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MEMBRANES, DIFFUSION, OSMOSIS, ACTIVE TRANSPORT, ETC.
CHAPTER 9 MEMBRANES, DIFFUSION, OSMOSIS, ACTIVE TRANSPORT, ETC.
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MEMBRANE STRUCTURE AND FUNCTION
Membranes organize the chemical activities of cells Membranes organize the chemical reactions making up metabolism Cytoplasm
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Membranes are selectively permeable
They control the flow of substances into and out of a cell Membranes can hold teams of enzymes that function in metabolism
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Membrane phospholipids form a bilayer
Head Phospholipids are the main structural components of membranes They each have a hydrophilic head and two hydrophobic tails Symbol Tails
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In water, phospholipids form a stable bilayer
The heads face outward and the tails face inward Water Hydrophilic heads Hydrophobic tails Water
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The membrane is a fluid mosaic of phospholipids and proteins
Phospholipid molecules form a flexible bilayer Cholesterol and protein molecules are embedded in it Carbohydrates act as cell identification tags
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The plasma membrane of an animal cell
Glycoprotein Carbohydrate (of glycoprotein) Fibers of the extracellular matrix Glycolipid Phospholipid Cholesterol Microfilaments of the cytoskeleton Proteins CYTOPLASM
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Proteins make the membrane a mosaic of function
Some membrane proteins form cell junctions Others transport substances across the membrane Transport
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Many membrane proteins are enzymes
Some proteins function as receptors for chemical messages from other cells The binding of a messenger to a receptor may trigger signal transduction Messenger molecule Receptor Activated molecule Enzyme activity Signal transduction
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Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell They spread from areas of high concentration to areas of lower concentration Molecule of dye Membrane EQUILIBRIUM EQUILIBRIUM
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Solute molecule with cluster of water molecules
Osmosis is the passive transport of water Hypotonic solution Hypertonic solution In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Selectively permeable membrane Solute molecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectively permeable membrane Solute molecule with cluster of water molecules NET FLOW OF WATER
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Water balance between cells and their surroundings is crucial to organisms
Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution The control of water balance (osmoregulation) is essential for organisms ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION ANIMAL CELL (1) Normal (2) Lysing (3) Shriveled Plasma membrane PLANT CELL (4) Flaccid (5) Turgid (6) Shriveled
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Transport proteins facilitate diffusion across membranes
Small nonpolar molecules diffuse freely through the phospholipid bilayer Many other kinds of molecules pass through selective protein pores by facilitated diffusion Solute molecule Transport protein
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Cells expend energy for active transport
Transport proteins can move solutes across a membrane against a concentration gradient This is called active transport Active transport requires ATP
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Active transport in two solutes across a membrane
FLUID OUTSIDE CELL Phosphorylated transport protein Active transport in two solutes across a membrane Transport protein First solute 1 First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell Second solute 4 Second solute binds to protein 5 Phosphate detaches from protein 6 Protein releases second solute into cell
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Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a membrane a vesicle may fuse with the membrane and expel its contents (exocytosis) FLUID OUTSIDE CELL CYTOPLASM
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or the membrane may fold inward, trapping material from the outside (endocytosis)
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Material bound to receptor proteins
Three kinds of endocytosis Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm
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Connection: Faulty membranes can overload the blood with cholesterol
Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors Phospholipid outer layer LDL PARTICLE Receptor protein Protein Cholesterol Plasma membrane Vesicle CYTOPLASM
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Chloroplasts and mitochondria make energy available for cellular work
Enzymes and membranes are central to the processes that make energy available to the cell Chloroplasts carry out photosynthesis, using solar energy to produce glucose and oxygen from carbon dioxide and water Mitochondria consume oxygen in cellular respiration, using the energy stored in glucose to make ATP
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Chemicals recycle among living organisms and their environment
Sunlight energy Nearly all the chemical energy that organisms use comes ultimately from sunlight Chloroplasts, site of photosynthesis CO2 + H2O Glucose + O2 Mitochondria sites of cellular respiration Chemicals recycle among living organisms and their environment (for cellular work) Heat energy
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