Session 2.2a - Lecture 2 - Membranes: Biological Function Flashcards

Question

How do we separate the erythrocyte membrane from the cellular constituents?

Answer 1

Spinning the mixture hard in centrifugation.

Answer 2

- Red supernatant with all the Hb in it | - White pellet of membrane at bottom of the tube

Answer 3

The liquid found in a tube that lies above a solid precipitate.

Answer 4

To separate the erythocyte membrane from the cellular constituents.

Answer 5

- Detergent - Denatures membrane - Coats all proteins with negative charges

Answer 6

Detergent called SDS.

Answer 7

Coat it with a negative charge - SDS.

Answer 8

Proteins are run through a gelatinous medium, with an electric potential across the gel. Proteins are covered in a negative charge and therefore will run according to size.

Answer 9

The gel will filter effectively those proteins run according to size - Small ones will run all the way through the gel - Big ones will get stuck near the top

Answer 10

1) RBC is chosen because it has a SIMPLE MEMBRANE SYSTEM: it has an outer plasma membrane but no organelles (therefore no membranes) in mature RBC 2) RBC is dropped into HYPOTONIC solution so it BURSTS to release Hb and cytoplasm contents 3) This mixture is CENTRIFUGED, leaving us with a RED SUPERNATANT with all the HB in it (CELLULAR CONSTITUENTS - OP) and a WHITE PELLET of MEMBRANE (ERYTHROCYTE MEMBRANE - BOTTOM) 4) Membrane is DENATURED with a DETERGENT called SDS 5) SDS also coats proteins with a NEGATIVE CHARGE 6) Proteins can then be run on an ELECTROPHORESIS GEL - a GELATINOUS MEDIUM that has an ELECTRIC POTENTIAL across it 7) The proteins will separate out according to size - the LARGEST proteins will STAY nearer the beginning whereas the SMALLEST proteins will RUN FURTHER

Answer 11

Electrophoresis of erythrocyte membrane proteins - proving evidence that there is proteins in membranes. Small things are at the bottom and large at the top (see direction of electrophoresis) e.g. Actin is small (bottom), Spectrin is large (top)

Answer 12

An erythrocyte membrane protein

Answer 13

A very large erythocyte membrane protein

Answer 14

Membranes can be fractionated (separated) and then run on a gel electrophoresis, which coats proteins in negative charges and separates them out for size, which is visible on a stain. As staining is for proteins, if staining occurs, then there is evidence for proteins.

Answer 15

SDS-PAGE of the erythrocyte membrane Direction of electrophoresis (down) - Spectrin a - Spectrin b - Band 3 - Glycophorin - Band 4.1 - Actin

Answer 16

- Spectrin a - Spectrin b - Band 3 - Glycophorin - Band 4.1 - Actin

Answer 17

See Fig. 4 SDS-PAGE of the erythrocyte membrane Direction of electrophoresis (down, or corresponds with proteins shown) - Spectrin a - Spectrin b - Band 3 - Glycophorin - Band 4.1 - Actin (Must be in this order - spectrin must be at top bc it is a large protein (1 mark) Large band for Band 3 bc it is prominent Approx. size and spacing of proteins).

Answer 18

Freeze it to make a crystal

Answer 19

With a very very sharp knife pushing gently onto the crystal - the crystal ultimatelt fractures due to the pressure of the knife and crystal.

Answer 20

Due to the pressure

Answer 21

Between the lamellae of the membrane, splitting it.

Answer 22

Two pieces - P fracture face - E fracture face

Answer 23

A sphere of frozen phospholipid with some proteins left behind and some pulled off, which will be shown on the converse fracture face (i.e. a protein will be pulled off on the P fracture face leaving a hole there, but will be found in the E fracture face and vice versa).

Answer 24

Remember this is frozen so nothing's moving at the moment.

Answer 25

1) FREEZE your CELL to form a CRYSTAL 2) Bring a very very SHARP KNIFE to bear on that crystal, and PUSH GENTLY gently gently - the crystal will ultimately FRACTURE due to PRESSURE of KNIFE and CRYSTAL. 3) If lucky, FRACTURE will be BETWEEN LAMELLAE of MEMBRANE, SPLITTING IT. 4) This leaves two fracture faces - P FRACTURE FACE and E FRACTURE FACE. 5) Some proteins are LEFT in the P fracture face and others PULLED OFF, leaving a HOLE, where the protein is found in the E fracture face, and vice versa. 6) The whole system is FROZEN so NOTHING'S MOVING.

Answer 26

Direction of fracture - Transmembrane protein - Lipid bilayer - Ice Fracture with knife P fracture face E fracture face

Answer 27

(1) . E face = inside of the monolayer that is closer to extracellular space (outside of cell) (2) . P face = inside of the monolayer that is closer to protoplasm (inside of cell)

Answer 28

See Fig. 5 Direction of fracture - Transmembrane protein - Lipid bilayer - Ice Fracture with knife P fracture face E fracture face

Answer 29

Effectively what we’ve done is our knife has fractured down the middle of the bilayer and pulled two halves apart so we either leave protein in place or we have a hole where there was a protein that’s been pulled with the other face of the membrane

Answer 30

Via electron microscopy

Answer 31

Electron-dense ion

Answer 32

Electron-dense ions, like osmium, can low-angle shadow a preparation - showing blobs where there are proteins and dips where there are holes (a bit like a molecular snow-drift blowing against a fence).

Answer 33

1) ELECTRON-DENSE ION is used, e.g. OSMIUM 2) This low-angle shadows the preparation, like a molecular snow-drift blowing up against a fence 3) Where there are PROTEINS you will see BLOBS, and where there were HOLES from the freeze fracture you will see DIPS

Answer 34

``` Plane of fracture (middle) Lipid bilayer (orange and red) Frozen cytosol (pink) Frozen extracellular water (Blue) Band 3 molecule (mainly in cytosol) Glycophorin molecule (mainly in extracellular water) ``` P fracture face (protoplasm, inside) cytosol E fracture face (extracellular, outside) extracellular water

Answer 35

See Fig. 6 ``` Plane of fracture (middle) Lipid bilayer (orange and red) Frozen cytosol (pink) Frozen extracellular water (Blue) Band 3 molecule (mainly in cytosol) Glycophorin molecule (mainly in extracellular water) ``` P fracture face (protoplasm, inside) cytosol E fracture face (extracellular, outside) extracellular water 1 mark - showing splitting down the lipid bilayer 1 mark - two halves, one facing the cytosol, one facing extracellularly 1 mark - protein in one half with corresponding hole in the other half, vice versa depending on proteins shown

Answer 36

It is not a sea of smooth lipid with an occasional blob in it, but the proteins are packed into the membrane - they are really highly represented within the whole structure

Answer 37

So when we start talking about communication between proteins in the membrane – not to imagine protein wandering around looking for someone to interact with, the interacting partner is likely to be right next door, waiting to work with them

Answer 38

This figure shows the membrane is packed with proteins, thus, the partner is likely to be right next door to it - proteins are not occasional items wandering around looking for their partners - their partners are probably waiting there for them to work with.

Answer 39

Freeze fracture electron micrograph

Answer 40

- Membrane fractionation and gel electrophoresis (separate the membrane and run it on a gel, proteins will move according to size, thus showing many different types of proteins) - Freeze fracture electron microscopy (shows proteins and shows that they are abundant in the membrane)

Answer 41

Freeze fracture electron micrograph of human erythrocytes P face E face [1 um]

Answer 42

See Fig. 6+ Freeze fracture electron micrograph of human erythrocytes ``` P face (protrudes out) E face (dips in) [1 um] ``` 1 mark - scale bar 1 mark - many blobs showing abundance of proteins.

Answer 43

Studded fairly DENSELY throughout the bilayer.

Answer 44

Yes, there are 3 modes of motion permitted.

Answer 45

- Conformational change - Rotational - Lateral NOT flip-flop

Answer 46

Just as our PLs can vibrate, our proteins can move – that’s good bc if we have a transporter that needs to grab something and put it into the cell we’ve got the possibility of moving to do that function

Answer 47

Proteins have quaternary structure, so we know that they have a 3D structure and that 3D structure is not fixed, it can undergo conformational change – it can go from diff states, but that protein will tend to flicker between certain stable states/conformations

Answer 48

Proteins can rotate – some proteins are free in the bilayer, sitting like ships in sea of lipid, can move around in lipid in that way.

Answer 49

Similarly, as you would imagine, they can move laterally, chug along through membrane and move somewhere else by changing places with lipid.

Answer 50

NO FLIP-FLOP (cannot move to other side of bilayer - think rugby players from back of lecture jumping to front of lecture theatre in PL, but cannot do that for proteins)

Answer 51

Flip-flop Bc we have so much hydrophilic structure in that part of the protein sticking out the outside of the cell (or into the inside of the cell - i.e. out the membrane) so the thermodynamic energy required to move it across the bilayer is too large, it just won’t happen, can’t put enough energy in, and even if it did happen think about this – if you start taking a big chunk of protein through the membrane you’re going to destroy the membrane and its integrity – no benefit to the cell to being able to chunk protein through a membrane via flip flop.

Answer 52

- Thermodynamic energy required to move proteins across bilayer is too large (large hydrophilic structure from proteins sticking out into cell/ECM needs to move across hydrophobic interior of the membrane) - Even if enough energy was acquired, it will destroy the integrity of the membrane (protein is too large, thus no benefit to cell to flip-flop)

Answer 53

So just as our PLs can vibrate, our proteins can move – that’s good bc if we have a transporter that needs to grab something and put it into the cell we’ve got the possibility of moving to do that function. However, lack of flip flop means once protein is in membrane going to be fixed by orientation.

Answer 54

Once protein is in membrane going to be fixed by orientation

Answer 55

Mobility of proteins in bilayers - Conformational change - Rotation - Lateral diffusion - No-flip-flop

Answer 56

See Fig. 7 - Conformational change (circle to square) - Rotation (arrow showing move around singularly) - Lateral diffusion (arrows showing can move left/right/forward/backwards) - No-flip-flop (X showing does not occur)

Answer 57

- Aggregates - Tethering - Interaction with other cells

Answer 58

When some proteins work with other proteins, thus forming aggregates.

Answer 59

Not dealing with one protein moving in the membrane now but a whole raft of protein in the membrane – clearly that raft is not going to move quite as freely as an individual protein in the membrane. So aggregation of protein will restrict mobility

Answer 60

A cell that binds with a part of the extracellular matrix or structure in the intracellular surface, involved in stability of the structure.

Answer 61

The basement membrane

Answer 62

Where a protein, e.g. an adhesion protein, in the membrane is fixed by its interaction e.g. extracellularly to the basement membrane, or intracellular to the cytoskeleton.

Answer 63

Our protein in the membrane might be an adhesion protein, might be making an interaction with the BM – if it’s doing that then that protein is fixed by its interaction with the BM, so tethering might also fix a protein to a position in the membrane – that could be extracellular but equally it could be intracellular

Answer 64

To the cytoskeleton of a protein, which fixes a protein by anchoring it to structures within the cell.

Answer 65

If 2 cells are interacting with each other – through protein-protein interactions - that too is going to fix protein position.

Answer 66

Through protein-protein interactions

Answer 67

So some proteins will be mobile and able to move, and some will be highly fixed depending on their function.

Answer 68

Mobility - conformational change - rotation - lateral Restrictions - no flip-flop - aggregates (proteins sticking together) - tethering (to other structures e.g. BM) - interaction with other cells

Answer 69

Restriction of membrane protein mobility Aggregates Tethering Interaction with other cells

Answer 70

See Fig. 8 Aggregates (one protein layer sticking together) Tethering (sticking of proteins to other structures e.g. BM, cytoskeleton) Interaction with other cells (two protein membranes interacting with each other)

Answer 71

• lipid mediated effects proteins tend to separate out into the fluid phase or cholesterol poor regions • membrane protein associations • association with extra-membranous proteins (peripheral proteins), e.g. cytoskeleton

Answer 72

In GENERAL, proteins will tend to go into cholesterol-poor regions.

Answer 73

So we’ve seen cholesterol tends to produce a common, stable membrane environment, but membranes are not homogeneous throughout the whole cell – so there will be regions where there is less cholesterol (bit more fluid) and regions where cholesterol is just slowing down the motions of things

Answer 74

Produce a common, stable membrane environment.

Answer 75

This slows down the motions of things, as cholesterol can reduce fluidity (at higher temperatures due to the rigid sterol ring - cholesterol means endothermic phase transition is abolished therefore less fluidity)

Answer 76

These regions are a bit more fluid as their movement is not being hindered by the packing of cholesterol (no cholesterol means endothermic phase transition is present therefore fluidity can occur).

Answer 77

Most proteins bc they are doing conformational change prefer to do that in a place where there is a bit more freedom of movement so they move to a more fluid area of membrane which is cholesterol-poor

Answer 78

These are often signalling proteins - ones that need perhaps a receptor and transducer and effector - needs some sort of systems that need to be assembled; these proteins often find themselves in cholesterol-rich regions.

Answer 79

Cholesterol-rich: often signalling proteins, need a system to be assembled so require more stability and less fluidity Cholesterol-poor: most proteins, bc they undergo conformation change so require more fluidity

Answer 80

• lipid-mediated effects: proteins tend to separate out into the fluid phase (cholesterol-poor regions) • membrane protein associations e.g. aggregates, tethering, interaction with other cells • association with extra-membranous proteins (peripheral proteins), e.g. cytoskeleton [tethering or interaction with other cells]

Answer 81

- Peripheral | - Integral

Answer 82

– Bound to surface – Electrostatic and hydrogen bond interactions – Removed by changes in pH or in ionic strength

Answer 83

– Interact extensively with hydrophobic domains of the lipid bilayer – Cannot be removed by manipulation of pH and ionic strength – Are removed by agents that compete for non-polar interactions e.g. detergents and organic solvents

Answer 84

On the surface (hence the name) - they don't insert themselves into the bilayer but are attached to the surface of the cell/membrane

Answer 85

By electrostatic (and hydrogen bond) interactions

Answer 86

- By putting in high salt, to compete those charge-charge interactions, or - Changing the pH (MCBG talk about pK values and ionisation of amino acid side chains) - can change the charge on proteins which can release them from the surface

Answer 87

Any protein that effectively can be washed off with a membrane but comes with the membrane is a peripheral membrane protein - it is found on the surface of the cells/membranes and is held together by electrostatic (hydrogen bond) interactions.

Answer 88

They travel all the way through the membrane - i.e. through both the hydrophilic and hydrophobic parts (hence the name)..

Answer 89

They are found travelling throughout the membrane, thus interact extensively with hydrophobic domain of the membrane

Answer 90

Can't be removed by washing with high salt or changing pH

Answer 91

Because they are embedded too deeply into the membrane, so their interactions are too strong, unlike peripheral membranes?

Answer 92

Only by agents that effectively compete for non-polar interactions of the bilayer

Answer 93

- Detergents | - Organic solvents

Answer 94

Because these are strong agents that effectively compete for the non-polar interaction of the bilayer, which is the only way to displace the protein from the bilayer (changing pH or high salts will not work as it is too deeply embedded within the bilayer, unlike with peripheral membrane proteins).

Answer 95

• Peripheral – Bound to surface – Electrostatic and hydrogen bond interactions – Removed by changes in pH or in ionic strength • Integral – Interact extensively with hydrophobic domains of the lipid bilayer – Cannot be removed by manipulation of pH and ionic strength (too deeply embedded) – Are removed by agents that compete for non-polar interactions e.g. detergents and organic solvents

Answer 96

- Singer-Nicholson model - Known as the fluid mosaic model - Proposed in 1972 - Lipid mosaic model of membrane structure - Dictates how proteins sit in the lipid membrane bilayer - Proteins can be either peripheral or integral

Answer 97

- Previous to that there were sandwich models, with lipid-protein sandwiches of all differing complexity - But this model was proposed which we still understand to be the case now

Answer 98

Fluid mosaic model We have a membrane bilayer with - integral proteins forming interaction with hydrophobic domain of the bilayer and - peripheral proteins held to the membrane by charge-charge interactions and therefore can be washed off with salt

Answer 99

Form interaction with the hydrophobic domain of the bilayer

Answer 100

Held by charge-charge interactions but can therefore be washed off with salt

Answer 101

Yes, but we would now draw proteins slightly more clustered together, as we now realise proteins are a bit more packed in the membrane than in 1972.

Answer 102

Lipid mosaic model of membrane structure (Singer-Nicholson model) Extracytoplasmic surface Cytoplasmic surface Hydrophilic (outside, light blue) Hydrophobic (inside, dark blue)

Answer 103

Yes, it is, but we would now draw proteins slightly more clustered together, as we now realise proteins are a bit more packed in the membrane than in 1972.

Answer 104

See Fig. 11 Lipid mosaic model of membrane structure (Singer-Nicholson model) Extracytoplasmic surface Cytoplasmic surface Hydrophilic (outside, light blue) Hydrophobic (inside, dark blue) 1 mark - fluid mosaic model (caption, including Singer-Nicholson model) 1 mark - hydrophilic and hydrophobic correctly labelled (nothing facing exterior can be hydrophobic) 1 mark - integral and peripheral proteins shown within lipid bilayer *Note: proteins would be more clustered than drawing shows, as we have now discovered proteins are more abundant than in 1972.

Answer 105

Through the lipid bilayer, thus, cross the hydrophobic domain.

Answer 106

If our transmembrane protein is going through the hydrophobic domain of the membrane we would expect it to have hydrophobic amino acids in that structure so that it’s stable within the hydrophobic domain.

Answer 107

An erythrocyte membrane protein that is transmembrane and heavily glycosylated. It has an alpha-helical structure.

Answer 108

In the erythrocyte membrane

Answer 109

- transmembrane - heavily glycosylated - alpha-helical

Answer 110

Transmembrane domains are often a-helical.

Answer 111

Small amino acids propose no problem so can be found anywhere.

Answer 112

- Phenylalanine (Phe) - Isoleucine (Ile) - Cysteine (Cys) - Leucine (Leu) - Alanine (Ala) - Threonine (Thr)

Answer 113

Most of the AA are hydrophobic so they're just the right chemical composition to stabilise with the hydrophobic domain of the bilayer (e.g. Phe, Ile, Cys, Leu etc.)

Answer 114

R groups of amino acid residues in transmembrane domains are largely hydrophobic

Answer 115

- Serine (Ser) - Histidine (His) - Tyrosine (Tyr)

Answer 116

These are occasional, and found towards the surface of the protein

Answer 117

Take a coding sequence from a genetic analysis of an individual (i.e. take a gene), put it into the computer, translate it into protein and predict which areas of that protein might be transmembrane domain due to the properties of the R groups - i.e. hydrophobic AA are likely to be found in the transmembrane domain.

Answer 118

About 20-22 amino acids in a-helical structure.

Answer 119

Transmembrane polypeptide Amino acid R groups Yellow = Small Orange = Hydrophobic Pink = Polar, uncharged R groups of amino acid residues in transmembrane domains are largely hydrophobic Transmembrane domains are often a-helical

Answer 120

See Fig. 12 Transmembrane polypeptide Amino acid R groups Yellow = Small Orange = Hydrophobic Pink = Polar, uncharged R groups of amino acid residues in transmembrane domains are largely hydrophobic Transmembrane domains are often a-helical Marks: 1 - small amino acids found anywhere 1 - small e.g. Gly 1 - hydrophobic amino acids found in the bilayer 1 - hydrophobic e.g. Phe, Leu, Ala, Thr, Ile, Cys 1 - polar, uncharged towards the edge 1 - polar uncharged e.g. His, Ser, Tyr 1 - largely hydrophobic 1 - alpha-helical structure 1 - 20-22 AA found in the transmembrane domain

Answer 121

A plot of amino acid sequence, where the - x-axis shows the amino acid number in the sequence as it goes on and the - y-axis shows the hydropathy index - the more positive the number the more hydrophobic

Answer 122

A measure of hydrophobicity - the more positive the number the more hydrophobic (and the more negative the more hydrophilic)

Answer 123

- Take AA sequence which we’ve determined from the genome - Can apply a window of 20 AA at the N-terminus and say is it hydrophobic or hydrophilic? - Move down an amino acid and measure again. Repeat for the whole sequence - Score for hydrophilicity or -phobicity

Answer 124

Which regions of a protein are hydrophobic and which are hydrophilic, thus tells you how many transmembrnae domains there are - largely hydrophobic domains are likely to run within the lipid bilayer.

Answer 125

1 - Glycophorin we believe will have a single transmembrane domain as only 1 portion is highly hydrophobic.

Answer 126

Light-fixing protein in purple bacteria – protein that allows you to fix energy from the environment

Answer 127

Not bc itself is particularly interesting but it’s a family member of about a 1000 GPCRs - it's an ancestral precursor of up to 1,000 molecules in our membranes responsible for signalling

Answer 128

They are a big family of receptors (7-TM domain receptors) - membrane proteins responsible for signalling.

Answer 129

7 - there are multiple TM domains, in fact 7 domains of hydrophobicity, so this protein is weaving in and out of the membrane, so it has multiple transmembrane spanning domains

Answer 130

If it has hydrophobic regions.

Answer 131

Orange represents hydrophobicity Blue represents hydrophilicity Therefore the amount of orange regions corresponds to the number of transmembrane domains a membrane protein has.

Answer 132

Hydropathy plots ``` Glycophorin NH2 COOH x-axis: Amino acid number 0 50 100 y-axis: Hydropathy index - + 1 TM domain (hydrophobic = orange) ``` ``` Bacteriorhodopsin NH2 COOH x-axis: Amino acid number 0 100 200 y-axis: Hydropathy index - + 1 2 3 4 5 6 7 TM domain (hydrophobic = orange) ```

Answer 133

See Fig. 13 Hydropathy plots ``` Glycophorin NH2 COOH x-axis: Amino acid number 0 50 100 y-axis: Hydropathy index - + 1 TM domain (hydrophobic = orange) ``` ``` Bacteriorhodopsin (GPCRs = 7 TM domain) NH2 COOH x-axis: Amino acid number 0 100 200 y-axis: Hydropathy index - + 1 2 3 4 5 6 7 TM domain (hydrophobic = orange) ```

Answer 134

Proteins have a directionality in the membrane - they have a specific orientation.

Answer 135

- Disulphide-linked structure is always facing outwards | - C-terminal region always faces cytoplasm.

Answer 136

- Important for FUNCTION of this protein and many others that they are orientated, they have a topology that's defined - e.g. we don’t want receptors being put in half facing out half facing in the ones facing in would be WASTING BIOSYNTHETIC effort

Answer 137

To optimise function and reduce wasting of biosynthetic effort.

Answer 138

Membrane protein topology - Disulphide bonds - Oligosaccharides - Transmembrane helix - Lipid bilayer - Sulphydryl groups - Cytosol

Answer 139

See Fig. 14 Membrane protein topology ``` COOH - Disulphide bonds (-S-S- x3) - Oligosaccharides (hexagons) - Transmembrane helix (through lipid bilayer) - (phospholipid bilayer)} Lipid bilayer - Sulphydryl groups (-SH x2) - Cytosol (pink) NH2 ``` (glycophorin)

Answer 140

They can be single- or multiple-membrane spanning (folding in and out of the membrane)

Answer 141

Either cytosol attached or on extracellular side of the membrane (so peripheral proteins can be found either side of the membrane).

Answer 142

Some of these proteins can be further modified by post-translational lipid modification.

Answer 143

Protein is allowed to be synthesised, then an enzyme modifies that protein to attach a lipid, e.g. a fatty acid

Answer 144

A fatty acid addition.

Answer 145

Integral or peripheral proteins - so the protein might have a TM domain but might also be linked to the membrane through a fatty acid modification.

Answer 146

What would have been a cytosolic protein becomes a membrane protein bc it has a post-translational modification that brings it and allows it to integrate into the membrane and can become an integral protein

Answer 147

- Either by adding an additional association to an integral membrane - Attaching a peripheral membrane integrally - Or taking a cytosolic protein and attaching it to the membrane via post-translational modification of lipids.

Answer 148

- Integral membrane proteins which travel through the membrane - Peripheral membrane proteins, which attach to the surface of membranes or integral membrane proteins - Post-translational lipid modifications can occur either - -- further associating an integral or peripheral protein - -- taking a cytosolic protein to become an integral membrane protein

Answer 149

They work with GPCRs to transduce a message into the cell

Answer 150

They work with GPCRs to transduce a message into the cell – no good if they are floating about in the cytoplasm, need them in the membrane

Answer 151

Via post-translational lipid modification.

Answer 152

Association of proteins with bilayers Extracellular Medium Lipid Bilayer Cytosol - Single or multiple transmembrane domains (integral membrane proteins) - Dolichol phosphate-linked polypeptide (to post-translational lipid polypeptide) - Postranslational lipid modifications (mystroylation [myristoylation], palmitoylation (to integral membrane proteins or cytosolic membrane proteins becoming integral) - Peripheral protein associations (attached to integral membrane proteins, on either ECM or cytosol side) *Learn this slide*

Answer 153

See Fig. 15 Association of proteins with bilayers Extracellular Medium Lipid Bilayer Cytosol - Single or multiple transmembrane domains (integral membrane proteins) - Dolichol phosphate-linked polypeptide (to post-translational lipid polypeptide) - Postranslational lipid modifications (mystroylation [myristoylation], palmitoylation (to integral membrane proteins or cytosolic membrane proteins becoming integral)) - Peripheral protein associations (attached to integral membrane proteins, on either ECM or cytosol side) *Learn this slide*

Answer 154

Red blood cells

Answer 155

Biconcave discs

Answer 156

By a structure UNDERNEATH the membrane on the CYTOPLASMIC side which maintains that shape

Answer 157

Bc those erythrocytes are going to be forced through capillaries of smaller diameter than the size of the erythrocytes - erythrocytes will be squeezed through some of these small capillaries, if there was no structure to maintain integrity of the cell, they would shear as they went through capillaries and then broken down, leading to anaemia

Answer 158

They could shear as they went through the capillaries, thus leading to anaemia.

Answer 159

- Membrane proteins underneath the membrane (on the cytosolic side) maintains an erythrocytes biconcave shape. - Biconcave shape is necessary for protein to squeeze through capillaries - Capillaries can have diameter smaller than erythrocytes - If biconcave shape is not maintained, erythrocyte can burst when passing through small capillaries - This can lead to anaemia

Answer 160

We need red cells to have some protein structure, to maintain their structure so when they are squeezing through tight spaces they're not ripped apart.

Answer 161

Erythrocytes | [5 um]

Answer 162

Fig. 15+ Erythrocytes Biconcave disc shape Scale bar - 5 um (1 RBC diameter)

Answer 163

Take our erythrocytes, burst them, spin them down, run them down on a gel electrophoresis to see the proteins, and we can begin to name those proteins

Answer 164

- Band 3 - Glycophorin - Spectrin - Band 4.1 - Actin

Answer 165

SDS-PAGE of the erythrocyte membrane Direction of electrophoresis --> - Spectrin a - Spectrin b - Band 3 - Glycophorin - Band 4.1 - Actin

Answer 166

See Fig. 16 SDS-PAGE of the erythrocyte membrane Direction of electrophoresis --> - Spectrin a - Spectrin b - Band 3 - Glycophorin - Band 4.1 - Actin

Session 2.2a - Lecture 2 - Membranes: Biological Function Flashcards

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