What is a triglyceride made up of?
3x fatty acids and a Glycerol, attatched through ester bonds
What is a phospho lipid made from?
A glycerol with 2x fatty acids and a phosphate. It forms a hydrophilic head made from the phosphate and glycerol and 2x hydrophobic tails which are the fatty acids (non-polar).
What do hydrophilic and hydrophobic mean?
Hydrophilic - water loving, polar/negatively charged
Hydrophobic - water fearing, non-polar
What is the phospholipid bilayer?
It is made up of 2x layers of phospholipids with their hydrophilic heads facing outwards and their hydrophobic tails facing eachother inwards. This forms the cell membrane.
What is the function of the cell membrane?
- Barrier between external and internal environment
- Involved in cell signalling
- Controls what substances can enter or leave the cell
What can enter or leave the cell via the phospholipid bilayer?
- small molecules eg O2, Co2
[REMINDER O2 only has a charge of 2- as an ion] - molecules with no charge/non-polar
- H2O which is an exception because it is polar however it is a very small molecule
What cannot enter or leave via the phospholipid bilayer?
- large molecules eg glucose
- charged particles eg ions/polar molecules
What is the function of cholesterol between the phospholipids?
- increases strength of cell membrane meaning damage is less likely
- reduces sideways movement
- regulates fluidity: if temp increases it decreases fluidity. If temp decreases it increases fluidity.
Where is the cholesterol found inbetween the phospho lipids made?
In the smooth endoplasmic reticulum.
How are the cholesterols placed in between the phospholipids?
The non polar hydrophobic group attracts to the tails whereas the polar, hydrophillic group attracts to the hydrophilic head.
Why is the cell membrane known as having a fluid mosaic model?
Fluid because the phospholipid molecules can move around within each layer sot he membrane is flexible and can change shape.
Mosaic because the phospholipid bilayer is studded with protein molecules and arrangement.
What is the difference between an intrinsic and an extrinsic protein?
Intrinsic proteins are fully embedded in the membrane from one side to the other whereas extrinsic proteins are found on one or the other side of the membrane.
What are the 2 types of intrinsic proteins?
Channel proteins or Carrier proteins
How does a channel protein work?
It has a central pore lined with hydrophilic amino acids and filled with h2o molecules allowing water soluble molecules and ions to diffuse through. They are selective about chemicals passing through. Some are always open but some only open afterwards.
How does a carrier protein work?
It can change shape or position to transfer molecules and ions from one side of the membrane to the other.
In more detail:
It has a binding site for a specific chemical. After this chemical binds it causes the protein tertiary structure to change, bringing the chemical across the membrane to release the other side.
Why do intrinsic proteins have hydrophobic amino acids on their surface?
So they can interact with the hydrophobic tails (fatty acids)
What is the function of extrinsic proteins?
- some play a structural role within membrane
- others act as enzymes
- some are receptors for other molecules such as hormones
How are glycoproteins and glycolipids formed?
They are formed when a carbohydrate molecule attaches to a protein or phospholipid via a glycosidic bond.
What is the function of a glycoprotein?
- allows cells to attach to each other to from tissue eg nervous tissue
- plays a role within the immune system - presenting antigens to T cells
- acts as a receptor for hormones
- cell recognition
What is the function of glycolipids?
- cell recognition
- presenting antigens to determine blood group
How do membrane proteins facilitate communication between cells?
Membrane proteins (especially receptor proteins) detect chemical signals such as hormones or neurotransmitters from environment and transmit them into cell to trigger a response
What is the function of extrinsic proteins?
They typically assist in cell signalling or structural support.
Glycoproteins are an example of extrinsic proteins
What is the significance of the fluidity of the cell membrane?
- membrane flexibility
- protein mobility
- vesicle fusion
- self healing after small disruptions
