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Year 1 Semester 2 > Lipids, Cell membranes and Signal transduction > Flashcards

Lipids, Cell membranes and Signal transduction Flashcards

1
Q

What are the 6 steps of cell-cell communication

A
  • Synthesis of signal
  • Release of the signalling molecule by the signalling cell: exocytosis, diffusion, cell-cell contact
  • Transport of the signal to the target cell
  • Detection of the signal by a specific receptor protein
  • A change in cellular metabolism, function or development triggered by the receptor-signal complex
  • Removal of the signal or desensitisation
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2
Q

What is endocrine signalling?

A
  • An example of long range signalling

- Hormone released by endocrine cell and carried in bloodstream to distal target cells

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3
Q

What is an example of endocrine signalling?

A

Follicle-stimulating hormone released from the pituitary acts upon the ovary

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4
Q

What is an example of neurotransmission?

A

Breathing - the phrenic and thoracic nerves send impulses from the brain to the diaphragm

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5
Q

What is paracrine signalling?

A
  • An example of short range signalling

- Signalling molecules only affect target cells in close proximity to secreting cells

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6
Q

What is an example of paracrine signalling?

A

Somatostatin release by pancreas cells acts locally

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7
Q

What is autocrine signalling?

A

Cells respond to substances that they themselves release

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8
Q

What is an example of autocrine signalling?

A

Some neurotransmitters and growth factors bind to the cells that release them

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9
Q

What is an example of membrane-bound proteins interacting to signal?

A

Signalling by T cells in the immune system

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9
Q

What is an example of membrane-bound proteins interacting to signal?

A

Signalling by T cells in the immune system

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10
Q

What are the two types of cell receptors?

A
  • Cell-surface receptors (hydrophilic signal molecule)

- Intracellular receptors (hydrophobic signal molecule)

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11
Q

In more detail what are the four receptor types?

A
  • Ligand-gated ion channels (ionotropic receptors)
  • G-protein-coupled receptors (metabotropic)
  • Kinase-linked receptors
  • Nuclear receptors
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12
Q

Examples of lipid soluble molecules

A
  • Steroid hormones

- Thyroxine

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12
Q

Examples of lipid soluble molecules

A
  • Steroid hormones

- Thyroxine

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13
Q

Explain the inositol phospholipid signalling pathway

A
  • Phosphatidylinositol 4,5-bisphosphate (PIP2) is a phospholipid found in the lipid bilayer
  • It is the substrate of the enzyme phospholipase C (PLC)
  • PLC liberates two signalling molecules from PIP2; inositol 1,4,5 triphosphate (IP3) and diacylglycerol (DAG)
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14
Q

How is calcium involved in cell signalling?

A
  • Calcium concentration transiently increases in the cell in response to IP3 release
  • Calcium binds to proteins to regulate their function
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15
Q

What is an example of calcium being used in signalling?

A

Ca2+/calmodulin - activates proteins/enzymes through direct interaction such as myosin light chain kinase

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16
Q

How is protein kinase C (PKC) involved in signalling?

A
  • Calcium binds to C2 domain of PKC
  • This allows C2 to interact with the plasma membrane
  • This causes C1 domain to recognise and bind to the diacylglycerol that has been released
  • This invokes a change in structure that causes the inhibitory domain of PKC to come away from the active sight activating the PKC and enabling it to phosphorylate and change the substrate molecules
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17
Q

What are some examples of PKC substrates?

A
  • Tumour suppressor p53 (transcription factor) - prevents tumour formation
  • Cav 1.2 (calcium channel) - heart muscle contraction
  • IKKalpha (cytokine) - B cell activation (immune function)
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18
Q

What are eicosanoids (prostanoids)?

A
  • Inflammatory mediators
  • Considered local hormones
  • Have specific effects on target cells close to their site of formation (autocrine/paracrine)
  • Rapidly degraded so are not transported to distal sites within the body
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19
Q

What are the 3 principal eicosanoids?

A
  • Prostaglandins
  • Thromboxanes
  • Leukotrienes
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20
Q

What is the main source of eicosanoids?

A

Arachidonic acid

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21
Q

What is arachidonic acid?

A

A 20 carbon unsaturated fatty acid containing 4 double bonds

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22
Q

What is the initial and rate-limiting step in eicosanoid synthesis?

A

Liberation of arachidonic acid by phospholipase A2 (PLA2)

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23
Q

How is PLA2 activated?

A

PLA2 is activated by a variety of receptor-mediated signals

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24
Q

What are the two ways that we can metabolise arachidonic acid to synthesise eicosanoids and which type does each synthesise?

A
  • Cyclo-oxygenase and peroxidase to give prostaglandins and thromboxanes
  • Lipoxygenases to give leukotreines
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25
Q

What can prostaglandins do?

A
  • Vasoconstriction/dilation
  • Inhibit/promote platelet aggregation
  • Effects depend upon receptor (e.g. EP1 receptor - vasoconstriction; EP2 receptor - vasodilation)
  • Inflammatory response, thermoregulation and pain
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26
Q

Where are thromboxanes synthesised?

A

In platelets

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27
Q

What are some actions of thromboxanes?

A
  • Stimulate platelet aggregation

- Vasoconstrictor

28
Q

How do leukotrienes get their name?

A
  • Leuko - because they are synthesised in white blood cells

- Trienes - because they contain a conjugated triene system of double bonds

29
Q

What are leukotrienes involved in?

A
  • Some contain the amino acid cysteine in their structure (anaphylactic shock)
  • Immunes response
  • Heavily implicated in asthma and allergy
30
Q

What is platelet-activating factor involved in?

A

-Platelet aggregation
-Vasoconstriction
-Inflammation
Immune response (also anaphylaxis)

31
Q

Aspirin inhibition

A
  • Aspirin acetylates a serine hydroxyl group near the active site, preventing arachidonate binding
  • Inhibition by aspirin is irreversible however, in most body cells re-synthesis of Cox-1 would restore cyclooxygenase activity
32
Q

Aspirin as an anticoagulant

A
  • Thromboxane A2 stimulates blood platelet aggregation, essential to the role of platelets in blood clotting
  • Many people take a daily aspirin for its anti-clotting effect, attributed to inhibition of thromboxane formation (via COX-1 inhibition) in blood platelets
  • This effect of aspirin is long-lived because platelets lack a nucleus and do not make new enzyme
33
Q

What are the two common ways to activate/deactivate signalling proteins?

A
  • Signalling by phosphorylation

- Signalling by GTP binding

34
Q

What are the two main types of kinases?

A
  • Tyrosine kinase

- Serine/threonine kinase

35
Q

What are the two types of GTP-binding proteins?

A
  • Trimeric G proteins

- Monomeric GTPases

36
Q

Roughly how many kinases and phosphatases does the human genome encode?

A
  • 520 kinases

- 150 phosphatases

37
Q

How are G-proteins involved in signal transduction?

A

Ligand binding activates a G-protein which in turn activates or inhibits another protein. Often this is an enzyme that generates a specific second messenger

37
Q

How are G-proteins involved in signal transduction?

A

Ligand binding activates a G-protein which in turn activates or inhibits another protein. Often this is an enzyme that generates a specific second messenger

38
Q

Describe G-protein coupled receptors (GPCR)

A

All G-protein coupled receptors have 7 membrane spanning regions with their amino termini on the extracellular face and their carboxy termini on the cytoplasmic face of the plasma membrane

39
Q

Define trimeric

A

Composed of three different subunits

40
Q

What subunits are trimeric G-proteins composed of?

A

alpha, beta and gamma

41
Q

Explain the G-protein mechanism of action

A
  • Binding of the ligand to the receptor changes its conformation, causing it to bind to the G-alpha protein in such a way that GDP is displaced and GTP is bound
  • This triggers G-beta-gamma dissociation activating downstream pathways
  • Activation is short-lived, as GTP bound to G-alpha hydrolyses to GDP in seconds, leading to the re-association of G-alpha with G-beta-gamma and inactivation of effector molecule
42
Q

How many types of G-alpha subunits are there?

A

20

42
Q

How many types of G-alpha subunits are there?

A

20

43
Q

What does G-alpha-q (Gq) do?

A

Stimulates phospholipase C

44
Q

What does Gs do?

A

Stimulates adenylate cyclase

45
Q

What does Gi do?

A

Inhibits adenylate cyclase, decreases cAMP

46
Q

How many types of G-beta subunits are there?

A

6

47
Q

How many types of G-gamma subunits are there?

A

12

48
Q

How many different combinations are there of G-beta and G-gamma subunits?

A

72

49
Q

What do G-beta-gamma dimers do?

A
  • Gate ion channels
  • stimulates PLA2
  • Stimulates adenylate cyclase
  • Stimulates PLC-beta, PLC-epsilon, PLC-eta
50
Q

How are the different phospholipase isoforms activated?

A
  • Beta - GPCR activation (G-alpha-q)
  • Gamma - receptor tyrosine kinases
  • Delta - kinases (possibly increase in Ca2+)
  • Epsilon - small GTPases
  • Zeta - fertilisation
  • Eta - increase in calcium, G-beta-gamma, other mechanisms
51
Q

What is the resting calcium concentration?

A

About 100nM

52
Q

What is the activated calcium concentration?

A

0.5-1microM

53
Q

How many isoforms of protein kinase C are there?

A

At least 12

54
Q

Describe protein kinase C’s (PKC) role in signalling

A
  • Most PKCs present as catcalytically inactive, soluble proteins in the cytoplasm
  • Rise in cytosolic calcium levels causes PKC to bind to the cytosolic leaflet of the plasma membrane, where it can be activated by the membrane-associated DAG and/or Ca2+
  • PKC then phosphorylates a wide variety of substrate proteins on serine and threonine residues
  • PKC has substrates in the cytoplasm and some isoforms can translocate to the nucleus to phosphorylate nuclear proteins, and can thus function in a transient way or in a more permanent way (gene transcription)
54
Q

Describe protein kinase C’s (PKC) role in signalling

A
  • Most PKCs present as catcalytically inactive, soluble proteins in the cytoplasm
  • Rise in cytosolic calcium levels causes PKC to bind to the cytosolic leaflet of the plasma membrane, where it can be activated by the membrane-associated DAG and/or Ca2+
  • PKC then phosphorylates a wide variety of substrate proteins on serine and threonine residues
  • PKC has substrates in the cytoplasm and some isoforms can translocate to the nucleus to phosphorylate nuclear proteins, and can thus function in a transient way or in a more permanent way (gene transcription)
55
Q

How is cyclic AMP synthesised?

A

Synthesised within cells from ATP by the enzyme adenylate cyclase

56
Q

What enzyme is used to degrade cyclic AMP?

A

cAMP phosphodiesterase

57
Q

What happens after cAMP is synthesised?

A

cAMP activates cAMP-dependent protein kinase (PKA) allowing PKA’s catalytic subunits to bind to and affect other molecules within the cell

58
Q

Where does PKA have substrates?

A

The membrane, cytoplasm and the nucleus

59
Q

What can PKAs do in the nucleus?

A

PKA can activate transcription of genes containing cAMP response elements elements, or CREs in their promoter. A specific transcription factor, the cAMP response element binding protein, CREB, binds to thus sequence and activates transcription of downstream genes. When CREB is unphosphorylated, it is inactive; only in its phosphorylated state does CREB activate transcription

60
Q

What does cholera toxin do?

A
  • Stimulates G-alpha-s in intestinal epithelial cells
  • Causes an overstimulation of cAMP production
  • Results in a release of water and ions including Na+, K+, Cl- and HCO20 into the lumen of the small intestine
  • Leads to rapid fluid loss and dehydration
61
Q

What does pertussis toxin do?

A

Inhibits G-alpha-i to increase cAMP production in lung epithelia

62
Q

What is Ras?

A

A small GTPase

63
Q

How do receptor tyrosine kinases work?

A
  • Signal molecule binds
  • Conformational change causes RTK to become phosphorylated
  • Other molecules bind to RTK to become phosphorylated to become activated and carry on the required mechanism through the cell
64
Q

GTPases and disease

A
  • Damage to these small GTPase switches can have catastrophic consequences for the cell and the organism
  • Several small GTPases of the Rac/Rho subfamily are direct targets for clostridial cytotoxins
  • Further, Ras proteins are mutated to a constitutively active (GTP-bound) form in approximately 20% of human cancers
64
Q

GTPases and disease

A
  • Damage to these small GTPase switches can have catastrophic consequences for the cell and the organism
  • Several small GTPases of the Rac/Rho subfamily are direct targets for clostridial cytotoxins
  • Further, Ras proteins are mutated to a constitutively active (GTP-bound) form in approximately 20% of human cancers
65
Q

What does MAPK stand for?

A

Mitogen-activated protein kinase

66
Q

What activates MAPK?

A

Ras proteins

Year 1 Semester 2 (26 decks)

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