Membrane Structure- Fluid Mosaic Model.
A membrane structure seperates a cell from its external environment.
It's on the out side of every cell.
It's made of a phospholipid bilayer, in which proteins are.
Parts of a Cell Membrane
- Phospholipids- Act as a barrier to most molecules.
- Glycoproteins and Glycoproteins- Involved in cell recognition and cell attachments.
- Integral Proteins- Transport molecules across the membrane or catalyse reactions.
- Cholesterol- Helps control membrane fluidity.
Functions of a Cell Membrane
- Control what goes in and out of the cell.
- Separate compartments with in the cell.
- Important in cell signalling.
- Allow electrical signal to pass through.
- Provide attachments to enzymes and other molecules involved in metabolism.
- Provides support for cells.
- Allow recognition by other cells- Antigens.
Cell Membranes use in Cell Signalling
- Help cell to react to changes in the environment by picking up signals at the surface- they coordinate hormones and impulses.
- Let ions through channels into and out of the cells.
- The receptors in the cell react with G-proteins which activates an enzyme causing a reaction inside the cell.
- The third is a receptor- enzyme which is made up of 2 parts. The reactor cell slots its self between them and it becomes an enzyme forcing a chemical reaction.
- Moves from a low to a high concentration.
- Carried out by transporter proteins in the plasma membranes.
- Active transport is used to change the shape of transporter proteins.
- It's used where we need Potassium and need less Sodium but it's going against the concentration gradient to take it in and out of our cells.
- Particles move from a high to a low concentration.
- Result of random movement.
- Substance has free moving particles , there movement will be down the concentration gradient.
- This is how particles move when they're being sprayed form an aerosol.
- Facilitated diffusion uses carrier proteins.
- Only water can be moved by osmosis.
- It must be across a partially permeable membrane.
- Moves from a High water potential to a Low water potential.
- Water moves in and out of a plant cell to make them turgid and give them support.
- Process of moving a substance into a cell through the cell membrane.
- Active process which requires energy.
- Puts out fingers of cytoplasm around the substance, creating a ring (vesticle.) Enzymes are sent out from the vacuole to digest the vesticle and then the substance is absorbed into the cytoplasm.
- Substances produced with in the cell need to be released from cell.
- Opposite to Endocytosis.
- Vesticle surrounds what needs to be moved out cell. Once in the vesticle it moves up the microtubles.
- It then fuses with the with the plasma membrane and empties out of the cell.
- Water diluted in a solution can move more easily than water in a concentrated solution.
- Pure water has a water potential of 0kPa
- Therefore water in a solution has a negative water potential because it moves more freely.
- A dilute solution will be less negative (-100kPa) than a more concentrated solution (-300kPa)
- Hypotonic:- A high water potential (less negative)
- Isotonic:- Same water potential (0)
- Hypertonic:- A low water potential (more negative)