2.1.4 - Cell Membranes

Question 1

Describe Cell Membranes
(4 Points)

Answer 1

~ Creates an enclosed space separating the internal cell environment from the external environment.

~ Control the exchange of substances from one side of a membrane to the other, acting as an interface of communication.

~ Are partially permeable, substances can cross membranes by diffusion and AT.

~ Contains receptor proteins.

Question 2

What Are Cell Membranes Composed Of?

Answer 2

Phospholipid bilayer.

Question 3

What Does A Phospholipid Consist Of?
(3 Points)

Answer 3

~ Molecule of glycerol.

~ Phosphate group, forming the phosphate head.

~ 2 fatty acid tails, making up the lipid tail.

Question 4

Describe The ‘Phosphate Head’ Of A Phospholipid
(3 Points)

Answer 4

~ Polar, can interact with polar water molecules.

~ Hydrophilic, as it attracts water.

~ They face out towards the water on either side of the membrane.

Question 5

Describe The ‘Lipid Tail’ Of A Phospholipid
(3 Points)

Answer 5

~ Non-polar, cannot interact with polar molecules.

~ Hydrophobic, as it repels water.

~ They face inwards.

Question 6

What Are The Other Structures Of A Cell Membrane
(4 Points)

Answer 6

~ Intrinsic and extrinsic proteins.

~ Cholesterol.

~ Glycolipids and glycoproteins.

~ Protein channels.

Question 7

Describe ‘Intrinsic/Integral’ Proteins As A Structure Of The Cell Membrane
(2 Points)

Answer 7

~ Embedded in the membrane with their precise arrangement determined by their hydrophilic and hydrophobic regions.

~ Are involved with cell transport and communication.

Question 8

Describe ‘Extrinsic/Peripheral’ Proteins As A Structure Of The Cell Membrane
(2 Points)

Answer 8

~ Found on the outer or inner surface of the membrane.

~ Are involved with cell transport and communication.

Question 9

Describe ‘Cholesterol’ As A Structure Of The Cell Membrane
(4 Points)

Answer 9

~ Found between the phospholipids, where it regulates
membrane fluidity / makes them more rigid by forming bonds with the phospholipids.

~ At low temps it increases membrane fluidity, stopping it from becoming too rigid, by stopping the phospholipid tails packing too closely together.

~ At high temps it stops the membrane becoming too fluid, as the cholesterol molecules bind to the hydrophobic tails stabilising them, causing the phospholipids to pack closely together.

~ Increases the mechanical strength and stability of membranes, stoping them from breaking down and bursting.

Question 10

Describe ‘Glycoproteins & Glycolipids’ As A Structure Of The Cell Membrane
(5 Points)

Answer 10

~ Present on the cell surface, aiding cell to cell communication.

~ Glycoproteins are proteins with a carbohydrate attached.

~ Glycolipids are lipids with a carbohydrate attached.

~ Bind with substances at the cells surface.

~ Some act as cell markers or antigens for cell to cell recognition.

Question 11

The Membrane Is ‘Partially Permeable’, What Does This Mean?
(2 Points)

Answer 11

~ Small, non-polar molecules can pass through the gaps between the phospholipids.

~ Large, polar molecules must pass through specialised membrane proteins such as channel and carrier proteins.

Question 11

Describe The ‘Fluid Mosaic Model’ Of The Phospholipid Bilayer
(3 Points)

Answer 11

~ Fluid, mosaic of phospholipids and proteins are constantly moving around the bilayer by diffusion.

~ Mosaic, as the scattered pattern produced by the components within the bilayer looks like a mosaic viewed from above.

~ This model was developed in 1972.

Question 11

What Is The Phospholipid Bilayer Often Described As?

Answer 11

Fluid mosaic.