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Year 1 IMS > Membranes > Flashcards

Membranes Flashcards

1
Q

What are the 2 types of passive transport across the mebrane?

A

1) Simple diffusion

2) Facilitated diffusion (passive mediated transport)

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2
Q

What 3 types of molecule can pass freely through the lipid membrane by simple diffusion?

A

1) Gases
2) Hydrophobic molecules eg. benzene
3) Small polar molecules eg. water and ethanol

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3
Q

What is an ionophore?

A

Protein which is able to transport particular ions across a lipid membrane in a cell

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4
Q

What is the difference between a carrier ionophore and a channel forming ionophore?

A

1) Carrier ionophore: on one side of membrane picks up ion and diffuses through the membrane to release it on the other side
2) Channel forming ionophore: channel formed through the membrane which allows ions to pass through

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5
Q

What are ion channels generally used for?

A

Selective and controllable as gated, needed in:

1) Maintaining osmotic balance
2) Signal transduction

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6
Q

By what type of transport is glucose taken up into erythrocytes?

A

Facilitated diffusion - channel forming protein

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7
Q

What does the hexokinase enzyme in the erythrocyte do to glucose?

A

Using ATP, adds a phosphate to make G-6-P which is no longer a substrate for the channel and glucose cannot pass out of the cell

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8
Q

The glucose transporter in an erythrocyte membrane is specific to what isomer of glucose?

A

D isomer

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9
Q

What are aquaporins?

A

Required for the bulk flow of water across membranes
Transmembrane protein made up of 4 subunits
Abundant in erythrocytes and kidney cells

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10
Q

Why are aquaporins needed?

A

Water can pass through the membrane by diffusion but in some circumstances greater flow of water across the membrane is needed

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11
Q

What subunits is the tetramer Na+/K+ ATPase made up of?

A

2 alpha subunits and 2 beta subunits

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12
Q

What is the process of Na+/K+ATPase doing its job?

A 
Coupled system
3Na+ bind to pore in cytosol
ATP then binds and is hydrolysed
Channel opens and 3Na+ move out
K+ binds to the surface
ADP and Pi are released 
Channel changes shape and 2K+ move in
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13
Q

What are the 2 types of co transport?

A

1) Symport: eg Na+/glucose transporter

2) Antiporteg. sodium calcium exchanger

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14
Q

How do cardiac glycosides (cardiotonic steroids) increase strength of heart contraction?

A

Inhibit Na+/K+ATPase leading to an increased conc of Na+ in cell and a reduced Na+ gradient across membrane
This gradient is required for antiport of Ca2+ out of cell
Get an increased conc Ca2+ in cell so storonger hear contraction

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15
Q

How is glucose taken up into the cells of the small intestine?

A

By co transport with Na+ which moves down its conc. gradient

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16
Q

What are the clinical features of AD?

A

1) Amnesia
2) Aphasia
3) Agnosia - difficult naming objects
4) Apraxia - difficulty in complex tasks
5) Visuospacial difficulties
6) Functional impairment
7) Mood disorders
8) Psychosis
9) Personality change

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17
Q

What happens to the brain in AD?

A

Atrophies

A PET scan shows how poorly glucose is metabolised in sufferers brain as cells degenerate

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18
Q

Why do lots of brain cells die in AD?

A

Malfunction in signalling between cells

Downstream cell requires stimulation(a signal) from upstream cell to survive

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19
Q

What are lipid rafts?

A

Patches in the lipid bilayer where the lipid composition doesnt match the overall composition (might contain a different type of lipid), these rafts have special functions

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20
Q

What are glycerophospholipids?

A

Form a major class of membrane lipids and are derived from glycerol-3-phosphate
Glycerol-3-phosphate molecule
2 fatty acid chains esterified to the hyrdoxyl groups of the glycerol -3-phospate molecule
Specific head group is also attached to the G3P molecule

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21
Q

Why do fatty acid chains contain an even number of C atoms?

A

Made by stepwise addition of the 2 C molecule acetate which is added by enzyme acetyl CoA

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22
Q

How many C atoms are in the fatty acid chains stearate and paltimate?

A 
Stearate = 16
Paltimate = 18
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23
Q

what kind of movement can the phospholipids have in the membrane?

A

Lateral movement on the same side of the bilayer

Can spin on their axis

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24
Q

What enzymes are involved in facilitating transverse diffusion of phospholipids (from one leaflet to other)?

A

Translocase enzymes

Can flip phospholipid across membrane in energy independent fashion

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25
Q

What are scramblase enzymes responsible for?

A

They reverse the work of translocase enzyme

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26
Q

What role do scramblase enzymes play in signalling involving phosphatidyl serine in the coagulation pathway?

A

When platelets are activated, scramblase enzyme moves PS to other side of membrane of platelet, exposure allows interaction with blood clotting factors on the surface

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27
Q

What is the role of scramblase enzymes and phosphatidyl serine in apoptosis?

A

Apoptotic cells release ‘eat me’ signals to attract phagocytes
One of these is PS which is exposed by scramblase enzymes

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28
Q

Other than apoptosis and in the coagulation pathway when else are scramblase enzymes activated?

A

When sperm fertilises an egg

29
Q

What is characteristic of unsaturated fatty acid chains?

A

Have a kink

Presence of cis-bonds results in a kink

30
Q

What do unsaturated phospholipids do to a membrane?

A

Stops the phospholipids packing together too closesly and increases membrane fluidity

31
Q

What are the enzymes involved in desaturation of fatty acid tails collectively known as?

A

Desaturases

32
Q

What does delta-9-desaturase enzyme do?

A

Coverts stearate to oleorate
Introduces a double bond at 9th C atom
Fatty acid needs to esterified to CoA while reaction happens and then is released afterwards

33
Q

Why are omega 3 and omega 6 fats essential in the diet?

A

Cant produce them in the body as dont possess desaturases which can desaturise enzymes as 3rd or 6th position
Omega 3 and 6 necessary for some signalling functions

34
Q

What are sphingolipids?

A

Have a sphingosine molecule as their backbone instead of glycerol
Sphingosine molecule has a long carbon chain which is like a fatty acid
Also has one fatty acid chain attached
Also has a head group (like glycerophospholipids)

35
Q

What headgroup is attached to sphingomyelin?

A

Choline

36
Q

What is the structure of cholesterol?

A

Rigid, compact, fused ring structure with a floppier aliphatic chain

37
Q

What does the presence of cholesterol in the membrane generally do?

A

Reduce fluidity - sphingolipids can pack closely with cholesterol
Can have rafts rich in cholesterol and sphingolipids

38
Q

What are gangliosides?

A

Family of sphingolipids which are abundant in the brain - have sugar groups attached to the sphingosine
They are glycolipids, sugar groups exposed on the outer face of the membrane

39
Q

Where in the cell when gangliosides are synthesised are sugars attached to the protein?

A

In the ER and golgi apparatus

40
Q

What happens to gangliosides in Tay Sachs disease?

A

After glycoproteins have travelled to the membrane, another process occurs whereby glycoproteins are taken in by endocytosis and sugar trees are trimmed back in lysosomes
In tay sachs disease you lack the enzyme that trims back these sugar trees - results in severe neurological process
Suggests the trimming of these trees is important in signalling in the cell

41
Q

What are the 2 storage forms of lipids that dont form membranes?

A

Triglycerides (triglycerols)

Cholesterol esters

42
Q

What is hepatosteatosis?

A

liver takes in more lipids than ever needed to be released as lipoproteins and large lipid droplets accumulate in the tissue

43
Q

Experiments with the C elegans nematode worm and its ability to metabolise at different temperatures showed what?

A

Membranes prone to solidify at cold temps
Unsaturated phospholipids increase membrane fluidity and allow diffusion of O2 through the more fluid membrane
De saturases are important to allow organisms to desaturate their membranes at low temperatures and still allow O2 diffusion

44
Q

What is the current treatment of AD?

A

1) Cholinesterase inhibitors
2) NMDA receptor antagonsists
3) Antipsychotic drugs

45
Q

What components of membranes tend to cluster in rafts?

A

1) Sphingolipids
2) Cholesterol
3) glycolipids
4) Certain proteins

46
Q

What are the 3 kind of membrane proteins?

A

1) Integral (intrinsic) membrane protein
2) Lipid linked membrane protein
3) Peripheral (extrinsic membrane proteins) (bound loosely to membrane surface or to more tightly bound proteins)

47
Q

What kind of amino acids are found in the transmembrane portions of intrinsic membrane proteins?

A

Hydrophobic amino acids

48
Q

What are the 2 structures that TM portions of proteins can form?

A

1) Alpha helices

2) Porin structures made up of beta barrels

49
Q

How can intrinsic membranes be removed from the membrane?

A

By disrupting the membrane with organic solvents or detergents

50
Q

What is glycophorin and where is it found?

A

Intergral membrane protein in erythrocyte plasma membrane

Glycosylated with a short TM region which forms an alpha helix

51
Q

What is bacteria rhodopsin and where is it found?

A

Integral membrane protein with 7 alpha helical TM regions
Creates a pore containing H+ pump
pumps H+ across membrane in a light stimulated manner
Simplest photosynthetic protein

52
Q

What are myristolated lipid linked membrane proteins?

A

Anchor made of myristic acid (many viral proteins are this)

53
Q

How is the prion protein attached to the membrane?

A

By an anchor of GPI (inosytol anchor)

54
Q

What anchor do prenylated proteins have?

A 
Farnesyl anchor (through a cysteine residue on end of protein)
Signalling proteins Ras and Rho tend to be like this
55
Q

How are palmitoylated proteins attached to the membrane?

A

By a palmitate lipid

56
Q

What anchor does the internal domain of an insulin receptor have?

A

Palmitate anchor, palmitoylated

57
Q

Spectrin and Actin are examples of what kind of membrane protein?

A

Peripheral membrane proteins

58
Q

How can peipheral membrane proteins be removed from the membrane?

A

Peripheral proteins dont directly interact with protein core
Instead interact with lipid head groups or with other membrane proteins via ionic interactions which can be disrupted with a high salt solution to wash them off

59
Q

What is the role of a cytoskeleton?

A

1) Maintaining shape and rigidity (removed = ghost cell)

2) Restricts lateral movement of integral membrane proteins

60
Q

What are the roles of spectrin, ankyrin, actin and band 4.1 in the cytoskeleton?

A

Spectrin: Long filaments
Ankyrin: bridges spectrin and band 3 protein (intrinsic membrane protein)
Actin: Joins spectrin filaments
Band 4.1: stabilises spectrin -actin interactions

61
Q

What is spherocytosis and elliptocytosis?

A

Mutations in genes coding for spectrin or ankyrin
Results in abnormally shaped erythrocytes
These RBCs are degraded more rapidly by the spleen and less effective at carrying o2 you end up with anaemia
Spherocytosis = spherical shape cells
Elliptocytosis = rugby ball shaped cells

62
Q

Where is amyloid precursor protein (APP) found in the membrane?

A

In rafts and non rafts

63
Q

3 types of secretase enzymes that cleave APP are alpha secretase (ADAM), gamma secretase (PS) and beta secretase (BACE), where does each cleave it?

A

ADAM: cleaves in middle of amyloid beta peptide - so doesnt form plaques
PS and BACE cleave at either end of amyloid beta peptide, so contribute significantly to plaques

64
Q

What is the connection between cholesterol rafts and AD?

A

Secretase enzymes PS and BACE that produce the amyloid beta peptide that forms plaques in AD is found in cholesterol rich rafts in plasma membranes
Reducing cholesterol with statins = less rafts = less amyloid beta plaque

65
Q

Where do sugars on glycoproteins tend to be located in the membrane?

A

Almost exclusively on the extracellular domain

66
Q

What are the roles of carbohydrates in membranes?

A

1) Stabilising membrane proteins or lipids

2) Intercellular recgonition

67
Q

The ABO blood group antigen is a carbohydrate attached to a membrane protein, what is the variable unit in A, B and O groups?

A

O group = variable unit is absent
A group = variable group is n-acetyl-galactosamine
B group = variable unit is galactose

68
Q

What is the head group in phosphatidic acid glycerophospholipid?

A

Water

Other than the water head group, the name of the phospholipid tends to be phosphatidly’followed by the head group’

69
Q

Lipid rafts can often be involved in endocytosis what is the name of the structures formed and what protein is involved in there formation?

A

Endocytosis through a Caveolae

Caveolin protein is involved in caveolae formation

Year 1 IMS (14 decks)

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