Cell Membranes

Question 1

What are the functions of membranes on the cell of the surface?

Answer 1

• Partially permeable barrier between cell and environment.
• Control which substances enter and leave the cell.
• Cell recognition.
• Cell communication.

Question 2

What are the functions of membranes within cells?

Answer 2

• Compartmentalisation.
• Control what goes in and out of organelles within a cell.
• Form vesicles.
• Form sites for chemical reactions.

Question 3

What is the fluid mosaic model?

Answer 3

-Describes the arrangement of molecules in a membrane, it is “fluid” because the phospholipids in bilayer keep moving.

Question 4

What are the components of a cell membrane?

Answer 4

• Phospholipids.
• Cholesterol.
• Channel proteins.
• Carrier proteins.
• Glycolipids/glycoproteins.

Question 5

What is the function of phospholipids in cell membranes?

Answer 5

• Phospholipid has a fatty acid hydrophobic tail and a phosphate hydrophilic head.
• Tails arranged to point inward and heads outward towards the water.
• Form a bilayer where the core is hydrophobic.

Question 6

What molecules does a phospholipid bilayer not allow through?

Answer 6

-Water-soluble substances-ions.

Question 7

What is the function of cholesterol in cell membranes?

Answer 7

-Cholesterol is a lipid which fits between phospholipids and bind to tails to make membrane less fluid and more rigid and regulate the stability.

Question 8

What is the function of channel proteins?

Answer 8

-Produce a hydrophilic channel for small and charged particles to go through.

Question 9

What is the function of carrier proteins?

Answer 9

-Involved in active transport to transport ions.

Question 10

What is the function of glycoproteins and glycolipids?

Answer 10

• Proteins and lipids with a carbohydrate chain attached to it.
• Stabilise membrane by forming hydrogen bonds with surrounding water molecules.
• Act as antigens.
• Act as receptors for cell signalling.

Question 11

What is cell signalling?

Answer 11

-How cells communicate with each other.

Question 12

How do cells communicate with each other?

Answer 12

• One cell releases a messenger molecule.
• Molecule travels to the target cell.
• Molecule detected by cell as it binds to the receptor.

Question 13

Why do cells communicate?

Answer 13

-To control processes and respond to changes in the environment.

Question 14

What are membrane-bound receptors and how do they work?

Answer 14

• Proteins in cell membrane act as receptors.
• Have specific shapes which are complementary to messenger molecule which binds to it.
• Target cells respond to messenger molecules.

Question 15

What happens when drugs bind to cell membrane receptors?

Answer 15

-Trigger a response in the cell or block the receptor and prevent it from working.

Question 16

What experiment can be done to investigate cell membrane permeability?

Answer 16

• The beetroot experiment.
• Cut 5 equal sized beetroot pieces, and rinse to remove excess pigment released.
• Place pieces in 5 tubes with 5cm^3 water.
• Place each tube in a different temperature for the same length of time.
• Remove pieces of beetroot leaving the liquid.
• Use colorimeter, the higher the permeability the more pigment is released and so the higher the absorbance.

Question 17

What factors affect membrane permeability?

Answer 17

• Temperature.

- Solvent.

Question 18

How does temperature affect cell membrane permeability?

Answer 18

• As temperature increases, kinetic energy increases, this causes the bilayer to become more fluid and move more, this causes it to lose it’s structure and become more permeable.
• Also, proteins will denature if temperature is too high.

Question 19

How does solvent affect cell membrane permeability?

Answer 19

-Solvents dissolve the lipids in the bilayer and so losing it’s structure and increasing the cell membranes permeability.