an example of a type 2 intracellular receptor?

Answer 59

Thyroid hormone receptor

Question 60

What is the associated ligand for the thyroid hormone receptor?

Answer 60

Thyroxine and triiodothyronine

Question 61

With type II intracellular receptors, what causes the direct transcriptional regulation?

Answer 61

Activated hormone-receptor complex

Question 62

What is a homodimer?

Answer 62

When two identical hormone receptor complexes join

Question 63

Intracellular receptors are essentially what?

Answer 63

Transcription factors

Question 64

Why do steroid hormones extert their actions on intracellular receptors?

Answer 64

They are membrane permeable

Question 65

When the hormone binds to the receptor, what dissociates?

Answer 65

The heat shock protein

Question 66

What is a ligand?

Answer 66

A molecule that binds to a receptor to exert a specific effect