- pripary component of mambrane
- composed of two layers of phospholipids
- give the membrane its fluid nature
- prevent the entry of most hydrophilic substances
- Hydrophobic molecules can pass freely and very small hydrophilic molecules.
- Limits the passage of some small molecules
- Help to stabilize the phospholipids
- Help maintain membrane fuidity and strucutre
- 2 types of membrane proteins
- Integral proteins: attached to the hydrophobic interior of the bilayer
- Peripheral proteins: lie on the either side of the membrane but are not attached to the interior
Functions of membrane proteins
- Structural support: attached to cytoskeleton
- Recognition: to immune system that its own
- Communication: receptor proteins
- Transport: channels in/out the cell
- Outer layer of short carbohydrate chains that are attached to membrane proteins or phospholipids
- The chains are binding sites for signaling molecules
- Serves to lubricate teh cells
- Acts as an adhesion layer between cells
The fluid-mosaic model
- Plasma membrane is more fluid than solid
- The plasma membrane is made of variety of micromolecules
- Most of the proteins and phospholipid molecules can drift laterally whithin the membrane
movement of molecules or ions from a region of their higher concetnration to a region of lower concetration.
the diference between the highest and lowest concentration of a solute within a given medium
Diffusion throught membranes
- Plasma membranse are semipermeable
- -Water can move freely though but many solutes cannot
- net movement of water across a semipermeable membrane form an area of lower solute concentration to an area of higher solute concentration.
- Concentration of water will depend on solute concentration
- Once the salt is added to right bicker of water, the left side is just pure water and therefore more concentrated comparing to right bicker of water, so it startes moving down its concetration gradient
Osmosis and cells
- Osmosis takes place across the plasma membrane all the time
- When osmotic imbalance occurs, cells are at risk of either drying out or flooding
- Plant cells are protected from overflooding by the cell wall by setting up a pressure level that keeps more water from coming in.
- Turgid state - a nice, crisp plant
- Flaccid- droppy plant, has lost its pressure, the expansion of a cell wall.
the concetration of solute both inside and outside the cell are equal
- the concentration of solute outside of the cell is lower than inside the cell.
- - cell will gain water
- the concentration of solute outside of the cell is higher than inside the cell
- a cell will lose water
- Solutes usually can't pass through the semipermeable membrane, but water can
- Water will move to where the solute is more concentrated
- A high concentration of solute means there is less water present
- A low concentration of solute means there is more water present
Transport in and out of the cell
- Active transport: - require the expenditure of energy
- Passive transport: - doesn't require expenditure of energy
- -1. Simple diffusion
- -2. Facilitated Diffusion
- A form of passive trasport - Molecules move in/out, by simple diffusion no energy required, no special protein channel required.
- - Small molecules, like O(in) and CO2(out of the cell)
- - Fat solubles, like hormones
- Molecules move down their concentration gradient
- Passage of paterials in/out the plasma membrane with help of transport proteins.
- ex. amino acids, sugar
- Each transport protein binds to a spacific type of molecule, changes its shape, exposing molecule to the inside or outside of the cell, as its released it gets back to its original shape.
- Moleculs move down their concentration gradient
Uses the same kind of shape-changing transport protein channels as in passive transport but with an addition of an energy source, so that things can move against their concentration gradient
A transport vesicle fuses with the plasma membrane and relsease its contents outside of the cell
- Large materials are moved into cells by an infolding of the plasma membrane
- Two major types: pinocytosis and phagocytosis
- Cell-surface receptors bind with molecules to be taken into the cell
- A depression forms in the cell membrane and then folds inward
- A vesicle forms and delivers the molecules to the inside of the cell
- The cell sends out extensions of its plasma membrane to surround the material
- The ends fuse together and enclose the material in a vesicle
- Lysosomes fuse with the vesicle and digest its contents