Chapter 4 transport across cell-membranes

Question 1

What does cholesterol do in the membrane?

Answer 1

It will restrict the lateral movement of other molecules in the membrane. This is useful as it makes the membrane less fluid at high temperatures and prevents water and ions leaking out of the cell.

Question 2

What is the function of peripheral proteins in the membrane?

Answer 2

To provide mechanical support or they are connected to proteins or lipids to make glycolipids or glycoproteins.

Question 2

What is the function of glycoproteins and glycolipids?

Answer 2

Cell recognition as receptors.

Question 3

What are protein channels?

Answer 3

Form tubes that fill water to enable water-soluble ions e.g. sodium ions to dissolve and diffuse through that channels.

Question 4

What do carrier proteins do?

Answer 4

Bind to larger molecules eg glucose and change shape to transport them to the other side of the membrane.

Question 5

What molecules can pass through the plasma membrane?

Answer 5

Lipid soluble molecules and very small molecules.

Question 6

What is simple diffusion?

Answer 6

This is the net movement of molecules from a high area of concentration to an area of lower concentration until equilibrium is reached. This does not require ATP.

Question 7

How do molecules move by simple diffusion?

Answer 7

By using their kinetic energy which they already have

Question 8

What is facilitated diffusion?

Answer 8

Passive process which uses proteins to transport molecules. This allows ions and polar molecules to diffuse through the phospholipid bilayer.

Question 9

How does a protein channel work?

Answer 9

It is embedded all the way through the bilayer and forms a tube filled with water and enables water-soluble ions to pass through.

Question 10

Why are channel proteins selective?

Answer 10

As they only open in the presence of certain ions when they bind to the protein.

Question 11

How do carrier proteins work?

Answer 11

Carrier proteins will bind with a molecule which causes a change in shape of the protein. This change in shape enables it to release the molecule on the other side of the membrane.

Question 12

What is osmosis?

Answer 12

The movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane.

Question 13

What is water potential?

Answer 13

The pressure created by water molecules. Pure water has a water potential of zero.

Question 14

What is an isotonic solution?

Answer 14

When the water potential is the same in the solution and the cell within the solution.

Question 15

What does hypotonic mean?

Answer 15

When the water potential of a solution is more positive (closer to zero) than the cell.

Question 16

What does hypertonic mean?

Answer 16

When the water potential of a solution is more negative compared to the cell

Question 17

What is active transport?

Answer 17

The movement of molecules and ions from and area of of lower concentration to an area of higher concentration using ATP and carrier and proteins. The carrier proteins act as pumps to move substances across the membrane.
This is very selective as only certain molecules can bind to the protein to be pumped.

Question 18

Describe the process of active transport

Answer 18

-Transport through carrier proteins which span the cell membrane.
-Molecule binds to a receptor complementary in shape on protein.
-ATP binds to to the carrier protein from inside of cell and it is hydrolysed into ADP and Pi.
-This phosphate group causes the carrier protein to slightly change shape, and releases the molecule to the other side.
-Phosphate ion is released and protein returns to its original shape.

Question 19

What is the process of co-transport and sodium ions in the ileum?

Answer 19

-Sodium ions are actively transported out of epithelial cell into blood.
-This reduces sodium ion concentration in epithelial cell.
-Sodium ions can then diffuse from lumen down their concentration gradient into epithelial cell.
-The protein that the sodium ions diffuse through is a co-transporter protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient.
-Glucose moves by facilitated diffusion from epithelial cell to blood.