1.4- Membrane Structure

Question 1

Two key features of membranes

Answer 1

semi-permeability and selectivity

Question 2

Define semi-permeability

Answer 2

some materials can’t cross without help

Question 3

Define selectivity

Answer 3

passage of some materials can be regulated

Question 4

What are cell membranes primarily composed of

Answer 4

phospholipids
- phosphate + lipids

proteins
- integral + peripheral

Question 5

Formation of the bilayer

Answer 5

Phospholipids arrange (spontaneously) into a bilayer.

Hydrophobic tails face inwards.

The two hydrophilic head regions associate with the intracellular (cytoplasm) and extracellular (interstitium) fluids.

The bilayer acts as a barrier to some materials, making the membrane selectively permeable.

Substances that are large and polar (charged) substances cannot cross the membrane due to its hydrophobicity.

Question 6

What is the bilayer held together by

Answer 6

weak hydrophobic bonds between fatty acid tails which allows for fluidity and flexibility

Question 7

Unsaturated fatty acids …

Answer 7

increase fluidity

Question 8

Saturated fatty acids..

Answer 8

decrease fluidity

Question 9

Where are membrane proteins located

Answer 9

within the phospholipid bilayer

integral and peripheral

Question 10

Integral protein

Answer 10

permanently penetrate the bilayer

Question 11

Peripheral protein

Answer 11

temporarily associate with one side of the membrane

Question 12

Example of integral protein

Answer 12

ATP synthase, an enzyme that synthesises ATP during aerobic cellular respiration.

glycoproteins, ion channels, carrier proteins, protein pumps

Question 13

How are peripheral proteins attached to the membrane

Answer 13

Temporarily attached to integral proteins, linked to the polar heads or held in place by the cytoskeleton or extracellular matrix

can be removed by polar solvents

Question 14

What is a glycoprotein

Answer 14

a protein with an attached carbohydrate

Question 15

TRACIE

Answer 15

Transport
Receptors
Anchorage
Cell Recognition
Intracellular joinings
Enzymes

Question 16

TRACIE def

Answer 16

The functions of membrane proteins:

TRANSPORT – facilitated diffusion and active transport

RECEPTORS – hormone signalling and neurotransmission

ANCHORAGE – attachment points for cytoskeleton and extracellular matrix

CELL RECOGNITION – markers for cellular identification

INTERCELLULAR JOININGS – connect and join two cells together

ENZYMES – localise and catalyse metabolic reactions

Question 17

What is glycosylation

Answer 17

attachment of carbohydrate chains to phospholipids and membrane proteins

Question 18

What is a glycolipid

Answer 18

carbohydrate chain on phospholipid

Question 19

What is a glycoprotein

Answer 19

carbohydrate chain on a membrane protein

Question 20

What do carbohydrate chains do

Answer 20

cell adhesion and recognition
ex. sperm binding to egg

Question 21

How does glycosylation maintain the structural integrity of the extracellular matrix

Answer 21

carbohydrate chains link the extracellular molecules to form a cohesive network

Question 22

Fluid-mosaic model

Answer 22

Fluid- individual phospholipids can move position
Mosaic- proteins are embedded in the bilayer

Question 23

2. Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane. [7]

Answer 23

Answer:
a. hydrophilic is attracted to/soluble in water and hydrophobic not attracted/insoluble ✔
b. hydrophilic phosphate/head and hydrophobic hydrocarbon/tail inphospholipids✔
c.phospholipid bilayerin water/in membranes ✔
d. hydrophilic heads «of phospholipids» face outwards/are on surface ✔
e. hydrophobic tails «of phospholipids» face inwards/are inside/are in core ✔
cholesterol is «mainly» hydrophobic/amphipathic so is located among phospholipids/in hydrophobic region of membrane ✔
some amino acids are hydrophilic and some are hydrophobic ✔
h. hydrophobic «amino acids/regions of» proteins in phospholipid bilayer «core» ✔
i. hydrophilic «amino acids/regions of» proteins are on the membrane surface ✔
j. integral proteinsare embedded in membranes due to hydrophobic properties/regionOR transmembraneproteins have a hydrophobic middle region and hydrophilic ends ✔
k. peripheral proteinson are on the membrane surface/among phosphate heads due to being «entirely» hydrophilicOR «carbohydrate» part ofglycoproteinsis hydrophilic so is outside the membrane ✔
l. pore ofchannel proteinsis hydrophilic ✔
Allow mark points shown in clearly annotated diagram.
In any part of the answer, accept polar instead of hydrophilic and non-polar instead of hydrophobic.