Cell Membranes Flashcards
What is the fluid mosaic model?
The model that shows how proteins and lipids are arranged in cell membranes.
It is fluid as components of membrane move in relation to each other
Mosaic due to the protein components in bilayer.
What is the width of the cell membrane?
7-8nm
What is an intrinsic protein?
Protein molecules spanning the phospholipid bilayer of the plasma membrane
Intrinsic protein functions are:
Transport proteins which transport water soluble molecules and ions in/out of cell.
Hydrophobic portion on outside, hydrophilic portion forms channel on inside of protein.
Can be enzymes
What is an extrinsic protein?
Protein molecules attached to surface of plasma membrane, can float or be fixed.
Can provide mechanical support.
What are the general functions of membrane?
Selectively permeable (controls movement of ions/molecules in/out
Absorption of nutrients
Secretion of chemicals
Forms boundary around cell -retains contents, internal boundary between organelles and cytoplasm (compartmentalisation)
Isolates digestive enzymes
RER - attachment of ribosomes
SER - Golgi body
What is a glycoprotein?
Protein with carbohydrates attached to it (e.g. glycocalyx)
What are glycoprotein functions?
- Stabilising membrane, carb section forms hydrogen bonds with water
- Receptor: carb chain can bind with chemicals that signals cell to respond. E.g. insulin binds to receptors on membrane of liver cells to signal to absorb glucose, drugs may block receptors
- Cell recognition: some act as self recognition sites, which indicates they belong to organism, stopping WBC attack
- Anti gen, if cells enter body of another organism, WBC attacks
What is a glycolipid?
Lipid with carbs attached to it.
Function of glycolipid?
Carbs chain extends to watery environment outside and stabilises membrane.
Acts as recognition site
What is the phospholipid component?
Makes up most of plasma membrane
Forms phospholipid bilayer
Hydrophilic head faces outwards, attracted to water surrounding cell.
Hydrophobic tail faces inwards, repelled by water
Small non polar molecules pass through bilayer via simple diffusion.
What is cholesterol?
A lipid soluble molecule that can combine with other lipids.
It’s a steroid
Forms between phospholipid molecules
Function of cholesterol?
Makes membrane more stable as pulls phospholipid tails together making it less fluid.
Very hydrophobic to prevent leakage of water and ions.
How does heat effect membranes
When temp increases, molecules that make membrane increase in kinetic energy and move faster.
So the membrane becomes more fluid and more permeable.
