1. What is energy? Energy: capacity to do work – Potential energy (Example: chemical bonds) – Kinetic energy (Energy of motion)

2. Two Laws of Thermodynamics 1. Energy cannot be created or destroyed –It can be converted from one form to another and transferred between objects or systems 2. Entropy tends to increase –Energy tends to disperse spontaneously –Some energy disperses at each energy transfer, usually in the form of heat

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

4. Energy Flows in One Direction Energy is not cycled –In from the sun; into and out of ecosystems All living things harvest external energy –Producers and consumers use energy to assemble, rearrange, and dispose of substances Substances cycle among organisms over time

5. What is ATP? Adenosine triphosphate (ATP) –Main energy carrier between cell reaction sites –Currency of the cell Phosphorylation –Phosphate-groups transfer to and from ATP –Couple metabolic reactions that release usable energy to metabolic reactions

6. What enzymes do? Enzymes are catalysts –Speed reaction rates by lowering activation energy –Proteins in nature Activation energy –Minimum energy needed to start a reaction Each enzyme functions best within a characteristic range of temperature, salt concentration, and pH

7. How enzymes work? Active site –Small cleft in enzyme’s surface where reactions occur How enzymes lower activation energy –concentrating substrate molecules –orienting substrates to favor reaction –inducing fit between substrate and active site –excluding water from active site Activation energy allows enzyme to react with substrate.

8. What are cofactors? Most enzymes require assistance of cofactors –Inorganic metal ions –Organic coenzymes (vitamins) Example: Catalase (Antioxidant) –Cofactor: Iron

9. Metabolic pathways Cells concentrate, convert, and dispose of most substances in orderly, enzyme-mediated reaction sequences Biosynthetic pathways –Construct large molecules from smaller ones –Require energy Photosynthesis –Main biosynthetic pathway in the biosphere –Autotrophs

10. Degradative pathways –Break down molecules to smaller products –Release usable energy Aerobic respiration –Main degradative pathway in the biosphere –Heterotrophs Oxidation–reduction (redox) reactions –Electron transfers used in metabolic pathways

11. How substances cross membranes? Diffusion –process by which molecules intermingle as a result of their energy of motion Passive –facilitated diffusion, solute moves down its concentration gradient and no energy input is required. Active Transport –Active transport uses energy to move a solute "uphill" against its gradient,

12. What is diffusion? Diffusion –Net movement of molecules to a region where they are less concentrated Number of atoms or molecules in a given volume Diffusion rates are influenced by: –Temperature –Molecular size –Gradients of pressure, charge, and concentration –Selective Permeability

13. What is facilitated diffusion? 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

14. What is active transport? Active transporters require ATP energy to move a solute against its concentration gradient –Maintain gradients across cell membranes –Example: Calcium pumps

15. What are endocytosis and exocytosis? Exocytosis –Cytoplasmic vesicle fuses with plasma membrane –Contents are released outside Endocytosis –Part of plasma membrane forms a vesicle that sinks into the cytoplasm

16. Three types of endocytosis Receptor-mediated endocytosis –Substance binds to surface receptors –Pit forms endocytotic vesicle Phagocytosis (“cell eating”) –Amoebas use pseudopods to engulf prey Bulk-phase endocytosis –Vesicle forms around extracellular fluid

17. 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

18. What is 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)