文档介绍：Chapter 2 Basic Functions of Cells
Cells are the structural and functional basic units of all anisms.
Cell structure:
–Cell Membrane: permeability barrier.
–Cytoplasm: organelles in cytoplasm.
–Nucleus: ic substance like DNA.
Section 1 Structure of Cell Membrane and Membrane Transport
1. Membranous Structure
Composition:
proteins-55%
phospholipids-25%
cholesterol-13%
other lipids-4%
carbohydrates-3%
The fluid mosaic model is used to elucidate the structure of membrane, which was first expounded by Singer and Nicholson in 1972.
(1) Lipid Bilayer
The basic lipid bilayer posed of phospholipids molecules which are amphipathic molecules. One end of each phospholipid has a charged region and is hydrophilic. The other end consists of two long fatty acid chains and is hydrophobic. The phospholipids in cell membranes anized into a bimolecular layer with the hydrophobic fatty acid chains in the middle.
(2) Membrane Proteins
two types: integral and peripheral
Integral proteins protrude all the way through the membrane. Some integral proteins called carrier, channel or ion pump mediate transporting substances cross the cell membrane.
Peripheral proteins are attached only to integrate proteins of one surface of the membrane and do not rate. Their function is almost entirely as receptor, enzymes, antigen or as other types.
(3) Membrane Carbohydrates
Carbohydrate covalently linked to some of the membrane lipids and proteins as glycoprotein and glycolipid locating on the outside of the membrane.
Act as recognition factor (ABO blood group) or receptor.
2. Transport of Substances through the Cell Membrane
Diffusion: Diffusion refers to the process by which molecules intermingle as a result of their ic energy of random motion. flux always proceeds from the region of higher concentration to the region of lower concentration.
(1) Simple Diffusion
–A simple physical diffusion of small hydrophobic molecules that can do this by themselves,such as O2, CO2, eth