Module 1 - 1.1.2 Cell Membranes

Question 0

If substances can move across the plasma membrane what does that mean the membrane is?

Answer 0

Partially permeable

Question 1

What is the name of the membrane that covers a cell?

Answer 1

Plasma membrane or cell surface membrane.

Question 2

Plasma membranes are:

Answer 2

• Partially permeable.
• They allow recognition by other cells.
• They allow cell communication.

Question 3

What is a phospholipid?

Answer 3

• Phospholipids have a ‘head’ and a ‘tail’.
• The head is hydrophilic (attracts water)
• The tail is hydrophobic (repels water)
  The molecules arrange themselves into a bilayer and the ‘heads’ face out towards water on either side of the membrane.
• The centre of the bilayer is hydrophobic so water-soluble substances (like ions) can’t pass through.

Question 4

What is the significance of Cholesterol in a cell membrane?

Answer 4

• Choloesterol is a type of lipid (fat)
• It’s present in all cell membranes (except for bacteria cell membranes)
• Cholesterol molecules fit between the phospholipids where they bind to the hydrophobic ‘tails’ of phospholipids causing them to pack more closely together making the membrane less fluid and more rigid.

Question 6

What are the jobs of proteins?

Answer 6

PROTEINS CONTROL WHAT ENTERS AND LEAVES THE CELL

• Some proteins form channels in the membrane to allow small or charged particles through.
• Other particles (carrier proteins) transport molecules and ions across the membrane by active transport and facilitated diffusion.
• Proteins can also act as receptors for molecules (e.g hormones) in cell signalling . This happens when a molecule binds to the protein and a chemical reaction is triggered inside the cell.

Question 7

What are the differences and similarities between gylcoproteins and glycolipids?

Answer 7

SIMILARITIES
-they are the site where drugs, hormones and antibodies bind.
- They act as receptors for cell signalling.
-The can be antigens.
-stabalise the membrane by forming hydrogen bonds with surrounding water molecules.
DIFFERENCES
- Glycoproteins are proteins with polysaccharides attached to them.
-Glycolipds are lipids (fats) with polysaccharides attached to them.

Question 8

When was the fluid mosaic model suggested?

Answer 8

in 1972.

Question 9

What are the steps of cell signalling?

Answer 9

1) One cell releases a messenger molecules (e.g a hormone)
2) The molecules travels to another cell (e.g. in the blood).
3) The messenger molecule is detected by the cell because it binds to a receptor on its cell membrane.

Question 10

What does it mean for receptor proteins to have specific shapes?

Answer 10

Only messenger molecules with complementary shapes can bind together.

Question 11

What is a target cell?

Answer 11

A cell that responds to a particular messenger molecule.

Question 12

What happens when the temperature of a membrane is below 0 degrees Celsius?

Answer 12

The phospholipids have little energy and therefore cannot move much. The tightly packed structure of the membrane makes the membrane rigid. Channel proteins and carrier proteins denature. When ice crystals form, they may pierce the membrane making it more permeable when it thaws.

Question 13

What happens when the temperature of a membrane is above 45 degrees Celsius?

Answer 13

Permeability of the membrane increases because the bilayer begins to melt/break down. water inside the cell expands putting pressure of the membrane. Additionally, carrier and channel proteins denature so they can’t control what enters or leaves the cell thus increasing permeability.