Cell Mem Flashcards
Diffusion
The net movement of particles from an area or higher concentration to an area of lower concentration.
Facilitated diffusion
Moves particles down a concentration gradient, from a higher to a lower concentration.
Carrier proteins
Large molecules attach to carrier in mem.
Protein changes shape.
Releases the molecule on the opposite side of mem.
Channel protein
Form pores in the membrane for charged particles to diffuse through down a conc gradient. Different channel proteins facilitate the different charged particles.
Osmosis
Diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential
Water potential
Potential of water molecules to diffuse out of or into a solution
Pure water
Highest water potential
Isotonic
Two solutions separated by partially permeable membrane and solute concentration that have the same water potential.
Solute
Any substance that is dissolved in a solvent.
Solvent
Water that the solute is dissolved in.
Solution
Solute and solvent together
Soon as you add a solute to water, you lower the
Water potential because water molecules are attracted to the solute and less free to move around.
The lower the water potential and the higher the salt solution,
The more negative the value
When is dynamic equilibrium reached
When water molecules have moved from high to low and equal number of water particles (no net movement).
Factors that affect rate of osmosis
- Water potential gradient
- Thickness of exchange surface
- Surface area of exchange surface
What happens to pure water outside the cell
Osmosis. Water goes into cell and will burst it - haemolysed
In plant cells, swelling in cytoplasm and vacuole will push against the cell wall and make it turgid.
What happens when high sugar conc outside the cell
Concentrated sugar solution makes low water potential so water moves out of the cell by osmosis down a water potential gradient. Animal cell shrinks and wrinkles.
Hypotonic
Contain low solute conc and high water
Hypertonic
High solute conc and low water
Simple dilutions
The stepwise dilution of a substance in a solution.
Use the dilution factor at each step. It’s constant.
C1V1=C2V2
How can you make sucrose solutions of any conc
By finding the scale factor.
- Known conc
- Find scale factor by conc of solution/ conc of solution you want to make.
- Make solution weaker by cm^3/ scale factor.
- Top up with distilled water with vol u want. So cm^3-weaker solution = distilled water
Use solution to find water potential of potato cells
- Cork borer to cut potatoes into identically sized chips, about 1cm in diameter.
- Divide chips into 3 groups and measure mass of each group using mass balance.
- Place 1 group into each of sucrose solution.
- Leave chips in solutions for at least 20 mins.
- Remove and dry gently and weigh again.
- Record and calculate % change in mass for each group.
- Make calibration curve - % change in mass against sucrose conc.
How to find water potential on a graph
The point where the curve crosses the x-axis (where % change in m is 0) and is the point where water potential of sucrose solution is the same as water potential of potato cells.
Find the conc at that point then look up the water potential for the conc of sucrose solution.
Experiment to investigate water potential
Use potato cylinders to find water potential of plant tissue.
Make servers solutions of different known conc to test in cylinders.
- 5 test tubes
- Add 10cm3 of the giving conc. I.e. 2M of sucrose solution to the first test tube and 5cm3 of distilled water to the other four test tubes.
- Use a pipettes and take 5cm3 of solution from the first test tube and add to distilled water in second and mix throughly.
- U now have 10cm3 of solution that’s half as concentrated as the solution 1M.
- Repeat process three more times.
Active transport
Moves particles from a low to high conc. Uses energy to move molecules and ions across membrane, against a conc gradient.
What are involved in active transport
Carrier proteins. The molecules attach to carrier, protein changes shape and this moves the molecules across the membrane releasing it onto other side.
Two main difference between facilitated diffusion
- Active transport moves from low to high. Facilitated is always high to low.
- Active transport requires energy - ATP releases energy as ADP and Pi when hydrolysed. Facilitated doesn’t require energy and it’s a passive process.
- Active transport doesn’t use channel proteins. Only carrier. Facilitated uses both.
What is a type of carrier protein that works with active transport / name a carrier protein
Co-transporters.
They bind two molecules at a time.
The conc gradient of one of the molecules is used to move the other molecule against its own conc gradient.
Explain an example of co-transport
Sodium ions move into the cell down their Conc gradient. That moves glucose into the cell against the conc gradient.
How does glucose enter the ileum epithelium cell with sodium ions
Glucose is absorbed from the lumen of the ileum into bloodstream in the small intestine by co-transport.
- Sodium ions transport out of ileum epithelial cells into the blood by the sodium potassium pump.
- A concentration gradient is created. Higher conc of sodium ions in the lumen of the ileum than inside the cells.
- Sodium ions diffuse from lumen of ileum into epithelial cells, down their conc. gradient. They do that through the sodium-glucose co-transporter proteins.
- The co-transporter carries glucose into the cell with the sodium. The conc of glucose inside cell increases.
- Glucose diffuses out of the cell into the blood down its conc gradient through a protein channel by facilitated diffusion.
Factors affecting rate of active transport
- Speed of individual carrier proteins - faster = faster.
- No. Of carrier proteins- more = faster.
- Rate of respiration in cells and availability of ATP - if respiration inhibited, active transport can’t happen.
Water potential (psi) measured in
kPA - kilopascals
0M salt solutions
0kPa
0.2M salt solutions
-100kPa
0.4M salt solutions
-200kPa
When won’t osmosis occur
When solution is isotonic
What does facilitated diffusion use
Carrier and channel proteins
Large molecules would diffuse ___ through phospholipid bluster because
Slowly because they’re so big
Charged particles would diffuse ___ through phospholipid bluster because
Ions diffuse slowly because they’re water soluble and the centre of the bilayer is hydrophobic
Factors affecting facilitated diffusion
- Conc gradient - higher = faster.
- No. Of channel or carrier proteins - once all particles in membrane are in use, facilitated diffusion can’t happen any faster even if u increase concentration gradient so the greater no. Of C or C, the faster.
What are aquaporins
Special channel proteins that allow facilitated diffusion of water through cell membrane.
What can diffuse thru
O2+CO2 because they’re small and non polar so they’re soluble in lipids and can dissolve hydrophobic bilayer.
Factors affecting rate of diffusion
- Conc gradient = higher - faster
- Thickness - thin = shorter
- Surface area = larger - faster
What do microvillis do
Increase surface area as they are folds of the cell surface membrane.
Polar
Can’t pass through - requires proteins and have a partially positive and negative charge.
Non polar
Can’t pass/ diffuse through bilayer
How can you investigate effect of solvents on permeability of cell membrane
Surround cells in increasing conc. if solvent increases membrane permeability because solvent dissolves the lipids in the cell membrane, causing it to lose structure
Effects of cholesterol
Fits between phospholipids and bind to hydrophobic tails, causing them to pack more closely. That restricts movement of phospholipids, making membrane less fluid and more rigid.
Maintains shake of animal cells.
Phospholipids
Head = hydrophilic - water lover
Tail = hydrophobic- water hater
Centre = hydrophobic. Membrane doesn’t allow water soluble substances through. Acts as a barrier.
Arranged in a bilayer- head out on either side
Some proteins have what attached
Polysaccharide chain (carbohydrate) called glycoproteins.
Some lipids gave what attached
Polysaccharide chain called glycolipids
Three features of cell surface membrane
Phillic head and phobic tail. String barrier from aqueous environment. Selective permeability.
Proteins intrinsic and extrinsic. Intrinsic span full plasma membrane surface. Channel and carrier.
Cholesterol- preventing water loss and limit lateral moving of membrane. Regulate membrane to have fluidity.
Barrier is
Partially permeable
Why fluid mosaic structure
Bilayer is fluid because phospholipids are always moving.
Proteins are scattered thru out bilayer like mosaic.
Include channel n carrier proteins.
Receptor proteins on cell surface membrane allow cell to detect chemicals released from other cells. Chemical signals cell to respond.
