Transport Across Membranes (Finished Up To Maths And Practical Stuff At End Of Booklet) Flashcards
What is the model of the cell membrane with proteins embedded in the phospholipid bilayer called
The fluid mosaic model
Why is the mosaic model ‘fluid’
Because the phospholipid parts of the membrane are free to move relative to one another
Also, some proteins are able to move, adding to the membranes fluid nature
What gives the membrane a mosaic structure
The distribution of proteins within the membrane
What determines a proteins position in the membrane
The proteins structure
Any hydrophobic amino acids will be positioned near the hydrophobic fatty acid tails in the centre of the phospholipid bilayer, with the hydrophilic regions exposed to the fluid outside the cell
Outline how the phospholipid bilayer is structured
The phospholipids form a bilayer, with the hydrophobic fatty acid tails pointing inwards and away from the water, and the hydrophilic heads (phosphate groups) pointing out towards the membrane surface
Outline how the phospholipid bilayer acts as a barrier
Acts as a barrier to water soluble substances, as the non-polar fatty acid tails prevent polar molecules or ions from passing across the membrane
Give 5 things from which the partially permeable membrane is made up of
A phospholipid bilayer
Proteins
Glycolipids
Glycoproteins
Cholesterol
What does hydrophilic mean
Attracted to water
What does hydrophobic mean
Repels water
What part of the fatty acid is hydrophobic and what part is hydrophilic
The glycerol head is hydrophilic
The fatty acid tails is hydrophobic
Why is the glycerol head hydrophilic
Because it has a negative charge, so is polar- this causes it to be attracted to the polar water molecules and therefore soluble in it
Why are fatty acid tails hydrophobic
What are they attracted to
Because it’s not charged, so isn’t attracted to the polar water molecules
However, they will attract other lipids
Label the different parts of this fatty acid
1- phosphate group
2- glycerol head
3- saturated fatty acid
4- unsaturated fatty acid
What is the purpose of cholesterol in the partially permeable membrane?
Why is this useful?
It is embedded in the phospholipid bilayer to restrict the lateral (sideways) movement of other molecules in the membrane
This is useful as it makes the membrane less fluid at high temperatures and prevents the gaps between the phospholipid bilayers from becoming too large - preventing water and dissolved ions from leaking out of the cell
What is a peripheral protein in a membrane, and explain what they do
A protein that doesn’t extend completely across the membrane.
They provide mechanical support, or are connected to carbohydrates to form glycoproteins.
What is the function of glycolipids and glycoproteins
They carry out cell recognition, as receptors
What is a glycolipid on a cell membrane
A lipid in the membrane with carbohydrate chains attached which project out into whatever fluid is surrounding the cell (they are found on the outer phospholipid layer)
What is a glycoprotein and what is it’s function on the cell membrane
It’s a protein with a carbohydrate chain attached which projects out into whatever fluid is surrounding the cell (they are found on the outer phospholipid layer) and its function is cell recognition as a receptor for hormones
What is an integral protein and what is it’s function, also give two types and how they work
Integral proteins are proteins in the cell membrane that span from one side to the other
Their function is to transport molecules across the membrane
E.g. channel proteins and carrier proteins
Channel proteins form tubes that fill with water to enable water - soluble ions to diffuse through them
Carrier proteins bind with other molecules and change shape to transport them to the other side of the protein
Where does the energy for active transport come from
ATP
Does co-transport require energy
No, it doesn’t require energy itself but the active transport that needs to occur before it does require energy
What can pass straight through the phospholipid bilayer and by what process
Small, non-polar or charged lipid-soluble molecules can diffuse straight through by simple diffusion
What can pass through the channel proteins and by what process
Anything that’s charged/polar and small can pass through the channel proteins, by ‘facilitated diffusion ‘
How does the concentration difference increasing effect the rate of diffusion with simple diffusion
As the conc. Difference increases, the rate of simple diffusion also increases
