Chapter 2: Cell membranes Flashcards
What is a plasma membrane?
A lipid bilayer composed of molecules that surround and protect the cytoplasm
What are the 4 roles of a membrane?
Transport, metabolism, stability, communication and signalling
What bonds do phospholipids contain?
Ester bonds
Function of the cell plasma membrane?
Separating the inside and the outside contents, cell recognition and signalling, separating the cytoplasm
What makes up a phospholipid?
Phosphate head, glycerol and fatty acids
2 factors that affect the plasma membrane?
Temperature and solvents (alcohols)
What is a glycolipid?
Lipids attached to carbohydrate chains. Called cell markers and are recognised but the cells of the immune system
What is a glycoprotein?
Intrinsic proteins. Play a role in cell adhesion. Has receptors that bind to chemical signals
What is an intrinsic protein?
Proteins that are embedded through both layers of the membrane and are used for transporting molecules through the membrane
What is an extrinsic protein?
Present on one side of the bilayer. Interacts with polar heads of the phospholipids
Why is it called a fluid mosaic model?
Fluid = flexible and free to move within the layer
Mosaic = embedded in a variety of shapes and sizes
Model = forms the basis of our understanding
What is a channel protein?
Hydrophilic channel that allows movement of polar molecules against concentration gradient. Diffusion.
What is a carrier protein?
Important role in active transport into cells
What practical can be used to investigate membrane permeability?
By using the beetroot pigment the measure how much has escaped the membrane
How does temperature affect membranes?
Increasing the temperature increases the phospholipids kinetic energy. Making the membrane more fluid which causes it to loose its structure and break down. No structure = particles escape easily. Carrier and channel proteins denature
How do solvents effect membranes?
The inside of the bilayer is hydrophobic. Organic solvents can dissolve membranes. Pure alcohols are toxic and destroy cells. Non-polar molecules can easily get through the membrane and cause damage. Makes the membrane more fluid as well
Diffusion definiton?
The net movement of particles from an area of high concentration to low concentration. It is a passive process.
Factors affecting the rate of diffusion?
Temperature - particles have more kinetic energy
Concentration difference
Distance of diffusion - short distances is fast
How does diffusion in membranes work?
Non-polar molecules such as O2 diffuse freely down the concentration gradient. Membrane has to be partially permeable
Factors affecting rate of diffusion in membranes?
Surface area and Thickness of membrane
2 types of diffuion
Simple and facilitated
What is facilitated diffusion?
Diffusion across a membrane through channel proteins. Again, with a partially permeable membrane. The more channel proteins, the more diffusion there is
What is active transport?
The movement of molecules or ions from an area of low concentration to high concentration. Requires energy and carrier proteins to move against the concentration gradient.
How is the energy supplied for active transport?
By ATP
What is bulk transport?
‘bulk’ mean ‘a lot at a time’ Another form of active transport. Large molecules cant fit in the carrier proteins so they are moved out by bulk transport.
Explain endocytosis?
Bulk transport of material into cells. The membrane invaginates (bends inwards) when in contact with transported material. Folds around it and fuses forming a vesicle. Vesicle then transports it around the cell
Explain exocytosis?
Reverse of endocytosis. Contents are usually formed in the golgi apparatus
Osmosis definition?
Net movement of water from an area of high water potential to low water potential across a partially permeable membrane. Passive process that will continue until equilibrium is reached
What is water potential?
The pressure exerted by water as they collide with a membrane.
What is water potential measure in?
Pascals (Pa) or Kilopascals (kPa) The symbol is the Greek letter psi
What does cholesterol do?
Regulates fluidity of the membrane, produces hormones like testosterone and oestrogen
What are the two types of cholesterol?
High-Density Lipoproteins (HDL) and Low-Density Lipoproteins (LDL)
Which cholesterol is considered the ‘bad’ one?
LDL, builds up in the arteries leading to coronary heart disease
What does hypotonic mean?
When the cell swells up and bursts as water moves into it
What does hypertonic mean?
When the cell shrinks and wrinkles from all the water leaves
What is an isotonic solution?
When the cell is functioning at a normal size in solution, no water enter or leave
What does ATP stand for?
Adenosine Triphosphate
Name a practical to investigate membrane permeability?
Beetroot in different water baths
What equipment should you use in the beetroot practical?
Colorimeter, cuvette, test tubes, water baths, mass balance, ruler, scalpel, cutting tile
