Lipids 2

Question 1

Triacylglycerols

4 points

Answer 1

1. Composition- 3 fatty acids esterified to a glycerol molecule
2. Neutral molecules - contain no charged groups
   Sometimes called neutral lipids
3. Form in which lipid energy stores are deposited in adipose tissue of animals (fats) and in seeds of oilseed plants (oils)
4. Fats and oils from different sources have a characteristic distribution of fatty acids

Question 2

Phosphoacylglycerols (Phospholipids)

Answer 2

1. membrane lipid family
2. Fatty acid esters of glycerol which also contain a phosphate group and other specific groups (X-Group)
3. The phosphate group replaces the fatty acid on C number 3 of a triacylglycerol molecule
4. amphipathic - molecules with 1 polar end and 1 nonpolar end
5. polarity dictates structure

Question 3

X-groups

Answer 3

1. They are very polar molecules and are often charged
2. Ethanolamine
3. Serine
4. Choline (When choline is part of the phosphoacylglycerol it is called phosphatidyl choline)
5. Inositol

Question 4

see desktop. should be able to draw phosphoacylglycerol

Answer 4

.

Question 5

Phosphoacylglycerols

Amphipathic molecules spontaneously form a number of specific structures including:
Amphipathic molecules spontaneously form a number of specific structures including:

Answer 5

1. monolayers (at liquid air interface)
2. micelles
3. bilayers

Question 6

Biological Membranes

4 points

Answer 6

1. The phosphoacylglycerol or phospholipid bilayer is the basis of biological membrane structure
2. Membrane structure due to the amphipathic nature of the phosphoacylglycerols
3. Acylglycerols cannot form bilayers because they are not amphipathic [not charged. They are neutral]
4. Sterols [e.g. cholesterol] are also found in membranes. They are amphipathic

Question 7

Membrane proteins

2 points

Answer 7

1. Integral Proteins

span the membrane (may have multiple transmembrane segments)

or partially immersed in lipid layer

2. Peripheral Proteins
   loosely attached: electrostatic interaction, bonding to integral protein, hydrophobic anchor, bonding to phosphoacylglycerol via carbohydrate chain

Question 8

Why have proteins and carbohydrates in membranes?

3 points

Answer 8

1. Cell recognition
2. Extracellular enzyme activities [on the surface of the cell]
3. Transport of compounds across the membrane:

Diffusion

Passive transport (facillitated diffusion)

Active transport

Question 9

Diffusion

5 points

Answer 9

1. Solute passes across membrane from area of high concentration to area of low concentration until concentration equalised
2. Driven by concentration gradient
3. Small polar molecules diffuse through small gaps in hydrophobic environment.
4. Larger polar molecules (particularly if charged) do not diffuse
5. Uncharged, lipophilic molecules diffuse readily

Question 10

Passive transport (facilitated diffusion)
5 points

Answer 10

1. Depends on the presence of specific proteins which transport the molecule from one side of the membrane to the other
2. Driven by concentration gradient
3. Activation energy (ΔG) very high for diffusion of hydrophilic molecule through bilayer.
4. Activation energy (ΔG) lowered by use of transporter protein.
5. Transporter protein makes non-covalent interactions that replace hydrogen bonding, allowing molecule to pass through the bilayer.
   e. g. glucose carrier protein

Question 11

Active Transport

Answer 11

1. Depends of the presence of specific transport proteins
2. Transport requires energy
3. Transport can be against a concentration gradient
   e. g. sodium potassium pump

ions actively pumped against concentration gradients

Question 12

Osmosis

3 points

Answer 12

1. The process by which a solvent passes across a semi-permeable membrane from a solution with a low osmotic pressure to one with a high osmotic pressure
2. Osmotic pressure is directly proportional to the molar concentration of all the solutes and ions which cannot pass across the membrane
3. A semi-permeable membrane is one which allows passage of solvent but not solute

Question 13

Tonicity

Answer 13

1. Biological membranes are selectively impermeable not semi-permeable
2. Allow free passage of solvent and some solutes but not all
3. Tonicity is due to the osmotic pressure exerted only by the solutes which cannot pass across the selectively permeable membrane

Question 14

primary Active transport
sodium potassium pump
4 points

Answer 14

1. 3 sodium ions and 1 ATP molecule bind to pump
2. ATP phosphorylates pump causing it to change shape

= sodium ions delivered to outside of cell

3. . ion binding sites open on extracellular face of pump.
   picks up 2 potassium ions. at same time inorganic phosphate released causing pump to change shape

= potassium delivered to inside of cell

4. high potassium ion conc inside cell.
   high sodium conc outside cell

Question 15

Secondary active transport

e.g. glucose

Answer 15

1. glucose molecules transported against conc gradient
2. energy doesn’t come from ATP. comes from energy stored in sodium ion gradient (created using ATP) = secondary transport
3. pump takes up sodium and glucose from outside of cell then changes shape = both go inside cell