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Semester 2 - Membranes and Receptors > Session 1 - Lipids, Proteins and Membrane Structures > Flashcards

Session 1 - Lipids, Proteins and Membrane Structures Flashcards

1
Q

Welcome to Semester 2 guys!

Functions of membranes? (5)

A
  1. Continuous, highly selective, permeability barrier
  2. Control of enclosed chemical environment
  3. Communication between cells and their environment
  4. Recognition e.g. signalling proteins, adhesion proteins, immune surveillance
  5. Signal generation in response to stimuli e.g. electrical/chemical

Castrated Criminals Can’t Really Sex

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2
Q

Name three types of lipid in a membrane?

A

Phospholipids
Glycolipids
Cholesterol

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3
Q

What are the main components of a phospholipid?

A 
Polar head group
Attached to.. 
Phosphate
Attached to..
Glycerol backbone 
Attached to.. 
Fatty acid chains
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4
Q

What are the main types of polar head groups?

A

Choline, amines, amino acids, sugars

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5
Q

What are the main types of fatty acid chains?

A

Hydrophobic

Can be saturated or unsaturated which contain cis C=C. Introduces a ‘kink’ to the fatty acid tail.

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6
Q

Why is sphingomyelin different to most Phospholipids?

A

Has no glycerol backbone but is still classed as a phospholipid as it has a phosphate. Contains sphingosine.

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7
Q

What is an ampipathic molecule?

A

contain both hydrophilic (the “head”) and hydrophobic (the “tail”) regions.

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8
Q

Where are unsaturated fatty acids found? Give an example

A

In the diet

Linolenic acid

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9
Q

What Sphingoyelin found? What is its function?

A

In myelin sheathes, aids in signal transduction

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10
Q

What is a glycolipid?

A

lipids with a carbohydrate group attached

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11
Q

Give the structure of a glycolipid

A

Sugar head group (Cerebroside or Gangioside)
Sphingosine backbone
Nitrogenous base
Fatty acid tail

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12
Q

Cerebroside?

A

monomer head group e.g. galactose

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13
Q

Ganglioside?

A

oligosaccharide head group

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14
Q

What is cholesterol derived from?

A

HMG-CoA

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15
Q

What is the enzyme used to convert precursor to cholesterol? What drug inhibits this enzyme?

A

HMG-CoA reductase

Statins

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16
Q

Give the structure of cholesterol

A

Polar head –OH which is attracted to exposed C=O in phospholipids’ fatty acid tails
Rigid, planar steroid ring
Non-polar hydrophobic carbon tail

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17
Q

What two things will an ampipathic molecule form in water?

A

A micelle or a bi-layer

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18
Q

Describe formation of a lipid bi-layer

A

Spontaneous
Driven by van der waals attractive forces between the hydrophobic tails
Electrostatic and hydrogen bonding between hydrophilic moieties; and interactions between hydrophillic groups and water stabilise the bilayer.

19
Q

What do unsaturated phospholipids do in a bilayer?

A

unsaturated phospholipids will reduce packing (due to the kink in the tail), so increasing its fluidity

20
Q

What are pure lipid bilayers impermeable to?

A

ions and most polar molecules, allowing only small, uncharged molecules to pass through

21
Q

What are the four modes of mobility of lipid bilayers?

A

1) Intra Chain motion (kink formation in fatty acyl chains)
2) Fast axial rotation (Phospholipid rotates)
3) Fast lateral diffusion (Phospholipid displace each other laterally)
4) Flip-flop movement of lipid molecules from one half of the bilayer to the other. This is least likely to happen due to the energies involved, which need to be high to achieve this.

22
Q

How can cholesterol stabilise phospholipid bilayers?

A
  • In high temperatures, they can form H+ bonds with other phospholipids, reducing the chain motion of membrane lipids, reducing fluidity
  • In low temperatures, they reduce phospholipids packing by just breaking up the phospholipids, breaking any bonds they form with one another, increasing fluidity.

Intercalation of the rigid planar conjugated ring structure reduces phospholipid packing and therefore increases fluidity.
Conversely, the rigid conjugated ring structure reduces phospholipid aliphatic tail mobility, so reducing fluidity.

23
Q

What does cholesterol stabilisation of lipid bilayers mean?

A

Maintain homegenous environment regardless of temperature

24
Q

What is an integral lipid protein, and what forces associate them with the membrane?

A

Embedded in the bilayer

Interact with the hydrophobic regions of the bilayer

25
Q

How can intergral proteins be removed?

A

by agents which compete for the non-polar interactions in the bilayer e.g. detergents/ organic solvents

26
Q

What is a peripheral protein associated with? How is it bound?

A

Associated with the surface

Bound to membrane surface by electrostatic and H-bond interactions

27
Q

How can a peripheral protein be removed?

A

By pH or ionic strength changes

28
Q

What is an erythrocyte (rbc) cytoskeleton made up of?

A

a network of spectrin and actin molecules attached to the membrane through adapter proteins.

29
Q

What does attachment of integral membrane proteins to cytoskeleton do in erythrocytes?

A

restricts the lateral mobility of the membrane protein

30
Q

What is erythrocyte cytoskeleton important?

A

important structure in maintaining the deformability necessary for the erythrocytes to make their passage through capillaries without lysis

31
Q

What is hereditary spherocytosis?

A

Spectrin levels depleted by 40-50% in erythrocytes

Cells much less resistant to lysis and become sphere-shaped

32
Q

What happens to erythrocytes in hereditary spherocytosis?

A

Cleared by the spleen as wrong shape > spleenomegaly > haemolysis is extravascular.
Leads to haemolytic anaemia due to shortened in vivo survival and inability of bone marrow to compensate for their reduced lifespan.

33
Q

What is hereditary elliptocytosis?

A

Spectrin molecules unable to form heterotetrameres (spectrin structure) resulting in fragile elliptoid cells
Alters deform-ability of erythrocyte

34
Q

Where do the N terminus and C terminus go in integral proteins

A

N-terminus outside membrane of ER, C-terminus inside cell cytoplasm

35
Q

Describe process of insertion into ER of integral protein

A
  • SRP binds to signal sequence of growing polypeptide at ribosome
  • Guides ribosome and polypeptide to SRP receptor
  • SRP released
  • Signal sequence at the N-terminus interacts with a signal sequence receptor within a protein translocator complex in the ER membrane
  • For membrane proteins the passage of the protein through the cell membrane must be stopped.
  • A stop transfer signal i.e. a highly hydrophobic primary sequence followed by charged amino acids in a-helical form which is long enough to span the hydrophobic core of the bilayer. This sequence forms the transmembranous region of the protein.
  • Result: transmembrane protein with it’s N-terminal directed into the ER lumen and it’s C-terminal into the cytoplasm of the cell
36
Q

What happens to membrane protein after ER processing?

A

Undergoes further processing as it passes from the ER to the cis/trans golgi . Vesicle will then fuse with the plasma membrane.

37
Q

What is a multiple membrane domain?

A

Folding of the nascent protein against the constraint of the first transmembrane segment is the driving force for the insertion of other domains.

38
Q

What is membrane asymmetry?

A

Asymmetrical orientation of proteins in biological membranes is important for function e.g. a receptor must have its recognition site directed towards the extracellular space.

39
Q

What do C=C in fatty acids chains do?

A

disrupt the hexagonal packing of phospholipids  increase membrane fluidity.

40
Q

What do membrane proteins do?

A

Embedded in bilayer and carry out distinctive functions e.g. enzymes, transporters, pumps, ion channels, receptors and energy transducers

41
Q

Give three ways proteins in lipid bilayers can move

A
  1. Conformational change
  2. Rotation
  3. Lateral diffusion
42
Q

Give one way proteins in lipid bilayer cannot move and why

A

1.NO FLIP-FLOP as they are large and could disrupt the amphipathic nature of the membrane

43
Q

What is protein mobility restrained by? (3)

A

Lipid mediated effects – proteins tend to separate out into the fluid phase or cholesterol poor regions
Membrane protein associations
Association with extra membranous proteins e.g. cytoskeleton (peripheral proteins)

Semester 2 - Membranes and Receptors (14 decks)

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