Chapter 5 Flashcards
What is the role of membranes ?
Membranes are partially permeable barriers between the cell and its environment, between organelles and the cytoplasm and within organelles.
Membranes are sites of chemical reactions
Membranes are sited of cell communication
What is the fluid mosaic model?
The fluid mosaic model is the model of the structure of a cell membrane in which phospholipids within the phospholipid bilayer are free to move and proteins of various shapes and sizes are embedded in various positions
The structure and function of the phospholipid bi layer
The phospholipid bilayer is made of fluid phospholipids with hydrophilic heads and hydrophobic tails and it allows some substances to diffuse through while stopping others like water soluble substances which cannot pass through the hydrophobic core .
Function of channel proteins
channel proteins provide a hydrophilic channel allowing the movement of polar molecules and ions
Function of cholesterol in the plasma membrane
Adds stability by binding to the hydrophobic tails packing them more closely together
Function of glycoproteins in the plasma membrane
Glycoproteins are intrinsic proteins attached to a carbohydrate chain that play a role in cell adhesion and cell signalling
Function of glycolipids in the membrane
Glycolipids are a lipid with an attached carbohydrate chain which act as antigens so the immune system can recognise cells as ‘self’
What are membrane bound receptors?
Membrane bound receptors are proteins which act as receptors that have specific shapes and respond to a particular message molecule
How does low temperature affect membrane structure and permeability?
Temperatures below 0 degrees hugely increase permeability because the phospholipids have little energy so the membrane is ridged and channel and carrier proteins deform and ice crystals pierce the membrane
How does average temperatures affect membrane permeability and structure ?
Temperatures between 0-45 degrees make the membrane partially permeable, the permeability will increase as temperature rises as phospholipids have more energy so move about more increasing fluidity but overall fairly low
How does high temperatures affect membrane permeability and structure ?
At high temperatures of 45 degrees or higher the phospholipids melt and proteins deform so permeability is incredibly high
How do organic solvents affect membrane permeability and structure ?
Organic solvents such as ethanol disrupt membranes making them more permeable
How can we investigate membrane permeability?
1) cut 5 equal pieces of beetroot and wash and dry to remove pigment
2) out then in test tubes with 5cm3 of water and place each one in a different temperature water bath (or place each one in a different concentration or different solvent)
3) after a set time remove the beetroot and use a colorimeter to measure the absorbance the higher absorbance the higher permeability
Diffusion
The net movement of particles from an area of high concentration to an area of lower concentration down a concentration gradient
What molecules diffuse through the membrane ?
Small non polar molecules can diffuse through spaces between phospholipids
What does passive means?
Passive means no energy is needed
What factors effect diffusion?
Concentration gradient, thickness of exchange surface, SA and temperature affects diffusion
How can we measure the effect of factors on diffusion ?
1) make up agar jelly and cut cubes of equal size
2) put each in a boiling tube of HCL and either
- heat to different temperatures
- use different concentrations of HCL
- cut cubes to different sizes and calculate the SA:V
3) then time how long each cube takes to go colourless to find diffusion rate
What is facilitated diffusion?
Facillitated diffusion is diffusion if larger molecules, ions and polar molecules across a membrane either through channel proteins or carrier protein which change shape when the molecule bonds and realise it at the other side
Also passive
What is active transport?
Active transport is the movement of particles across the membrane against a concentration gradient using energy
What happens during active transport?
1) Molecule binds to receptors on the carrier protein
2) Inside the ATP binds and is hydrolysed into ADP and phosphate. The binding of the phosphate causes the protein to change shape
3) The ion is released inside the cell and ADP and phosphate recombine to make ATP making the protein its original shape
What is endocytosis?
Endocytosis is the bulk transport of materials into a cell via invagination of the cell-surface membrane forming a vesicle using ATP
What is exocytosis
Exocytosis is the bulk transport of material out of cells the vesicle fuses with the cell surface and its content is released using ATP
What is osmosis?
Osmosis is the diffusion of water molecules across a partially permeable membrane down the water potential gradient
What is the effect of a plant/animal cell being put in a hypotonic solution?
The net movement of water molecules will be into the cell the plant cell will become Turgid and the animal cell will burst
What is the effect of putting a plant/animal cell in an isotonic solution?
There is no net movement of particles so both cells stay the same
what Is the effect of putting a plant/animal cell in a hypertonic solution?
The net movement of water molecules will be out of the cell so a plant cell will become flaccid and the contents will put away with it which is called plasmolysis and an animal cell will shrink
How can we find the concentration inside a potato cell?
1) Cut equal pieces of potato
2) Measure the starting mass of each
3) put it in a different concentration of sucrose solution only for a set time
4) Reweigh and calculate the percentage change in mass
5) Plot and where the line meets the axes is the concentration inside the cell
