Table 5-1, p. 80

Energy In, Energy Out Chemical reactions –Reactants (molecules in) –Products (molecules out) Endergonic reactions (energy-requiring) –Photosynthesis Exergonic reactions (energy-releasing) –Aerobic respiration

Fig. 5-3, p. 74 Exergonic reactions, such as aerobic respiration, end with a net output of energy. Such reactions help cells access energy stored in chemical bonds of reactants. glucose (C 6 H 12 O 6 ) + 6 O 2 6 CO H 2 O energy in energy out Endergonic reactions, such as photosynthesis, proceed only with a net input of energy. Cells can store energy in the products of such reactions.

Fig. 5-4, p. 75 ENERGY OUT With each conversion, there is a one-way flow of a bit of energy back to the environment. Nutrients cycle between producers and consumers. NUTRIENT CYCLING producers consumers ENERGY OUT Energy continually flows from the sun. ENERGY IN Sunlight energy reaches environments on Earth. Producers of nearly all ecosystems secure some and convert it to stored forms of energy. They and all other organisms convert stored energy to forms that can drive cellular work.

Fig. 5-12, p. 80

Enzymes in Metabolism Activation energy –Minimum energy needed to start a reaction Enzymes are catalysts –Speed reaction rates by lowering activation energy –Most are proteins

Fig. 5-6, p. 76 activation energy with enzyme Time Energy starting substances: glucose and phosphate activation energy without enzyme product: glucose-6-phosphate

Fig. 5-27, p. 89

Enzyme Action How enzymes lower activation energy –By concentrating substrate molecules –By orienting substrates to favor reaction –By inducing fit between substrate and active site –By excluding water from active site

Fig. 5-8, p. 78 active site altered, substrate can bind allosteric activator allosteric binding site vacant enzyme active site substrate cannot bind X X active site altered, can’t bind substrate allosteric binding site vacant; active site can bind substrate allosteric inhibitor

Fig. 5-10, p. 79

Fig. 5-11, p. 79

Diffusion –Net movement of molecules to a region where they are less concentrated Diffusion rates are influenced by: –Temperature –Molecular size –Gradients of pressure, charge, and concentration

Fig. 5-16, p. 82 water dye

Fig. 5-17, p. 83 Glucose and other large, polar, water-soluble molecules, and ions (e.g., H +, Na +, K +, Cl –, Ca ++ ) cannot cross on their own. lipid bilayer Oxygen, carbon dioxide, small nonpolar molecules, and some molecules of water cross a lipid bilayer freely.

Fig. 5-18, p. 84

Working With and Against Gradients Many solutes cross membranes through transport proteins (open or gated channels) Facilitated diffusion (passive transport) does not require energy input –Solute diffuses down its concentration gradient through a transporter –Example: Glucose transporters

Fig. 5-19, p. 85

Fig. 5-21, p. 86 The fluid volume rises in the second compartment as water follows its concentration gradient and diffuses into it. hypotonic solution in first compartment hypertonic solution in second compartment Initially, the volumes of the two compartments are equal, but the solute concentration across the membrane differs.

Which Way Will Water Move? Osmosis –The diffusion of water across a selectively permeable membrane –Water molecules follow their concentration gradient, influenced by solute concentration

Tonicity Relative concentrations of two solutes separated by a semipermeable membrane –Hypertonic fluid (higher solute concentration) –Hypotonic fluid (lower solute concentration) –Isotonic solutions (two solutions with the same tonicity)

Fig. 5-22, p liter of 10% sucrose solution 2% sucrose solution 1 liter of distilled water 1 liter of 2% sucrose solution

Fig. 5-23, p. 87

Active Transport Active transporters require ATP energy to move a solute against its concentration gradient –Maintain gradients across cell membranes –Example: Calcium pumps

Fig. 5-20, p. 86 An ATP molecule binds to a calcium pump. higher concentration of calcium ions outside cell compared to inside calcium pump The shape of the pump returns to its resting position.

Membrane Traffic To and From the Cell Surface Exocytosis –Cytoplasmic vesicle fuses with plasma membrane –Contents are released outside Endocytosis –Part of plasma membrane forms a vesicle that sinks into the cytoplasm

Endocytosis and Exocytosis

Phagocytosis