Cell Signalling

Question 1

What is cell signalling?

Answer 1

The process which cells talk to one another that controls all aspects of cell behaviour

Question 2

What is a signal?

Answer 2

Something that comes from outside a cell + induces a response in that target cell

Question 3

What is a receptor?

Answer 3

Proteins on/in target cell that receive the signal via binding of ligands + bring about a response

Question 4

What is the simple model for cell signalling?

Answer 4

1. Signal reception
2. Signal transduction
3. Response

Question 5

Why does cell signalling work?

Answer 5

No cell exists in isolation; all cells interact with their environment + with their neighbours

Question 6

What aspects of cell behaviour does cell signalling control?

Answer 6

Growth
Differentiation/development
Metabolism
Apoptosis

Question 7

What is autocrine signalling?

Answer 7

A cell signalling to itself

Question 8

What is paracrine signalling?

Answer 8

A signal inducing a response in a target cell close to the signalling cell

Question 9

What is endocrine signalling?

Answer 9

A signal that comes via the blood from a distant site e.g. hormone signalling

Question 10

Define the term ligand.

Answer 10

Signalling molecules are generally referred to as ligands when binding to their receptors so ligand is a generic term for molecules that bind to specific sites on proteins

Question 11

What are the 2 different types of ligands?

Answer 11

1. Agonist: active a pathway

2: Antagonists: do not activate a pathway

Question 12

What are the 2 different types of signal?

Answer 12

1. Direct contact

2. Gap junctions

Question 13

What is direct contact?

Answer 13

Protein on one cell binds to a receptor protein on the surface of an adjacent cell + triggers a response

Question 14

What is a gap junction signal?

Answer 14

Cells within small groups often communicate via these junctions (allow exchange of small molecules) in plasma membranes of adjacent cells to help coordinate metabolic reactions

Question 15

How do gap junctions work?

Answer 15

Rapidly close if [Ca2+]/[H+] increases (important is neighbouring cells die as this would increase Ca2+)

Question 16

Why do electrical synapses and neuronal junctions use gap junctions for coupling cells?

Answer 16

Allows ions to move quickly + directly from one neuron to another avoiding delay which is characteristic of chemical synapses

Question 17

What can be noticed about gap junctions during embryo development?

Answer 17

Cells make + break gap junction connections in specific patterns indicating that they are important in signalling

Question 18

How do cell surface receptors work?

Answer 18

1. EC part binds the signal
2. Binding changes conformation of IC part
3. IC cascade of reactions initiated which determines cellular response

Question 19

How do intracellular receptors work?

Answer 19

Nuclear/cytoplasmic enzymes/TFs bind a signal + alter gene expression so they are slower-acting than cell-surface receptors

Question 20

What type of protein are cell surface receptors?

Answer 20

Transmembrane

Question 21

What features can cell surface receptors have?

Answer 21

Ion channels
Intrinsic enzyme activity
Linked to protein kinases
Coupled to target proteins via G protein

Question 22

What is an example of channel-linked receptors?

Answer 22

ACh in skeletal muscle contraction where ACh binds, channel opens + ions flow across membrane

Question 23

What is an example of an enzyme-linked receptor?

Answer 23

Tyrosine-kinase activation by GFs -> leads to phosphorylation to control enzyme activity

Question 24

What is an example of a GPCR?

Answer 24

GABA activation of K+ ion channels by directly acting on G-protein subunits in CNS neurones

Question 25

What is an example of a hormone that uses an intracellular receptor?

Answer 25

Steroid hormones

Question 26

How can cellular behaviour be changed?

Answer 26

1. Altered gene transcription
2. Altered ion balance across plasma membrane
3. Altered activity level of existing enzymes

Question 27

What are enzymes?

Answer 27

Proteins that make chemical reactions proceed w/o being altered by those reactions themselves

Question 28

What do enzymes names usually end in?

Answer 28

‘-ase’ e.g. kinase, phosphatase

Question 29

What is a single component signalling system?

Answer 29

A minority of signalling pathways have the receptor + effector as the SAME protein

Question 30

What is the process by which single component systems work?

Answer 30

1. EC domain binds ligand
2. Cytoplasmic domain has catalytic activity
3. Binding of ligand activates enzyme converting substrate to product
4. Product changes cell behaviour

Question 31

What is the difference between first and second signalling messengers?

Answer 31

1st: EC ligand that binds receptor
2nd: small diffusible IC signalling molecules that act downstream

Question 32

What is the benefit of having a cascade of second messengers?

Answer 32

Allows for signal amplification + integration

Question 33

What do enzymes of signalling systems often do?

Answer 33

Phosphorylation: addition of phosphate (PO4)

Question 34

Why is phosphorylation/dephosphorylation a useful process?

Answer 34

Quick
Reversible
Lasting effect
Energy efficient 
Signal amplification 
Signal integration

Question 35

What enzymes carry out phosphorylation + dephosphorylation?

Answer 35

Kinases add phosphate groups (phosphorylation)

Phosphatases remove phosphate groups (dephosphorylation)

Question 36

What does voltage-gated Ca2+ influx do when acting as a specific signalling event?

Answer 36

Promotes fusion of neurotransmitter-containing vesicles with the cell membrane in the NMJ