Module 2 - Plasma membranes

Question 1

5 key components of cell membranes

Answer 1

1. Phospholipid bilayer: made of phospholipids with hydrophilic heads and hydrophobic tails
2. Cholesterol: adds stability
3. Proteins: intrinsic or extrinsic
4. Glycoproteins: proteins attached to carbs
5. Glycolipids: lipids attached to carbs

Question 2

Phospholipid bilayer

Answer 2

Structure means water-soluble substances cannot pass through but lipid soluble substances can dissolve and pass through cell membrane

Question 3

Cholesterol

Answer 3

Have a hydrophilic and hydrophobic region. Hydrophobic region bind to phospholipid fatty acid tails so they pack closely together, fluidity is reduced

Question 4

Intrinsic and extrinisic proteins

Answer 4

Instrinsic: embedded through both sides of the bilayer and include channel and carrier proteins, they transport large molecules and ions across the membrane
Extrinsic: present on one side of the bilayer and provide support for the membrane or involved in cell signalling

Question 5

What are glycoproteins and glycolipids involved in?

Answer 5

Cell adhesion: attachment of one cell to another
Cell recognition: allows cells to recognise one another
Cell signalling: communication between cells

Question 6

What are the 2 main types of cell membranes?

Answer 6

Cell-surface membrane: act as a barrier between the cell and its environment, they controll substances that leave and enter the cell
Membranes around organelles: barrier between organelle and cytoplasm and divides cell into different compartments (compartmentalisation)
Both are partially permeable

Question 7

Effect of temperature on permeability of membranes

Answer 7

Low temp: phospholipids do not have much kinetic energy, they are packed closely together to form a rigid cell membrane decreasing permeability
Medium temp: more kinetic energy so move faster and aren’t as packed together which increases permeability
High temp (40+): bilayer breaks down, channel and carrier proteins denature so cannot control what enters and exists the cell so permeability increases

Question 8

WHat are solvents and what impact does it have on the permeability of membranes?

Answer 8

Liquids that have the ability to dissolve substances
Solvents like ethanol dissolve phospholipids so membrane becomes more fluif and disrupts its structure to make it more permeable. High conc. of solvent means peremability increases

Question 9

What is diffusion?

Answer 9

net movement of particles from an area of high to low concentration and eventually reach equilibrium where all particles are evenly distributed, it does not require energy so is a passive process

Question 10

Why can oxygen and carbon dioxide diffuse via simple diffusion?

Answer 10

They are small so can pass through spaces between phospholipids
Non-polar so can dissolve in the hydrophic core of the cell membrane

Question 11

What does facilitated diffusion require?

Answer 11

Large and polar molecules can cross cell membranes via carrier and channel proteins. They are highly specific and only allow a small number of molecules to pass through

Question 12

Carrier proteins

Answer 12

1. large molecule attaches to carrier protein
2. protein changes shape
3. releases the molecule on the opposite side of the membrane

Question 13

Channel proteins

Answer 13

They form pores in cell membrane that ions can travel through