Cell Membrane Flashcards
What is the purpose of membranes?
Controls what enters/exits cell.
Site of chemical reactions.
Cell recognition & Cell signalling.
What are the functions of phospholipids in the membrane?
Allows diffusion of LIPID-SOLUBLE substances to leave/enter cell.
Prevents movement of WATER-SOLUBLE substances leaving the cell.
Explain why phospholipids form a bilayer in plasma membranes [3 marks]
Contains polar phosphate head - hydrophilic and faces outwards to aqueous environment, interacting w/ water. (1)
Contains non-polar fatty acid tails - hydrophobic so it faces inwards and away from aqueous environment. (1)
What is the fluid-mosaic model?
The arrangement of molecules in the cell membrane can be described as the fluid-mosaic model.
Why is the cell membrane fluid in the fluid-mosaic model?
1) Phospholipids form a bilayer.
2) These molecules are able to MOVE around so membrane is FLEXIBLE.
3) Membrane is constantly changing SHAPE.
Why is the cell membrane mosaic in the fluid-mosaic model?
1) Molecules like proteins, glycolipids, glycoproteins are embedded through membrane.
2) Proteins in membrane vary in SIZE & shape.
3) Creates mosaic pattern.
What are the 2 types of proteins? [1 mark]
Intrinsic proteins
Extrinsic proteins
What are intrinsic proteins? Give examples.
Connects 1 side of phospholipid bilayer to the other.
E.G.
Channel proteins
Carrier proteins
What are extrinsic proteins? Give examples.
Embedded in the surface of phospholipid bilayer.
E.G.
Receptors
What are glycoproteins? [3 marks]
A protein attached to a carbohydrate chain on the cell-surface membrane.
FUNCTIONS:
1) Act as RECOGNITION site for hormones, neurotransmitters and other cells.
2) Helps cells ATTACH together to form TISSUES.
Glych sounds like glob, sticky, attaches.
What are two functions of cholesterol embedded in the cell membrane? [2 marks]
FUNCTIONS
1) Reduce fluidity and permeability of the cell membrane…to make bilayer stable.
2) Increase rigidity of the cell membrane.
What is an oligosaccharide?
Smaller than poly, bigger than di (few carb units)
Explain the role of glycolipids in membranes [1 mark]
Cell signalling & Cell recognition
Explain the functions of intrinsic and extrinsic proteins in membranes. [2 marks]
EXTRINSIC
> Binding sites for receptors (e.g. hormones)
> Cell signalling
> Bind cells together
INTRINSIC
> Channel proteins - for facilitated diffusion
> Carrier proteins - for facilitated diffusion and active transport.
Name and explain 3 factors that affect membrane permeability?
> Temperature =
high temperature denatures membrane proteins - phospholipid molecules have more kinetic energy & move further apart.
> pH =
changes tertiary structure of membrane proteins.
> Use of a solvent =
may dissolve membrane.
