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BSMS 102 > Theme 3 - intracellular signalling > Flashcards

Theme 3 - intracellular signalling Flashcards

1
Q

give four examples of intracellular signals

A

ions, proteins, gases and second messengers

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2
Q

name three molecules that need receptors to get through the membrane

A

proteins, peptides and charged molecules

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3
Q

name two ways ligands can cause downstream effects

A

by directly interacting with the cell surface receptor or binding co-receptors or accessory molecules on the cell surface

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4
Q

what type of proteins are most signalling molecules and where are they found?

A

hydrophilic proteins in the cytoplasm

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5
Q

where are hydrophobic signalling molecules most likely to be found?

A

embedded in the membrane

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6
Q

name three cellular processes that may be changed due to a signalling cascade activating an effector protein

A

altered metabolism, altered cell shape or altered gene expression

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7
Q

give an example of where signal amplification occurs

A

in the eye - rhodopsin detects low levels of light

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8
Q

what is distribution in signal amplification?

A

activation of one molecule that then goes on to activate many others

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9
Q

name three ways in which signalling molecules are controlled

A

by post translational modifications (phosphorylation), binding GTP/GDP or interaction with activators such as Ca++ and cAMP

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10
Q

how does a kinase phosphorylate a protein?

A

removes a phosphate from ATP in the cytoplasm which is then added to another protein, causing a shape change

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11
Q

how do phosphatases turn a signal off?

A

hydrolyse and take the phosphate group off the protein

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12
Q

does phosphorylation always activate proteins?

A

usually it does but it can also inactivate them

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13
Q

what three amino acids can a phosphate group be added on to?

A

tyrosine, threonine and serine

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14
Q

why can phosphate groups only be added onto specific amino acids?

A

they have a free hydroxyl group where a kinase can attach a phosphate

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15
Q

give three examples of serine threonine kinases

A

CaM kinase (calcium calmodulin dependent kinase), PKA (produces glucose), PKC (leaning and memory), MAPK (cytokine production)

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16
Q

what are the two subclasses of tyrosine kinases?

A

receptor and non receptor tyrosine kinases

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17
Q

give an example of a non receptor tyrosine kinase

A

Src

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18
Q

give an example of an RTK

A

EGFR (the receptor itself in a kinase)

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19
Q

what are small GTPases and where are they usually found?

A

GTP binding proteins that are usually found in the cytoplasm

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20
Q

what is an inactive small GTPase bound to?

A

GDP

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21
Q

what needs to happen for a small GTPase to bind GTP?

A

GDP needs to be released so it can preferentially bind GTP in the cytoplasm

22
Q

how does a small GTPase switch the signal off?

A

proteins have their own intrinsic GTPase activity which is a motif in its protein sequence that hydrolyses GTP back to GDP

23
Q

give an example of a GTPase

A

Ras

24
Q

how long does it take for Ras to activate and inactivate?

A

activates in 10 seconds and turns itself off in 10 mins

25
Q

what mutations can lead to signalling errors?

A

ras - mutation from glycine to valine at amino acid 12

26
Q

what does mutations in ras cause the protein to be?

A

constitutively active - no longer hydrolyses GTP to GDP so can’t switch itself off

27
Q

name two provisional activators of proteins

A

Calcium and cAMP

28
Q

how does calcium regulate proteins?

A

binds calmodulin which induces a conformational change so it can engage with target protein Cam Kinase which then phosphorylates myosin

29
Q

what type off folding predominates in GPCRs?

A

alpha helices

30
Q

what is a G protein bound to in the inactive state

A

alpha subunit is bound to GDP and alpha, beta, gamma are attached

31
Q

what happens when GTP binds the alpha subunit of a G protein?

A

the alpha subunit dissociates from the beta gamma subunit

32
Q

does the alpha subunit have GTPase activity?

A

yes - it can switch itself off

33
Q

which G proteins are involved in adenylate cyclase and cAMP signalling?

A

Gs and Gi

34
Q

which ligand binds which receptor to activate the Gs signalling cascade?

A

adrenaline binds an adrenergic receptor

35
Q

what is the role of adenylate cyclase?

A

sits in the membrane and converts ATP to cAMP when contacted by a GTP bound Gs protein

36
Q

what is PKA activated by and what does it do?

A

activates when cAMP binds and it goes to the nucleus to phosphorylate transcription factors to drive glucose production

37
Q

what receptors are involved in Gq activation?

A

M1 muscarinic acetylcholine receptors

38
Q

what does an activated Gq bind?

A

PLC - causes cleavage of PIP2 to DAG and IP3

39
Q

what is the effector molecule in the Gq cascade?

A

PKC - which is activated by DAG and calcium and cause phosphorylation of other molecules

40
Q

which receptor slows down heart rate when activated?

A

M2 muscarinic Ach receptors

41
Q

how does binding of Ach to an M2 receptor lead to decrease heart rate?

A

Ach binds the M2 receptor, beta gamma unit says in the membrane and binds to K+ channels causing them to ope, this causes K+ to move out the cell and hyperpolarise the cell therefore heart rate slows down and decreased FOC

42
Q

Name two conditions that are implicate G protein signalling

A

cholera and whooping cough

43
Q

what type of G protein does cholera toxin inhibit and what are the consequences of this?

A

inhibits GTPase activity Gs therefore it cant switch itself off - prolonged activity causes water and chloride ions to move out of intestinal cells - dehydration, diarrhoea and sometimes death

44
Q

what toxin is produced by whooping cough?

A

bordetella pertussis - pertussis toxin

45
Q

what G protein does bordetella pertussis inhibit and what are the consequences?

A

pertussis toxin stops Gi associating when its GPCR and also releases an active form of adenylate cyclase - double wham of not being able to switch off adenylate cyclase and introducing an extra active version - prolonged signalling which stimulates coughing

46
Q

where can kinase activity occur on an enzyme coupled receptor?

A

built into the receptor or association with a molecule that has kinase activity

47
Q

how many TM domains do enzyme coupled receptors usually have?

A

one - type I transmembrane receptor

48
Q

what happens to an enzyme coupled receptor when a ligand binds?

A

dimerisation

49
Q

Initial signalling cascade of an RTK

A

ligand binds and two receptors are brought together to form a dimer, then they can cross phos/phos themselves - this activates the receptorand phos sites allow proteins to dock and have further downstream effects

50
Q

what type of enzyme activity do RTKs have?

A

intrinsic (built in)

BSMS 102 (14 decks)

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