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IMS topic 4 - Lipids > Intracellular signalling > Flashcards

Intracellular signalling Flashcards

1
Q

What is signal transduction (intracellular signalling)?

A

Signal transduction converse extracellular signals (1st messengers) into a change in cellular function, and is responsible for regulating every aspect of physiological function at the cellular level (e.g. cell division, exocytosis, apoptosis, gene expression)

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2
Q

What are the 4 main stages of signal transduction?

A

Reception
Signal transduction
Cellular and gene expression responses

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3
Q

Explain the hierarchy of signal transduction

A

Occurs in a specific order to transmit a signal. The first messenger binds to a receptor on cell surface, activating the G-protein which stimulates an effector enzyme (e..g adenylyl cyclase), the effector enzyme catalyses production of 2nd messenger molecules (e.g. cyclic AMP), this stimulates a protein kinase to phosphorylate specific target proteins, to alter their function and elicit a cellular response

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4
Q

How do signal transduction pathways amplify the signal? What are the main points of amplification?

A

A single molecule of first messenger can induce many downstream signalling molecules to lead to a large cellular response.
G-protein activation - it will stay activated as long as the receptor remains activated, so activates many molecules of effector enzyme
Effector enzymes - catalyse without being used up
Protein kinase - an enzyme that can phosphorylate many molecules

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5
Q

Define cross talk between signalling pathways

A

Another 1st messenger may bind to a different receptor to activate or inhibit the original signal transduction pathway

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6
Q

What is the role of G-proteins in signal transduction?

A

bind guanine nucleotides, and are also enzymes (GTPases) that catalyse the hydrolysis of GTP to form GDP
When bound to GTP they are switched on, to switch them back off GTP is hydrolysed back to GDP

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7
Q

How are G-proteins attached to the internal surface of the cell membrane?

A

PRENYLATION; anchored to the membrane by a lipid tail (farnesyl or geranylgeranyl groups)

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8
Q

What are the two major groups of G proteins?

A

receptor associated G proteins

small monomeric GTPases

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9
Q

What is the structure of heteromeric G proteins

A

Three different subunits (alpha, beta and gamma). Different classes have different alpha subunits which contain the GTPase activity, but all share common beta and amma subunits, which are also signalling molecules

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10
Q

What is the basic structure of small GTPases? (e.g. RAS, RHO)

A

1 subunit

involved in cell signalling, cytoskeletal regulation , vesicle trafficking

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11
Q

When are G-proteins switched on and off?

A

switched ON by ligand binding to receptor, which induces a conformational change in the receptor that allows the G-protein to bind to the receptor
Switched OFF by GTPase activity, hydrolysing GTP back to GDP

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12
Q

What are the main roles of Gi and Gs?

A 
Gi = inhibitory
Gs = stimulatory
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13
Q

Explain signal transduction involving Gs stimulatory G proteins

A

Ligand binds to receptor causing conformational change in the receptor so the G protein releases GDP and swaps it for GTP. G protein is switch on and binds to the receptor. The GTP bound alpha subunit dissociates from beta and gamma subunits. GTP bound Gs alpha subunit binds to and activates adenylyl cyclase which catalyses conversion of ATP to second messenger cyclic AMP.
GTPase activity of Gs alpha subunit hydrolyses GTP to GDP, reverting G protein back to OFF state
GDP bound alpha subunit reassociates with beta and gamma subunits
Cyclic AMP is broken down to AMP by phosphodiesterase, which switches the signal off.
If the receptor is still active, the process is repeated.

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14
Q

What is the opposing effect of Gi on cyclic AMP levels?

A

Gi inhibits adenylate cyclase to stop production of second messenger cyclic AMP and stop signal amplification
G

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15
Q

What breaks down cyclic AMP to AMP and cyclic GMP to GMP

A

phosphodiesterases

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16
Q

What causes the effects of cholera?

A

cholera toxin acts on Gs G protein to prevent GTPaser activity of Gs; GTP remains bound to Gs and it stays in the on state so there is accumulation of cyclic AMP
In intestinal epithelial cells, cAMP increases loss of Cl- ions through chloride channels, creating an osmotic gradient so water is excreted into the intestinal lumen

17
Q

What causes the effects of the pertussis toxin (whooping cough)?

A

Pertussis toxin prevents GDP/GTp exchange by Gi so Gi protein is locked in the off position. It is unable to inhibit adenylate cyclase resulting in accumulation of cyclic AMP.
Increased insulin secretion and increased sensitivity to histamine

18
Q

What catalyses the production of cyclic AMP from ATP?

A

adenylate cyclase

19
Q

What catalyses the production of cyclic GMP from GTP?

A

Guanylate cyclase

20
Q

How is cyclic GMP produced?

A

Activation of soluble guanylate cyclase by NO or activation of membrane bound guanylate cyclase in response to neuropeptides

21
Q

Give an example of a well known phosphodiesterase (PDE)

A

Caffeine

Viagra

22
Q

What produces DAG, IP3 and Ca?

A

Activation of G protein Gq

23
Q

How does Gq become activated?

A

Ligand binding to the receptor causes the receptor to associate with G protein Gq, which stimulates the displacement of GDP by GTP to switch the G protein on. The alpha unit dissociates from the beta and gamma subunits.
GTP bound Gq stimulates membrane localised phospholipase C (PLC) which catalyses production of two different second messengers; DAG and IP3 from a membrane lipid

24
Q

What is IP3?

A

A polar molecule that can diffuse through the cytosol to the endoplasmic reticulum where it stimulates the release of Ca2+ ions into the cytosol, which stimulates various cellular processes

25
Q

What does DAG do?

A

Generated by PLC and remains in the membrane and stimulates protein kinase C (PKC) that phosphorylates target proteins leading to cellular responses
PKC can also be activated by Ca2+ released from the ER

26
Q

How does intracellular calcium act as a second messenger? (it is not formed, but released into the cytosol from intracellular stores, or enters the cell from extracellular sources)

A

Upon receptor activation, IP3 binds to receptors in the ER membrane resulting in efflux of Ca from the ER
Ca acts as a second messenger to activated various molecules (e.g. calcium dependent kinases)

27
Q

What happens to calcium after it carries out its role as second messenger?

A

It is taken back up into he ER through a calcium ATPase or is pumped/exchanged back out of the cell

28
Q

What is the role of protein kinases?

A

They facilitate the transfer of a phosphate group from ATP to a specific amino acid residue (serine, threonine or tyrosine) on a specific protein. PHOSPHORYLATION. This alters protein function

29
Q

Where on amino acids is the phosphate group from ATP usually added?

A

On R groups containing a hydroxyl group

30
Q

Can a single S/T/Y residue be phsophyrlated by multiple kinases?

A

Yes

31
Q

What are dual specificity kinases able to do?

A

Phosphorylate all 3 residues, Serine, threonine and tyrosine

32
Q

What is the role of phosphates?

A

Remove phosphate groups from specific amino acid residues to oppose the effects of kinases and switch the switch in the opposite direction ( to activate or inhibit protein function)

33
Q

Whats more specific, kinases or phosphatases?

A

Kinases

34
Q

Which disease are protein kinase inhibitors used as therapeutic agents for?

A 
Cancer
HIV
AIDS
Rheumatoid arthritis
Alzheimer's
35
Q

Why is dysregulation of kinases linked to cancer development?

A

Changes in protein kinase expression levels and activities and alterations in the degree of post translational modifications contribute to cancer development

IMS topic 4 - Lipids (6 decks)

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