Chapter 5- Plasma membranes Flashcards
(24 cards)
Define compartmentalisation
Compartmentalisation- The formation of separate membrane bound areas within a cell
Define the plasma membrane
The cell surface membrane that separates the cell from its external environment, formed from a phospholipid bilayer
Which end of the phospholipid is hydrophobic?
The fatty acid tails
Why is it called the fluid mosaic model?
Because the phospholipids are free to move within the layer relative to each other (fluid) and the surface of the membrane is embedded with different kinds of proteins, glycolipids, and other organic molecules (mosaic)
What are the two types of membrane proteins?
Intrinsic proteins- penetrate both layers of the phospholipid bilayer
Extrinsic proteins- only penetrate one side of the bilayer
Give three examples of intrinsic proteins
Carrier proteins- have a role in passive and active transport
Channel proteins- provide a hydrophilic channel to allow polar molecules through membranes
Glycoproteins- act as receptors for chemical messengers and involved in cell signalling
What is the difference in the role between glycolipids and glycoproteins?
Glycoproteins are involved in cell communication and cell adhesion
Glycolipids provide cell markers as either self or non self
Give an example of an extrinsic protein
Cholesterol- a lipid (sterol) involved in maintaining the fluidity of the bilayer
Give an example of a polar and a non polar solvent
Water- polar
Alcohol- less polar than water
Benzene- non polar
Why do alcohols cause impairment?
They disrupt the membranes of cells- some cells like neuronal transmitters need intact cell membranes to function properly. This reduces the speed of nerve impulse transmission
How does passive transport occur?
Utilising the natural motion of particles
Define equilibrium
Movements in both directions are equal
Define endocytosis and exocytosis
Exocytosis- The bulk transport of material into cells
Endocytosis- the bulk transport of material into cells
Define phagocytosis and pinocytsosis
Phagocytosis- the bulk transport of solids into cells
Pinocytosis- the bulk transport of liquids into cells
Describe the process of active transport through a carrier protein
Molecule binds to receptors outside the cell
On the inside of the membrane ATP binds to receptors and is hydrolysed to ADP and an inorganic phosphate
Phosphorylation changes the shape of the carrier protein to open up the inside of the cell
Molecule or ion is released into the cell
Phosphorylation reverses
Carrier protein returns to the original shape
Define water potential
The pressure exerted by water molecules as the collide with a membrane or container, measured in kilo Pascals (kPa)
What is the water potential of pure water?
0kPa
Describe the relationship between solutions and water potential
The more concentrated the solution the more negative the water potential
Describe hydrostatic pressure
The diffusion of water into a solution in a closed system, resulting in an increase in pressure
What causes cytolysis?
A cell is placed into an environment of a higher water potential, causing water to move into the cell. This over fills the cell to a volume it can’t tolerate and the membrane bursts
What is the opposite effect of cytolysis?
Crenation
What do we call it when cells have a water potential equal to their environment?
Isotonic
Why is it important that plant cells have strong cell walls?
Because they can’t control the environment surrounding them- an increase in hydrostatic pressure means an increase in turgor
What happens when a plant cell is placed into a solution of lower water potential?
Water leaves the cell, reducing the volume of cytoplasm, pulling the cell surface membrane away from the cell wall
