The structure of the cell membrane

Question 1

what are functions of membranes WITHIN organelles

Answer 1

• compartmentalisation- seperating contents of organelles to cytoplasm
• Organelles like lysosomes use membranes to seperate their hydrolytic enzymes to the cell.
• Membranes are a surface for enzymes to attach
• control what enters and leaves the organelle due to them being partially permeable.
• form organells or vesicles

Question 2

describe the structure of the phospholipid membrane

Tip for exam - name everything in bilayer and where it is and its structure.

Answer 2

Phospholipids have a hydrophilic head facing outwards, and an hydrophobic tail facing inwards

Cholestrol embedded between phospholipids to increase fluidity

The membrane also contains glycoproteins and glycolipids sticking out of the bilayer which act as receptor molecules involved in cell signalling.

Bilayer also contains proteins such as channel or carrier proteins

Question 3

which component of the cell membrane becomes more fluid with the increase of temperature?

Answer 3

Phospholipid bilayer

Question 4

which component of the cell denatures when temperatures become too high

Answer 4

carrier or channel proteins.

Question 5

what is meant by the term active transport

Answer 5

movement of substances up a concentration gradient using ATP or channel/carrier proteins

Question 6

The phospholipid bilayer is partially permeable, what does this mean?

Answer 6

allows the passage of some molecules such as smaller solutes of water molecules, whilst restricting the entry of other molecules.

Question 7

Explain the fluid mosaic model

Answer 7

the fluid represents the phospholipids.
as they move sideways or the lipids and proteins can move by diffusion.

Mosaic- the scattered pattern of proteins and other structures look like a mosaic above

Question 8

what is the width of the phospholipid membrane

Answer 8

7nm

Question 9

where are the carrier and channel proteins located in the phospholipid bilayer

Answer 9

They span the whole bilayer, known as integral

Question 10

describe the structure of a phospholipid

Answer 10

Hydrophilic, polar head, with phosphate group and glycerol molecule

Hydrophobic, unsaturated/ saturated fatty acid tail, non polar

Question 11

State features of the cell membrane on a nerve cell

Answer 11

Channel/ carrier proteins in the membrane covering the long axon allow the entry/exit of necessary ions for electrical impulses.

Question 12

Describe the plasma membrane adaptation for white blood cells.

Answer 12

White blood cells have protein receptors allowing them to recognise antigens on foreign cells.

Question 13

what is a glycolipid

Answer 13

a carbohydrate chain attached to a lipid

Question 14

what is a glycoprotein

Answer 14

a carbohydrate molecule attached to a protein molecule

Question 15

what are the functions of the cell membrane

Answer 15

• site for chemical reactions

-contains receptors and is a site for cell communication

-control/ regulate the entry/ exit of materials.

• may contain enzymes.

-separates cell contents from external environment.

Question 16

the fatty acid tails of the phospholipid are non polar, why is this good

Answer 16

No water soluble molecules can leak through the membrane. glucose or amino acids.

Question 17

what can happen to the membrane if temp is too high?

Answer 17

proteins can denature

membrane can become too fluid

Question 18

how does cholesterol act to prevent the membrane from being too fluid at high temperature

Answer 18

cholestrol binds to the hydrophobic tails of the lipid and causes them to pack closely together.

Question 19

what is the function of the glycocalyx

Answer 19

They act as receptors to specific substances.
For example

Question 20

how does a carrier protein work

Answer 20

They have a binding site to specific substances, once bounds, they change shape to carry the substance across the membrane

Question 21

when do carrier proteins require ATP

Answer 21

When transporting substances against their conc gradient “Secondary Active transport”. Need atp

Question 22

what is a channel protein

Answer 22

a hydrophilic passageway for water and polar ions along their conc gradient