CELL MEMBRANES

Question 1

What are organelles?

Answer 1

Sub-cellular bodies found in the cytoplasm of cells.

Question 2

What are eukaryotes?

Answer 2

Group of organisms with cells. genetic material contained in a membrane-bound nucleus, contains membrane-bound organelles, e.g. mitochondria & chloroplasts.

Question 3

What are prokaryotes?

Answer 3

Group of organisms e.g. bacteria, have a few organelles, don’t have genetic material contained in a membrane bound nucleus.

Question 4

What is the cell surface membrane?

Answer 4

Membrane that forms outer boundary of cytoplasm of a cell, controls movement of substances in/out of cell.

Question 5

What are vesicles?

Answer 5

Membrane ‘bags’ that hold secretions made in cells.

Question 6

What are polar lipids?

Answer 6

Lipid molecules with one end attached to a polar group. E.g. phosphate group forming polar part of a phospholipid.

Question 7

What are gated channels?

Answer 7

Protein channels through lipid bilayer of a membrane, closed or opened depending on conditions in the cell.

Question 8

What is the fluid mosaic model?

Answer 8

Current model of the structure of the cell membrane, including; proteins forming pores, channels and carrier systems in a lipid bilayer.

Question 9

Why must the membrane layer be flexible?

Answer 9

Allowing the cell to change shape very slightly as its water content changes.

Question 10

How are chemical reactions within the cell affected by the membrane?

Answer 10

• It maintains right conditions for reactions to occur in certain parts of the cell.
• Enzymes and other factors are held close together so that reactions can proceed smoothly.

Question 11

The membrane is made of mainly what two molecules?

Answer 11

Lipids and proteins.

Question 12

What is a unit membrane?

Answer 12

When water or aqueous solutions are on each side, phospholipids form a bilayer with hydrophilic heads pointing in the water while hydrophobic tails stay protected in the middle.

Question 13

A simple lipid bilayer allows what to pass through it?

Answer 13

Fat-soluble organic molecules.

Question 14

What is the problem with a simple lipid bilayer?

Answer 14

Vital chemicals the cells need are ionic, they cannot pass through lipids or even polar lipids?

Question 15

How is it that vital chemicals can pass through the membrane if they cannot pass through lipids?

Answer 15

Because the membrane also consists of proteins and other molecules.

Question 16

How does the proportion of unsaturated fatty acids affect the membrane?

Answer 16

The more unsaturated fatty acids, the more fluid the membrane.

Question 17

Where are the proteins in the lipid bilayer?

Answer 17

Many of the proteins have a hydrophobic part, which is buried in the layer, and a hydrophilic part, which can be involved in a variety of activities.

Question 18

What is a main function of membrane proteins?

Answer 18

Help substances move across the membrane.

Question 19

How do proteins help substances pass through the membrane?

Answer 19

Proteins can form pores/channels - some permanent, some temporary - that allow specific molecules to move through. Some of the protein pores are active carrier systems, using energy to move molecules. Others are simply gaps that allow ionic substances to move through.

Question 20

How do proteins act as specific receptor molecules?

Answer 20

They make cells more sensitive to a particular hormone/enzyme, to control reactions linked to that membrane.

Question 21

What are glycoproteins?

Answer 21

Proteins with a carbohydrate part added. Important on the surface of cells as part of the way cells recognise each other.

Question 22

What is the evidence for the fluid mosaic model?

Answer 22

X-ray diffraction & advanced electron microscopy have added to our knowledge.

Question 23

How can we determine a cell membrane’s structure/ function?

Answer 23

Identifying protein channels in the membrane that have a very specific function that can be measured helps to confirm our model of cell membranes.