2.5 Biological Membranes Flashcards
What is the fluid mosaic model?
Theory of cell membrane structure with proteins embedded in a sea of phospholipids
What is a glycolipid?
A lipid /phospholipid with a chain of carbohydrate molecules attached.
What is a glycoprotein?
A protein with a chain of carbohydrate molecules attached.
What is the plasma membrane?
Cell surface membrane.
How can substances get into the cell?
- small = diffuse
- some substances dissolve in lipid layer and pass through
- protein channels and carrier proteins.
What are the roles of the plasma membrane?
- separates from external environment
- regulates transport of materials
- contain enzymes
- has antigens so immune system recognises as self
- chemical signals to other cells
- receptors for chemical signals
- site of chemical reactions
What are the inner membranes of mitochondria called?
Cristae
What are Cristae used for?
Large surface area for aerobic respiration and localise enzymes for respiration.
What are the inner membranes of chloroplasts called?
Thylakoid membranes.
What do thylakoid membranes do?
House chlorophyll and some photosynthesis.
What are there on the plasma membranes of epithelial cells that line the small intestine?
Digestive enzymes that catalyse the final stages of the breakdown of certain sugars.
What makes the fluid mosaic model fluid?
The lipid molecules can change places with each other.
How thick is the phospholipid bilayer?
7nm
What do carbohydrate molecules on the outside of the membrane do?
Attract water with dissolved solutes.
What is another name for the outside of the membrane?
Glycocalyx
What does cholesterol do?
Gives mechanical stability and flexibility and resist the effects of temperature changes.
What are channel and carrier proteins?
Integral proteins.
How is that glycocalyx formed?
From carbohydrate chains attached either to lipids or proteins on the membrane.
How are the membranes of neurones specialised?
Protein channels and carriers in the long axon allow ions to bring the conduction of electrical impulses.
How are the plasma membranes of white blood cells specialised?
Have special proteins receptors that enable them to recognise the antigens on foreign cells.
Define diffusion.
The net movement of molecules from and area of high concentration of that molecule to an area of low concentration.
May or may not be across a membrane
Is passive
Define facilitated diffusion.
The net movement of molecules from an area of high concentration of that molecule to an area of low concentration, across a partially permeable membrane via protein channels or carriers
Is passive
Why is water a special case for diffusion?
Molecules are polar and insoluble in the lipid in the phospholipid bilayer.
Why is water able to diffuse through cell membranes?
It is present in great concentrations.
What are specific water channel proteins called?
Aquaporins
How is the concentration gradient maintained?
The molecules that enter the cells are used for metabolic reactions.
What factors affect the rate of simple diffusion?
- temperature
- diffusion distance
- surface area
- size of diffusing molecule
- concentration gradient
What molecules undergo facilitated diffusion?
Small molecules that have polarity are insoluble in lipid as they cannot interact with the hydrophobic tails of the lipid bilayer.
Define osmosis.
Passage of molecules down their water potential gradient, across a partially permeable membrane.
Define water potential.
Measure of the tendency of water molecules to diffuse from one region to another.
What is the unit of water potential.
KPa
What is the water potential of pure water?
0kPa
What is it called when a cell swells and bursts due to too much water?
Cytolysis
What is it called when animal cells shrivel?
Crenated
What is it called when the cytoplasm of plant cells shrinks and the membrane pulls away from the cell wall?
Plasmolysed
What is plant tissue with Plasmolysed cells called?
Flaccid
Define active transport.
The movement of substances against their concentration gradient across a cell membrane, using ATP and carrier proteins.
Define endocytosis.
Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, into a cell.
Define exocytosis.
Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, out of a cell.
What ions are actively transported?
Sodium and potassium ions.
How many sodium ions bind to the site on active transport?
3
What is ATP hydrolysed to form?
ADP + P
How many potassium ions bind to their site with active transport?
2
What is phagocytosis?
When one cell engulfs another.
What is pino(endo)cytosis?
Cells ingesting liquids.
Is ATP needed for endocytosis?
Yes, to move vesicles using molecular motor proteins along cytoskeleton threads.
What determines membrane fluidity at cold temperatures?
The proportions of unsaturated and saturated fatty acids within a cell membrane.
What also buffers the effect of lowered temperature?
Cholesterol prevents phospholipid molecules from packing together too closely.
How do solvents, such as acetone and ethanol, damage membranes?
They dissolve lipids.
What is broken by strong reducing agents?
Disulfide bonds.
Roles of membranes
- partially permeable barriers between the cell and its environment, between organelles and the cytoplasm and within organelles
- sites of chemical reactions
- sites of cell communication (cell signalling).
What is cell signalling?
communication between cells
Why can’t water soluble substance pass through the membrane?
The centre of the bilayer is hydrophobic
Functions of membranes within cells
Forms vesicles
Isolation of ontents from cytoplasm
Site of processes/ reaction
Surface for attachment (of enzymes/ribosomes)
Control what substances enter and leave organelles- selective permeability
Creation of concentration gradients
Functions of membranes within cells
Forms vesicles
Isolation of ontents from cytoplasm
Site of processes/ reaction
Surface for attachment (of enzymes/ribosomes)
Control what substances enter and leave organelles- selective permeability
Creation of concentration gradients
What molecule can easily pass through the phospholipid bilayer?
fat-soluble substances
What membranes do not have cholesterol?
Bacterial membranes
What is the function of glycolipids and glycoproteins?
- stabilise the membrane by forming hydrogen bonds with surrounding water molecules
- where drugs, hormones and antibodies bind
- receptors for cell signalling
- antigens
Describe the role of membrane bound receptors
- proteins
- specific shapes
- drugs use them to trigger a response from the cell or block the receptor and prevent it from working
How can you investigate factors affecting membrane fluidity?
BEETROOT
- cut five pieces and rinse
- place in test tubes containing water
- different temperatures for known time
- remove beetroot, leaving coloured water
- colorimeter
- higher permeability = more pigment released = more absorbance
How does temperature affect membrane permeability?
- <0 degrees, packed together, proteins deform, memrbane more permable, ice crystals may form + pierce membrane
- 0-45 degrees - can move around and arnt packed = partially permeable
- > 0 bilayer breaks down, water expands inside and puts pressure, proteins deform
How does changing the solvent affect membrane permeability?
- ethanol dissolves lipids so increases
How can you investigate diffusion in model cells?
1) make agar jelly with phenolphthalein and dilute sodium hydroxide (it will be a LOVELY shade of pink)
2) fill beaker with dilute HCl
3) Cut cubes of jelly and put them in the acid
4) the cubes will go colourless
How can you investigate water potential in the lab?
POTATO
- different conc sucrose solutions
- put potato in and weigh
- calculate % change in mass
What molecules do facilitated diffusion?
polar and charged
carbohydrates
amino acids
ions
Examples of hydrophobic molecules that can enter membranes?
O2
CO2
N2
steroids
Examples of small uncharged polar molecules that can enter membranes
H2O
glycerol
urea
ethanol
Examples of large uncharged polar molecules that cant enter membranes
glucose and sucrose
