Biology Class 5

“Cell Surface and Cytoskeleton”_

Biology 5th Class

A. Cell Membrane Structure Cell membrane is a phospholipid bilayer embedded with mobile proteins. Types of membrane proteins • Transport Proteins – move substances across membrane • Cell Surface Proteins – establish “self” • Cellular Adhesion Molecules (CAMs) – enable cells to stick together • Receptor Proteins – transmit messages into a cell B. Movement across Membranes (selectively permeable) 1. Simple Diffusion (passive) - Substances move across phospholipids from high to low concentration, (no energy) OSMOSIS is the movement of WATER Water is driven to move because the membrane is impermeable to solute(s) 2. Facilitated Diffusion - Substance moves through a transport protein from high concentration to low concentration 3. Active Diffusion - Substance moves through a transport protein from low concentration to high concentration (requires energy). Substance moves against its concentration gradient 4. Exocytosis & Endocytosis - Movement of large particles across membranes with the help of vesicles. • •

Exocytosis – vesicles move particles OUT of the cells Endocytosis – vice/versa Three types of endocytosis 1. Pinocytosis – cell drinking (liquid) 2. Phagocytosis – cell eating (solid) 3. Receptor mediated endocytosis

C. Cytoskeleton The Structural framework of a cell 1. Microtubules – hollow, thick, elements made of the protein tubulin Functions: 1. move chromosomes apart during cell division 2. form cilia and flagella 2. Microfilaments – long, thin elements made of the protein actin Functions: 1. connect cells to each other 2. move vesicles and organelles within cytoplasm 3. help cells move D. Intercellular Junctions (connect cells of multicellular organisms to form tissues) 1. Animal Cell Connections Tight Junctions – cell membranes of adjacent cells are fused, creating a tight cell Gap Junctions – channels that allow exchange of materials 2. Plant Cell Connections Plasmodesmata – channels that link the cytoplasm of adjacent plant cells