Plasma Membranes Flashcards
Roles of cell surface membranes?
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
Roles of other membranes
Separate cell membranes components from cytoplasm
Isolate enzymes that may damage the cell e..g lysosomes
What is compartmentalisation
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
Phospholipids
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
Micelles
Lipid molecules that arrange themselves ina. Spherical form in aqueous solution
LIPOSOME
Spherical vesicles having at least 1 lipid bilayer
Phospholipid bilayer (
Hydrophobic layer formed from tails forms a barrier to many molecules adn separates cell components from the outside world
How thick are phospholipid bilayer a
7-9 nm
Intrinsic proteins
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
What is an example of an intrinsic protein
Channel protein
Glycoproteins
Channel proteins
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
Glycoproteins( intrinsic proteins)
Embedded in cell surface membrane with carbohydrate chains
Play a role in cell adhesion and cell signalling and communication
What is adhesion
When cells join together to for might junctions in certain tissues an as receptors for chemical signals
What is cell signalling and communication
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
Examples of cell signalling
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
Glycolipids
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)
Cholesterol
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
Extrinsic protiens
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
What happens wwhen there’s HIGH temp - membranes
Increases fluidity Higher kinetic energy Higher permeability Leaky Cell signalling- my be worse Carrier adn channel proteins denature Less of structure
Low temp - effect on membranes
Saturated fatty acid become compressed
Kinks push adjacent phospholipids away
Membrane fluidity maintained
Cholesterol also buffers affect to maintain fluidity
Solvents affect n membranes- WATER
Forms a bilayer ( phospholipids)
Organic solvents and alcohol affect on membranes
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
Fluid mosaic model
In 1972, American scientists signer and Nicholson proposed model
Proteins
Phospholipids free to move
