Plasma membranes Flashcards
What is a Plasma membrane
Basically the cell surface mmebrane of all cells and organelles
Why are plasma membranes described as fluid mosaic
This is due to the mixture of different components
The fluid part refers to the movement of the molecules as they can move up and down and side to side
What are the different components that make up the plasma membrane (5)
Phospholipids
Proteins- Channel, Carrier, Extrinsic and Intrinsic
Glycolipids
Glycoproteins
Cholesterol
How does the phospholipid bilayer affect entry and exit of substances in and out of the cell? (4)
- It allows the movement of lipid soluble and non charged molecules
- Prevents the movement of Water soluble/Polar molecules
- Membrane is partially permeable
- Large molecules do not move through;small molcecules do
What is a phospholipid made up of
A glycerol molecule
Phosphate group -hydrohphilic-
Two fatty acids -hydrohphobic-
What is the function of cholesterol
It can restrict the lateral movement of other molecules in the membrane (more cholesterol= less fluid or more ridgid)
Provides strength and ridgity
What is the importance of cholesterol
- Makes the membrane less fluid at high temps
- Prevents water and dissolved ions leaking out of the cell
What is the difference between Peripheral/extrinsic and Integral/intrinsic proteins?
- Peripheral/extrinsic do not extend completely across the membrane
- Integral/Intrinsic spans across from one side of the bilayer to the other
What is the function of the peripheral/extrinsic proteins
- To provide mechanical support
- They connect to proteins or lipids to make glycoproteins and glycolipids—> act as receptors,cell recognition,
What is the function of integral/intrinsic proteins
Transport molecules across the membrane through carrier and channel proteins
What is the function of glycoproteins/lipids
Cell recognition ;act as receptors
What do channel proteins do
Form tubes that fill with water to enable water soluble ions to diffuse
What do carrier proteins do
Bind with larger molecules, such as glucose and amino acids and change shape to transport them to the other side of the membrane
What are the factors allowing substances to pass through the membrane (simple diffusion)
Lipid soluble substances e.g. some hormones: estrogen
Very small molecules e.g. O2 CO2 H2O
What are the factors that do not allow molecules to pass through the membrane in Simple diffusion
Water soluble (polar) substances
Sodium ions
Large molecules e.g. glucose
What are the limitation imposed by the phospholipid bilayer
Only certain molecules can passively pass through the phospholipid bilayer.
This is due to it being made of phospholipids which have a polar, hydrophilic head and nonpolar, hydrophobic fatty acid tails shielded by the heads. They are arranged closely in the fluid mosaic model too which only allows small molecules to pass through.
In a phospholipid bilyaer, what direction do the heads point
Outwards, towards the tissue fluid or cytoplasm
What features of a particle would allow it to diffuse directly through the phospholipid bilayer
Small and non polar (uncharged)
What structure in the membrane has the function ‘to allow the facillitated diffusion of large or charged particles’
Channel proteins
