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year 1 flash cards > TOPIC 7 - membranes, lipids and signalling > Flashcards

TOPIC 7 - membranes, lipids and signalling Flashcards

1
Q

How many membranes do gram positive bacteria have?

A

No outer membrane and a thick peptidoglycan layer

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2
Q

How many membranes do gram negative bacteria have?

A

Outer and inner membrane and a thinner peptidoglycan layer

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3
Q

Where are membranes in eukaryotic cells?

A
  • nucleolus
  • mitochondria
  • lysosomes
  • endoplasmic reticulum
  • golgi
  • vesicles
  • chloroplasts (in plants)
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4
Q

What are the functions of membranes?

A
  • functional barrier
  • provide cells with energy
  • organise and regulate enzyme activities
  • signal transduction
  • substrates for biosynthesis and signalling molecules
  • protein recruitment platform
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5
Q

What are membranes composed of?

A

Proteins and lipids

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6
Q

What are the three types of lipids?

A
  • glycerophospholipids
  • sphingolipids
  • sterols
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7
Q

How are phospholipids amphiphatic?

A

They have a polar head and non polar tail so can from bilayer structures

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8
Q

What group is on the end of a fatty acid chain?

A

A terminal carboxylic acid

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9
Q

How does a lipid bilayer form?

A

Lipids spontaneously aggregate to bury their hydrophobic tails in the interior and expose their hydrophilic heads to water

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10
Q

How do you name fatty acids?

A

Fatty acids vary in chain length, double bond number, double bond position and hydroxylation
XX:Y n-y
XX = number of carbons in the chain
Y = number of double bonds
n-y = position of first double bonded carbon

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11
Q

What are the shapes of saturated and unsaturated lipid tails?

A

Saturated - no double bonds, straight

Unsaturated - one or more double bond, can be straight (trans bond) or have a 30º kink (cis bond)

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12
Q

Can a phospholipid have tails of different lengths

A

Yes, it influences how the phospholipids pack against one another
- straight chains= thicker membranes

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13
Q

What do glycerophospholipids consist of?

A
  • 2 fatty acid tails
  • a glycerol backbone
  • a head group
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14
Q

Are the glycerophospholipid tails usually saturated or unsaturated?

A

sn-1 is usually saturated or monounsaturated

sn-2 is more often monounsaturated or polyunsaturated

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15
Q

Which glycerophospholipids have a net negative charge/anionic phospholipids ?

A

PS - Serine
PI - Inositol
PG - Glycerol
CL - Cardiolipin

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16
Q

What glycerophospholipids have zero charge/ Zwitterionic phospholipids ?

A

PE - ethanolamine

PC - Choline

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17
Q

What glycerophospholipids contain amines that can form H bonds?

A

PS - serine

PE - ethanolamine

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18
Q

How many tails does cardiolipin have?

A

4 - makes it bulky and so affects its packing

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19
Q

How many PIP species?

A

7 - PI(4,5)P2 is the most abundant

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20
Q

What leaflet of the membrane are PIPs found?

A

Inner (cytoplasmic)

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21
Q

What do sphingolipids consist of?

A

A sphyngoid base, N-acyl chain and head group

-both tails likely to have no double bonds = saturated

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22
Q

What bond is there between the acyl chains and glycerol backbone in glycerophospholipids?

A

Ester

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23
Q

What bond is there between the acyl chain and sphingoid base backbone in sphingolipids?

A

Amide linkage - the amide group allows it to form hydrogen bonds and so can interact with cholesterol or polar parts of proteins

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24
Q

What is the most common sphingolipid?

A

Sphingomyelin (SM) has a phosphocholine headgroup

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25
Q

Are the acyl chains of sphingolipids or glycerophospholipids longer?

A

Sphingolipid acyl chains tend to be longer and more saturated

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26
Q

What are glycolipids?

A

Glycosphingolipids

- have different oligosaccharides as head groups (composed of mainly sugars)

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27
Q

What leaflet of the membrane are glycolipids found?

A

Exclusively on the outer leaflet (only make up about 5% of the membrane)

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28
Q

What role do glycolipids have?

A

Interaction of the cell with its surroundings (cell to cell adhesion) and allow membranes to act as recognition sites (sugar site exposed to the outside)

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29
Q

How many sugars do ganglioside GM1, GM2 and GM3 have?

A

GM1 - 4
GM2 - 3
GM3 - 2
-If these lipids found on outer membrane= tend to aggregate= have these suagrs and sugras can interact with outer sugars = clustering

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30
Q

What do sterols consist of?

A

Hydroxyl group and a hydrocarbon tail

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31
Q

What is the most common sterol in animals?

A

Cholesterol

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32
Q

What effect does cholesterol have on membranes?

A
  • increases thickness
  • increases packing
  • increases compressibility
  • decreases mobility of lipids and proteins
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33
Q

What type of tail does cholesterol interact more tightly with?

A

Straight saturated tails - more packing due to its shape

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34
Q

What affects membrane curvature?

A

The relative size of the head group and hydrophobic tails of lipids affect the shape of the lipid and the spontaneous curvature of the membrane

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35
Q

What are the two types of lipid diversity?

A

Chemical/structural - defines specific properties of lipids

Compositional between tissues, organelles and leaflets - affects collective behaviour of lipids

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36
Q

Why is lipid asymmetry functionally important?

A

Change in membrane leaflet composition could act as a signal - eg phosphatidylserine in animal cells translocate to the extracellular monolayer when cell is dying - acts as a signal to neighbouring cells

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37
Q

What enzyme aids the movement of PS lipids?

A

Scramblases

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38
Q

What is lipid interdigitation?

A

When lipids from separate leaflets overlap due to lipid length asymmetry. This couples the two leaflets together and decreases thickness

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39
Q

What is rotational movement of lipids?

A

Spinning of lipids around their axes, does not alter their position but affects interactions with neighbouring molecules

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40
Q

What is lateral movement of lipids?

A

Neighbouring lipids exchange places within a bilayer leaflet

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41
Q

What is transverse movement of lipids?

A

Exchange of lipids between leaflets - can move spontaneously by transverse diffusion or it can be mediated by proteins

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42
Q

What are the three phases of lipids when in the lamellar (bilayer) phase?

A

Lamellar liquid crystalline - membrane more fluid due to loose packing
Solid gel - long unsaturated lipid tails pack more tightly
Liquid-ordered - presence of cholesterol

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43
Q

What is the fluid mosaic model?

A

The bulk of the lipids forms the bilayer providing the solvent for embedded proteins.
The bilayer is fluid – lateral mobility of lipids and of some proteins. It is mosaic in the sense that proteins are scattered across it.
Most proteins are integral and some are peripheral.
This model emphasises the fluidity of the bulk lipids allowing random diffusion

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44
Q

What is the concept of membrane domains/rafts?

A

Suggests that in a eukaryotic plasma membranes there will be different areas ‘domains’ with different composition of cholesterol and sphingomyelin .
Proteins are either excluded or included in the raft regions

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45
Q

What are lipid droplets?

A

Storage organelles that help to maintain the lipid and energy homeostasis.
Hydrophobic core of neutral lipids enclosed by a phospholipid monlayer.
originate from ER

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46
Q

Where do lipid droplets originate from?

A

The endoplasmic reticulum and are initiated when neutral lipids are produced

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47
Q

How do neutral lipids form?

A

Result from the esterification of a fatty acid to a triacylglycerol or a sterol to a sterol ester

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48
Q

Where are neutral lipids normally and what happens if their storage is impaired?

A

Normally dispersed in the leaflets of ER bilayer, as their concentration increases neutral lipids accumulate (demixing)
If fatty acid storage in lipid droplets is impaired can result in diseases such as type 2 diabetes and fatty liver disease

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49
Q

What is a monotopic protein?

A

an integral membrane protein that inserts into the membrane but does not span it

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50
Q

what is a bitopic protein?

A

integral membrane protein with one helix that spans the bilayer once
type 1 - N-terminal is outside
type 2 - N-terminal is inside

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51
Q

what is a polytopic protein?

A

integral membrane protein with segments spanning the membrane, connected by loops

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52
Q

what is a oligomeric protein?

A

integral membrane protein formed when multiple bitopic proteins oligomerize (join together, but not connected by loops)

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53
Q

Give the 5 functions of integral proteins

A

transport - move molecules across the membrane by changing shape
enzymatic activity - participate in electron transport and metabolism of phospholipids and sterols
signal transduction - transfer information in response to the binding of a ligand or molecule
cell-cell interactions - glycoproteins are recognised by other cells
attachment to cytoskeleton/extracellular matrix - can be non-covalently bound to cytoskeleton, regulates cell shape and stabilises protein position in membrane. also facilitate cell-cell adhesion

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54
Q

what is the transmembrane region of integral proteins made up of?

A

amino acids with hydrophobic side chains

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55
Q

how is glucose transported into cells?

A

glucose transporters (GLUTs) - made up of 12 ⍺-helices

  1. glucose binds to membrane outer surface, causing a conformational change
  2. at inner surface, glucose is released and protein returns to its original conformation
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56
Q

what can cause ion channels to open?

A

ligand biding, electric potential, pH, temperature, pressure or lipids

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57
Q

what do potassium channels do in the

  • cardiovascular system?
  • epithelial cells?
A
  • regulate heartbeat

- regulate passage of salt and water

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58
Q

how many subunits do potassium channels have?

A

4

- each subunit has two transmembrane helices and a pore half helix

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59
Q

what do mechanosensitive channels respond to?

A

mechanical stress (touch, sound and gravity)

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60
Q

what are the critical roles of ß barrel proteins?

A

cell structure and morphology, nutrient acquisition, protection of bacteria against toxic threats

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61
Q

what are peripheral membrane proteins?

A

proteins that bind to the surface of the membrane or to an integral protein

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62
Q

how do peripheral proteins bind?

A

interact with anionic lipid head-groups or with charged groups on another protein

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63
Q

what are lipid binding molecules?

A

positively charged surfaces on a peripheral protein that recognise specific lipids in the membrane - means they bind in specific places

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64
Q

what type of membrane proteins are cytoskeleton?

A

peripheral membrane proteins

  • form a scaffold on the cytosol side of membrane
  • attach to integral proteins
  • in RBC’s this is important as cytoskeleton allows cell to undergo stress without fragmentation
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65
Q

what is hereditary elliptocytosis?

A

condition of RBC’s which causes disruption of interactions with the cytoskeleton, forming elliptically shaped cells - causes anaemia

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66
Q

what is hereditary spherocytosis?

A

condition of RBC’s as a result of loss of cohesion between plasma membrane and cytoskeleton due to defective anchoring - cells become spherocyte

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67
Q

define dementia

A

an umbrella term for the serious deterioration in mental functions, such as memory, language, orientation and judgement
alzheimers is the most common cause

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68
Q

what are the clinical features of alzheimers?

A
  • amnesia
  • aphasia (language problems)
  • agnosia (difficulty recognising and naming objects)
  • apraxia (difficulties in complex tasks)
  • visuospatial difficulties
  • functional impairment
  • mood disorders
  • psychosis
  • personality change
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69
Q

what causes alzheimers?

A

neurons malfunction causing the chemical and electrical signalling to go wrong - the nerve cells die and the connections deteriorate
- post mortems find senile plaques made of amyloid-beta peptide

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70
Q

what are amyloid-beta peptides?

A

short peptides derived from the larger membrane bound amyloid precursor protein (APP), goes onto form senile plaques which are abundant in alzheimer brains

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71
Q

how does cholesterol impact alzheimers?

A
  • more amyloid plaques in those dying of heart disease

- in cholesterol rich areas of the membrane there is more cleavage of APP and so more amyloid-beta peptide is made

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72
Q

what is an O-linked glycoprotein?

A

a carbohydrate attached to the oxygen atom in the side chain of serine or threonine
- often 2-5 sugars

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73
Q

what is an N-linked glycoprotein?

A

carbohydrate attached to the amide nitrogen atom in the side chain of asparagine
- usually large and branched with up to 30-40 sugars

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74
Q

what sequence must the amino acids be for an asparagine residue to accept an oligosaccaride?

A

asn - X - ser

asn - X - thr

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75
Q

why do cells communicate with each other?

A
  • regulate their development and organisation into tissues
  • control their growth and division
  • co-ordinate their functions
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76
Q

give an example of a disease where cell signal is lost/ no longer sent

A

Type 1 diabetes

  • beta cells are damaged
  • so no insulin produced
  • insulin receptors do not mobilise glucose transporters
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77
Q

give an example of a disease where the target cell ignores the signal

A

type 2 diabetes

  • insulin binds to receptors
  • but receptors do not send signal to mobilise glucose transporters
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78
Q

give an example of a disease where the signal doesn’t reach its target

A

multiple sclerosis

  • damage to myelin sheath
  • signal from brain doesn’t reach extremities
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79
Q

give an example of a disease where there is too much signal

A

brain damage (ie stroke)

  • blood vessels blocked so neurone cells die due to lack of O2
  • glutamate released which causes neighbouring cells to die
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80
Q

give an example of a disease where there are multiple breakdowns

A

cancer

  • hallmarks of cancer
  • eg cell proliferation - too much cell signal so too much growth factor produced so too much cell division
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81
Q

what is autocrine signalling?

A

where a cell produces the signal and has the receptors

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82
Q

what is endocrine signalling?

A

signal is released from a cell into the blood stream and travels to a remote target cell

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83
Q

what is paracrine signalling?

A

signal is released to a nearby cell

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84
Q

what is juxtacrine signalling?

A

contact signalling by plasma membrane-bound molecules (eg T helper cells and antigen presenting cells)

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85
Q

what is gap junction signalling?

A

physical connection between cells via channels (eg cardiomyocytes)-allows movement of some cytoplasmic contents between cells

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86
Q

give 4 examples of extracellular signalling molecules (1st messengers)

A
  • growth factors
  • neurotransmitters
  • hormones
  • cytokines
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87
Q

what is the difference between exocrine, endocrine and paracrine hormones?

A

exocrine - secreted directly into the blood
endocrine - secreted into ducts first: distant cells
paracrine - diffuse through interstitial tissues to target cells - act on nearby cells

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88
Q

what are the four classes of receptor?

A 
(cell surface)
- ligand gated ion channel
- G protein coupled receptor
- receptor tyrosine kinase
(intracellular)
- nuclear hormone receptor
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89
Q

ligand-gated ion channels

A
  • ionotropic receptors
  • binding and opening is very fast - involved in fast synaptic transmission
  • ligand binding site on extracellular side
  • example - nicotinic acetylcholine receptor (increases Na+ and K+ permeability, Na+ in and K+ out - causes membrane depolarisation)
  • also GABA, GlyR and 5-HT3R
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90
Q

G-protein-coupled receptors

A
  • metabotropic (ie no pore but triggers signalling response) or heptahelical receptors
  • couple to an intracellular effector system via a G-protein
  • examples - muscarinic ACh receptor, adrenoceptors, angiotensin II receptors
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91
Q

what does the renin-angiotensin system control

A

blood pressure (negative feedback system)

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92
Q

outline RAS

A
  • low blood pressure = renin released by kidneys
  • renin converts angiotensinogen to (through cleaving) angiotensin I
  • ACE 1 (from lungs and kidney) converts angiotensin I to agiotensin II
  • agiotensin II has a variety of effects to increase blood pressure
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93
Q

what affects does angiotensin II have

A
  • increase nervous activity (contraction of vessels)
  • retention of water
  • aldosterone secretion (retention of water)
  • vasoconstriction
  • ADH secretion (reabsorption of water in collecting duct)
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94
Q

why is understanding RAS important?

A

plays an important role in pathogenesis of heart failure (all work by reducing BP)

  • can control bp by inhibiting renin release or stop trigger of RAS syestem
  • ACE inhibitors
  • AT1 receptor antagonists
  • aldosterone receptor antagonists
  • example of negative feedback
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95
Q

kinase-linked receptors

A
  • single transmembrane helix with a large extracellular binding domain and an intracellular catalytic domain
  • some receptors are enzymes themselves- catalytic receptors
  • some act through cytoplasmic tyrosine kinases
  • extracellular c terminus and intercellular n terminal
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96
Q

nuclear hormone receptors

A
  • intracellular receptors in the cytosol or nucleus - ligand activated transcription factors
  • Regulate gene transcription
  • monomeric structure
  • hormones diffuse across membrane Interact with cytosolic or nuclear receptors and form hormone-receptor complexes, bind to regions of DNA and affect gene transcription
  • examples - steroid and thyroid hormones
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97
Q

what are the 5 neurotransmitters?

A
  • acetylcholine (ACh)
  • monoamines (noradrenaline, adrenaline, dopamine, histamine, serotonin)
  • amino acids (glutamate, aspartate, glycine, GABA)
  • peptides (endorphins, substance P, neurokinins, neurotensin)
  • lipids (anandamide)
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98
Q

outline the lifecycle of a neurotransmitter

A
  1. synthesis
  2. storage - synaptic vesicles
  3. release
  4. receptor activation
  5. neurotransmitter inactivation and reuptake
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99
Q

what are 5 treatments for depression

A
  1. monoamine reuptake inhibitors (tricyclic antidepressants, selective seretonin reuptake inhibitors, seretonin/noradrenaline reuptake inhibitors)
  2. monoamine oxidase inhibitors
  3. atypical antidepressants
  4. electroconvulsive therapy
  5. mood-stabilising drugs
100
Q

how do reuptake inhibitors work?

A

prevent neurotransmitters going back into presynaptic cleft so they stay in synapse longer and more stimulation of receptors

101
Q

how do autoreceptor blockers work?

A

inhibit negative feedback, Ca2+ still released into presynaptic cleft so neurotransmitter still released into synapse

102
Q

how do monoamine oxidase inhibitors work?

A

stop breakdown of serotonin, so more serotonin in vesicles so more released into synapse

103
Q

what type of signalling do gasotransmitters take part in?

A

paracrine - pass readily across cell membranes

104
Q

outline the enzymatic production of NO

A

L-arginine converts to NO + L-citrulline aided by eNOS, nNOS and iNOS

105
Q

outline the enzymatic production of CO

A

haem + O2 = NADPH

HO-2 and HO-1 remove Fe2+ and bilirubin = CO

106
Q

outline the enzymatic production of H2S

A

homocysteine with CBS = cystathionine
cystathionine with CSE = L-cysteine
L-cysteine with CSE, CBS, 3MST = H2S

107
Q

where do we get cholesterol from?

A

25% from diet, 75% synthesised in the liver

108
Q

how soluble is cholesterol?

A

insoluble in blood plasma so transported with a carrier - lipoprotein

109
Q

give the 4 classifications of lipoproteins from biggest to smallest and their function

A

Chylomicrons, VLDL - large not v dense, made in intestines - transport dietray fats from intestines to tissues
VLDL - transport lipids made in liver to peripheral tissues
LDL - smaller, denser- main cholesterol carrier, provide cholesterol to peripheral tissues
HDL - transport cholesterol to liver from peripheral tissues “good cholesterol”

110
Q

what is an apolipoprotein?

A
  • single protein strand that runs around the outside of lipoprotein
  • allows lipids to be transported to areas they are required in the body
  • determine start and end points for cholesterol transport
  • LIPID+APOLIPOPROTEIN = LIPOPROTEIN
111
Q

where is cholesterol found in a lipoprotein?

A

free cholesterol is found in the external monolayer

cholesterol esters and triacylglycerols are in the hydrophobic particle core

112
Q

what are the 4 major classes of apolipoprotein?

A

ApoA - present in HDL, mediates efflux from tissues and influx to liver
ApoB - facilitates LDL uptake into tissues
ApoC - activator of lipoprotein lipase
ApoE - stabilises LDL for cellular uptake

113
Q

how is synthesis of apoplipoproteins regulated?

A

intestine - dietary fat intake= made according to demand

liver - hormones (insulin, glucagon) and drugs (statins, alcohol)

114
Q

what are the main functions of apolipoproteins?

A
  • regulate key enzymes in lipoprotein metabolism

- ligands for interaction with lipoprotein receptors, targeting lipoproteins to the correct tissues

115
Q

what are the structural differences between LDL and HDL?

A

LDL has ApoB apolipoprotiens
HDL has Apo A-I and Apo A-II, so highly resistant to being oxidised = anti inflamatory properties
(LDL oxidation = chief culprit of CV disease in form artherosclerosis)

116
Q

What are the different types of membrane transport?

A
  • Passive transport (simple diffusion, facilitated diffusion)
  • active transport (ATP-driven and ion-driven)
117
Q

Describe simple diffusion.

A
  • Type of passive transport
  • Can be used by gases, hydrophobic molecules and small polar molecules
  • No metabolic energy required
  • No specificity
  • Rate of diffusion proportional to conc. gradient
118
Q

Describe facilitated diffusion.

A
  • Type of passive transport
  • Occurs down the conc. gradient
  • No metabolic energy required
  • Depends on integral membrane proteins (carriers, permeates, channels, transporters)
  • Specific
  • Effected by temperature and pH
  • Able to be inhibited
119
Q

What are ionophores?

A
  • Example of facilitated diffusion
  • Ion carrying proteins
  • Carrier ionophores (carry molecule across) or channel-forming ionophores (molecule passes through channel)
120
Q

What are ion channels?

A
  • Example of facilitated diffusion
  • Allow rapid and gated passage of ions
  • Highly selective- stimulated by a specific stimulus that allows it to open
  • Down conc. gradient
  • Essential for maintaining osmotic balance, signal transduction and nerve impulses
121
Q

How is glucose transported across the membrane?

A
  • Integral membrane protein GLUT1
  • Facilitated diffusion
  • GLUT1 has 12 alpha helical transmembrane domains and a central pore where glucose binds
  • Transporter undergoes conformational change when glucoses binds
  • Important that glucose conc. is higher outside of the cell
122
Q

How is a low conc. of glucose maintained within the cell?

A

Hexokinase forms G6P from glucose using ATP

123
Q

What are aquaporins?

A
  • Example of facilitated diffusion
  • Water channel proteins required for the bulk flow of H2O across membranes
  • 6 transmembrane alpha helices come together to form a pore
  • Tetramer with four pores through which H2O can pass
  • Abundant in erythrocytes and kidney cells
124
Q

Describe ATP-driven active transport.

A
  • Na+, K+, Ca+ and H+ transport is directly coupled to ATP hydrolysis
  • There is a high conc. of K+ and low conc. of Na+ inside the cell = Na+/K+ gradient
  • Facilitated by Na+/K+ ATPase
  • Na+/K+ ATPase is a tetramer with two alpha and two beta subunits. It pumps 3 Na+ ions out and 2K+ ions into the cell which polarises the cell membrane
  • ATP hydrolysis induces conformational changes, pumping Na+ and K+ against their conc. gradients
  • coupled system: ATP is not hydrolysed unless Na and K+ are transported and visa versa
125
Q

Describe ion-driven active transport.

A
  • Coupled to the movement of an ion (Na+ or H+) down its conc. gradient
  • Symports: both molecules move in the same direction, e.g. Na+/glucose transporter
  • Antiports: both molecules move in opposite directions, e.g. Na+/Ca2+ exchanger
126
Q

What are Cardiac Glycosides (Cardiotonic Steroids)?

A
  • Used in congestive heart failure
  • Naturally occurring plant steroids (e.g. Digitalin, Ouabain, Digoxin, Digitoxin) that inhibit Na+/K+ ATPases
  • In healthy people digitalis causes heart failure but in lower doses it strengthens the heart beat of patients with congestive heart failure- used at treatment
  • Inhibition of Na+/K+ ATPase leads to increased conc. of Na+ inside the cell as less pumped out and a decreased Na+ gradient across the membrane. This decreases Na+/Ca2+ exchange, so there is a greater conc. of Ca2+ inside the cell. Increased intracellular Ca2+ leads to enhanced strength of cardiac muscle contraction
127
Q

How do intestinal epithelial cells transfer molecules from the intestinal lumen to the blood?

A
  • Movement of glucose from the lumen into the cell is driven by movement of Na+ ions down the conc. gradient (Na+/glucose transporter transports both into cells)
  • Glucose diffuses into the blood via GLUT1
  • Low conc. of intracellular Na+ is maintained by Na+/K+ ATPase
  • As glucose flows through cell, water follows by osmosis due to osmotic gradient
128
Q

How does oral rehydration therapy work?

A

Uptake of glucose is dependant on Na+ so an oral solution of both glucose and Na+ is given. This increases osmotic pressure in epithelial cells, so H2O follows.

129
Q

How are macromolecules moved across membranes?

A

Exoctyosis/endocytosis

130
Q

What is exocytosis and what are its different types?

A

Exocytosis is the excretion/secretion of molecules. It can be constitutive or regulated.

131
Q

What is constitutive exocytosis?

A

Constitutive exocytosis is used by all cells. Secreted proteins & plasma membrane. It is continuous or regulated.

132
Q

What is regulated exocytosis?

A

Regulated exocytosis is used only by specialised cells such as neurones and pancreatic cells. It is Ca2+ dependent.

133
Q

What is endocytosis and what are its different types?

A

Endocytosis is the ingestion/uptake of molecules. It can be phagocytosis, pinocytosis or receptor-mediated endocytosis

134
Q

What is phagocytosis?

A
  • Ingestion of large particles (bacteria/debris)
  • Specialist cells - macrophages, neutrophils, dendritic cells
  • Bacteria/debris is degraded by enzymes in the lysosomes and the remnants are displayed on the surface of the phagocyte to alert other immune cells to fight the infection
135
Q

What is pinocytosis?

A
  • Cell ‘drinking’
  • Uptake of fluid
  • All cells are able to do this
136
Q

What is receptor-mediated endocytosis?

A
  • Selective (receptor recognition)
  • Uptake from extracellular fluid via Cathrin-coated vesicles and pits
  • The ligand being taken up must first bind to a specific cell surface receptor
  • Receptor-molecule complexes accumulate in a Cathrin-coated pit and are endocytose in a clathrin-coated vesicle
  • fuse with endosome and lysosomes = lysosome degradation
  • cell membrane recycled by cell
  • Way of concentrating specific macromolecules that are present at low conc.
  • E.g. cholesterol uptake via LDL receptor
  • Receptor-mediated endocytosis may be exploited by viruses to gain entry to cells (eg. rhinovirus and covid-19)
137
Q

what is signal transduction

A

also known as intracellular signalling

= converts extracellular signal into cellular response

138
Q

what are the 3 main stages of signal transduction

A

1- reception
2- signal transduction
3- cellular response

139
Q

what are the 4 Important features of signal transduction pathways

A

Hierarchy, amplification, specificity, complexity

140
Q

what is hierarchry

A

things happen in a particular order to transmit signal from outside to inside cell
eg. 1st messenger, receptor, G protein, effector enzyme, 2nd messenger, protein kinase, target protein , cellular response

141
Q

what is amplification

A

A single molecule of first messenger can induce many downstream signalling molecules and lead to a larger cellular response

142
Q

what are the main points of amplification

A

1-G-protein activation - is activated by the receptor as long as the receptor remains in an activated state = single G-protein molecule can activate many molecules of effector enzyme
2-Effector enzyme -catalyse reactions without being used up. So a single effector enzyme molecule can catalyse the production of many molecules of second messenger.
3- ) Protein kinase - single protein kinase molecule can catalyse the phosphorylation of many molecules of protein substrate

143
Q

what is the process in glycogen breakdown pathway

A 
1- binding of epinephrine to G protein receptor
2- activates G protein 
3- g protein activates adenylyl cyclase
4- which turns ATP to cAMP
5- a activates protein kinase A
6- activates phosphorylase kinase 
7- activates glycogen phosphorylase 
8- turns glycogen to glucose-1-phosphate
144
Q

what is specificity

A

signal transduction pathways are highly specific

one stimulus can cause different cellular function depending on what receptor and where it binds

145
Q

what hormone/1st messenger activates different processes on different cells

A

adrenaline

as it binds to different receptors and activates different signalling pathways

146
Q

3 examples of different cellular functions regulated by Adreneline

A
  • in muscle/liver = glycogen degradation
  • in adipose = fatty acid production
  • in cardiovascular = increases heart rate and blood pressure
147
Q

what is complexity

A

Signal transduction pathways are highly COMPLEX
due to number of different types of receptor, G-proteins, effector enzymes, second messengers, protein kinases and downstream substrates

148
Q

what is ‘cross talk’

A

when signalling pathways interact with one another

allows for fine tuning of cellular responses

149
Q

what are Main components of signal transduction pathways

A

G proteins, effector enzymes, 2nd messengers, kinases

150
Q

what are G proteins

A

Guanine nucleotide binding proteins

151
Q

what does GTP do

A

high energy molecule that activates G proteins

152
Q

what are G proteins also known as

A

GTPases

153
Q

what do G proteins do to GTP

A

hydrolyse GTP to GDP

create lipid anchored membrane proteins to associate them with different parts of membrane via process prenylation

154
Q

what are the 2 major groups of G proteins

A
  • G prtoeins (receptor associated) :
    heterotrimeric(3 subunits) (a,b,y subunits)
  • small GTPases:
    monomeric (one subunit)- Rho and Ras
155
Q

why are G proteins reffered to as molecular switches

A
  • switched on by ligand binding to receptor

- switched off by intrinsic GTPase activity

156
Q

how are G proteins switched off

A

removal of phosphate group by GTPase from GTP = GDP

off always bound to GDP

157
Q

how are G proteins switched on

A

binding of ligand = confrontational change = allows G protein bind to receptor = GDP exchanged to GTP
on always bound to GTP

158
Q

What is the Gs protein

A

trimeric G protein
combination of a, B, and gamma subunits
alpha subunit is the one that binds to GDP/GTP

159
Q

step 1 - what happens when ligands bind to Gs protein

A

confrontational change in receptor
causes the G-protein to release GDP and swap it for GTP = ON
alpha unit separates from beta and gamma subunits

160
Q

step 2- what happens in the activation of effector enzyme and 2nd messnegr

A

GTP-bound Gs-alpha subunit binds to and activates adenylyl cyclase which catalyses conversion of ATP to the second messenger cyclic AMP

161
Q

step 3 - what happens in hydrolysis of GTP to GDP

A

The GTPase activity of the Gs-alpha subunit hydrolyses GTP to GDP (with release of inorganic phosphate, Pi)= G-protein “OFF” state

162
Q

Step 4 - what happens in re-association

A

The GDP-bound alpha subunit then re-associates with the beta and gamma subunits
system resets itself

163
Q

step 5- what happens to the 2nd messenger

A

loss of second messenger

Cyclic AMP is broken down to AMP by phosphodiesterases

164
Q

what happens if the receptor is still active?

A

process will be repeated so the signal continues to be amplified

165
Q

what enzyme and 2nd messenger does Gs effect?

A
  • adenylate cyclase - stimulation

- increase in cAMP

166
Q

what enzyme and 2nd messenger does Gai effect?

A
  • adenylate cyclase - inhibition

- decrease in cAMP

167
Q

what enzyme and 2nd messenger does Gaq effect?

A
  • phospholipase C stimulation

- increase DAG, IP3

168
Q

what 2 G proteins have opposing effects

A

Gs and Gi on cyclic AMP levels

169
Q

what G protein does cholera toxin target

A

Gs

170
Q

what G protein does pertussis toxin (whooping cough) target

A

Gi

171
Q

what is the name of the bacteria causing cholera

A

Vibrio cholerae bacteria in contaminated water & food

172
Q

what is the treatment for cholera

A

Oral rehydration therapy

water, salts, glucose

173
Q

what is the mechanism for the cholera toxin on Gs

A
  • Cholera toxin prevents GTPase activity of Gs =therefore GTP remains bound to Gs and it stays in the “ON” state
  • over-stimulation of adenylate cyclase and accumulation of cyclic AMP
  • intestinal epithelial cells, elevated cAMP increases loss of Cl- ions through chloride channels
  • resultant osmotic gradient= water excreted into the intestinal lumen= diarrhoea and dehydration
174
Q

what bacteria is whooping cough caused by

A

Bordetella pertussis

175
Q

what is the virulence factor of whooping cough

A

Pertussis toxin

176
Q

what is the virulence factor of cholera

A

Virulence factor = Cholera toxin

177
Q

mechanism of pertussis toxin on Gi

A

inhibition of Gi G-protein

  • Pertussis toxin prevents GDP/GTP exchange by Gi
  • the Gi protein is locked in the “off”
  • unable to inhibit adenylate cyclase, resulting in accumulation of cyclic AMP
  • physiological effects = increased insulin secretion and increased sensitivity to histamine
178
Q

what are second messengers

A

• Short-acting intracellular molecules that are rapidly formed or released as a result of receptor activation

179
Q

Five common second messengers

A 
•	Cyclic AMP (cAMP)
•	Cyclic GMP (cGMP)
•	Diacylglycerol (DAG)
•	Inositol 1,4,5-trisphosphate (IP3)
- intracellular calcium (Ca2+i)
180
Q

production of cAMP?

A

cyclic AMP from ATP; a reaction catalysed by adenylate cyclase (also called adenylyl cyclase)

181
Q

production of cGMP?

A

cyclic GMP from GTP; a reaction catalysed by guanylate cyclase (also called guanylyl cyclase

182
Q

what breaks down cAMP and cGMP

A

Cyclases and Phosphodiesterases (PDEs)

  • some Phosphodiesterases break down cAMP or anther one will specifically breakdown cGMP
  • same cyclases can break both down
183
Q

well known PDE inhibitors?

A

caffeine and Viagra

  • Caffine inhibits breakdown cAMP
  • Viagra inhibits breakdown of cGMP
184
Q

step 1 of Gq activation?

A
  • ligand binding GDP/GTP exchange,ON, due to confrontational change
  • alpha subunit dissociates from beta/gamma subunits
185
Q

step 2 of Gq activation?

A

activation of effector enzyme and production 2nd messenger

  • alpah subunit binds Phospholipase C
  • catalyses production of two different second messengers 1,2-diacyclycerol (DAG) and inositol 1,4,5-trisphosphate (IP3)
  • release of stored Ca2+ ions into the cytosol due to interaction of ER with IP3
  • DAG and stimulates protein kinase C (PKC) that phosphorylates target proteins leading to cellular response
  • release of calcium also stimulates responses
186
Q

why is Ca importnant 2nd messenger?

A

(NB: not “formed” but is “released” into the cytosol)
1-activate various molecules (e.g calcium-dependent kinases) to modulate cellular function
2- trigger opening of calcium channels in the plasma membrane = more Ca floods in

187
Q

how is calcium removed from the cell

A

taken back up into the ER through a calcium ATPase in the ER membrane, or is pumped or exchanged out of the cell

188
Q

what are protein kinases?

A
  • enzymes that transfer Pi from ATP to a SPECIFIC AA residue: Ser, Thr,Thy on a SPECIFIC protein
  • phosphorylation may activate or inhibit protein function
189
Q

what are the 3 main groups of protein kinase

A
  • serine/theronine kinases
  • thyrosine kinases
  • dual specificity kinases
190
Q

function of serine/theronine kinases

A
  • phosphorlyate Ser and or Thr residues

- eg. PKA,PKC,PKG

191
Q

function of thyrosine kinases

A

-phosphorlyte only Tyr residues

192
Q

function of dual specificity kinases

A

phosphorlyate Ser, Thr, Tyr resides

eg.MAP kinase kinases- MKKs

193
Q

how is LDL receptor gene expression regulated (endocytosis of LDL)?

A

intracellular cholesterol concentration, binding of LDL to receptor (binds to apoB or apoE) stimulates endocytosis into hepatic or peripheral cells

  • form a coated vesicle
  • become uncoated and triskelions return to plasma membrane
  • ph decreases and LDL -> amino acids, cholesterol, fatty acids
  • receptors recycled to membrane
194
Q

what does high intracellular levels of cholesterol do to LDL uptake and so why is excess LDL bad?

A

suppresses LDL receptor synthesis - prevents excess cholesterol uptake
as a result excess cholesterol remains in the blood as LDL

195
Q

what does high levels of HDL correlate with?

A

low incidence of atherosclerosis as is resistant to oxidation through apoAand scavenges excess cholesterol, returns to liver and is excreted as bile
REVERSE CHOLESTEROL TRANSPORT

196
Q

what is normal level of cholesterol in a healthy adult?

A

175 mg/100ml

197
Q

what are the cardiac, cerebral and peripheral manifestations of atherosclerosis?

A

cardiac - chest pain, palpitations, hear tattack
cerebral - stroke, cerebral haemorrhage
peripheral - pain, ischaemia , ulceration and gangrene

198
Q

what is the cholesterol synthetic pathway?

A
  1. HMG-CoA
    - —> HMG-CoA reductase
  2. mevalonate (key intermediate)
  3. IPP
  4. FPP
  5. Squalene (fatty precursor)
  6. cholesterol
199
Q

what do statins do?

A

prevent cholesterol synthesis in the liver as inhibit HMG-CoA reductase —> less mevalonate —> less cholesterol —> more expression of LDL receptor —> more uptake of cholesterol from blood

200
Q

what is pleiotropism?

A

extra unintended affects from a drug - could be good or bad

201
Q

what are statins pleiotropic effects?

A
  • improve endothelial dysfunction
  • antioxidant
  • inhibition of inflammatory response
  • stabilise atherosclerotic plaques
202
Q

what do kinases do

A

put phosphate groups onto molecules

- very specific action

203
Q

what do phosphateses do

A

remove phosphate groups from AA

-not very specific

204
Q

how can kinases modulate protein function

A
  • Phosphorylation to induce change in protein conformation / function
  • § Phosphorylation of a transcription factor that alters gene transcription and hence protein expression levels
205
Q

Protein kinase inhibitors as therapeutic agents in…

A 
Cancer
Cardiovascular Disease
HIV/AIDS
  Rheumatoid Arthritis
 Alzheimer’s Disease
206
Q

how can disregulation in kinases be linked to cancer?

A

in solid tumours changes in protein kinase expression levels and activities + posttranslational modifications can contribute to cancer development

207
Q

what are kinase therapies used for?

A
  • as a cancer drug therapy
  • Conventional chemotherapy can be ineffective and harmful- by combining chemotherapeutics and protein kinase inhibitors= more succesfull
208
Q

functions of lipids?

A
  • energy storage - as fat deposits
  • major components of cell membranes
  • signalling molecules
  • required to solubilise fat soluble vitamins
  • biosynthetic precursors (eg. steroid hormones from cholesterol)
209
Q

function of lipoproteins?

A

-means of lipid (trigyceriol and cholesterol) transport in blood

210
Q

LIPID+ APOLIPOPROTEIN=?

A

LIPOPROTEIN

211
Q

similarities between apoA and apoB structure

A
  • surface monolayer of phospholipids and free cholesterol

- hydrophobic core of mainly cholesterol esters and some triglycerides

212
Q

How are lipids transported by lipoproteins?

A
  • Triglycerides hydrolysed by lipoprotein lipase to fatty acids= taken up by target tissues for energy production (eg muscle) or stored (adipose tissue).
  • this means Chylomicrons shrink, remnants transported back to liver.
  • VLDL transport lipids to target tissues- same process as above
213
Q

how to HDL work?

A
  • HDL= opposite function to LDL and can remove cholesterol from the tissues.
  • HDL synthesised in the blood and acquire their cholesterol by extracting it from cell membranes and transporting back to the liver.
  • The liver is the only organ that can dispose of significant quantities of cholesterol, primarily in the form of bile salts.
214
Q

what is the main function of lipoproteins

A
  • Membrane-bound receptors to enable cholesterol entry to hepatic and peripheral cell
  • Lipoprotein receptors=necessary for cholesterol uptake into cells.
215
Q

what happens to VLDL remnants?

A

-VLDL remnants remain in the blood, become LDL that are then taken up by target cells by the LDL receptor, digested in the lysosome to release the cholesterol.

216
Q

how is LDL taken into cells?

A
  • apoB recognised by receptors in clathrin coated pit
  • membranes takes this in by endocytosis
  • clathrin released back onto surface
  • receptor and cholesterol processed in vesicle then released to endosome
  • receptors released from LDL receptor
  • receptors recycled back to plasma membrane
  • cholesterol processed by lysosome and degraded to fatty acidsf
217
Q

how does reverse cholesterol transport work?

A
  • nascent HDL extracts cholesterol form cell membrane of macrophage and swells
  • turns to mature HDL
  • recognisable by scavenger cells on liver
  • cholesterol in membrane of HDL processed in liver and secreted in bile
218
Q

mutations with LDL receptors are a common cause of?

A

FAMILIAL HYPERCHOLESTEROLAEMIA= cells lacking LDL receptors= amount LDL in blood increases

219
Q

major consistent of arhteroscelroic plaque?

A

cholesterol-enriched LDL

220
Q

how do arhterocelrtic plaques form?

A

1-fatty streak in lumen (at young ages - process takes decades)
2- fibrous plaque forms = reduces area blood flows
3- advanced plaque = complete occlusion - plaque rupture on top of blood clot = MF

221
Q

what drugs control hypercholesterolaemia?

A

-Statins
Prevent cholesterol synthesis in the liver
-Cholesterol absorption inhibitors
Prevent uptake from the intestine
-Fibrates
Reduce triglycerides and increase HDL, less effective

222
Q

how do statins work?

A
  • inhibit HMG-CoA reductase
  • decreases cholesterol synthesis
  • increased expression of LDL receptor
  • increase uptake cholesterol from blood
223
Q

what are Ras and Rho?

A

small G proteins only function when prenylated

224
Q

what prenylates Rho and Ras

A

FPP and GGPP = called isoprenoids

  • required for a process known as PRENYLATION (sticking a lipid tail onto intracellular signalling molecules) = so associated with cell membrane and signal cascade
  • Ras is farnesylated whilst Rho is geranylgeranylated
225
Q

why is lipid tail G proteins important?

A

Without lipid tail G proteins floating in cytosol and cant signal

226
Q

what is PCSK9?

A
  • Protease enzyme expressed by liver & intestine

* Important role in lipid metabolism

227
Q

why is PCSK9 important?

A
  • Promotes intracellular degradation of LDL-R
  • Prevents recycling of LDL-R to cell surface
  • Reduces LDL-R population on cell membrane
  • Link between PCSK9 mutations and coronary heart disease
  • Implicated in familial hypercholesterolaemia
  • Genetic variation in PCSK9 (gain/loss of function)- beneficial if loss of function? LDL receptors remain in tact?
228
Q

how does PCSK9 work?

A
  • PCSK9 binds LDL and internalised with LDL receptor
  • degrades receptor and cannot be recycled to accept LDL at surface
  • PCSK9 inhibitor stops this from happening
229
Q

what are neutral lipids a result of?

A

-the esterification of a fatty acid to triacylglycerol or a sterol (such as cholesterol) to sterol ester

230
Q

what is a sterol ester

A
  • cholesteral with lipid tail attached to one side of cholesteral
  • At low concentrations, neutral lipids are dispersed between the leaflets =no deformation
  • As their concentration increases, neutral lipids accumulate (de-mixing- membranes start deforming ) = may threaten burst membrane
231
Q

what are the 3 proteins that help lipids move between leaflets?

A
  • P type fliptases – proteins which help lipids move from outside to inside of cells-require energy from ATTP
  • ABC fliptase- help proteins move from inner to outer membrane – ATP
  • Scrambalses- can move proteins in any directions- no ATP but Ca needed
232
Q

what membrane curvature do cylindrical lipids from?

A

cylindrical shape so can pack next to each other tightly= flat membrane

233
Q

what membrane curvature do conical shape lipids form?

A

negative curvature ‘U shape’

234
Q

what membrane curvature do inverted conical lipids form?

A

only one tail= create a positive curvature ‘N shape’

235
Q

why CO bad?

A
  • highly toxic
  • exposure is common
  • chronic exposure leads long term neurological CV disorders
236
Q

why is CO good?

A
  • endogenous signalling molecule
    -cardioprotective
    neuroprotective
237
Q

what are. gasotransmitters?

A

gaseous molecules synthesised in the body. They include nitric oxide (NO), carbon monoxide (CO) and hydrogen sulphide (H2S).

238
Q

what other effects do kinase linked enzymes have?

A 
•Act by indirectly regulating gene transcription
•Roles in controlling:
cell division 
tissue repair 
apoptosis
-cellualr effects: cellular poliferation
239
Q

what is angiotensin II made of?

A
  • Octapeptide
  • Angiotensin II receptors are GPCRs]
  • only 8 AA
240
Q

what do hormones regulate?

A 
•body energy needs
•protein and nucleic acid metabolism
•mineral and electrolyte metabolism
•synthesis and release of hormones
Activity is regulated through negative or positive feedback mechanisms
241
Q

how do cells communicate with one another?

A
  • Remote signalling by secreted molecules
  • Contact signalling by plasma membrane-bound molecules (‘Juxtacrine’ signalling)
  • Contact signalling via gap junctions- channels that form between two cells and allow molecules to move across
242
Q

which isomoer of glucose is the glucose transporter specific for?

A

D-isomer of glucose relative to the L-isomer or to other related sugars

243
Q

what ions are directly transported into a cell by ATP hydrolysis?

A

Na+, K+, Ca2+ and H+ transport is directly coupled to ATP hydrolysis
e.g. Na+/K+ ATPase
§ Coupled system: ATP is not hydrolysed unless ions (eg.Na+ and K+) are transported and vice versa

244
Q

what does the Na+/K+ gradient ensure?

A
  • controls cell volume
  • makes nerve and muscle cells electrically excitable
  • facilitates ion-driven active transport of amino acids and sugars
245
Q

what is the symport system?

A

both molecules travel in same direction

246
Q

what do intestinal epithelial cells do?

A

•Line the lumen of small intestine
•Large surface area for absorption from villi and microvilli
•Absorb nutrients from digested food (sugars, amino acids, lipids, etc.)
•Transfer nutrients into the blood
•Similar cells found in kidney tubules
-cells are polarised - have 2 distinct sides: the apical (brush-border) membrane that faces the lumen of the gut and the basolateral surface that faces the bloodstream

year 1 flash cards (23 decks)

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