Lecture 16 - Signal Transduction Mechanisms and Receptors

Question 1

1) what are types of signaling mols?
2) Where can the receptors be located?
3) What is the result of interaction btw signaling mols and receptors?

Answer 1

1) hormones, ligands, neurotransmitters, GFs
2) cell surface or intracellular
3) can alter ion transport, metabolism (control pts), gene expression (turn on/off), and cell movement (across surface, muscle contractions)

Question 2

What are the 4 modes of intercellular signal transduction?

Answer 2

juxtacrine, endocrine, paracrine and synaptic

***chemical mechanisms of transmmission

Question 3

Define juxtacrine

Describe juxtacrine transduction

Answer 3

relative distance btw 2 cells interacting

sender cell expresses polypeptide/macromol on surface –> interacts with receptor on target cell –> causes some change inside cell (pathways, concentrations)

Question 4

Describe endocrine transduction

Answer 4

sender cell secretes hormone that diffuses into blood vessel –> travels long distances and binds with receptor on target cell –> causes change

***long distance communication

Question 5

Describe paracrine transduction

Answer 5

similar to endocrine but interacting with target cell close by

sender cell secretes local mediator (mol) –> binds with receptor on target cell –> causes change inside cell

Question 6

Describe synaptic transduction

Answer 6

sender neuron has neurotransmitters at terminal end of nerve –> they are released and travel across gap (synapse) and bind to recepors on target cell –> causes change in cell

Question 7

True or False:

1) Cell types only have receptors for 1 hormone
2) All Hormones have receptors in only 1 tissue
3) Some hormones have receptors in more than one tissue

Answer 7

1) False - some cell types have receptors for multiple hormones
2) False - some hormones have receptors in only 1 tissue
3) True

Question 8

Name some cells and the signaling mols they secrete

Are these metabolic signaling mols highly regulated?

Answer 8

1) Pancreatic A cells - glucagon (polypeptide)
2) Pancreatic B cells - insulin (polypeptide)
3) Adrenal cortex - cortisol (steroid - small hydrophobic mols derived from cholesterol)
4) Adrenal medulla - epinephrine (catecholamine - derived from simple AA, tyrosine)

yes, their synthesis and secretion are highly controlled and their destruction is usually swift (in liver)

Question 9

What common signaling mols interact with intracellular receptors?

Explain the interaction with an intracellular receptor

Answer 9

steroids, thyroid hormones

1) steroid can simply diffuse across membrane –> interacts with receptor in cytoplasm –> receptor/steroid complex is translocated to the nucleus –> acts as txn factor and alters gene expression

***steroids can target certain cells/tissues based on nature of which receptor is expressed

Question 10

What type of signaling mols interact with cell surface receptors?

Explain the interaction btw these type of receptors and signaling mols?

Answer 10

hydrophilic hormones, neurotransmitters, GFs

1) hormone binds with receptor on cell surface –> change in concentration of certain mols inside cytoplasm (second messengers)

Question 11

What is a second messenger?

Give some examples

Answer 11

substance which changes in concentration in the target cell in response to receptor activation

1) Ca+ - highly controlled, typically low in concentration
2) cAMP - derived from ATP, most important 2nd messenger
3) cGMP - derivde from similar mechanism as AMP
4) diacylglycerol and inositol trisphosphate - derived from phosphotidalinositol

Question 12

1) What’s a protein kinase?
2) What’s a protein phosphatase?
3) Do these gene families portray substrate specificity?
4) What do these action do to protein?
5) Where are these enzymes located?

Answer 12

1) uses ATP to phosphorylate OH groups of AAs with hydroxyl side chains –> puts a P gp on
- Serine, threonine, tyrosine
2) dephosphorylate these side chains - takes P gp off
3) yes
4) (de)phosphorylation changes activity or function of protein
5) at key metabolic/fn control points

***control cellular activities by controlling [] of 2nd messengers

Question 13

Name the types of cell-surface receptors

Answer 13

1) ligand-gated ion channel receptor - shut most of time –> ligands bind to receptor –> channel opens up and ions may flow thru
2) enzyme-linked receptors - several subunits become associated when hormone binds to binding sites (binding sites on each subunit) –>Activates catalytic domain on subunits
3) cytokine receptors - several subunits come together with binding of mol –> subunits bind to another enzyme which activates it
4) G-protein coupled receptors - 7 transmembrane domain receptor binds neurotransmitter or hormone –> interaccts with G protein –> activates G protein –> interacts with enzyme and activates it –> changes [] of 2nd messenger

*one of most abundant gene families

Question 14

1) describe signaling by protein phosphorylation
2) describe signaling by GTP-binding regulatory protein

Answer 14

1) hormone receptor activates kinase –> transfers P gp from ATP to intracellular protein –> activates it –> causes change in cell –> eventually phosphatase is activated –> takes P gp off –> intracellular protein becomes inactive
2) hormone receptor interacts with G protein –> release GDP and binds new GTP –> activates G protein –> activates something/causes change –> GTP hydrolysis (takes P off GTP) –> inactivates G protein

Question 15

What are the two main points about receptor - ligand interaction?

Answer 15

1) takes very low concentrations of ligands to bind to their receptors
2) good amount of cellular response can happen with only a fractino of receptors bound/activated

Question 16

What happens when there’s a prolonged activation of synapse?

Answer 16

if structures stay open too long (activated state), receptors have mechanisms to prevent this –> channel will close to prevent prolonged ion flow (closed channel with neurotransmitters still bound