5.1 Structure and function of membranes

Question 1

Membranes

Answer 1

Structures separating contents of cells from environment, separate organelles and the cytosol· Keep reactions in separate parts allow certain conditions of cellular reactions

Question 2

What is compartmentalisation

Answer 2

Formation of separate membrane-bound areas cells, vital to cell metabolism including many different and often incompatible reaction

Question 3

What structure do all membranes in a cell have

Answer 3

plasma membrane formed as a phospholipid bilayer

Question 4

What is a phospholipid bilayer

Answer 4

Hydrophilic phosphate heads form inner and outer layer (top and bottom)
Hydrophobic fatty acid tails

Question 5

Why is the most recent model named ‘Fluid-mosaic model’

Answer 5

Phospholipids are free to move within the layer relative to each other, giving membrane flexibility
–> proteins embedded within bilayer vary in shape and size, forming a mosaic like structure)

Question 6

What are the two types of membrane proteins

Answer 6

intrinsic and extrinsic proteins

Question 7

Intrinsic proteins & types

Answer 7

transmembrane proteins that are embedded through both layers of a membrane
-They have amino acids with hydrophobic R groups on external surfaces to interact with hydrophobic core, keeping them in place
- Channel proteins and carrier proteins

Question 8

Channel proteins

Answer 8

proteins that acts as a pore in membrane, creating a hydrophilic channel
–> this allows the diffusion of polar molecules and ions down a conc. gradient

Question 9

Carrier proteins

Answer 9

proteins that carry substances from one side of membrane to another
–> important form both passive and active transport

Question 10

Glycoproteins & function

Answer 10

intrinsic proteins embedded into cell-surface membrane with attached carbohydrate (sugar) chains of varying length & size
–> role in cell adhesion and receptors for chemical signals

Question 11

Cell signalling

Answer 11

when chemical binds to a receptor, it elicits a response from cell

Question 12

Examples of cell signalling

Answer 12

receptors for neurotransmitters (acetylcholine) at nerve cell synapses
–> binding of neurotransmitters triggers/prevents an impulse

Receptors for peptide. hormones like insulin & glucagon
–> affects uptake and storage of glucose

Question 13

Glycolipids and function

Answer 13

lipids with attached carbohydrate chains
–> known as cell markers or antigens & can be recognised by cells of immune system as self or non self

Question 14

Extrinsic proteins

Answer 14

Both layers of the Phospholipid Bilayer and some can move between them

Question 15

Cholesterol

Answer 15

lipid with a hydrophilic end (OH group) and hydrophobic end ( the rest)
–> positioned between phospholipids with hydrophilic end (OH) interacting with head / hydrophobic end interacting with tails

–> prevents membrane becoming too solid by stopping phospholipid molecules from grouping too closely and crystallising