Unit 1.3 - Cell membranes and transport Flashcards
What is the importance of the hydrophobic tails in the phospholipid bilayer?
Tails point towards each other, to the centre of the membrane.
What is the cell membrane made of?
phospholipids and proteins
1) What is the importance of the inner layer of the phospholipid?
2) What is the importance of the outer layer of the phospholipid?
1) Hydrophilic heads points towards the cell and interacts with the water in the cytoplasm.
2) Hydrophilic heads point outwards, interacting with water surrounding the cell.
What are biological membranes?
Phospholipid bilayers which contain protein molecules.
What does the phospholipid component of a membrane allow?
Allows lipid soluble molecules across, but no water-soluble molecules.
What is the function of cholesterol?
Stabilises the membrane.
1) Where are extrinsic proteins found?
2) What are their functions?
1) Either surface of bilayer
2) Structural support, form recognition sites by identifying cells and receptor sites for hormone attachment.
1) Where are intrinsic proteins found?
2) What are their functions?
1) Extend across both layers of the phospholipid bilayer.
2) Act as channel and carrier proteins for the active or passive transport of molecules.
Who was the fluid mosaic model proposed by?
Singer and Nicolson in 1972.
Fluid-Mosaic Model
1) What is meant by the term fluid?
2) What is meant by the term mosaic?
1) Individual phospholipid molecules are free to move within a layer relative to one another.
2) Proteins embedded in bilayer vary in shape, size and distribution among the phospholipids.
What do plant and animal cell membranes contain?
Glycoproteins, glycolipids and sterols.
1) What is the sterol in animal cell membranes?
2) Where does it occur?
3) What effect does this have on the membrane?
1) Cholesterol
2) Between phospholipid molecules
3) More stable at high temperatures and more fluid at low temperatures.
Permeability
How does small molecules move across the cell membrane?
e.g. oxygen, moves between phospholipid molecules and diffuse across the membrane.
Permeability
How does lipid-soluble molecules move across the cell membrane?
e.g. vitamin A, dissolves in phospholipid and diffuses across the membrane. Layer is hydrophobic so lipid-soluble move more easily than water-soluble.
Permeability
1) How does water soluble molecules move across the cell membrane?
2) How does this effect the cell-surface membrane?
1) e.g. glucose and ions, can’t readily diffuse through phospholipids, so pass through intrinsic protein molecules, which form water-filled channels across the membrane.
2) Selectively-permeable to water and some solutes.
What is the size of the phospholipid bilayer?
7-8nm.
What is simple diffusion?
Diffusion of small lipid soluble molecules which is a passive transport.
How does the concentration gradient affect the rate of diffusion?
Greater difference in the concentration of, more molecules diffuse in a given time.
How does the thickness of the exchange surface affect the rate of diffusion?
Thinner membrane, more molecules diffuse in a given time.
How does the surface area of the membrane affect the rate of diffusion?
Larger area, more molecules diffuse across in a given time.
How does the size of a diffusing molecule affect the rate of diffusion?
Smaller molecules diffuse faster than larger ones.
How does the nature of diffusing molecules affect the rate of diffusion?
Lipid-soluble molecules diffuse faster than water-soluble molecules.
How does temperature affect the rate of diffusion?
Increased temperature, increases rate as molecules/ions gain kinetic energy.
What is the relationship between rate of uptake and oxygen concentration?
Directly proportional - external conc. oxygen around a root increases, conc. gradient becomes steeper.