Membranes Flashcards
What are the major components of a cell plasma membrane and how are they arranged?
Lipid bilayer - hydrophilic heads outwards, hydrophobic tails inwards
Proteins - integral and peripheral
Carbohydrates (minor) - short chains attached to outside of cell membrane
Describe the molecular structure of membrane lipids
Hydrophilic head (negatively charged) made of phosphate plus another part
Hydrophobic tail (no charge) made of glycerol plus a fatty acid
What does the lipid bilayer do?
3
Makes up basic structure of membrane
Hydrophobic region forms barrier
Allows membrane to be fluid and change shape
What does the presence of cholesterol do to the cell membrane?
Stiffens membrane
Describe the different structures of integral membrane proteins
Transmembrane - cross the membrane (using alpha helices)
Some within membrane but do not cross it
Some linked to lipid component of membrane
Why is the membrane important?
Barrier between cell and world
Selectively permeable - controls entry and exit of substances
Maintains ion gradients
Allows cell to be joined to other cells
Allows cell to receive and respond to signals
Proteins in membrane dictate function
What is one half of the lipid bilayer called?
A leaflet
Describe how peripheral membrane proteins are joined to membrane
Not embedded in membrane
Form strong interactions to cytoplasmic/extracellular surface of membrane
List 8 functions an integral membrane protein can have
Ligand-binding receptor Adhesion molecules Movement of water soluble substances Pores and channels Carriers Pumps Enzymes Intracellular signalling
Give an example of a ligand for an integral protein which is a receptor
Hormone
What do adhesion molecules do?
Link cell to extracellular matrix or other cells
Play a role in cell shape, differentiation, adaptation, and growth
eg. cadherins
What do pores and channels do?
Passively allow specific substances across the membrane
eg water or ions
What do carriers do?
Allow substances to cross the membrane via facillitated diffusion
Can be coupled
(uses conformational change but no energy required)
What do pumps do?
Use ATP to transport substances across membrane against a concentration gradient
Where can membranes containing enzymes be found?
Small intestine
