Membranes Flashcards
Components of a phospholipid bilayer
- Glycoproteins/Glycolipids
- Cholesterol
- Hydrophobic tails
- Hydrophillic heads
- Surface/Intrinsic/extrinsic proteins
Nature of a phospholipid bilayer
- Negative charge on surface and no charge on tails
- Permeable to small non-polar molecules
- Impermeable to small polar molecules, ions and large molecules
- 7nm thickness
Role of channel proteins
Allow the movement of large molecules and hydrophillic molecules across a membrane
Role of ion channels
Transporting ions e.g. sodium and chloride ions
Role of carrier proteins
Transport large water insoluble molecules and ions against their concentration gradient using ATP
Role of protein receptors
- Detect specific hormones and nerve transmitter and allow them to bind to corresponding cells
- Allows drugs to bind to affect cell metabolism
- Activates enzymes within a cell
Role of glycoproteins and glycolipids
Involved in cell signalling to allow recognition by the immune system
Bind tissues together
Can act as hormone receptors
Role of cholesterol
- Cholesterol gives eukaryotic cell membranes mechanical stability and maintains fluidity
- Helps make the barrier more complete against water molecules trying to pass straight through
Effect of temperature on a cell membrane
- As temperature rises, KE increases
- This causes the phospholipid molecules to vibrate more
- The molecules will gain enough KE to cause leakages in the membrane, making the membrane fully permeable
Types of transport across membranes
- Simple diffusion
- Osmosis
- Facilitated diffusion
- Active transport
- Cytosis
Functions of membranes
- Divides cell content into different compartments to make different functions more efficiently
- Regulates movement of substances in and out of the cells or organism
- Recognises specific molecules and other cells
- Membranes can allow electrical signals to pass along them (e.g. axon of a motor neurone)
- Membranes provide attachment sites for enzymes and other molecules involved in metabolism
Fluid mosaic
Description of the arrangement of molecules in membranes.
Antigen
Complementary to messenger molecule like hormones which bind to them and bring about a change in the cell
Cell signalling
The molecule mechanism by which cells detect and respond to external stimuli and send messages to other cells
Membrane proteins
- An enzyme that is built into the membrane with the active site sticking out into the adjacent solution
- Several enzymes are ordered as a team to carry out sequential steps of a metablic pathway
Organelles with 2 membranes surrounding them
- Chloroplasts
- Mitochondria
- Lysosomes
Term used to describe membranes that only allow some molecules through
Partially permeable
Types of transport across membranes
- Osmosis
- Facilitated diffusion
- Diffusion
- Active Transport
- Cytosis
Active transport
- Against a concentration gradient
- Requires ATP
- Uses specific carrier proteins to transport specific molecules
- Carry molecules at a faster rate than diffusion
- Carrier proteins change shape
- Can accumulate content outside cell or inside cell
Endocytosis
Phagocytosis – organic matter or bacterium is engulfed
Pinocytosis – liquid mass
Exocytosis
- Movement out of cell
- Vesicles moved by cytoskeleton
- Requires ATP
Osmosis
- Small water moelcules fit between gaps in the phospholipid bilayer
- Water moves down the concentration gradient
- The movement of water will reach a dynamic equilibrium
- Water diffuses across both ways
Diffusion
- Passive process (use their own KE)
- Down a diffusion gradient
- Will reach a dynamic equilibrium
- Diffusion will keep occuring in both directions
- Will transport the lipid soluble, non-polar and small molecules
- No proteins used
- Phospholipid layer must have gaps for this to occur
Facilitated diffusion
- Requires ATP
- Ion channels are specific to certain ions/molecules
- Will transport large non-polar molecules and small charged particles
- Utilise channel or carrier proteins
- Down a concentration gradient
Factors afftecting the rate of diffusion
- Surface area
- Concentration gradient
- Temperature
- Diffusion distance
Why does an increase in surface area increase the rate of diffusion
There are more points of contact and potential gaps that the molecules can fit through
Why does an increase in the concentration gradient lead to an increase in the rate of diffusion
If there is a greater concentration gradient, there will be a greater net movement of molecules across the membrane
Why does an increase in temperature result in a increase in the diffusion rate
The phospholipid molecules will move more vigorously causing more gaps to appear for diffusion
Why does a decrease in diffusion distance increase the rate of diffusion
The molecules will have to travel a shorter distance
Water potential
0 is the highest water potential and kPa is used as the unit
What will happen to a plant and animal cell when placed in pure water
The plant cell will become turgid
The animal cell will haemolyse
What will happen to a plant and animal cell when placed in saline solution
The plant cell will become plasmolysed
The animal cell will become crenated
