Overview of cell signalling

Question 1

Cells receive signals from the environment beyond the plasma membrane, e.g.

Answer 1

• antigens
• hormones
• neurotransmitters
• light
• touch
• pheromones

Question 2

Signals are integrated and cause changes in the cell’s composition and function, such as:

Answer 2

• differentiation and antibody production
• growth in size or strength
• cell division
• movement

Question 3

How do communications between cells occur ?

Answer 3

Electrically or chemically

Question 4

Electric current passes through ?

Answer 4

Gap junctions

Question 5

Chemical signals bind to ?

Answer 5

Receptors on target cells and relays information via second messengers to activate effectors in the nucleus or cytoplasm

Question 6

What may signals act over ?

Answer 6

Short or long distances

Question 7

Explain the signal acting for Endocrine Signalling, Paracrine Signalling, Neuronal and Contact-dependent ?

Answer 7

• Endocrine signalling: long distance, slow acting
• Paracrine signalling: short distance, relatively fast
• Neuronal: long distance, very fast
• Contact-dependent: short distance, can be slow or fast

Question 8

What is Signal transduction?

Answer 8

This is the conversion of one type of signal into another

Question 9

An environmental signal is first received ?

Answer 9

By interaction with a cellular component, most often a cell-surface receptor

Question 10

The information that the signal has arrived is then converted into ?

Answer 10

• Other chemical forms, or transduced: this is usually a multi-step process
• The signal is often amplified before evoking a response

Question 11

Feedback pathways regulate?

Answer 11

The entire signalling process

Question 12

What do ion channels act as?

Answer 12

Receptor, transducer and amplifier in one protein

Question 13

Ionotropic ion channels are activated by ?

Answer 13

A ligand binding; voltage-operated channels are activated by a change in membrane potential

Question 14

What is a Receptor ?

Answer 14

• A membrane-bound or soluble protein or protein complex, which exerts a physiological effect (intrinsic effect) after binding its complementary ligand
• Receptors are specific

Question 15

Membrane-bound receptors are necessary to allow ?

Answer 15

Hydrophilic signalling molecules to transmit their signal across the plasma membrane

Question 16

What do Many intracellular signalling proteins act as ?

Answer 16

Molecular switches that cycle between “on” and “off” states in response to a signal (i.e. it is reversible - important for terminating a signal)

Question 17

Protein kinases (enzymes which phosphorylate) are very common, as are G-proteins, which bind ?

Answer 17

GTP/GDP

Question 18

Note that any enzymatic step, or repeated cycle, will cause?

Answer 18

Amplification of a signal

Question 19

Signalling complexes form at?

Answer 19

Receptors: these may be a pre-formed complex activated by a signal molecule, or activation of the receptor may trigger recruitment of intracellular signalling molecules

Question 20

What does this signalling complex enable ?

Answer 20

A localised response

Question 21

Different intracellular signalling molecules may also be recruited in different contexts via ?

Answer 21

Modular interaction domains: this enables modularity

Question 22

Intracellular signalling proteins integrate incoming signals via ?

Answer 22

Different receptors: the response depends on the strength and effect of each signal

Question 23

In this way, the cell can respond to ?

Answer 23

Different demands and sometimes competing requirements

Question 24

In addition to molecular switches, there are a number of ways signals can be deactivated:

Answer 24

Feedback loops are important here

Question 25

Adaptation to a sustained signal over time, e.g. by receptor down-regulation, can lead to ?

Answer 25

Issues like drug tolerance and insulin resistance

Question 26

Inappropriate activation of signal pathways leads to?

Answer 26

Problems like cancer