Biological membranes - Plasma membrane and membranes inside cells

Question 1

what are the 5 roles of the cell surface membrane

Answer 1

• selectively permeable barrier
• cell signalling e.g receptor site for hormones or neurotransmitters
• cell recognition
• cell to cell adhesion to form tissues
• enzyme attachment

Question 2

explain the selectively permeable barrier role of the cell surface membrane

Answer 2

• separates cell content from environment
• transports specific substances into/out of the cell
• barrier to some large, polar molecules

Question 3

state the four roles of membranes inside cells

Answer 3

compartmentalisation
sites of chemical reactions
provide an internal transport system e.g vesicles
controls the movement of substances into/out of organelles

Question 4

explain the compartmentalisation role of membranes inside cells, giving examples

Answer 4

isolation of chemical reactions e.g reaction of photosynthesis in chloroplast and aerobic respiration in mitochondria
lysosome membranes isolate hydrolytic enzymes which could damage the cell
nuclear envelope isolates the DNA to prevent it from being damaged

Question 5

explain the sites of chemical reactions role of membranes inside cells, giving examples

Answer 5

• provide attachment sites for enzymes and pigments
  e.g cristae in mitochondria give a large surface area for ATP synthase and other enzymes needed for aerobic respiration
  e.g chlorophyll in thylakoid membranes of chloroplasts
• RER holds ribosomes
• thylakoids and cristae allow formation of concentration gradients

Question 6

name the parts of the fluid-mosaic model

Answer 6

glycoprotein
glycolipid (together making glycocalyx)
cholesterol
phospholipid bilayer (hydrophilic heads and hydrophobic tails)
extrinsic protein
intrinsic protein

Question 7

describe the structure of phospholipids

Answer 7

phosphate group attached to glycerol, which is attached to two fatty acids by ester bonds

Question 8

what are the functions of phospholipids in membranes (4)

Answer 8

• gives the membrane fluidity
• barrier to large water soluble molecules and polar molecules (ions)
• allows lipid-soluble molecules (non-polar) to pass through
• unsaturated fatty acid tails have kinks in them. this prevents close packing, allowing movement of phospholipids within the bilayer, making the membrane more fluid and permeable

Question 9

what are the structures of proteins within the membrane

Answer 9

alpha helix proteins
globular proteins
intrinsic proteins
extrinsic proteins

Question 10

what are the functions of proteins in the membrane (5)

Answer 10

• structural support
• transport - channel protein (allow polar molecules through) , carrier protein
• enzymes
• helps cells adhere together
• receptors for hormones (have specific shape)

Question 11

is cholesterol polar or non-polar

Answer 11

non-polar

Question 12

what are the functions of cholesterol in the membrane

Answer 12

fits between the phospholipids, regulates the fluidity of membranes (more cholesterol less fluidity), reduces lateral movement of phospholipids, giving the membrane stability and flexibility

Question 13

what are the two components of the glycocalyx

Answer 13

glycoproteins, glycolipids

Question 14

what are the functions of the glycocalyx (5)

Answer 14

• receptor sites for hormones/neurotransmitters
• cell markers e.g ABO blood system
• act as antigens, allowing cells to recognise “self”
• helps cells adhere to one another, forming tissues
• forms hydrogen bonds with water the stabilise the membrane

Question 15

what is the general width of the cell surface membrane

Answer 15

7nm

Question 16

Suggest why a low pH might cause red pigment to leak out of beetroot cells

Answer 16

Denatures proteins, therefore membrane permeability is increased