structure of the cell surface membrane

Question 1

All membranes around and within cells are similar in which ways and are known as what?

Answer 1

They all have the same basic structure and are known as plasma membranes.

Question 2

what is the Cell surface membrane?

Answer 2

The plasma membrane that surrounds cells and forms the boundary between the cell cytoplasm and the environment, this allows different conditions to be established inside and outside of the cell.

Question 3

Functions of the phospholipids in the membrane

Answer 3

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

Question 4

What is Arrangement of phospholipids in the surface membrane?

Answer 4

Two layers of phospholipids, one with its hydrophilic heads pointing outwards and one pointing inwards. The hydrophobic tails of both phospholipid layers point into the centre of the membrane.

Question 5

What do Extrinsic proteins do?

Answer 5

Never extend completely across membrane (on surface or partly embedded only). Provide mechanical support to the membrane or with glycolipids act as cell receptors for molecules i.e. hormones.

Question 6

What do Intrinsic proteins do?

Answer 6

Completely span the phospholipid bilayer. Some act as carriers to transport water-soluble molecules across the membrane. Others are enzymes.

Question 7

Functions of the proteins in the membrane are to:

Answer 7

1. Provide structural support.
2. Carriers to transport water-soluble substances across membrane.
3. Allow active transport across membrane by forming ion channels.
4. Form recognition sites by identifying cells.
5. Help cells adhere together.
6. Act as receptors e.g. for hormones.

Question 8

Why is the structure of the cell-surface membrane known as the fluid-mosaic model (Fluid)

Answer 8

Fluid because the individual phospholipid molecules can move relative to one another. The membrane therefore has a flexible structure and constantly changing in shape.

Question 9

Why is the structure of the cell-surface membrane known as the fluid-mosaic model (Mosaic)

Answer 9

Mosaic because the proteins embedded in the phospholipid bilayer vary in shape, size and pattern in the same way as the stones or tiles of a mosaic.

Question 10

What does Glycoprotein

Answer 10

Branching carbohydrate portion of a proteins which acts as a recognitions site for chemicals e.g. hormones.

Question 11

What does Glycolipid

Answer 11

Acts as a recognition site e.g. for cholera toxins

Question 12

What does Cholesterol molecules in cell-surface membranes

Answer 12

Adds strength.