Biological Membranes Flashcards
What 2 places can you find membranes?
Around a cell and around Eukaryotic organelles
What do membranes do?
Controls what enters and leaves Selectively/partially permeable Responsible for compartmentalisation Site of cell receptors and cell signalling Site of chemical reactions
What are some examples of where membranes are important?
Rough ER- ribosomes attach to it
Lysosomes-contain the acid/enzymes which would damage the cell if they were free
Mitochondria- contain respiratory enzymes
What are the 4 parts of a membrane?
Cholesterol
Phospholipid bilayer
Glycoproteins/glycolipid
Channel/carrier proteins
Cholesterol
Type of lipid with hydrophilic/phobic end
Lie alongside phospholipids
Regulates fluidity of membrane
Too stiff-stops phospholipids grouping together and crystallising
Too fluid-hydrophilic end interacts with head and hydrophobic end interacts with tail of phospholipids pulling them closer together.
Phospholipid bilayer
2 layers
Hydrophilic head (glycerol and phosphate) on the outside
Hydrophobic tail (fatty acid) on inside
Fluid (can move)
Prevent water soluble substances from passing through.
Only small uncharged particles can pass through.
Glycoproteins/lipids
Sugars stuck to protein/lipid Receptors for molecules, like hormones, to bind Help cells join together Cell signalling Cell recognition
Carrier/channel proteins
Can be intrinsic (go all the way through) or extrinsic (only on 1 side) Channel proteins (intrinsic) allow hydrophilic substances like ions to get through Carrier proteins (intrinsic or extrinsic) change shape up let molecules through Carry charged/large molecules across Normally specific to a molecule
What if the fluid mosaic model?
Fluid because the phospholipids are able to move past each other.
Mosaic because the other components are places all around the membrane.
How wide are membranes?
7nm
Definition of diffusion
Movement of particles from an area of high concentration to an area of low concentration, down the concentration gradient until an equilibrium is reached
No extra energy is needed
Factors that affect diffusion
Concentration gradient Temperature Stirring/moving Surface area Type/size of ion/molecule
4 examples of molecules that can diffuse across the cell surface membrane
Oxygen (very small and uncharged)
Carbon dioxide (very small)
Water (very small)
Fat soluble substances (dissolve in phospholipids to get across)
3 molecules that can’t diffuse across cell membranes
Ions (small but charge repels them) Glucose (too big) Amino acids (too big)
Definition of facilitated diffusion
Movement of particles from an area of high concentration to an area of low concentration, down the concentration gradient, with the aid of a channel/carrier protein until an equilibrium is reached
No extra energy is needed as particles have their own kinetic energy
What things use facilitated diffusion?
Anything that can’t pass through using normal diffusion (ions, glucose, amino acids etc)
What factors affect facilitated diffusion?
Concentration gradient Temperature Stirring/moving Surface area Type/size of ion/molecule AND NUMBER OF CHANNEL/CARRIER PROTEINS
Definition of osmosis
Movement of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable membrane down the water potential gradient
What is the highest water potential number?
0 (every other water potential number is below 0)
Which 3 types of transport across membranes are passive?
Simple diffusion
Facilitated diffusion
Osmosis
Which transport across membranes is active?
Active transport
Which types of transport across membranes don’t need extra energy?
Simple diffusion
Facilitated diffusion
Osmosis
(They just need kinetic energy)
Where does the energy for active transport come from?
ATP
Which types of transport across membranes use a protein?
Facilitated diffusion (carrier or channel)
Active transport (must be carrier)
What is bulk transport?
Lots of substances/molecules being transported at once. Requires ATP (this is a type of active transport)
What does pino exocytosis mean?
Bulk movement of liquid out of a cell
What does pino endocytosis mean?
Bulk movement of liquid inside a cell
What does phago exocytosis mean?
Bulk movement of a solid out of a cell
What does phago endocytosis mean?
Bulk movement of a solid inside of a cell
In which 2 organelles are membranes involved in chemical reactions?
Mitochondria
Chloroplasts
How are membranes involved in cell signalling?
Membranes contain receptors for signalling molecules. When the signalling molecule binds to the receptors, it triggers a series of reactions within the cell.
How do drugs that bind to receptors on membranes work?
The drugs may be a similar shape to the signalling molecule so bind to the receptor and block it, reducing/increasing the response.
What is ATP specifically used for in exocytosis and endocytosis?
Moving vesicles
Used so vesicles can fuse to the plasma membrane
What is the difference between simple and facilitated diffusion?
Simple doesn’t need any membrane proteins.
Facilitated requires carrier/channel proteins because molecules are too big to pass through the membrane.
How is ATP used in exocytosis?
Makes the membranes ‘pinch off’ to form vesicles
Moves the vesicles around the cell
