1. Lipids, Proteins and Membrane Structure

Question 0

What proportion of the dry weight of a membrane do lipids make up?

Answer 0

40%

Question 1

Why would different regions of a cell membrane have different proteins?

Answer 1

Different regions can have different functions e.g. Adherence, secretion/absorption, synapses, interaction with basement membrane etc.

Question 2

What proportion of the dry weight of the membrane do proteins make up?

Answer 2

60%

Question 3

What else makes up the dry weight of the membrane bilayer.

Answer 3

Carbohydrates

Question 4

When hydrated, how much of the total weight does water make up and how is water associated with the membrane?

Answer 4

20%

Hydrogen bonded to the cell membrane surface

Question 5

What four groups make up a phospholipid molecule?

Answer 5

Polar head group
Phosphate group
Glycerol
Fatty acid chains

Question 6

What are the most predominant lengths of fatty acid chains?

Answer 6

C16

C18

Question 7

What can produce a kink in the phospholipid?

Answer 7

Cis orientated double bond in a fatty acid tail

Question 8

What four chemicals can act as polar heads?

Answer 8

Choline
Amines
Amino acids
Sugars

Question 9

What makes a glycolipid different to a phospholipid?

Answer 9

Carbohydrate molecule instead of a phosphate head

Question 10

What are the two types of glycolipid?

Answer 10

Cerebrosides

Gangliosides

Question 11

What type of head group is present on a ganglioside glycolipid?

Answer 11

Oligosaccharide

Question 12

What type of head group is present on a cerebroside lipid?

Answer 12

Sugar monomer

Question 13

What are the forces that interact between hydrophobic tails in a membrane?

Answer 13

Van der Wall’s forces

Question 14

What are the two types of lipid bilayers that can form?

Answer 14

Phospholipid bilayer

Lipid mycelle

Question 15

What 4 types of motion can phospholipids undergo?

Answer 15

Flexion (vibration)
Rotation
Lateral diffusion
Flip flop

Question 16

Which type of phospholipid motion requires the most energy and why?

Answer 16

Flip flop as it is the least thermodynamically favourable

Question 17

What do the Cis bonds in the fatty acid tails of phospholipids result in?

Answer 17

Reduced phospholipid packing
More movement
More fluidity of membrane

Question 18

What does our diet need to include for phospholipids and where can we get this from?

Answer 18

Polyunsaturated fats
Vegetable oils
Tuna/Salmon
Seeds

Question 19

What property does the planar ring in cholesterol have?

Answer 19

Rigidity

Question 20

What percentage of lipids in a phospholipid bilayer are cholesterol?

Answer 20

45%

Question 21

How does cholesterol interact with the phospholipid bilayer?

Answer 21

Locks onto adjacent phospholipid via a hydrogen bond

Question 22

How does cholesterol reduce fluidity of the membrane at high temperatures?

Answer 22

Reduces the phospholipid’s fatty acid chain’s motion

Question 23

How does cholesterol increase fluidity of the membrane at low temperatures?

Answer 23

Reduced phospholipid packing

Question 24

What is cholesterol's overall effect on the membrane?

Answer 24

Maintains a constant fluidity at a wide range of temperatures

Question 25

What are the 3 functional pieces of evidence for proteins existence in the membrane?

Answer 25

Facilitated diffusion Ion gradients Specificity of cell responses

Question 26

What are the 2 biochemical pieces of evidence for protein existence in the membrane?

Answer 26

Membrane fractionation | Freeze fracture

Question 27

What type of mobility can proteins NOT do in membrane bilayers and why?

Answer 27

Flip flop Requires too much energy as they have large hydrophilic moieties which associate with the polar heads and water on the outsides of the membrane

Question 28

What are the 3 types of mobility proteins can do in bilayers?

Answer 28

Conformational change Rotation Lateral diffusion

Question 29

What restricts protein movement in bilayers?

Answer 29

Protein aggregation Tethering (e.g. Cytoskeleton) Interaction with other cells

Question 30

What are peripheral membrane proteins and how do they bond?

Answer 30

Proteins bound to the surface of a membrane Hydrogen bonds Electrostatic bonds Disulphide bonds

Question 31

How can peripheral proteins be removed from the membrane?

Answer 31

pH change | Ionic strength

Question 32

What are integral proteins?

Answer 32

Proteins that interact extensively with hydrophobic domains of the lipid bilayer (can be transmembrane proteins)

Question 33

How can integral proteins be removed from the membrane?

Answer 33

Detergents | Organic solvents

Question 34

What type of secondary structure do transmembrane domains often have and how many residues does it take to cross the membrane?

Answer 34

Alpha helix | 18 - 22 amino acid residues

Question 35

What is a hydropathy plot?

Answer 35

Checking individual residues to check how hydrophobic/hydrophilic their R groups are 18-22 hydrophobic residues indicates a membrane cross hence a hydropathy plot can be used to tell how many times a protein crosses the membrane

Question 36

What forms the cytoskeleton network on the erythrocyte membrane?

Answer 36

Actin | Alpha and beta spectrin molecules wound together to form a heterotetramer

Question 37

Which adapter proteins do band 3 and glycophorin A attach to respectively?

Answer 37

Ankyrin and band 4.1

Question 38

Which integral proteins do ankyrin and band 4.1 bind to respectively?

Answer 38

Band 3 and glycophorin A

Question 39

What is hereditary spherocytosis and what is it's cause?

Answer 39

Erythrocytes become more spherical hence are less resistant to lysis and get cleared by the spleen Cause by a 50% depletion in spectrin due to one allele not being expressed

Question 40

What is hereditary eliptocytosis and what is its cause?

Answer 40

Erythrocytes are fragile eliptoid shaped cells | Caused by defect in spectrin molecule stopping heterotetramers from forming

Question 41

What are the main signs/symptoms of haemolytic anaemias?

Answer 41

Low erythrocyte count hence low Hb | Fatigue

Question 42

What is the treatment for haemolytic anaemias?

Answer 42

Blood transfusions

Question 43

What is the sequence of hydrophobic amino acids called which cause that section of the synthesised protein to stay in the membrane?

Answer 43

Stop transfer signal