5.1 The structure and function of membranes

Question 1

Explain the fluid mosaic model used to describe membranes

Answer 1

Fluid as components can move freely along the membrane = not fixed in one place
Mosaic as contains components of different sizes and shapes that are able to fit together

Question 2

What’s the function of membranes

Answer 2

Selectively permeable barrier between cell + external environment, organelles + cytoplasm
Site of chemical reactions
Sites of cell signalling

Question 3

Describe the structure of the phospholipid bilayer

Answer 3

Hydrophilic phosphate heads form inner + outer surface of membrane.
Fatty acid tails form a hydrophobic core inside the membrane

Question 4

What are the 2 types of proteins in plasma membranes

Answer 4

Intrinsic and extrinsic

Question 5

What are intrinsic proteins, what do they do and give 2 examples

Answer 5

Embedded through both layers of the membrane They have amino acids with hydrophobic R-groups on their external surfaces which Interact with the hydrophobic core of the membrane, which keeps them in place. Eg. Carrier proteins and channel proteins

Question 6

What’s the function of Chanel proteins and how are they held in place

Answer 6

Provide hydrophilic channel - allows passive movement of polar molecules + ions down a conc. gradient through membranes. They are held in place by Interactions between hydrophobic core of membrane + hydrophobic R-groups on the outside of proteins.

Question 7

What’s the function of carrier proteins

Answer 7

Enable passive transport down a concentration gradient + active transport against a concentration gradient. This often involves the protein’s shape changing.

Question 8

What type of protein are glycoproteins, what do they do

Answer 8

Intrinsic proteins with Carb. chains attached to their surface .
Function is Cell adhesion (when cells join to form tight junctions in certain tissues).
Receptors for chemical signals.

Question 9

Role of cholesterol

Answer 9

Is an amphipathic (dual hydrophilic and hydrophobic ability) lipid it regulates fluidity = the more cholestrol, the more fluid the membrane

Question 10

What do glycoproteins act as

Answer 10

1. they act as an antigen = recognition site for other molecules/cells
2. acts as a receptor = receive certain growth hormones signalling cells to do other things

Question 11

How do compartmentalisation work

Answer 11

it provides specific conditions for reactions to occur