ICPP - Intracellular Signalling Pathways Flashcards

1
Q

Why are many receptors located at the cell membrane rather than within the cell?

A

The majority of extracellular signalling molecules do not easily cross the cell membrane due to being hydrophilic.

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2
Q

What is signal transduction?

A

Any process by which a biological cell converts one kind of signal or stimulus into another.

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3
Q

What happens when a ligand binds to a receptor?

A

It brings about a change in cellular activity (directly or indirectly).

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4
Q

True or false - receptor sub-types are not general and work for many different types of ligand?

A

False - they are specific for one (or a limited number of) ligands.

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5
Q

What do agonists do?

A

Bind to the receptor and activate it (leading to intracellular signal transduction events).

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6
Q

What do antagonists do?

A

Bind to the receptor but do not activate it, blocking the effects of agonists at the receptor.

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7
Q

What do sensory GPCRs sense?

A

Light, odours and tastes

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8
Q

Which of these can GPCRs not respond to?

Ions, neurotransmitters, peptide and non-peptide hormones, large glycoproteins.

A

Trick question, all of them.

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9
Q

What is the basic structure of a GCPR?

A

Single polypeptide chain, 7 transmembrane spanning regions, extracellular N-terminal, intracellular C-terminal.

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10
Q

Which two regions of GPCRs can be responsible for ligand binding?

A

2-3 of the transmembrane domains, or the N-terminal region

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11
Q

Why are GPCRs also known as 7TM receptors?

A

They pass through the membrane seven times.

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12
Q

How do GPCRs respond to ligand binding?

A

They change the conformation of the protein structure.

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13
Q

What happens to the G protein when the GPCR changes conformation?

A

The GDP which is attached to it is swapped for GTP, causing it to split into an alpha and beta-gamma subunit.

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14
Q

Why are G proteins described as “structurally trimeric but functionally dimeric”?

A

They are made up of three subunits but they only split into two.

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15
Q

What do the alpha-GTP and beta-gamma subunits do once a G protein has split up?

A

They interact with effector proteins (second messenger-generating enzymes, ion channels)

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16
Q

How is G protein signalling terminated?

A

GTPase hydrolyses the GTP on the alpha subunit, turning it back to GDP. The subunits reform the inactive heterotrimeric complex.

17
Q

The human genome encodes 20 G alpha, 5 G beta and 12+ G gamma proteins. How many possible combinations are there?

A

Over 1000

18
Q

True or false - the alpha subunit is the primary determinant of which G protein the GCPR interacts with.

A

True

19
Q

Adrenaline/noradrenaline can bind to beta-adrenoceptors, alpha 1 and alpha 2 adrenoceptors, all using the alpha subunit. What are the respective effectors?

A

Adenylyl cyclase (increase), adenylyl cyclase (decrease), phospholipase C (increase)

20
Q

Acetylcholine can decrease adenylyl cyclase and increase phospholipase C using the alpha subunit. Which GCPR does it respectively bind to?

A

M2/M4 muscarinic receptor, M1/M3 muscarinic receptor.

21
Q

What is the common name of the illness caused by the pertussis toxin?

A

Whooping cough

22
Q

Which stage of the G protein function cycle does the pertussis toxin interfere with?

A

It prevents the GDP on the alpha unit from being swapped for GTP, meaning the subunits never separate.

23
Q

Which stage of the G protein function cycle does the cholera toxin interfere with?

A

It prevents the GTP on the separated alpha subunit from being hydrolysed, so the subunits never rejoin and the CTFR proteins remain stuck open.