Cell Signalling

Question 1

What are the four classifications of cell signal?

Answer 1

Endocrine
Juxtacrine
Paracrine
Autocrine

Question 2

What is an endocrine signal?

Answer 2

A hormone signal, travelling in the bloodstream, secreted from one cell type and travelling a long distance to target cells in other organs/tissues

Question 3

What is a juxtacrine signal?

Answer 3

Signalling between cells that are in direct contact with one another

Question 4

Give three examples of situations in which juxtacrine signalling occurs.

Answer 4

Cell to cell signalling via surface proteins
ECM cll signalling
Gap junction signalling

Question 5

What is paracrine signalling?

Answer 5

Signalling between nearby cells by diffusion

Question 6

What is autocrine signalling?

Answer 6

When cells release signals which bind to receptors on the same cell to initiate a response

Question 7

What are growth factors?

Answer 7

Extracellular signalling molecules that promote cell growth or proliferation, they can be endocrine, paracrine or autocrine

Question 8

Why should cytokines not be referred to as growth factors?

Answer 8

Because they could have a negative effect on growth as well as a positive effect

Question 9

Are steroid hormones hydrophilic or hydrophobic and as such where are their receptors located?

Answer 9

Hydrophobic so they have intracellular receptors

Question 10

The hormone-receptor complex of what type of steroid hormones acts as what kind of molecule?

Answer 10

A transcription factor

Question 11

What are the three main types of receptors used by hydrophilic signalling molecules to transduce their signal across the plasma membrane?

Answer 11

G protein coupled receptors
Enzyme linked receptors
Ion channel linked receptors

Question 12

What kind of receptors are receptor tyrosine kinases?

Answer 12

Enzyme linked receptors

Question 13

Give examples of signalling molecules which bind to receptor tyrosine kinases.

Answer 13

Insulin
EGF
PGDF
FGF

Question 14

Describe how signal binding to receptor tyrosine kinases transduces the signal across the plasma membrane.

Answer 14

RTKs usually exist as two separate monomers but dimerization occurs upon signal binding. This cause cross phosphorylation and the phosphorylated receptor acts as a docking site for intracellular proteins. This activates other proteins downstream until finally the target is reached

Question 15

Nerves use electrical signalling. Describe the changes in membrane potential that produce a signal in the nerve cell.

Answer 15

Depolarisation - sodium channels open, sodium floods in, excess positive charge in the cell
Repolarisation - sodium channels close, potassium channels open, potassium ions flow out and negative membrane potential is restored

Question 16

How is charge transmitted in myocytes?

Answer 16

Through gap junctions

Question 17

An ion channel receptor is itself an ion channel. T/F?

Answer 17

True

Question 18

How do ion channel receptors work?

Answer 18

Ligand binding causes a conformational change that opens the ion channel and the ion can then move through the channel along its concentration gradient

Question 19

The GABA-A receptor is an example of an ion channel receptor. How does it work?

Answer 19

Ligand binding causes a conformational change in the receptor allowing chloride ions to pass through into the cell along their concentration gradient. This causes hyperpolarisation which inhibits depolarisation and therefore inhibits neurotransmission.

Question 20

What kind of receptor are the receptors for adrenaline and serotonin?

Answer 20

G protein coupled receptors

Question 21

Why are G protein coupled receptors described as being serpentine?

Answer 21

They cross the plasma membrane seven times

Question 22

G proteins are heterotrimeric (composed of three subunits ). T/F?

Answer 22

True

Question 23

What are the three subunits of a G protein?

Answer 23

Alpha
Beta
Gamma

Question 24

How is a G protein activated?

Answer 24

The GDP which is bound to the G protein is converted to GTP

Question 25

Beta-gamma effectors are often ion channels. T/F?

Answer 25

True

Question 26

What are the three main alpha subunit effectors?

Answer 26

Adenylyl cyclase
Phospholipase C
RhoDEFs

Question 27

What do second messengers do?

Answer 27

Transduce a signal from the cell surface to the effector proteins to produce the cell’s response

Question 28

Adenylyl cyclase makes cAMP. What does this second messenger do?

Answer 28

Activates protein kinase A

Question 29

DAG is a second messenger, what does it do?

Answer 29

Activates protein kinase C

Question 30

Describe signalling through receptor tyrosine kinase by the example of EGF

Answer 30

EGF binds to its receptor (a receptor tyrosine kinase) which results in the cytoplasmic domain of the receptor becoming a docking site for GRB2 which binds go sos which allows the activation of ras. Ras can then activate a MAP kinase cascade which eventually leads to gene expression and promotion of cell growth