2.5 Plasma membrane Flashcards
What does the cell surface membrane do?
Acts as a barrier, controls movement in and out of cell
What is compartmentaillsation?
formation of separate membrane bound areas in a cell,
What can compartmentalisation be used for?
incompatible reactions, so allows for specific conditions of the reactions
What is a phospholipid
Hydrophilic phosphate head, hydrophobic fatty acid tails
What is the phospholipid bilayer, draw it
2 phospholipids, Phosphate heads face outwards, tails point inwards
What are the properties of phospholipids that makes it suited to be in the membrane
cells exist in aqueous environments, and are also aqueous, , heads can interact with water
Why is the phospholipid bilayer a theory
Membrane is seen as two black lines during electron microscopy
What is the fluid mosaic model?
Shows the components of a plasma membrane
Compare intrinsic and extrinsic proteins
Intrinsic - embedded through BOTH layers of phospholipids
Extrinsic - proteins that are present on only one side of bilayer, some can move between layers
What are channel proteins?
Intrinsic protein, with hydrophobic channel that allows for diffusion of polar molecules
What are carrier proteins?
Intrinsic proteins that are part of active transport, they change shape
What are glycoproteins
Intrinsic proteins, that have a carbohydrate chan. Play a role in cell adhesion (two cells join to form a junction), and receptors in cell signalling (chemical binds to receptor, causing a response)
What are glycolipids
lipid with a carbohydrate tail attached, act as cell markers, so a cell can be recognised
What is cholesterol
lipid with a hydrophilic end and hydrophobic end, regulates the fluidity of the membrane, adding stability
How does temperature impact membrane structure?
temperature is increased, so phospholipids move more, making the membrane loose it’s structure, so molecules can pass easier
if temp gets too high, eventually breaking down Carrier and channel proteins will denature, decreasing permeability
How does solvents impact membrane structure?
Organic solvents (less polar then water) will dissolve membranes. making it more fluid/permeable
Pure alcohol will destroy cells, non-polar alcohol disrupts the membrane, making it more fluid/permeable
What is diffusion?
Net, passive movement of particles from a high concentration to a low concentration. until there is an equilibrium
What are the factors effecting the rate of diffusion?
Temperature - higher temp = faster diffusion (particles have high kinetic energy)
Concentration difference. (greater difference the faster the rate of diffusion
What is simple diffusion
Absence of a barrier or membrane
What molecules can diffuse across a partially permeable membrane? Why?
non polar molecules (no charges)
Hydrophobic tails repels substances with positive or negative charges
Small polar molecules can pass through easier then large ones
What is the rate of diffusion across a membrane affected by?
Surface area - larger exchange surface = higher rate of diffusion
Thickness of membrane - thinner exchange surface = higher rate of diffusion
What is facilitated diffusion? What does this allow for?
Diffusion with involve carrier proteins (without the need for energy) or channel proteins. Allows for movement of polar molecules and ions
What is facilitated diffusion impacted by?
Temperature, Concentration gradient, membrane surface area and thickness, and number of protein channels
More protein channels = higher rate
What is active transport
A selective, active movement of molecules from a low concentration to a high concentration. Requiring energy
Explain active transport
Molecule binds to the channel of the carrier protein. ATP binds to the carrier protein and gets hydrolysed. This causes the carrier protein to change shape, opening to the inside of the cell. ADP and P group bond to form ATP, the carrier
What is bulk transport
Active transport of large molecules are transported in and out of a cell. Like enzymes, hormones and bacteria
What is endocytosis
Bulk transport into cells
What is phagocytosis?
What is pinocytosis?
Phagocytosis - Endocytosis of solids
Pinocytosis - Endocytosis of liquids
Explain endocytosis
Cell surface membrane bends inwards as it comes into contact with material. Membrane enfolds the material, forming a vesicle, Which pinches off and moves into the cytoplasm
What is endocytosis
Vesicles (formed by the Golgi apparatus) move towards and forms with the cell surface membrane, contents of the vesicle are released to the outside of the cell
Why does Bulk transport require energy?
ATP is needed for the movment of vesicles along the cytoskeleton, changing shape of cells to engulf materials, fusion of cell membranes as vesicle or as they meet the cell surface membrane
What is osmosis
the passive diffusion of water across a partially permeable membrane
What is water potential?
the pressure exerted by water molecules as they collide with a container or membrane
What is water potential measured in
Pascals (Pa) Killa Pascals (KPa) ψ
What is pure water measured as. What is other water measured as?
0Kpa, all other solutes have a negative water potential (more concentrated, the more negative)
In a closed system, what does the diffusion of water into a solution lead to
Hydrostatic pressure
What is the effect on an animal cell if it is placed in a solution that has a higher water potential then the cytoplasm
Water moves into the cell, cell may burst (cytolysis)
What happens is an animal cell is placed in a solution that has a lower water potential then the cytoplasm?
Cell looses water, causing a shrunken or shrivelled (crenation)
What is the effect on a plant cell if it is placed in a solution that has a higher water potential then the cytoplasm
Water enters the cell, increased hydrostatic pressure, pushing the membrane against the rigid cell wall, (pressure is called turgor), the turgor resists entry of further water (turgid)
What happens to a plant cell if it is placed in a solution that has a lower water potential then the cytoplasm?
Water is lost, the cytoplasm looses volume, causing the cell surface membrane away from the cell wall (plasmolysed)
