Plasma Membranes

Question 1

Roles of cell surface membranes?

Answer 1

Controls movement of substances into and out of the cell
Recognition site for our bodies immune system
Receptor site for hormones and neurotransmitters
May be folded- increasing the surface area
Helps cell attachment adn tissue formation
May contain enzymes too aid metabolic reactions

Question 2

Roles of other membranes

Answer 2

Separate cell membranes components from cytoplasm

Isolate enzymes that may damage the cell e..g lysosomes

Question 3

What is compartmentalisation

Answer 3

Formation of separate membrane bound area in a cell
Important to a cell as metabolism includes many different and often incompatible reactions
E.g. Chemical gradients- specific conditions required

Question 4

Phospholipids

Answer 4

Hydrophilic head s
Hydrophobic tail
1 phosphate group, 1 glycerol, 2 fatty acids
Well suited for membranes are outer surface of hydrophilic heads can interact with water- in side of membranes in usually aqueous

Question 5

Micelles

Answer 5

Lipid molecules that arrange themselves ina. Spherical form in aqueous solution

Question 6

LIPOSOME

Answer 6

Spherical vesicles having at least 1 lipid bilayer

Question 7

Phospholipid bilayer (

Answer 7

Hydrophobic layer formed from tails forms a barrier to many molecules adn separates cell components from the outside world

Question 8

How thick are phospholipid bilayer a

Answer 8

7-9 nm

Question 9

Intrinsic proteins

Answer 9

Transmembrane proteins that rare embedded through BOTH layers of the membranes

Amino acids with hydrophobic r groups that are on ther external surface which interact with the hydrophobic core of the membrane, keeping them in place

Question 10

What is an example of an intrinsic protein

Answer 10

Channel protein

Glycoproteins

Question 11

Channel proteins

Answer 11

Provide a hydrophilic channel that allows diffuse of polar molecules and ions
Held in position by interactions between hydrophobic core of membrane and the hydrophobic groups on the outside of the proteins
Can only transport substances until there’s EQUAL amounts of it on both sides of the membrane

Question 12

Glycoproteins( intrinsic proteins)

Answer 12

Embedded in cell surface membrane with carbohydrate chains

Play a role in cell adhesion and cell signalling and communication

Question 13

What is adhesion

Answer 13

When cells join together to for might junctions in certain tissues an as receptors for chemical signals

Question 14

What is cell signalling and communication

Answer 14

When the chemical binds to the recpetor, it elicits a response from the cell- this may cause a direct response or send off a cascade of events inside the cell

Question 15

Examples of cell signalling

Answer 15

Receptors of neurotransmitters
The binding of neurotransmitters triggers or presents an impulse in the next neurone

Receptors for peptide hormones
Including insulin and glucagon which affect the Utahe of storage of glucose by cells

Question 16

Glycolipids

Answer 16

Similar to glycoproteins
Lipids with an attatched carbohydrate ( sugar) chain
These are called cell markers or antigens- can be recognised by the cells I the immune system as self( f the organism) or NON SELF( cells belonging to another organism)

Question 17

Cholesterol

Answer 17

A lipid with hydrophilic end and hydrophobic end
Regulates fluidity of membranes
Positioned between phospholipids in the bilayer - hydrophilic heads interacting with hydrophilic end and hydrophobic with tails PULLING them together
Adds stability making them rigid
Prevent Membranes becoming TOO solid, stopping phospholipid grouping too close and crystallising

Question 18

Extrinsic protiens

Answer 18

PERIPHERAL PROTEINS

• present in one side of the bilayer
• have hydrophilic R groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic protiens
  Can be present in either ad move between layers

E..g enzymes

Question 19

What happens wwhen there’s HIGH temp - membranes

Answer 19

Increases fluidity 
Higher kinetic energy 
Higher permeability 
Leaky 
Cell signalling- my be worse 
Carrier adn channel proteins denature 
Less of structure

Question 20

Low temp - effect on membranes

Answer 20

Saturated fatty acid become compressed
Kinks push adjacent phospholipids away
Membrane fluidity maintained
Cholesterol also buffers affect to maintain fluidity

Question 21

Solvents affect n membranes- WATER

Answer 21

Forms a bilayer ( phospholipids)

Question 22

Organic solvents and alcohol affect on membranes

Answer 22

Organic solvents-Most are less polar than water, some are non polar, Dissolve membranes, disrupting cells

Alcohols- used used in antiseptic wipes as alcohols dissolve membranes of bacteria in wound DESTROY cells , less concentrated cause damage
When membrane is disrupted- more fluid and more permeable

Question 23

Fluid mosaic model

Answer 23

In 1972, American scientists signer and Nicholson proposed model
Proteins
Phospholipids free to move