1. Proteins and The Cell Membrane Unit 5: Homeostasis and Cell Transport

2. Do you know the functions of these proteins associated with the cell membrane? Transporters Channel Protein Carrier Protein Enzymes Cell Surface Receptors = Receptor Protein Cell Surface Identity Markers = Cell Recognition Protein Attachments to Cytoskeleton = Junction Protein

3. Transporters Channel Protein  Involved in the passage of molecules through the membrane  Facilitated Diffusion uses channel proteins Carrier Protein  Combine with a substance to help move it across the membrane.  Ion Pumps are carrier proteins.

4. Enzymes Enzyme Proteins are embedded in the membrane and catalyze specific reactions. ATP synthase is an enzyme embedded in the inner mitochondrial membrane as well as the thylakoid membrane of the chloroplast. Adenylate cyclase is an enzyme involved in ATP metabolism. Cholera bacteria release a toxin that interferes with the functioning of this enzyme resulting in Na+ and water leaving intestinal cells. Individuals may die from severe diarrhea.

5. Receptor Proteins Receptor Proteins have specific shapes that can only bind to specific molecules. Receptor Proteins receive signals when the molecules bind with them. Pygmies are short, not because they do not produce enough growth hormone, but because their plasma membrane growth hormone receptors are faulty and cannot interact with growth hormone.

6. Identity Markers = Cell Recognition Proteins Glycoproteins enable cells of multicellular organisms to recognize each other. The HMC (major histocompatibility complex) glycoproteins are different for each person, so organ transplants are difficult to achieve. Cells with foreign HMC glycoproteins are attacked by white blood cells responsible for immunity.

7. Attachments to Cytoskeleton = Junction Proteins Cells within multicellular organisms are part of tissues. Junction proteins join cells so that a tissue can fulfill a function. Junction proteins help attach cells to neighboring cells and to the cytoskeleton of each cell. The nervous system of animal embryos rely upon the junction proteins during development. The junction proteins help pinch off to form neural tube!

8. Summing it all up! Which proteins embedded within the cell membrane catalyze specific chemical reactions? Which proteins are responsible for cells receiving signals from other cells? Which proteins are involved with the major histocompatibility complex? Which proteins join cells together to form tissues? Which proteins act as ion pumps? Which proteins enable substances to diffuse through the cell membrane?