Module 2: Plasma membranes

Question 1

What is the difference between simple diffusion and facilitated diffusion in biological membranes?

Answer 1

Simple diffusion does not require proteins, while facilitated diffusion does.

Question 2

What is the term for the engulfing of liquids by the cell membrane in biological membranes?

Answer 2

Pinocytosis

Question 3

What is the term for the specific uptake of macromolecules by the cell membrane in biological membranes?

Answer 3

Receptor-mediated endocytosis

Question 4

What is the term for the transport of substances across channel proteins?

Answer 4

Facilitated diffusion

Question 5

What is the phospholipid bilayer?

Answer 5

Hydrophilic phosphate heads on the outside which can interact with water, and the hydrophobic fatty acid tails on the inside. Hydrophobic core.

Question 6

What is the fluid mosaic model? Why is it called this?

Answer 6

Components of the plasma membrane with glycoproteins, cholesterol etc.

Fluid - phospholipids are free to move within the layer next to each other which gives the membrane flexibility.
Mosaic - proteins embedded in the bilayer vary in size.

Question 7

What are the 2 types of protein in the cell surface membrane?

Answer 7

1. Intrinsic proteins are embedded through both layers of the membrane. They have amino acids with hydrophobic R groups on the external surface which interact with the hydrophobic core f the membrane, keeping them in place.
2. Extrinsic proteins are embedded in one side of the bilayer, held by weak hydrophilic interactions with the phosphate heads.

Question 8

Describe the function of the 2 types of intrinsic proteins.

Answer 8

1. Channel proteins - hydrophilic channel that allows the PASSIVE movement of POLAR molecules/ions down a concentration gradient through the bilayer.
2. Carrier proteins - used in diffusion but mainly active transport where ATP changes the shape of the protein allowing molecules to pass through.

Question 9

What are glycoproteins and what is their function?

Answer 9

Extrinsic protein that has a carbohydrate chain attached.

Cell adhesion (where cells join together to form tight junctions in certain tissues) and acts as receptors for chemical signals. When a chemical binds to the receptor, it causes a response inside the cell known as CELL SIGNALLING.

Question 10

Define cell signalling.

Answer 10

Cells communicating with each other by sending and receiving signals.

Question 11

Give an example of cell signalling.

Answer 11

Receptors for neurotransmitters such as acetylcholine at nerve cell synapses that triggers an impulse on the next neurone.

Question 12

3 roles of glycoproteins in membranes?

Answer 12

1. Cell signalling
2. Act as antigens
3. Cell adhesion

Question 13

What are glycolipids and what is their function?

Answer 13

Lipids with a carbohydrate chain attached. They are cell markers + antigens which can be recognised by cells in the immune system as self or non-self.

Question 14

What molecules can pass through the phospholipid bilayer?

Answer 14

Small, uncharged or lipid-soluble molecules can pass through.

Water soluble molecules cannot pass through.

Question 15

Function of cholesterol?

Answer 15

Cholesterol is a sterol that has a hydrophilic end (interacts with the heads) and a hydrophobic end (interact with tails)
Cholesterol is positioned between the fatty acids and regulates fluidity. It also restricts the movement of phospholipids and also avoids the phospholipids grouping too closely together, making the membrane more rigid. Stability/flexibility.

Question 16

What happens to the phospholipid bilayer as temperature increases?

Answer 16

They’ll have more KE and move more, so the membrane becomes more fluid and increases the permeability as this disrupts the structure. More molecules can pass through it.

Carrier and channel proteins will denature at higher temps.

Question 17

Impact of water on the phospholipid bilayer?

Answer 17

Water, a polar solvent, keeps the non-polar tails away from water to form the hydrophobic core. The polar phosphate heads interact with water, keeping the bilayer intact.

Question 18

Impact of less/non-polar organic solvents on the phospholipid bilayer?

Answer 18

Organic solvents will dissolve bilayer as they are lipid-soluble, disrupting bilayer and reduces the transport of materials. This is why alcohol is used in antiseptic wipes.

Question 19

What is diffusion?

Answer 19

Net movement of particles from an area of their high conc to area of low conc. It is a passive process. Equilibrium doesn’t mean the particles stop moving but the movements are equal in both directions.

Question 20

3 factors that affect the rate of diffusion?

Answer 20

1. Conc gradient
2. Temperature
3. SA:Volume

Question 21

Do non-polar molecules pass through the phospholipid bilayer?

Answer 21

Yes, non-polar molecules like O2 can diffuse through it as the interior of the membrane is primarily composed of hydrophobic lipids, which readily interact with nonpolar substances, allowing them to diffuse across the membrane freely.

Question 22

DO polar molecules pass through the phospholipid bilayer?

Answer 22

Some small, slightly polar molecules like water and ethanol can cross the cell membrane by passive diffusion (very slowly), but it depends on the size and polarity of the molecule.

Large polar molecules, like glucose, cannot pass through the cell membrane by passive diffusion. This is because they are too large and charged to pass through the nonpolar region of the cell membrane.The cell membrane’s interior is hydrophobic, meaning it repels polar molecules.

To cross the cell membrane, large polar molecules and IONS require the help of transport proteins.

Question 23

How do micelles form?

Answer 23

When one phospholipid layer is exposed to water, the hydrophilic heads face the water and the hydrophobic tails point inwards away from water.

Question 24

Active transport