5.1 - The Structure And Function Of Membranes

Question 1

Compartmentalisation

Answer 1

Formation of separate membrane bound areas in a cell.

Question 2

Why is compartmentalisation vital

Answer 2

Metabolism includes many different and incompatible reactions.
Separate parts allows specific conditions required for cellular reactions to be maintained
(e.g. chemical gradients)
Protects vital cell components

Question 3

Plasma membrane

Answer 3

Cell surface membrane that separates cell from external environment

Question 4

What are membranes formed by

Answer 4

Phospholipid bilayer

Question 5

Structure of phospholipid bilayer

Answer 5

Hydrophilic phosphate head
Forms the inner and outer surface of membrane
Fatty acid tails are hydrophobic
Form hydrophobic core inside membrane

Question 6

How are phospholipids perfectly suited for their role as a membrane

Answer 6

Cell exist in aqueous environments.
Organelles in aqueous environment
Hydrophilic phosphate heads can interact with water

Question 7

When were membranes first scene

Answer 7

After invention of electron microscope.
Images taken in ‘50s show two black parallel lines
Supported earlier theory that membranes were made up of a bilayer

Question 8

Fluid-mosaic model

Answer 8

1972 Singer and Nicolson
Proteins occupy various positions in the membrane
Fluid - phospholipids are free to move within layer relative to each other.
Gives membrane flexibility
Mosaic - Proteins embedded in bilayer vary in size, shape, and position.

Question 9

Two types of membrane protein

Answer 9

Intrinsic

Extrinsic

Question 10

Intrinsic

Answer 10

Transmembrane proteins
Embedded in both layers
Amino acids with hydrophobic R groups on external surface
Interact with hydrophobic core keeping them in place

Question 11

Intrinsic proteins involved in transport across the membrane

Answer 11

Channel proteins

Carrier proteins

Question 12

Channel proteins

Answer 12

Hydrophilic channel
Passive movement of polar molecules and ions down a concentration gradient through membranes
Interact with hydrophobic core due to amino acids with hydrophobic R groups on outer surface, keeping them in place

Question 13

Carrier proteins

Answer 13

Passive transport and active transport

Involves shape of protein changing

Question 14

Glycoproteins

Answer 14

Intrinsic
Embedded in cell surface membrane
Carbohydrate chains of varying lengths and shapes
Cell adhesion
Receptors for chemical signals

Question 15

Cell communication / signalling

Answer 15

Chemical bonds to receptor
Elicits response from cell
Either direct or sets off chain of events inside cell

Question 16

Examples of cell communication

Answer 16

Receptors for neurotransmitters (acetylcholine) at nerve synapses
Binding of neurotransmitters triggers or prevents impulse in next neurone
Receptors for peptide hormones (insulin)
Affect uptake and storage of glucose in cells.

Question 17

Glycolipids

Answer 17

Lipids
Attached carbohydrate chains
Cell markers or antigens
Recognised by immune system as self or non self

Question 18

Extrinsic proteins

Answer 18

One side of bilayer
Hydrophilic R groups on outer surface
Interact with polar heads or intrinsic proteins
Present in either layer and can move between

Question 19

Example of extrinsic protein

Answer 19

Cholesterol

Question 20

Cholesterol

Answer 20

Lipid
Hydrophilic end interacts with phosphate
Hydrophobic end interacts with fatty acid tails
Regulates fluidity of membranes
Adds stability without making rigid
Positioned between phospholipids
Pulls heads and tails together
Prevent membrane from becoming too solid by stopping phospholipids from grouping too close together and crystallising

Question 21

Particular position of proteins

Answer 21

Proteins need to be in particular positions for chemical reactions to take place

Question 22

Example of proteins needing to be in particular places

Answer 22

Electron carriers and enzyme ATP synthase have to be in correct positions within cristae for production of ATP in respiration
Enzymes of photosynthesis are found on membrane stacks within chloroplasts