2.5: Biological membranes Flashcards
What does it means by fluid?
Components can move freely along the membrane
What are the functions of the plasma membrane?
- Compartmentalisation
Provides specific conditions for certain reactions to occur - Site of chemical reaction
Holds proteins/enzymes that are involved in certain chemical reactions - Acts as a barrier
Partially permeable membrane, only allows small, lipid-soluble/non polar substances to diffuse across (phospholipid bilayer)
What is a carrier protein?
It is a protein on the inside that is able to change its shape using energy to face outwards.
Used to transport moleules across membrane
- Involved in active transport mainly sometimes passive (facilitated diffusion)
Because it uses energy to change shape
What is a channel protein?
Allows faciltated diffusion
Because polar molecules cannot pass through the phospholipid bilayer
What are the similarities of channel and carrier protein?
They are both selective so they have specific channels for specific molecules
E.g aquaporins are channel proteins that only allow water to go through
What is a glycolipid and glycoprotein?
Glycolipid - carbohydrate chain attached to a phospholipid
Glycoprotein - carbohydrate chain attached to a protein
They can be receptors or antigens
What is the role of cholesterol?
regulates fluidity
What makes up the fluid mosaic model?
Carrier and channel proteins
glycolipids and glycoprotiens
cholesterol
What is inbetween different phospholipids?
Weak intermolecular forces that stabilise the structure
What are the factors affecting membrane structure?
- Temperature
- Solvent
What does an increase in temperature do?
- Gain kinetic energy
- The weak intermolecular forces inbetween the phospholipids break
- Denatures protein channel/carriers
- There are more gaps for simple diffusion to take place
- Affects permeability
What does a non polar solvent do?
A non polar solvent can insert themselves within the bilayer which causes some of the fatty acid tails to bend. This is because the head is hydrophilic (polar) and the tails are hydrophobic(non polar).
- This disrupts the weak intermolecular forces
- This disrupts the bilayer
- There are bigger gaps which increases permeability
What is diffusion?
Net movement of particles down concentration gradient
What is facilitated diffusion?
Diffusion across protein channel on plasma membrane
(has selective permeability)
What are the factors increasing the rate of diffusion?
- Temperature
- Concentration difference
- Surface area to volume ratio
- Thickness of membrane (diffusion distance)
What does an increase in temperature do?
Increasing temp increases kinetic energy. Particles vibrate more quicker
What does an increase in concentration difference do?
The steeper the concentration gradient, the quicker the concentration difference
What does an increase in surface area to volume ratio do?
Larger ratio the quicker the diffusion rate
What does the increase thickness of membrane do?
Thinner the membrane, shorter the distance, quicker diffusion rate
What is osmosis?
Net movement of water molecules down a water potential gradient
What happens when there is a lower concentration of water molecules
There is a higher concentration of solute molecules
What happens when there a higher concentration of water molecules?
There is a lower concentration of solute molecules
What happens when plant cells are in a low solute concentration?
Water moves in by osmosis down a water potential gradient. Then the cell wall prevents bursting and a membrane pushes against the wall. The cell is turgid.
What happens when a plant cell is in a high solute concentration?
Water moves out of cells by osmosis down a water potential gradient. Plant cell membrane pulls away from cel wall as water leaves. The cell is plasmolysed
What happens when an animal cell is in a low solute concentration?
Water moves in by osmosis by down a water potential gradient, animal cell bursts open. It is cytolysed
What happens when an animal cell is in a high solute concentration?
Water moves in by osmosis down a water potential concentration gradient. Animal cell shrinks and appears wrinkled. It is crenated
What is water potential?
The tendency of water to move from one region to another by osmosis
- In pure water the WP is the highest
- Ad more solute moelecules are added the WP decreases
cell potential = solute potential + pressure potential
What is pressure potential?
The hydrostatic pressure to which water is subjected.
- Usually positive and is 0 when cells are in equilibrium
sometimes referred to as turgor or water pressure
What is solute potential?
A measure of reduction in the water potential due to the presence of solute molecules
- It is the negative component of water potential
sometimes referred to as the osmotic potential or osmotic pressure
What is Active transport?
The movement of particles against the concentration gradient using eneregy/ATP involving carrier proteins
What do protein carriers do?
Change their shape to transport (or exchange) substances acrosss a membrane
What is conformational change?
Structural/shape change
What is bulk transport?
Active transport of large molecules
What is endocytosis?
The bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, into a cell
Phagocytosis = solids
Pinocytosis = liquids
What is exocytosis?
The bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, out of a cell
involves the fusion of vesicles with plasma membrane
What is the process of active transport?
- Molecule or ion binds to the carrier protein on receptor site
- ATP binds to carrier protein on the inside
- Hydrolysis of ATP to ADP and phosphate (Pi) causes the carrier protein to change shape. This releases the molecule or ion on the opposite side of the membrane.
- The phosphate (Pi) is released from the carrier protein, causing the carrier protein to return to its original shape, ready to be used again.
What are the factors affecting active transport?
- Temperature - At higher temperatures, particles have more kinetic energy and travel faster. Respiration also increases with temperature. Very high temperatures denature carrier proteins, decreasing the rate of active transport.
- Thickness of membrane - Particles travel shorter distances through thin exchange surfaces, so travel faster
- Number of carrier proteins - The more of these proteins, the faster the rate of active transport
- Rate of respiration - The more respiration, the more ATP available for active transport
