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MOLECULES TRANSPORT VIA CELL MEMBRANE by DESSY C. SIANTURI, M.Si. MGMP BIO SMAN3 MEDAN.
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MOLECULES TRANSPORT VIA CELL MEMBRANEbyDESSY C. SIANTURI, M.Si.MGMP BIO SMAN3 MEDAN
A cell is separated from its environment by a selectively permeable plasma membrane. The plasma membrane is commonly described as a fluid mosaic. It is like a mosaic in having diverse protein molecules embedded in a matrix of phospholipids. Its component proteins and phospholipid molecules can move about, so it is quite fluid and flexible. The phospholipids in a membrane form a two-layer framework called a phospholipid bilayer. The steroid cholesterol helps stabilize the phospholipids. Carbohydrate molecules are attached to some of the molecules that make up the membrane.
PLASMA MEMBRANE REGULATE THE MOLECULE THAT CAN PASS THROUGH INTO OR OUT OF CELLTHE MOLECULE THROUGH VIA THE PHOSPHOLIPIDS OR VIA THE PROTEIN INTEGRATED BETWEEN PHOSPHOLIPIDS
The plasma membrane is selectively permeable-- it lets some substances through and not others. The hydrophobic interior of the bilayer is one reason membranes are selectively permeable. Hydrophobic molecules-- those that are soluble in lipids-- can easily pass through the membrane. In addition, small molecules like water and O2 can sneak between the phospholipids of the membrane. On the other hand, large hydrophilic molecules like glucose, and ions such as sodium ions and hydrogen ions, cannot pass through the membrane.
THE KINDS OF MOLECULES TRANSPORT VIA CELL MEMBRANE :1. PASSIVE TRANSPORTA. SOLUTE DIFFUSION B. OSMOSIS ( WATER DIFFUSION) C. FACILITATED DIFFUSION2. ACTIVE TRANSPORTA. PROTON PUMP B. Na/K PUMP3. ENDOCYTOSIS & EXOCYTOSIS
Diffusion is the tendency for particles of any kind to spread out from where they are more concentrated to where they are less concentrated. This process can also be described as molecules moving down their concentration gradient.
Diffusion across a biological membrane is called passive transport, since the cell expends no energy is to move the molecules. Oxygen and carbon dioxide molecules move into and out of cells by passive transport.
THE EFFECT OF HYPEROSMOSIS FOR PLANT & ANIMAL CELL1. PLASMOLISIS
If a membrane is permeable to water, what happens when a solute cannot pass through the membrane? Experiment by dragging glucose molecules inside the cell, outside the cell, or both. Try different concentrations of glucose on each side. Before you run each experiment, predict which way water will diffuse and what will happen to the cell. Proteins embedded in the membrane play a key role in selective permeability. For example, this transport protein spans the membrane and provides a "doorway" through which a particular solute (the red triangles) can diffuse down its concentration gradient. This process is called facilitated diffusion. Facilitated diffusion is a type of passive transport, since the molecules are diffusing through the membrane and the cell expends no energy to move them.
