deck_472623

Question 1

Welcome to Semester 2 guys! Functions of membranes? (5)

Answer 1

1.Continuous, highly selective, permeability barrier2.Control of enclosed chemical environment3.Communication between cells and their environment4.Recognition e.g. signalling proteins, adhesion proteins, immune surveillance5.Signal generation in response to stimuli e.g. electrical/chemical Castrated Criminals Can’t Really Sex

Question 2

Name three types of lipid in a membrane?

Answer 2

PhospholipidsGlycolipidsCholesterol

Question 3

What are the main components of a phospholipid?

Answer 3

Polar head groupAttached to.. PhosphateAttached to..Glycerol backbone Attached to.. Fatty acid chains

Question 4

What are the main types of polar head groups?

Answer 4

Choline, amines, amino acids, sugars

Question 5

What are the main types of fatty acid chains?

Answer 5

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

Question 6

Why is sphingomyelin different to most Phospholipids?

Answer 6

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

Question 7

What is an ampipathic molecule?

Answer 7

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

Question 8

Where are unsaturated fatty acids found? Give an example

Answer 8

In the dietLinolenic acid

Question 9

What Sphingoyelin found? What is its function?

Answer 9

In myelin sheathes, aids in signal transduction

Question 10

What is a glycolipid?

Answer 10

lipids with a carbohydrate group attached

Question 11

Give the structure of a glycolipid

Answer 11

Sugar head group (Cerebroside or Gangioside)Sphingosine backboneNitrogenous baseFatty acid tail

Question 12

Cerebroside?

Answer 12

monomer head group e.g. galactose

Question 13

Ganglioside?

Answer 13

oligosaccharide head group

Question 14

What is cholesterol derived from?

Answer 14

HMG-CoA

Question 15

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

Answer 15

HMG-CoA reductaseStatins

Question 16

Give the structure of cholesterol

Answer 16

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

Question 17

What two things will an ampipathic molecule form in water?

Answer 17

A micelle or a bi-layer

Question 18

Describe formation of a lipid bi-layer

Answer 18

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.

Question 19

What do unsaturated phospholipids do in a bilayer?

Answer 19

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

Question 20

What are pure lipid bilayers impermeable to?

Answer 20

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

Question 21

What are the four modes of mobility of lipid bilayers?

Answer 21

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.

Question 22

How can cholesterol stabilise phospholipid bilayers?

Answer 22

• 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.

Question 23

What does cholesterol stabilisation of lipid bilayers mean?

Answer 23

Maintain homegenous environment regardless of temperature

Question 24

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

Answer 24

Embedded in the bilayer Interact with the hydrophobic regions of the bilayer

Question 25

How can intergral proteins be removed?

Answer 25

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

Question 26

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

Answer 26

Associated with the surfaceBound to membrane surface by electrostatic and H-bond interactions

Question 27

How can a peripheral protein be removed?

Answer 27

By pH or ionic strength changes

Question 28

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

Answer 28

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

Question 29

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

Answer 29

restricts the lateral mobility of the membrane protein

Question 30

What is erythrocyte cytoskeleton important?

Answer 30

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

Question 31

What is hereditary spherocytosis?

Answer 31

Spectrin levels depleted by 40-50% in erythrocytesCells much less resistant to lysis and become sphere-shaped

Question 32

What happens to erythrocytes in hereditary spherocytosis?

Answer 32

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.

Question 33

What is hereditary elliptocytosis?

Answer 33

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

Question 34

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

Answer 34

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

Question 35

Describe process of insertion into ER of integral protein

Answer 35

- 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

Question 36

What happens to membrane protein after ER processing?

Answer 36

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

Question 37

What is a multiple membrane domain?

Answer 37

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

Question 38

What is membrane asymmetry?

Answer 38

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.

Question 39

What do C=C in fatty acids chains do?

Answer 39

disrupt the hexagonal packing of phospholipids  increase membrane fluidity.

Question 40

What do membrane proteins do?

Answer 40

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

Question 41

Give three ways proteins in lipid bilayers can move

Answer 41

1.Conformational change2.Rotation3.Lateral diffusion

Question 42

Give one way proteins in lipid bilayer cannot move and why

Answer 42

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

Question 43

What is protein mobility restrained by? (3)

Answer 43

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