Biological Membranes Flashcards
What are some roles of membranes within cells
Compartmentalisation e.g. processes such as respiration
Site for chemical reactions e.g. rough ER
Form a concentration gradient
What are some roles of cell surface membranes
Acts as a partially permeable barrier
Signal receptors
Why is the phospholipid bilayer described as a fluid mosaic model
The phospholipids are able to move around giving the bilayer fluidity
The different types of proteins give a mosaic pattern
What are phospholipids
A glycerol connected to a
2 hydrophobic fatty acid tails
1 hydrophilic phosphate head
What is cholesterol’s function
Binds to the hydrophobic fatty acid tails and reduces fluidity by making the phospholipids pack more closely together
What is cholesterol’s function
Binds to the hydrophobic fatty acid tails and reduces fluidity by making the phospholipids pack more closely together
What are glycoproteins
They are intrinsic proteins with an attached carbohydrate embedded in the cell surface membrane
Acts as receptors for cell signalling
And binding sites for signalling molecules to bind to
What are glycolpidsTh
They are lipids with attached carbohydrates
They are cell markers or antigens
What are the 2 main types of intrinsic proteins embedded in the cell surface membrane
Channel proteins - allow polar molecules and ions to diffuse through the phospholipid bilayer
Carrier proteins - allow typically large molecules to pass through the membrane.
ATP sometimes involved
How does temperature affect permeability
At really cold
At normal and as temp is increasing
At very hot
Really cold - Ice crystals will form and pierce the bilayer increasing permeability
At normal temperature the bilayer is partially permeable, fluid and stable
As temperature increases the phospholipids gain kinetic energy leaving temporary gaps for any molecules that diffuse through normally
If temperature increases further the bilayer may lose it’s stability and will become even more permeable. Proteins will start to denature so membrane will become completely permeable
How does solvent affect permeability
Non-polar solvents can sit between fatty acid tails breaking H-bonds and disrupting the membrane
An increase in concentration will lead to an increase in permeability
e.g. alcohol wipes clean wounds by disrupting membranes of bacteria
What is passive transport
Passive transport is the movement of a molecule from an area of high concentration to an area of low concentration .
This process doesn’t require the use of ATP
What is simple diffusion
For example oxygen is non polar so it can diffuse from an area of high concentration to an area of low concentration
What is facilitated diffusion
The movement of molecules with the aid of a channel or carrier protein.
For example large and polar molecules use this method
What is osmosis
The net movement of water molecules from a high water potential to a low water potential across a partially permeable membrane
How would you investigate osmosis with potato cells
Using same age of potato cut into equal lengths using a cork borer and a scalpel
You can alter your sucrose concentration using serial dilution or a dilution technique
Makes sure volume is the same
Record initial mass and put in solution for the same amount of time
Record final mass and calculate percentage change
More comparable
Where there is 0% change that’s the water potential
How would you investigate the effect of temperature on membrane permeability
Cut samples of the same mass/length of beetroot
Leave to blot on paper so excess pigment is removed
Place each sample in a different temperature of water bath for the same amount of time
After remove the samples just leaving your coloured solutions
Looking can be subjective so using a calibration curve can help obtain a more accurate value
Using a red filter and a blank using colorimetry
Plot a graph of absorbance against temperature
What is active transport
The net movement of molecules against its concentration difference and can also use membrane bound proteins that change shape to move molecules across the membrane
Both these processes require the use of ATP
What is bulk transport and what are the two main types
Large molecules that are too large to fit through channel or carrier proteins
Endocytosis - Bulk transport of materials into cells
e.g. phagocytosis (solids) and pinocytosis (liquids)
Exocytosis - Unusually vesicles that are containing molecules move out of the Golgi apparatus and fuse with the cell surface membrane releasing its contents
What water potential does pure water have how does increasing solute concentration have an effect?
0kPa so this means increasing solute concertation will decrease the water potential
What does Hypertonic Isotonic Hypotonic mean when describing solutions
Hypertonic - Water potential is lower outside
Isotonic - Water potential is the same so net movement of water molecules is the same
Hypotonic - Water potential is higher outside
How would an animal cell e.g. a red blood cell react to different solutions
Hypertonic - RBC would shrink, Hb is more concentrated so cell would have a dark look and
become crenated
Isotonic - RBC would have a normal appearance as water in = water out
Hypotonic - RBC would swell and burst - Cytolysis
How would an plant cell react to different solutions
Hypertonic - Flaccid and if water further leaves becomes plasmolysis the plasma membrane
pulls away from the cell wall, the space is also filled with the external solution
Isotonic - There is no change
Hypotonic - The cytoplasm pushes the plasma membrane out against the cell wall making the
plant Turgid. The cell does not burst
Why does the animal cell swell and burst but not the plant cell when placed in a hypotonic solution
Animal cell does not have a cellulose cell wall to withstand the high pressure
