(c) The McGraw-Hill Companies, Inc. Chapter 6 Biology Sixth Edition Raven/Johnson (c) The McGraw-Hill Companies, Inc.

Membranes Allows a cell to interact with its environment Delicate skin of proteins embedded in a thin sheet of lipid

Phospholipid Bilayer Membranes are only two molecules (not atoms) thick The lipid that makes up the membrane is a phospholipid

Hydrophilic polar heads lie on the outward-facing surfaces. Hydrophobic nonpolar tails extend to the interior. -a fluid consistency and a mosaic pattern of embedded proteins.

Components of the Cell Membrane Lipid Bilayer Transmembrane proteins Network of supporting fibers Exterior proteins and glycolipids

Figure 6.7

Non-Polar sections of protein force the molecule to stay within in the membrane. Polar ends extend on either side of membrane

A single nonpolar segment is adequate to anchor a protein Attach to the spectrin network of the cytoskeleton Receive signals

Channel and carrier proteins have several non-polar helical segments Allows passage of water soluble molecules or ions

Beta – pleated sheets form a large open tunnel Allows water and other materials to pass through

Movement from an area of high concentration to an area of low concentration Ion channels allow movement of ions by diffusion Most channels are specific only for a certain type of ion

Carriers transport ions as well as other solutes Physically binds with the solute Movement is determined by the concentration gradient 3 characteristics of facilitated diffusion 1. It is specific 2. It is passive 3. It saturates

Water molecules move through specialized channels called aquaporins along a concentration gradient Concentration of all solutes in a solution determines the osmotic concentration Cell membrane is a differentially permeable membrane

Bulk Passage Into and Out of the Cell Endocytosis – 3 types: Phagocytosis, Pinocytosis, and receptor-mediated endocytosis - brings items into the cell Exocytosis – discharges materials from the cell

Phagocytosis – particulate (solid) matter

Pinocytosis – material is liquid

Receptor-mediated endocytosis – specific molecules

Exocytosis – discharges material from the cell

Requires energy (ATP) Involves a highly selective carrier protein Moves substance against a concentration gradient

Works through a series of conformational changes – the first is energized by ATP (active transport) This process can occur up 100 times per second!

Moves protons against their gradient Down gradient – high  low concentration (no energy required) Up gradient – low  high concentration (energy required)

The Down gradient for Na+ is greater than the Up gradient for glucose Protein here is a symport – both items move in same direction Antiport – items move in opposite directions Na+/Ca++ (counter transport)

The End.