Lecture 15: Cellular membrane processes Flashcards
(33 cards)
How thick is the cell membrane?
8 nm
What is the model for the cell membrane called?
Fluid mosaic model
What is the composition of the cell membrane?
50% lipid and 50% protein held together by hydrogen bonds
What are the 3 types of lipid molecules found in cellular membrane?
Glycolipid
Phospholipid
Cholesterol
What is a phospholipid?
A phosphate head and two fatty acid tails 0 amphipathic
Makes up 75% of lipids
What does amphipathic mean?
Contains both a polar and non-polar region
What does membrane fluidity mean?
The lipids and proteins are able to move around within the plane of the membrane leaflet - on a side of phospholipids however cannot move between phospholipid layers
What are the determinants of fluidity?
Lipid tail length
Cholesterol
Double bonds in fatty acid tails
How does lipid tail length affect fluidity?
Longer lipid tail lengths decrease fluidity
How does cholesterol level affect fluidity?
More cholesterol molecules within the cell membrane make it less fluid
How does number of double bonds affect fluidity?
More double bonds in the fatty acids of the phospholipids increase fluidity
What are integral proteins?
Proteins in the cell membrane which extend completely across the membrane
What are peripheral proteins?
Attached to either inner or outer surface of cell membrane and are easily removed
Example is proteins that bind to the cytoskeleton of the cell determining the shape of the membrane
What are features of integral membrane proteins?
Amphipathic - have hydrophobic and hydrophilic regions
The hydrophobic regions usually coil up into helices making up the inner part of the protein
What are the functions of membrane proteins?
Receptor proteins Cell signaling Linkers Enzymes Ion channels Transporter proteins
What is a channel protein?
A transport protein which allows specific substsances to move through a water-filled pore.
What is a transporter protein?
A transport protein which moves specific substances across membrane by changing shape
What does selective permeability mean?
Allows some substances to pass and blocks other substances
What molecules can pass the phospholipid bilayer (with no proteins involved)?
- Non-polar uncharged molecules (oxygen, nitrogen)
- Lipid soluble molecules (steroids, fatty acids)
- Small uncharged polar molecules (water, urea, CO2)
What molecules cannot pass the phospholipid bilayer without transport proteins?
- Large uncharged polar molecules (glucose, amino acids)
- Ions (sodium, potassium, chlorine, calcium)
What is diffusion?
Movement of substances across a selectively permeable membrane down a concentration gradient
What is equilibrium?
The state in which there is no diffusion occurring as the concentration is equal to each other
Why does diffusion occur?
Due to particle’s having kinetic energy - more molecules move away from an area of high concentration to an area of low concentration
What are the factors that affect the rate of diffusion?
Surface area Distance of diffusion Size of molecule Temperature Steepness of concentration gradient
