Zusammenfassung der Ressource
Cell Membrane
- Membranes
- All cells surrounded by membranes
- In eukaryotics surrounds some organelles too
- Acts as a barrier to control what enters or leaves
- Partially permeable - allows some molecules through
- Can move through by diffusion, osmosis or active transport
- Fluid mosaic model
- Composed of lipids, proteins, carbohydrates
- Phospholipids form a continuous bilayer
- Bilayer is fluid as it moves continuously
- Cholesterol are present in the membrane
- Proteins scattered throughtout like a mosaic
- Polysaccharides can attach to proteins and lipids
- Glycolipid, Glycoprotein
- Different components play different roles
- Phospholipids form a barrier to dissolved substances
- As hydrophobic centre of bilayer repels water
- Cholesterol provides stability
- Cholesterol is present in all cell membranes except bacteria
- Does this by binding between phospholipids to the hydrophobic tails
- Causes them to pack closer together, restricting movement making it more ridgid
- Important for animal cells with no cell wall
- Important for RBC that arent supported by other cells
- Proteins in membranes have many functions
- Include channel proteins, carrier proteins, and receptor proteins
- Permeability test
- Changing temperature changes the membrane permeability
- Below 0
- Phospholipids pack close together and become rigid
- Channel and carrier proteins deform, increasing permeablility
- Any ice that forms can pierce the membrane causing very high permeablility
- 0-45 celsius
- Phospholipids move around and the higher the temp the more permeable it is
- Above 45
- Bilayer starts to melt
- Water expands, puts pressure on membrane
- Proteins deform increasing permeability of cell membrane
- Simple Diffusion
- Net movement of particles, molecules, or ions from an area of high to low conc down its conc gradient
- Can diffuse across membranes as long as they can move freely through the membrane
- When diffusion directly across a membrane its called simple diffusion
- Higher conc gradient the faster the rate of diffusion
- Microvilli increase surface area for faster diffusion
- Passive process - no energy used
- Osmosis
- Net Diffusion of water molecules across a partially permeable membrane
- From an area of high water potential to low water potential
- Water potential (WP) is likelihood of water molecules to diffuse in or out of a solution
- Equal WP of solution said to be isotonic
- Rate depends on factors
- WP gradient, Higher gradient, faster conc
- As solutions undergo osmosis, difference in WP decreases
- Rate of osmosis levels off over time
- Thickness of exchanged surface
- Thinner the osmosis path the faster rate of osmosis
- Surface area of exchange surface
- Larger S.A. the higher rate of osmosis
- Investigating WP Using serial Dilutions
- Make five serial dilutions of sucrose solution by a known factor
- Add identical potato cylinders in solutions
- After 20 mins, dry chips and weight each chip
- Calculate the % change in mass
- Net movement of water from a less negative WP to a more negative WP
- Active Transport (AT)
- Active process - uses energy in form of ATP
- Usually movement of molecules and ions against a conc gradient
- Carrier proteins used to move molecules from low to high conc
- Molecule attaches to protein, causing it to change shape, moving molecule across membrane
- Co-transporters are a type of carrier protein used in AT
- Bind two molecules at a time
- High to Low conc gradient used for one of the molecules used to move the other one against its conc gradient
- Facilitated Diffusion
- Passive
- Large molecules, ions, and polar molecules diffuse slowly across membranes
- Number of Channel and carrier proteins increase rate of diffusion of these molecules/ions
- Higher conc gradient the faster the rate of diffusion