Signalling 1

Question 1

list three types (bi)chemical signalling molecules

Answer 1

Hormones
Neurotransmitter
Growth factors

Question 2

What are two classifications of signalling molecules?

Answer 2

Distance they act over

Chemical structure

Question 3

Name some lipid based hormones

Answer 3

testosterone, cortisol, prostaglandins

Question 4

what are are eicosanoid hormones derived from?

Answer 4

Lipids

Question 5

What are steroid hormones derived from?

Answer 5

Cholesterol

Question 6

Give 2 examples of protein hormones?

Answer 6

Growth factor, insulin

Question 7

What are 4 ranges a signalling molecule can act? and what is each way called

Answer 7

Neighbouring/adjacent cells (juxtacrine -via cell to cell contact)
Nearby cells (paracrine - via diffusion)
Same cell (autocrine)
Over whole body (endocrine)

Question 8

What are the 3 steps in signal transduction?

Answer 8

Reception/detection of signal
Transduction (relaying signal from receptor to part of cell where response is initiated)
Response

Question 9

List 7 responses a cell can have in response to a signal

Answer 9

Divide
Differentiate
Migrate
Change shape
Increase/decrease cell activity 
Produce new proteins
Transcribe new Genes
Release hormones 
Grow
Die

Question 10

Describe the two types of receptors and give examples

Answer 10

For Hydrophilic signalling molecules = cell surface receptors e.g. for insulin, adrenaline, some neurotransmitters, most peptide hormones

For Hydrophobic (lipophilic) signalling molecules = intracellular receptors e.g. for steroid hormones (oestrogen, testosterone), nitric oxide

Question 11

Describe how hydrophobic signalling molecules work in a cell

Answer 11

E.g. oestrogen, testosterone.
Signalling molecules enters cell and binds to intercellular rectory proteins. Hormone receptor complex forms which acts as a transcription factor. It binds to DNA and alters gene expression.

Question 12

List the 3 main types of cell surface receptors and give an example of each

Answer 12

Ion channel linked e.g. glutamate neurotransmitter
G-protein coupled e.g. adrenaline, NT: serotonin
Enzyme linked e.g. RTK

Question 13

Describe how an ion channel linked receptor works

Answer 13

Signalling molecule binds to receptor (receptor can be ion channel or coupled to an ion channel)
Ion channel opens and ions flow either in or out of the cell along a concentration gradient
Change in electrical properties of the cell occurs

Question 14

Briefly describe the structure of a G protein coupled receptor

Answer 14

It is a large heterotrimeric, transmembrane protein

Question 15

Describe and draw how a G protein couple director works

Answer 15

Signalling molecule binds to receptor. The G protein which is coupled to the receptor undergoes a conformational change and is active activated. The activated G protein goes off and activates an enzyme. The enzyme transmits the signal in the cell

Question 16

In enzyme linked receptors where can the enzymatic activity be?

Answer 16

Enzymatic activity can either be in the catalytic domain (where catalysed reaction occurs) or it can be coupled to an independent enzyme

Question 17

What type of molecules act as Ligands to receptor tyrosine kinases?

Answer 17

Growth factors

Question 18

what is the role of RTK?

Answer 18

It is an enzyme that adds a phosphate group to the amino acid tyrosine in a target protein

Question 19

Describe how a ligand acts on RTK

Answer 19

Ligand is often a dimer (2 monomers joined together) and as it binds to RTK, the receptor dimerises (2 monomers come together).

The kinase activity of the cytoplasmic domain of RTK is activated and it autophosphorylates.

Cytoplasmic domain has tyrosine resides that can be phosphorylated. Cross phosphorylation of the different monomers of the dimer occurs and it causes shape change due to addition of phosphate group.

Intracellular Proteins bind to the phospho-tyrosine docking sites and the signal is transmitted

Question 20

what are the 2 main methods of transduction of a signal?

Answer 20

Enzyme cascades

Second messengers

Question 21

Give an example of an enzyme cascade and what ligand is it used by

Answer 21

MAP Kinase Cascade, used by growth factors such as EGF

Question 22

Describe the MAP kinase cascade

Answer 22

Ligand (e.g. EGF) binds to its receptor (EGFR) and the receptor TK becomes phosphorylated.
Relay proteins bind to the phosphorylated form of receptor TK and activate RAS.
RAS mediates signals from the receptor and docked proteins and activates a MAP kinase cascade.
RAS activates Raf, which activates and phosphorylates MEK. MEK activates and phosphorylates ERK.
ERK can alter the transcription of target genes

Question 23

What is a second messenger? Give 2 examples

Answer 23

A small molecule produced in large amounts inside a cell after receptor activation. It coordinates cell response. E.g. calcium ions and cAMP

Question 24

describe an example of when second messengers are used

Answer 24

Adrenaline activates G protein coupled receptor. Activated G protein goes on and activates enzyme adenylyl cyclase. Adenylyl cyclase produces cAMP, which activates protein Kinase A. Protein Kinase A goes onto phosphorylate target proteins.

From here, PKA can flow one of 2 pathways
It can either:
Activate phosphorylase kinase, which phosphorylates and activates and enzyme (PHOSPHORYLASE), which breaks down glycogen to release glucose into bloodstream
OR
Inhibit an enzyme called glycogen synthase which produces glycogen from glucose

Question 25

In cancer what change occurs to the GF/RTK pathway? What treatment can be used?

Answer 25

The RTK pathway is usually overactive causing over expression or a mutation to occur.
Treatment: antibodies or kinase inhibitors

Question 26

what functions as the off switch in the adrenaline and cAMP pathway

Answer 26

Phosphodiesterase: breaks down cAMP which stops the system and switches the signal off

Question 27

give 2 examples of peptide hormone signalling molecules

Answer 27

growth hormone

Insulin

Question 28

give 2 examples of peptide growth factor signalling molecules

Answer 28

Epidermal growth factor

Erythropoietin