5.1. STRUCTURE AND FUNCTION OF MEMBRANES Flashcards
What are the different types of cell membrane?
-Plasma membrane (AKA cell surface membrane)
-Tonoplast membrane
-Outer mitochondrial membrane
-Inner mitochondrial membrane
-Outer chloroplast membrane
-Nuclear envelope
What type of membrane is the cell surface membrane?
Partially Permeable
What is compartmentalisation?
Formation of separate membrane-bound areas
What does compartmentalisation allow?
-metabolic reaction to be separated
-different environmental conditions in different parts of the cell
-chemical concentration gradients to be made
-protection of cellular components
What does the plasma membrane surround?
The cytoplasm of living cells, physically separating the intracellular components from the extracellular environment
What is the main ability of membranes?
They are flexible (fluid) and able to break and fuse easily
What are the roles of the Cell Surface Membrane?
Environment (homeostasis)
Transport
Cell to Cell Signalling (communication)
Detection of changes in the environment
Site of Chemical Reactions
Anchorage for cytoskeleton/extracellular matrix
Cell to Cell Joining
What does the Cell surface membrane not do?
Does NOT provide support for the cell shape
What are membranes made out of?
Phospholipids
What is the structure of a phospholipid?
-consists of a polar head (hydrophilic) composed of a glycerol and a phosphate molecule
-consists of two non-polar tails (hydrophobic) composed of fatty acid chains (hydrocarbon)
What is the definition of hydrophilic?
Water-loving
What is the definition of hydrophobic?
Water-hating
Why are phospholipids classed as amphipathic?
As they contain both hydrophilic and lipophilic regions
What is the definition of lipophilic?
Fat- loving
How are phospholipids arranged?
-into a bilayer
-hydrophobic tails face inwards and are shielded from the surrounding polar fluids
-hydrophilic heads face outwards into the cytosolic and extracellular fluids
What does bilayer mean?
Two layers
What does a kink in the tails represent?
A double bond - increases fluidity
What are micelles?
Phospholipids form micelles when submerged in water
What is the common structure all phospholipids share?
-polar organic molecule
-phosphate group
-glycerol molecule
-two fatty acid tails
What was the first model for plasma membranes?
By Davson and Danielli in 1935
-when under a membrane, showed a ‘trilaminar’ appearance
-model was described as a lipo-protein sandwich
-dark segments representing two protein layers were artifacts
What is a trilaminar?
3 layers (two dark outer layers and a lighter inner region)
What is an artefact?
defraction of electrons through cell membrane
- shows something that isn’t there
What is the fluid-mosaic model?
-By singer and nicolson
Proteins were embedded within the lipid bilayer and were constantly moving
According to the fluid-mosaic model, how easily can proteins move within the bilayer?
dependent on the number of phospholipids with unsaturated fatty acids