Leyland 1 Lipids & membranes

Question 1

MEMBRANES

Function:

Answer 1

• surround every cell & also some organelles within cells (eg mitochondria)
• highly selective barrier -> COMPARTMENTS e.g. from environment or organelles

Question 2

integral membrane proteins

Answer 2

through the membrane

amphipathic (with hydrophobic section through phospholipid bilayer)
• need detergent (disrupts membrane structure) to remove & solubilise
• held by hydrophobic interactions with lipids

Question 3

peripheral membrane proteins

Answer 3

on outside of membrane

• largely hydrophilic surface -> a.a. tend to be hydrophilic to interact
• can be removed from the membrane fairly easily eg by increasing [NaCl] to disrupt ionic interactions.-> electrostatic

Question 4

LIPIDS

Answer 4

• Structurally diverse ->
• Generally insoluble in water (hydrophobic) -> diff properties = diff function
• Most only contain C, H, O
(phospholipids contain P, N)

Question 5

FATTY ACIDS

Answer 5

basic building blocks

CH3(CH2)nCOOH
where n = 14 -18 (ie 16 - 20 C in total) – long CH chain & CH2 grps COOH at end
insoluble, dissociation in solution => ionised form
Amphipathic: molecule with hydrophobic and hydrophilic properties

Question 6

Types of lipids in biological membranes

Answer 6

1. Phospholipids
2. Glycolipids
3. Cholesterol

Question 7

Altering the membrane with lipid properties:

Answer 7

• longer the chain =more likely to be solid

- double bonds more likely to be liquid

Question 8

PHOSPHOLIPIDS

Answer 8

• amphipathic

FA   G
FA   L
       Y
       C
       E
       R
      O - Phosphate - alcohol
       L
Hydrophobic
                          Hydrophillic

Question 9

Phospholipids commonly found in membranes

Answer 9

Phosphoatidylserine
Phosphatidylcholine
Phosphatidylethanolamine
Phosphatidylinositol

Question 10

GLYCOLIPIDS

Answer 10

amphipathic

Fatty acid unit
Glycolipid
Sugar unit (glucose/galactose)

Question 11

CHOLESTEROL

Answer 11

– amphipathic (not in bacteria)

Question 12

similarities between membrane lipids

Answer 12

• all amphipathic molecules

* have similar shape and can be depicted using the same shorthand form

Question 13

PROPERITES OF BIO MEMBRANES

Answer 13

1. all amphipathic molecules, spontaneously form bilayers in water.
2. composed of sheets of lipids only 2 molecules thick.

Question 14

2. composed of sheets of lipids only 2 molecules thick.

HYDROPHOBIC INTERACTIONS

Answer 14

• hydrophobic (non-polar) molecules do not interact with water
• electrostatic by H-bonds
• cluster together to exclude water

Question 15

Polar molecules

Answer 15

hydrophilic

Question 16

Non-polar molecules

Answer 16

hydrophobic

Question 17

micelles

Answer 17

polar heads outside interacting with water & hydrophobic tails inside interacting with each other, excluding water
• Amphipathic fatty acids readily form

Question 18

bilayers

Answer 18

• Phospholipids are more suited to forming bilayers to achieve stable structure in aqueous environment. -> seal tears easily

• Lipid bilayers are 3nm thick
• Hydrophobic core
• Hydrophilic surface

Question 19

Liposomes

Answer 19

mimic cell membranes of a biological cell.
- double bilayer, used to transport things into cell by fusing with membrane e.g. DNA transcription.
Lipids are highly impermeable to ions and most polar molecules

Question 20

Transmembrane a helices

Answer 20

most common structural motif in lipid proteins
- span the membrane in many TransMembrane proteins
• ~ 20 amino acids per membrane-spanning a-helix
• contain mostly hydrophobic amino acids
• few charged amino acids
• approximately 20 amino acids in length