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