MCB and Biomembranes

Question 1

What are the roles of biological membranes?

Answer 1

• Form boundary around all cells- helps maintain structural integrity
• Aids establishment of conc. gradient (membranes are fluid and selectively permeable)
• Compartmentalisation
• Communication and transport
• Organelles can also have specialised membranes

Question 2

Describe the phospholipid bilayer

Answer 2

• All eukaryotic bio membranes have similar phospholipid bilayers
• Driven by the hydrophobic edict due to hydrophobic tails and hydrophilic heads

Question 3

Describe lipids

Answer 3

• Spontaneously associate to exclude water from hydrophobic regions (energetically favourable)
• Includes fatty acids, waxes, glycerol and triacylglycerols, phospholipids and cholesterol
• Lipid structure varies and involved in compartmentalisation, energy storage and cell signalling

Question 4

Describe phospholipids

Answer 4

• They are amphipathic
• Partly polar and partly non-polar
• 2 OH groups in glycerol moiety linked to fatty acids, 3rd phosphorylated
• Phosphate linked to a variety of small polar alcohol head groups (e.g. choline, serine etc,)
• Naming phosphatidyl- variable head group

Question 5

What is the cytosolic face?

Answer 5

Membrane face that faces the cytoplasm

Question 6

What is the ectoplasmic face?

Answer 6

Faces outside the cell or inward toward organelle

Question 7

What are flippases?

Answer 7

Enzymes that aid the ‘flip-flop= movement of lipid, and maintains asymmetry- natural for ‘programmed cell death’

Question 8

What is the signature phospholipid of the mitochondria?

Answer 8

Cardiolipin

Question 9

What is the name of carbohydrates presented on the outside of the cell?

Answer 9

Glycolipids (blood-type determining antigens)

Question 10

What is another example of membrane lipids?

Answer 10

Cholesterol

Question 11

What are sphingolipids?

Answer 11

• Sphingosine instead of glycerol as carbon backbone to create sphingomyelins
• Most common sphingomyelin has choline polar head group
• Enriched in the myelin sheath that surrounds neuron axons

Question 12

What is the liquid crystalline phase?

Answer 12

• Lipids within bio membranes contain mobile fatty acid chains (c-16 to 22)
• Unsaturation prevents tightly packed acyl chains, resulting in mobility
• Lipids move around plane of bilayer
• • Essential for membrane proteins that require fluidity to operate and interact

Question 13

How do you label?

Answer 13

(Number of carbons: number of double bonds’n’-placement of double bond)

Question 14

What receptors are directly involved in the propagation of signals?

Answer 14

• G-protein couple receptors (most diverse type of membrane receptor)
• Nuclear receptors (Sensing steroid and thyroid hormones)

Question 15

What are the precursors of signalling molecules and cellular messengers?

Answer 15

• Sphinogsine-1-phosphate
• Diacylglycerol
• Inositol phosphates
• Prostaglandins
• Steroid hormones

Question 16

Describe membrane composition and regions

Answer 16

• Protein to lipid ratios differs among bio membranes
• Patches of varied lipid density, essential for signalling
• Cholesterol enriched areas from lipid rafts, interaction between saturated tails of sphingolipids with cholesterol stabilises fluid phase
• Increased stability
• Cholesterol transport, endocytosis and signal transduction with lipid rafts

Question 17

What is an integral membrane protein?

Answer 17

Deeply embedded in the bilayer

Question 18

What is a peripheral membrane protein?

Answer 18

Associated to lipids or other proteins within the membrane

Question 19

What is a transmembrane protein?

Answer 19

• Integral proteins that traverse the membrane
• Composed of amino acids with non-polar side chains
• Often interact with he hydrophobic lipid tails and form complex structure, e.g. pores

Question 20

What types of molecules can diffuse across the membrane?

Answer 20

Small non-polar or uncharged polar molecules

Question 21

What types of molecules undergo facilitated diffusion across the membrane?

Answer 21

Larger polar molecules and require a transporter

Transporters are substrate specific and catalyse passive movement

Question 22

What is a uniport?

Answer 22

Transporter where molecule goes in one direction

Question 23

What is a symport?

Answer 23

Transporter where two things go in together (co-transport)

Question 24

What is an antiport?

Answer 24

Transporter where one thing goes in whilst one goes out

Question 25

What is the rate of transporter diffusion dependent on?

Answer 25

• Transporter concentration

Question 26

What type of transport is used in sodium-potassium pumps?

Answer 26

• Primary active transport
• Creates a potential difference
• Requires energy

Question 27

What is secondary active transport?

Answer 27

Molecules are moved through a membrane anti port as a result of the diffusion of another substance

• ATP not directly used
• Energy stored in ion gradients is used to power secondary transporters

Question 28

What are two examples of diseases linked to membranes?

Answer 28

• Menkes- X-linked lethal disorder, copper transporting ATPase defective
• Wilson’s- another copper ATPase, failure to excrete copper from liver into bile- toxic accumulation