Chapter 5 Flashcards
Where are membranes found?
Surrounding the outside of a cell
Found inside a cell surrounding an organelle
What are the 4 main roles of a membrane?
Compartmentalisation- separating out areas for specific conditions
Site of chemical reactions- holds proteins involved in certain reactions
Cell signalling- membranes contain receptors that can lead to a response
Barrier- partially permeable membranes- controls what goes in/out
Why is it called fluid in the mosaic model?
This is because the phospholipids are free to move within the layer relative to each other.
Why is is called mosaic in the fluid mosaic model?
The proteins randomly embedded in the bilayer are different sizes and shapes.
What are intrinsic proteins?
Transmembrane proteins that are embedded through both layers of the membrane.
Held in place due to the interaction between R groups and the hydrophobic core of the membrane.
Role- transport across the membrane.
What are channel proteins?
Hydrpphillic channel
Passive movement of polar molecules and ions
Down concentration gradient
What are carrier proteins?
Passive transport
Active transport
Into cell
Shape of protein changes
What are glycoproteins?
Embedded in the cell-surface membrane
Has a carbohydrate attached
Role- cell adhesion
Role- receptors for hormones
Role-cell signalling
Role-act as antigens for cell recognition
Role- attach to water molecules
What are glycolipids?
Lipids with attached carbohydrate chain.
Role- Cell marker recognised by the immune system as self or no self.
What are extrinsic proteins?
Only present one side of the membrane
Loosely attached so can easily be displaced from the membrane
Hydrophilic R groups which interact with polar heads of phospholipids/intrinsic proteins
What is cholesterol?
A lipid with a hydrophilic head and a hydrophobic end.
Role: it binds to phospholipids phosphate heads, increasing the packing of the membrane, reducing the fluidity of membrane. Regulates the fluidity/stability of membranes.
How it stays in place?
Hydrophobic end interacting with tails.
Hydrophilic end interacting with the heads.
Pulling them together
How does temperature affect membrane structure?
Increased kinetic energy will lead to the breaking of weak intermolecular forces between fatty acids tails. This will lead to an increase in the permeability.
The increased kinetic energy will also denature channel and carrier proteins and this will affect the permeability.
How does solvent affect membrane structure?
It can enter the phospholipid blister and disrupt the interactions between fatty acid tails.
This will increase the permeability and fluidity and will break the membrane.
Why is diffusion?
It is the passive net movement of particles down the concentration gradient, until equilibrium is reached.
Can diffusion occur across a membrane?
Diffusion can occur without a membrane.
Particles can diffuse through a membrane without assistance if they are non-polar.
Polar particles need a protein channel to move through a membrane.
What is facilitated diffusion?
Diffusion across a protein channel on a plasma membrane.
What are the factors that affect the rate of diffusion?
Temperature- increase the KE
Concentration difference- Steeper difference between two concentrations.
Surface area to volume ratio- increases diffusion
Thickness of membrane- thinner the membrane , shorter diffusion distance.
What do carrier proteins do?
Carrier proteins move large molecules into or out of the cell, down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules.
1) First, a large molecule attaches to a carrier protein in the membrane.
2) Then, the protein changes shape.
3) This releases the molecule on the opposite side of the membrane.
What do channel proteins do?
It forms pores in the membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles.
What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher. This requires energy and carrier proteins.
Factors affecting active transport
Carrier proteins are needed for active transport.
No matter how high the concentration of particles the rate of movement is limited by the number of carrier proteins.
Carrier proteins availability is a limiting factor.
What is the process of active transport?
1) Molecules or ions bind to the channel of the carrier protein.
2) ATP binds to the inside of the carrier protein and is hydrolysed.
3) The phosphate molecule is left and the carrier protein changes shape. Molecules or ions are released.
4) Phosphate molecules is released and recombines with ADP to make ATP.
5) Carrier protein returns to shape
Examples of active transport
Sodium potassium pump to transport nervous impulses.
Minerals moving into the root hair cell.
Hydrogen ions out of companion cells.
What is bulk transport?
Form of active transport that moves large molecules and whole cells.
