chapter 6 biology sixth edition raven/johnson (c) the mcgraw-hill companies, inc
TRANSCRIPT
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Chapter 6
BiologySixth Edition
Raven/Johnson
(c) The McGraw-Hill Companies, Inc.
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Membranes
• Allows a cell to interact with its environment
• Delicate skin of proteins embedded in a thin sheet of lipid
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Phospholipid Bilayer• Membranes are only two molecules (not atoms)
thick• The lipid that makes up the membrane is a
phospholipid
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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.
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Components of the Cell Membrane• Lipid Bilayer• Transmembrane proteins• Network of supporting fibers• Exterior proteins and glycolipids
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Figure 6.7
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Non-Polar sections of protein force the molecule to stay within in the membrane.
Polar ends extend on either side of membrane
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A single nonpolar segment is adequate to anchor a protein
Attach to the spectrin network of the cytoskeleton
Receive signals
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Channel and carrier proteins have several non-polar helical segments
Allows passage of water soluble molecules or ions
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Beta – pleated sheets form a large open tunnel
Allows water and other materials to pass through
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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
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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
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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
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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
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Phagocytosis – particulate (solid) matter
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Pinocytosis – material is liquid
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Receptor-mediated endocytosis – specific molecules
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Exocytosis – discharges material from the cell
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Requires energy (ATP)
Involves a highly selective carrier protein
Moves substance against a concentration gradient
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Works through a series of conformational changes – the first is energized by ATP
(active transport)
This process can occur up 100 times per second!
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Moves protons against their gradient
Down gradient – high low concentration (no energy required)
Up gradient – low high concentration (energy required)
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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)
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The End.