5.1 The Structure And Function Of Membranes

Question 1

What is compartmentalisation and why’s it vital

Answer 1

Formation of separate membrane bound areas in a cell

Vital as it allows specific conditions required for cellular reactions to take place in separate parts of a cell

Question 2

What is teh plasma membrane

Answer 2

Cell surface membrane that separates the cell from its external environment

Question 3

What are membranes formed from

Answer 3

A phospholipid bilayer

Question 4

What is teh structure of phospholipid bilayers

Answer 4

Hydrophilic phosphate heads of phospholipids form the inner and outer surface
They sandwich the fatty acid tails of the phospholipids forming a hydrophobic core

Question 5

Why is teh structure of phospholipid bilayers good for the environment they are in

Answer 5

The outer surface is hydrophilic so they can interact with water in the aqueous environment and protect the hydrophobic core

Question 6

What is the fluid-mosaic model

Answer 6

Phospholipids are free to move with the layer relative to each other
Gives membrane flexibility
Proteins in bilayer vary in shape size and position

Question 7

What are the two types of membrane proteins

Answer 7

Extrinsic

Intrinsic

Question 8

What are intrinsic proteins

What are the two types of intrinsic proteins

Answer 8

Transmembrane proteins embedded through both layers of the membrane
Have amino acids with hydrophobic r-groups on their external surface
These interact with hydrophobic core of membrane
Channel proteins
Carrier proteins
Glycoproteins

Question 9

What are channel proteins

Answer 9

Intrinsic
Provide hydrophilic channel allowing passive movement of polar molecules down a conc gradient
Held in position by interactions of hydrophobic core and hydrophobic r-groups on proteins

Question 10

What are cattier proteins

Answer 10

Important role in passive transport and active transport into cells
Often involves shape of proteins changing

Question 11

What are glycoproteins

Answer 11

Intrinsic
Embedded in cell surface membrane with attached carbohydrate chains of varying lengths and shapes
Play a role in cell adhesion
Act as receptors for chemical signals

Question 12

How do glycoproteins act as receptors for chemical signals

Answer 12

Chemical binds to receptors which elicits a response from the cell
Cause a direct response or set off a cascade of events inside teh cells
This is called CELL SIGNALLING

Question 13

What are types of cell signalling

Answer 13

Receptors for neurotransmitters - binding of neurotransmitters triggers or prevents an impulse in teh next hormone
Receptors for peptide hormones like insulin and glucagon affecting the uptake and storage or glucose

Question 14

What are glycolipids

Answer 14

Lipids with attached carbohydrate chains
They are cell markers or antigens
Recognised by cells of the immune system as self or non self

Question 15

What are extrinsic proteins

Answer 15

Present in 1 side of the bilayer
Normally have hydrophilic r-groups on their outer surfaces and interact with the polar heads of phospholipids
Some move between layers

Question 16

What is cholesterol

Answer 16

A lipid with a hydrophilic end and hydrophobic end

Regulates the fluidity of membranes

Question 17

Where is cholesterol positioned in membranes

Answer 17

Between phospholipids in a membrane bilayer with hydrophilic end interacting with heads and hydrophobic end interacting with tails

Question 18

What is cholesterols job in the Membrane

Answer 18

Adds stability to membranes without making them too rigid

Prevent membranes becoming too solid by stopping phospholipids from grouping too closely and crystallising