Cell Surface Membrane Structure

Question 1

What does a cell surface membrane do?

Answer 1

Controls the movement in and out of the cell.

Question 2

What does the cell surface membrane form a boundary between?

Answer 2

The cytoplasm and environment

Question 3

What is the bilayer made up of?

Answer 3

Phospholipids with hydrophilic phosphate heads on both sides as they are attracted by water and hydrophobic tails in the centre of the membrane which are repelled by water.

Question 4

What are the 3 functions of the phospholipid bilayer?

Answer 4

1. Allow lipid soluble substances to enter and leave the cell
2. Prevent water soluble substances entering and leaving the cell
3. Makes the membrane flexible and self sealing

Question 5

What are found embedded in the phospholipid bilayer throughout the membrane?

Answer 5

Proteins

Question 6

What do proteins do that never cross it?

Answer 6

Provide mechanical support or act as receptors

Question 7

What are the two types of proteins called that span the whole membrane?

Answer 7

Channel or carrier proteins

Question 8

What are channel proteins?

Answer 8

Water filled tubes that allow water soluble ions to diffuse across.

Question 9

What are carrier proteins?

Answer 9

Bind to larger molecules like glucose and amino acids then change their shape in order to move them across the membrane.

Question 10

What are the 5 functions of proteins?

Answer 10

1. Structural support
2. Act as channels allowing water soluble molecules through
3. Carrier proteins allow active transport across membranes
4. Act as receptors to identify cells
5. Help cells adhere together

Question 11

What molecules add strength to the membrane?

Answer 11

Cholesterol

Question 12

How does cholesterol add strength to the membrane?

Answer 12

1. Very hydrophobic prevents water and dissolved ions being lost
2. Pulls together fatty acid tails limiting movement

Question 13

What are the 3 functions of cholesterol?

Answer 13

1. Reduce lateral movement of phospholipid molecules
2. Makes membranes less fluid at high temperatures
3. Prevent leakage of water and dissolved ions frok the cell

Question 14

What are glycolipids made up of?

Answer 14

A carbohydrate covalently bonded with a lipid

Question 15

What do glycolipids do?

Answer 15

Carbohydrate part extends from the phospholipid bilayer into watery environment outside where it acts as a cell-surface receptor

Question 16

What are the three functions of glycolipids?

Answer 16

1. As recognition sites
2. Help maintain stability of membrane
3. Help Cells attached to one another to form tissues

Question 17

What are glycoproteins is made up of?

Answer 17

Carbohydrate chains attached to intrinsic proteins on the outer surface of the membrane

Question 18

What do glycoproteins act as? What is. 2 examples?

Answer 18

Cell surface receptors e.g. hormones and neurotransmitters

Question 19

Are the three functions of glycoproteins?

Answer 19

1. Act as recognition sites
2. Help Attach cells to one another and form tissues
3. Allow cells to recognise each other

Question 20

What molecules can’t pass through the cell surface membrane due to its permeability?

Answer 20

Non - lipid soluble molecules, too large molecules molecules with the same charge as protein channels and polar charged molecules

Question 21

How do you large molecules have to pass across the cell surface membrane?

Answer 21

Channel and carrier proteins.

Question 22

What model is used to describe cell surface membranes?

Answer 22

Fluid-mosaic model

Question 23

Why are cell-surface membranes referred to as fluid Mosaic models?

Answer 23

Fluid-Visual phospholipid molecules can move making it flexible and constantly change shape
Mosaic- Proteins embedded in phospholipid bilayer vary in shape size and pattern like the tiles of a mosaic