Chapter 7-Membrane structure and function.
Biology-1406
Chapter-7
Membrane Structure and Function
Every cell is surrounded by a cell or plasma membrane.
Think of this membrane as a gatekeeper, allowing only specific substances to enter and leave the cell
Functions of the Cell Membrane
To isolate the cells contents from the external environment
To regulate the exchange of substances entering and leaving the cell
Communicate with other cells
Structure of the Cell (Plasma)
Membrane
Fluid Mosaic Model-according to this, the cell or plasma membrane is composed of proteins floating in a fluid double layer of phospholipids.
Materials move in and out of the cell by several different methods:
Diffusion- the movement of a substance from an area of high concentration to an area of low concentration.
Osmosis- the movement of water across a selectively permeable membrane from an area of high concentration to an area of low concentration.
The following terms apply to Osmosis.
Hypertonic- when the concentration of solute is greater outside the cell than inside the cell. Water will leave the cell in this situation.
Hypotonic-this is when the concentration of solute is less outside the cell than inside the cell. Water will enter the cell in this situation.
Isotonic- this is when the concentration of solute outside and inside the cell are the same.Water will enter and leave the cell at the same rate in this situation.
Moving Substances Into and Out of the Cell
Facilitated Diffusion- the movement of a substance across the plasma membrane from an area of high concentration to an area of low concentration with the help of a carrier protein molecule.
Active Transport- the movement of a substance from an area of low concentration to an area of high concentration. This requires energy (ATP). An example of this is the Sodium-Potassium Pump.
Sodium-Potassium Pump
This cellular pump moves sodium ions from an area of low concentration (inside your cells) to an area of high concentration (outside your cells) and at the same time moves potassium ions from an area of low concentration (outside your cells) to an area of high concentration (inside your cells). ATP is required to do this.
Transporting of larger molecules
The movement of larger molecules (such as proteins and sugars) into and out of the cell involves two processes.
Exocytosis- the cellular secretion (leaving the cell) of large molecules by the fusion of vesicles with the plasma membrane.
Endocytosis- the cellular uptake of large molecules by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.
Types of Endocytosis
Phagocytosis- cellular eating
Pinocytosis- cellular drinking
Receptor mediated endocytosis- in this situation protein receptors that line the plasma membrane pick up particles that are to be transported into the cell.
