Objectives Identify the different membrane proteins and know their functions Understand the arrangement of how proteins are oriented in the lipid bilayer
How are the Proteins Oriented? Arrangement of molecules on one side of the membrane differs from that on the other side – Asymmetrical Peripheral proteins: positioned at the surface of the membrane Integral proteins: span the lipid bilayer, with their hydrophilic domains extending past both surfaces
What Are Their Functions? Transport Proteins: passively allow water- soluble substances to move through their interior, which opens on both sides of bilayer – Passive and active transport proteins
What Are Their Functions? Passive Transporters – Integral membrane proteins that do not require energy to function – Have channel through interior – Assist solutes or water by letting them diffuse through channel, down concentration or electrical gradients – Gated channels
What Are Their Functions? Active Transport – Integral membrane proteins that use ATP to pump substances across the membrane – Pump solute across membrane to side where it is more concentrated and less likely to move on its own
What Are Their Functions? Receptor Proteins: have binding sites for hormones (and like substances) that can trigger changes in cell action, as in growth process – Signal might make a cell synthesize a certain protein, block or speed up a reaction, secrete a substance, or get ready o divide – Like an antenna
What Are Their Functions? Recognition Proteins: identify the cell as a certain type, help guide cells into becoming tissues, and function in cell-to-cell recognition and coordination – Certain glycoproteins and glycolipids – Project above plasma membrane and identify cell
What Are Their Functions? Adhesion Proteins: glycoproteins that help cells stay connected to one another in a tissue – Embedded in plasma membrane – Ex. Collagen; part of extracellular matrix
What Are Their Functions? Communication Proteins: form channels that match up across the plasma membranes of two cells – Let signals and substances rapidly flow from cytoplasm of one into the other – Chemical and electrical signals – Gap junctions
What Are Their Functions? Enzymes: often peripheral membrane proteins that function to accelerate reactions without being changed themselves
Review 1.What is the difference between a peripheral and integral protein? 2.What is the difference between active and passive transport proteins? 3.What is the name of the protein that projects above the plasma membrane and identifies the cell?
Answers 1.Peripheral proteins are positioned at the surface of the membrane. Integral proteins span the lipid bilayer, with their hydrophilic domains extending past both surfaces. 2.Passive transport proteins are integral membrane proteins that do not require energy to function, move from areas of high concentration to low concentration. Active transport proteins are integral membrane proteins that use energy to pump substances across the membrane, move from areas of low concentration to high concentration. 3.Recognition proteins.