Lipids and signalling Flashcards
1
Q
What are the 3 types of cell to cell signalling?
A
1) Remote
2) Juxtacrine
3) Gap junctions
2
Q
What are the 3 modes of cell to cell signalling?
A
1) Remote
2) Juxtacrine
3) Gap junctions
3
Q
What are the 3 stages of remote signalling?
A
1) reception
2) transduction - sometimes called a signalling cascade, can be multi stepped
3) response - activation of the response which is required
4
Q
What are 3 common types of ligands in cell signalling?
A
1) growth factors
2) neurotransmitters
3) hormones
5
Q
What are the 4 methods of cell to cell signalling?
A
1) Paracrine - signalling molecule acts on nearby cells
2) Autocrine
3) Endocrine - signalling molecule released into blood
4) Neuronal - in response to nerve stimulus, can be autocrine or paracrine, receptor may be on a muscle cell or gland or another nerve
6
Q
What are the 2 types of signalling that hormones can be used for?
A
1) Endocrine hormones released into the bloodstream from endocrine glands
2) Hormones with paracrine function diffuse through interstitial spaces to nearby target tissues
7
Q
By what mechanisms are hormone activity regulated?
A
Regulated through positive or negative feedback mechanisms
8
Q
Where are receptors of hydrophilic and lipid based hormones generally located?
A
1) Hydrophillic - on cell membrane
2) Lipid based - inside cell
9
Q
Are catecholamines and peptide hormones hydrophilic or lipid based?
A
Hydrophillic
10
Q
What kind of hormones are ADR, NA, DOPA, serotonin and histamine?
A
Catecholamines
11
Q
What kind of hormones are glucagon, insulin and angiotensin 2?
A
Peptide hormones
12
Q
What kind of hormones are oestrogen, testosterone, aldosterone, cortisol?
A
Steroids
13
Q
What kind of hormones are Thyroxine (T4), tri-iodothyronine (T3)?
A
Thyroid hormones
14
Q
What kind of hormone is calcitrol?
A
Sterol hormone
15
Q
Are steroids, thyroid hormones and sterol hormones hyrdophillic or lipid based hormones?
A
Lipid based hormones
16
Q
Why can different cells respond differently to the same signalling molecule?
A
Multiple receptor subtypes exist, each with their own transduction mechanism
17
Q
How does the response of muscle cells, cardiac myocytes, and salivary glands to ACh differ?
A
1) Muscle cell (R1 receptor subtype) - contraction
2) Cardiac muscle (R2 receptor subtype) - relaxation
3) Salivary glands (R3 receptor subtype) - secretion
18
Q
What are the 4 main types of receptor?
A
1) ligand gated ion channel
2) g protein coupled receptor
3) kinase - linked receptor
Above 3 are cell surface receptors
4) Nuclear receptor - intracellular receptor
19
Q
What are the 4 main types of receptor?
A
1) ligand gated ion channel
2) g protein coupled receptor
3) kinase - linked receptor
Above 3 are cell surface receptors
4) Nuclear receptor - intracellular receptor
20
Q
What are ligand gated ion channels and how do they work?
A
Ionotropic receptors, involved in rapid signalling between electrically excitable cells, binding and channel opening is very fast, allows specific ions to for through a channel and alter cell membrane potential
21
Q
What is the rough structure of a ligand gated ion channel?
A
4/5 heteromeric sub units surrounding a central pore
22
Q
What is the structure of nicotinic ACh receptors (nAChR)?
A
pentameric assembly of 2 alpha, 1 beta, 1 gamma and 1 omega subunit, each sub unit has 4 membrane saving regions, 2 alpha sub units are the bit ACh binds to, allow Na+ into cell and K+ out
23
Q
Name 3 ligand gated ion channel receptors that have a similar pentameric arrangement to nAchR?
A
1) GABA
2) GlyR (Glycine receptor)
3) 5-HT3 receptor
24
Q
What are g protein coupled receptors sometimes referred to as?
A
metabotropic or heptahelical receptors
25
What is the rough structure of GPCR?
single polypeptide, 7 membrane spanning units, N terminus on extracellular side, C terminus in cytosol, hormones bind to either extracellular loop regions or transmembrane regions
26
What kind of receptors are angiotensin 2 receptors?
GPCR's
27
What are the effects of activation of the AT1 angiotensin 2 receptors?
1) Vasoconstriction
2) Increased NA from sympathetic terminals
3) Stimulation of proximal tubular Na+ absorption
4) Aldosterone secretion from adrenal cortex
5) Vascular growth (hyperplasia and hypertrophy)
28
What are the effects of AT2 angiotensin 2 receptor activation?
1) Anti hypertrophic effects
| 2) anti-hypertensive effects
29
What is the rough structure of kinase linked receptors?
Single transmembrane helix, with a large extracellular binding domain and in intracellular catalytic domain
30
What is the difference between catalytic and non catalytic kinase linked receptors?
1) Catalytic - receptor itself is an enzyme eg. insulin receptor
2) Non catalytic -act through cytoplasmic tyrosine kinases eg. cytokine receptors
31
What happens following ligand binding to a kinase linked receptor?
receptor dimerization occurs and they become activated, the interaction between the intracellular domains of the 2 receptors allows activity, act by directly regulating gene transcription
32
What are nuclear receptors?
intracellular receptors which regulate the transcription of certain genes, have a monomeric structure with separate ligand and DNA binding domains
33
How does signalling through nuclear receptors work?
Hormone diffuses across plasma membrane and interacts with cytosolic or nuclear receptors, this forms a hormone-receptor complex (upon binding cytosolic complexes translocate to the nucleus), within the nucleus the complex binds to DNA at special sites called 'hormone responsive elements' and affects gene transcription
34
What are the 5 types of neurotransmitters?
1) Acetyl choline
2) Peptides
3) monoamines
4) am
35
What are the 5 types of neurotransmitters?
1) Acetyl choline
2) Peptides
3) monoamines
4) amino acids
36
What are the 5 types of neurotransmitters?
1) Acetyl choline
2) Peptides
3) monoamines
4) amino acids
5) lipids
37
What are the 5 stages in the lifecycle of a neurotransmitter?
1) Synthesis (in the nerve terminal except for neuropeptides)
2) Storage (in synaptic vesicles within the nerve terminals)
3) Release (by exocytosis)
4) Receptor activation (don't forget negative feedback by pre synaptic auto activation)
5) Neurotransmitter inactivation
38
What are the 2 distinct types of depression?
1) Unipolar - mood swings are always in the same direction
| 2) Bipolar - depression alternates with mania
39
Of what do depressive patients have a functional deficit of and what is the role of antidepressants?
Functional deficit of monoaminergic transmission (monoamines - NA, dopamine (DA), serotonin (5-HT))
Role of anti depressants is to increase this transmission
40
What are the 5 types of treatment for depression?
1) Monoamine reuptake inhibitors (tricyclic antidepressants, selective serotonin/noradrenaline reuptake inhibitors - TCAs, SSRIs, SNRIs)
2) Monoamine oxidase inhibitors - MAOIs
3) Miscellaneous atypical antidepressants - action is poorly understood, may act as non-selective antagonists at pre synaptic auto receptors
4) Electroconvulsive therapy
5) Mood stabilising drugs eg. Lithium
41
What are gasotransmitters?
Gaseous molecules synthesised in the body including NO,CO,H2S, pass readily through membranes and are involved in paracrine signalling
42
Which gasotransmitter is produced from Heme?
CO
43
Which gasotransmitter is produced from L-arginine?
NO
44
Which gasotransmitter is produced from homocysteine?
H2S
45
In terms of cell signalling what are 'hierarchy' and 'amplification' characteristics of?
Intracellular signalling pathways
46
What is meant by hierarchy in terms of signal transduction?
components of the pathway are arranged in a specific order in order to transmit the signal - this isn't always linear and bits can branch off
47
In the effect of adrenaline on skeletal muscle and liver cells, what is the signalling hormone, receptor and cell response?
1) Signalling hormone = adrenaline
2) Receptor = beta adrenergic receptor
3) Cellular response = break down of glycogen to form glucose
48
How long does a G protein remain activated?
G protein remains activated by the receptor as long as the ligand remains in the active site
49
How long does a G protein remain activated?
G protein remains activated by the receptor as long as the ligand remains in the active site - a single G protein can continue to shuttle back and forth and activate many molecules of effector enzyme
50
In terms of cell signalling what is cross talk?
interaction between 2 different intracellular signalling pathways, a signalling component produced in a second pathway modulates the cell response to the first by stimulating or inhibiting the first pathway
51
What are the different effects of adrenaline on 1) muscle or liver tissue, 2) adipose tissue, 3) cardiovascular tissue?
1) Muscle or liver tissue - glycogenolysis
2) Adipose - fatty acid production
3) Cardiovascular - heart rate, blood pressure
52
What are the 4 main components of intracellular signal transduction pathways?
1) G proteins (activate effector enzymes)
2) Effector enzymes (produces second messenger)
3) 2nd messengers
4) kinases
53
What is the relationship between G proteins and guanine nucleotides (GTP and GDP)?
G proteins bind guanine nucleotides, GTP is a high energy molecule which activates G proteins, G proteins are GTPases - they can catalyse the hydrolysis of GTP to GDP (which switches the G protein off and therefore can self regulate)
54
How are G proteins attached to the lipid membrane?
Anchored to the internal surface of the cell by a lipid tail (prenylated)
55
What are the 2 major groups of G proteins?
1) G proteins (receptor associated)
| 2) Small GTPases
56
What are small GTPases?
Monomeric (1 subunit attached by a lipid tail)
Include Ras and Rho
Involved in cell signalling, cytoskeletal regulation and vesicle trafficking
57
What is the structure of G proteins (receptor associated)?
heteromeric (have 3 subunits, alpha beta and gamma), The alpha and gamma subunits are bound to the membrane by lipid tails, the alpha subunit is the one that changes and gives the G protein its specificity, the alpha subunit contains the GTPase activity
58
When a ligand binds to a GPCR what happens to the G protein?
1) G proteins are active when bound to GTP and inactive when bound to GDP
2) Binding of the ligand to the receptor causes a conformational change in the receptor which allows the G protein to bind to the receptor
3) This stimulates the G protein to exchange its GDP for GTP (switching it on so it can activate the enzyme)
4) G protein, hydrolyses the GTP back to GDP, due to its intrinsic, GTPase activity, returning it to the off position
59
What effector enzyme and 2nd messenger is linked to Gas G proteins?
Effector enzyme = adenylate cyclase (stimulation)
| 2nd messenger = increase cAMP
60
What effector enzyme and 2nd messenger is linked to Gai G proteins?
effector enzyme = adenylate cyclase (inhibition)
| 2nd messenger = decrease cAMP
61
What effector enzyme and 2nd messenger is linked to Gaq G proteins?
Effector enzyme = phospholipase C (stimulation)
| 2nd messenger = DAG and IP3 increase
62
What happens in terms of movement of subunits of G protein when the G protein becomes activated?
1) Binding of the ligand activate the G protein
2) GTP bound alpha subunit dissociates from the beta and gamma sub units
3) The GTP bound alpha subunit binds to and activates the effector enzyme
4) GTPase activity of the alpha subunit hydrolyses GTP to GDP releasing inorganic phosphate, switching the G protein off
5) The GDP bound alpha subunit then re associates with the beta and gamma sub units
6) If the receptor is still active then the process will be repeated and the signal will continue to be amplified
63
From what is the 2nd messenger cyclic AMP synthesised?
adenylyl cyclase catalyses the production of cAMP from ATP
64
What is the name of the enzyme which breaks down cAMP?
Phosphodiesterases break cAMP down to AMP
65
In terms of G proteins what does the cholera toxin do?
effects of the cholera toxin are due
66
What is the name of the enzyme which breaks down cAMP and cGMP?
Phosphodiesterases (PDEs) break cAMP and cGMP down to AMP and GMP respectively
67
In terms of G proteins what does the cholera toxin do?
effects of the cholera toxin are due to the cholera toxin activating the Gs G protein, the cholera does so by inactivating the GTPase activity of Gs so GTP remains bound and Gs stays active. Gs overstimulates adenylyl cyclase and you get a build up of cAMP, in intestinal cells elevated cAMP opens Cl- channels so increased loss of Cl- ions into the lumen
68
In terms of G proteins what does the Bordetella pertussis (whooping cough) toxin do?
Inhibits the Gi G protein, prevents GDP to GTP exchange by Gi, Gi therefore remains permanently switched off so its unable to inhibit adenylyl cyclase and cAMP therefore accumulates. This has many effects including increased insulin secretion and sensitivity to histamine that contribute to some symptoms of the disease.
69
What are the 5 most common second messengers?
1) cAMP (ATP -> cAMP)
2) cGMP (GTP -> CGMP)
3) Diacylglycerol (DAG) - PIP2 -> DAG + IP3
4) Inositol 1,4,5-triphosphate (IP3)
5) Intracellular Ca2+
70
How is cAMP formed by from ATP by adenylyl cyclase?
Enzyme removes 3 phosphates and joins 1 back on looping round to form a cyclic structure (releasing an inorganic diphosphate molecule too)
71
What are the 2 different types of guanylyl cyclases?
1) Soluble form in cytosol which is activated by NO
| 2) Membrane bound form that is activated by a ligand
72
Name 2 well known PDE inhibitors?
Caffeine and Viagra (sildenafil)
73
What is the role of PDEs in cell signalling?
Break down the second messenger thus needed to switch off the signalling pathway
74
Which kind of G protein and 2nd messenger are involved in angiotensin 2 acting on the AT1 receptor and adrenaline acting on alpha 1 adrenergic receptor?
Gq - DAG and IP3 production
75
Which membrane bound enzyme catalyses the production of DAG and IP3 from PIP2?
Phospholipase C
76
How are IP3 and DAG made from PIP2 and what does this cause?
1) PIP2 = membrane bound lipid, IP3 is released into the cytosol and DAG remains bound to the membrane
2) IP3 is a polar molecule which diffuses through the cytosol to the ER where it interacts with Ca2+ channels to stimulate the release of stored Ca2+ ions into the cytosol
3) increases in cytosolic Ca2+ concentration stimulates various cellular processes
4) DAG remains in the membrane and stimulates protein kinase c which phosphorylates target proteins leading to a cellular response
5) PKC can also be activated by Ca2+ released from the ER
77
What sort of molecules can be activated by Ca2+?
calcium dependent kinases
78
After signal transduction how is cytosolic Ca2+ concentration returned to its normal low levels?
Ca2+ is taken back up into the ER through calcium ATPase in the ER membrane or is pumped out of the cell
79
What is the oxytocin receptor an example of?
Phosphoprotein, phosphorylated only at intra cellular domains as this is where the kinases are located
80
What are the 3 main types of protein kinases?
1) Serine/threonine kinases - phosphorylate Ser and or Thr residues
2) Tyrosine kinases - phosphorylate only Tyr residues receptor tyrosine kinase = insulin receptor
3) Dual-specificity kinases = phosphorylate Ser/Thr or Tyr residues
81
What are the 2 main groups of phosphatases?
1) Ser/Thr directed phosphoprotein phosphatases PPPs
| 2) Tyr directed phosphoprotein phosphatases PTPs
82
What are the 2 ways that protein kinases can alter protein function?
1) Phosphorylation to induce a change in protein conformation or function
2) Phosphorylation of a transcription factor that alters gene transcription (can switch it on or off) and hence regulate expression levels of many proteins
83
What is the relationship between protein kinases and cancer?
Dysregulation of protein kinases (due to mutations in genes coding for kinases) is directly linked to cancer development.
84
Which protein kinase is activated by cAMP?
Protein kinase A
85
Which protein kinase is activated by Ca2+?
Protein kinase C and Ca/CaM kinase
86
Which protein kinase is activated by DAG?
Protein kinase C
87
Which protein kinase is activated by cGMP?
Protein kinase G
88
How is guanylate cyclase activated?
by NO or neuropeptide (diffuses through the membrane)
89
Which kind of G protein is the beta 1 adrenergic receptor linked to?
Gs
90
Which kind of G protein is the muscarinic M2 Acetyl choline receptor linked to?
Gi
91
Which kind of G protein is the AT1 angiotensin 2 receptor linked to?
Gq
92
What are the functions of lipids in the body?
1) energy stores
2) components of cell membranes
3) solubilise fat soluble vitamins
4) precursors to other biological molecules (hormones etc.)
5) signalling molecules
93
Is cholesterol a lipid?
YES
94
Lipids are insoluble how are the carried in the blood?
lipoproteins
95
How much cholesterol comes from the diet and how much is synthesised in the liver?
75% synthesised in the liver
| 25% comes from the diet
96
What are the constituents of lipoproteins?
Lipid + apolipoprotein = lipoprotein
97
What is the generalised structure of a lipoprotein?
External monolayer = phospholipids, cholesterol and apolipoproteins
Core = cholesterol and triglycerols
98
What mediates the functions of lipoproteins?
function is mediated by apolipoprotein present in the lipoprotein - lipoproteins are assigned to specific functions due to posession of apolipoproteins
99
What kind of macromolecule is an apolipoprotein?
Protein strand
100
What is the role of chylomicrons?
Transport of dietary fats (triglycerides, cholesterol) from intestine to the tissues
101
What is the role of VLDL's?
Transport lipids made in the liver to peripheral tissues
102
What is the role of LDLs?
Provide cholesterol for peripheral tissues, the main cholesterol carrier
103
What is the role of HDLs?
Transport of cholesterol from tissues to the liver
104
What is the specific function of ApoA and which kind of lipoprotein is it commonly found in?
Present in HDL
| Mediates efflux of cholesterol from peripheral cells and influx to the liver
105
What is the specific function of ApoB?
recognises ApoB/ApoE receptors, facilitates LDL uptake into cells
106
What is the specific function of ApoC?
activator of lipoprotein lipase, transferred between lipoproteins
107
What is the specific function of ApoE?
Stabilises VLDL for cellular uptake, a ligand for the ApoB/E (LDL) receptor, constituent of several classes of lipoproteins
108
ApoA/E receptors are receptors for which kind of lipoprotein?
LDL receptors
109
Which 2 organs are apolipoproteins synthesised in?
Liver and intestines
110
How is synthesis of apolipoproteins regulated?
In intestines: regulated by dietary fat intake
| In liver: regulated by hormones (insulin, glucagon, sex hormones, alcohol, statins, fibrates)
111
ApoB100 and ApoE are ligands for what kind of receptors?
LDL receptors
112
ApoA-I is a ligand for which receptor?
HDL receptor
113
What role do lipoproteins have in lipoprotein metabolism?
Regulate key enzymes in lipoprotein metabolism
114
Which kind of lipoprotein has a single molecule of ApoB encircling the lipoprotein and has a mostly cholesterol ester core with a little bit of triglyceride?
LDL
115
What role does LDL have in inflammation?
In native form LDL = not pro inflammatory
| LDL can be oxidised and is highly prone to oxidation - this modified LDL is pro inflammatory and pro atherogenic
116
Which lipoprotein contains mainly ApoA-I and ApoA-II and has a core of mostly cholesterol esters but some triglycerides?
HDL
117
Why is HDL less susceptible to oxidation than LDL?
ApoA-I and ApoA-II have properties which protect the lipids against oxidative modification - very productive against inflammation - this is one reason for the anti-inflammatory properties of HDL
118
What is the course of lipid transport from the gut?
1) Chylomicrons made in the small intestine (go through lymphatic system to blood)
2) Triglycerides in chylomicrons hydrolysed by lipoprotein lipase to fatty acids that are taken up by target tissue
3) Chylomicrons shrink and the remnants are transported back to the liver
4) VLDL are made in the liver and transport lipids to target tissues
5) VLDLs acted on by lipoprotein lipase to release fatty acids (which are taken up by tissues)
6) VLDL remnants in blood become LDL that are taken up by target cells with the LDL receptor and digested in the lysosome to release cholesterol
119
Where are HDL synthesised and what do they do?
Synthesised in the liver and aquire their cholesterol by extracting it from cell membranes and transporting it back to the liver
120
How is cholesterol excreted?
Via the liver (cholesterol used to synthesise bile salts)
121
How is LDL receptor gene expression regulated?
Regulated by the intracellular cholesterol conc. - if cholesterol conc falls, gene expression increases, more receptors produced and exposed, more cholesterol taken up from the blood
122
LDL attaches to the LDL receptor and then taken up in what kind of vesicle?
Clathrin coated vesicle
123
Binding of the LDL to LDL receptor stimulates what?
Endocytosis, LDL released from the receptor in endosome, receptor is recycled back to the membrane, Cholesterol is released and used as required - eg. for membrane synthesis or steroid hormone synthesis
124
Why does excess dietary cholesterol remain in the blood as LDL rather than being taken up into cells?
High intracellular cholesterol = low receptor expression = excess cholesterol not taken up
125
How does HDL help to protect against atherosclerosis?
HDL produced in nascent form - in this form it is able to scavenge cholesterol (Eg. from the blood), as it gather more cholesterol it forms the mature form of HDL which can bind to the scavenger receptor in the liver and is taken up (cholesterol can be used in bile salt synthesis)
126
How is dyslipidaemia defined?
Elevated total or LDL cholesterol, low levels of HDLs
127
What is the most common heritable dyslipidaemia?
Familial hypercholesterolaemia
128
How does familial hypercholesterolaemia lead to high levels of cholesterol in the blood?
Prevents gene expression of LDL receptor, less receptors = less LDL taken up so more in blood
129
Other than lack of LDL receptor gene expression in familial hypercholesterolaemias what do other hereditary hypercholesterolaemias relate to?
Genetic defects in the structure of apolipoproteins eg. familial defective ApoB-100 leads to impaired binding of LDL to surface receptor receptors
130
What is Lipoprotein A?
Has unknown function, link to an increase in CV disease
Different structure to other lipoproteins - it has a long polypeptide chain linked to ApoB-100 called apolipoprotein(a) with multiple krinkle structures
131
How is cholesterol produced?
1) HMG-CoA converted to mevalonate
2) Mevalonate converted to IPP
3) IPP converted to FPP
4) FPP converted to Squalene
5) Squalene converted to Cholesterol
NB. FPP is also converted to Small G protein prenylation - Ras and Rho (could be via GGPP) which are involved in cell signalling functions and gene expression
132
Statins inhibit which enzyme involved in the synthesis of cholesterol?
Inhibits HMG-CoA Reductase
133
What are the pleiotropic effects of statins?
Statins prevent the prenylation of Ras and Rho so they cant acts as signalling molecules, the normal effects of Ras and Rho that statins prevent are:
1) Increase in adhesion molecule of endothelial cells that makes them more sticky for platelets
2) Increase inflammatory cytokine production (which makes plaques more likely to rupture)
3) Decrease vaso-dilation thus reducing flow to tissues
134
What are cholesterol absoprtion inhibitors and when are they used?
Used in hypercholesterolaemia - prevent uptake of cholesterol from the intestine eg. Ezetimibe - also claimed by commercial dietary products - they contain plant steroids which are taken up preferentially to cholesterol
135
What are fibrates and what are they used for?
Reduce triglyceride synthesis and increase HDL but less effective in reducing LDL eg. Gemribrizol and fenofibrate
136
What is the normal 3 things given in treatment of hypercholeseterolaemias?
1) Statins
2) Cholesterol uptake inhibitors
3) Fibrates
