Transport Mechanism Lesson PDF

TRANSPORT MECHANISM  CELL MEMBRANE ALL cells have a cell membrane made of proteins and lipids SOME cells have cell membranes and cell walls – ex: plants, fungi and bacteria Plant cells have a cell wall made of cellulose – that cellulose is fiber in our diet...

TRANSPORT MECHANISM  CELL MEMBRANE ALL cells have a cell membrane made of proteins and lipids SOME cells have cell membranes and cell walls – ex: plants, fungi and bacteria Plant cells have a cell wall made of cellulose – that cellulose is fiber in our diet Bacteria and fungi also have cell walls, but they do not contain cellulose Cell membranes and cell walls are porous allowing water, carbon dioxide, oxygen and nutrients to pass through easily  CELL MEMBRANE Function: Cell membrane separates the components of a cell from its environment—surrounds the cell “Gatekeeper” of the cell—regulates the flow of materials into and out of cell—selectively permeable Cell membrane helps cells maintain homeostasis—stable internal balance  TRANSPORT MECHANISM PASSIVE TRANSPORT ACTIVE TRANSPORT DIFFUSION PUMP VESICLE OSMOSIS ENDOCYTOSIS FACILITATED DIFFUSION ENDOCYTOSIS  PASSIVE TRANSPORT Moves along concentration gradient Molecules move from higher concentration to lower concentration Doesn't require energy for molecules to move  SIMPLE DIFFUSION Diffusion is the movement of small particles across a selectively permeable membrane like the cell membrane until equilibrium is reached. Moves easily without regulation due to small size of molecules No change in concentration  OSMOSIS Osmosis is the diffusion of water through a selectively permeable membrane like the cell membrane Water diffuses across a membrane from an area of high concentration to an area of low concentration.  CELL OSMOSIS ISOTONIC contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.  CELL OSMOSIS HYPERTONIC contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrink (plasmolysis).  CELL OSMOSIS HYPOTONIC contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode. FACILITATED DIFFUSION is the movement of larger molecules like glucose through the cell membrane – larger molecules must be “helped” Proteins in the cell membrane form channels for large molecules to pass through Proteins that form channels (pores) are called protein channels Molecules can only pass through the cell membrane with the help of transport proteins.  ACTIVE TRANSPORT Active transport is the movement of molecules from LOW to HIGH concentration. Energy is required as molecules must be pumped against the concentration gradient. Proteins that work as pumps are called protein pumps. Transport proteins are specific to the type of molecules they can transport across cell membrane. Rate of transport is at maximum when all membrane transport proteins are all used up. Transport proteins are sensitive to inhibitors. SODIUM-POTASSIUM PUMP is a protein in the cell used to regulate Na+ and K+ gradients across the membrane. As gradients change, cells can produce electrical signals. The pump pushes three Na+ to the outside of the cell for every two K+ that are pushed inside the cell. This results in a higher concentration of Na+ outside the cell and a larger concentration of K+ inside the cell. The role of Na,K-ATPase is to regulate the Na+ and K+ levels across the cell membrane. SODIUM-POTASSIUM PUMP  ENDOCYTOSIS Cell membrane bends inward to form vesicles containing the macromolecule to be transported. The cell engulfs particles into a pouch formed by the in folding of the cell membrane. The resulting pouch is then pinched off from the plasma membrane and forms a vesicle inside the cell. This vesicle then fuses with a lysosome which contains enzymes that will break and digest the engulfed particles before these are released into the cytoplasm.  TYPES OF ENDOCYTOSIS PHAGOCYTOSIS Also called as “cell-eating”. The cell engulfs solid particles into much larger vesicles, sometimes called vacuoles. Many unicellular organisms, including protozoans, obtain food through phagocytosis. In human, neutrophils and monocytes- two types of white blood cells- specialize in phagocytosis. Both engulf and destroy unwanted cells and materials inside the body.  TYPES OF ENDOCYTOSIS PINOCYTOSIS Also called as “cell-drinking”. It is similar to phagocytosis except that the cell engulfs droplets of fluid instead of solid particles, also forming large vacuoles within it. This is one mechanisms by which cells maintain water balance.  EXOCYTOSIS is the reverse of endocytosis. Wastes and cell products inside the cell are packaged in Golgi vesicles which then fuse with the cell membrane to be transported out of the cell. Like endocytosis, exocytosis is an equally important process for the cell to maintain a stable internal environment.