Energy – the ability to do work or bring about a change Cells need energy to maintain their organization

1. Energy – the ability to do work or bring about a change • Cells need energy to maintain their organization • Cells need energy to carry out reactions used to grow, develop, and reproduce

2. Forms of energy: • Kinetic energy – energy of motion • Ex: you raise your arm • Potential energy – stored energy; capable of producing energy, but not being used yet • Ex: food we eat has potential energy • Chemical energy – composed or organic molecules such as carbohydrates • Ex: food we eat, ATP

3. First law of thermodynamics (the law of conservation of energy) – energy cannot be created or destroyed, but it can be changed from one form to another • Energy flows; it does not cycle • As materials change from one form of energy to another, some energy is given off as heat (a form of energy)

4. Second law of thermodynamics – energy cannot be changed from one form to another without a loss of usable energy • Heat given off through the conversion of chemical energy to kinetic energy is not a usable form of energy • For this reason, living things are dependent upon an outside source of energy – the sun

5. Metabolic Pathways and Enzymes • Cellular reactions are usually part of a metabolic pathway, a series of linked reactions • Many reactions have molecules in common • Energy can be released in small amounts rather than all at once • Illustrated as follows: • E1 E2 E3 E4 E5 E6 • A → B → C → D → E → F → G • Letters A-F arereactants orsubstrates, B-G are the products in the various reactions, and E1-E6 areenzymes. 0 http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter8/animations.html

6. 0 • Enzyme - a protein molecule that functions as an organic catalyst tospeed a chemical reaction. • An enzyme brings together particular molecules and causes them to react. • The reactants in an enzymatic reaction are called thesubstratesfor that enzyme. • For series of reactions below, A is substrate for E1 and B is product. B then becomes substrate for E2 and C is product. Continues to end of pathway. • E1 E2 E3 E4 E5 E6 • A → B → C → D → E → F → G

7. 0 • Energy of activation (Ea) - the energy that must be added to cause molecules to react with one another • Enzyme lowers the amount of energy required for reaction to occur • Enzymes allow reactions to take place at lower temperatures – otherwise, reactions would not be able to occur at normal body temperatures

8. Energy of activation (Ea) 0 When no enzyme is present – more energy required When an enzyme is added – less energy required

9. Enzyme-Substrate Complexes 0 • Every reaction in a cell requires a specific enzyme. • Enzymes are named for their substrates:

10. Active site – part of enzyme that attaches to substrate • Active site may undergo a slight change in shape in order to accommodate the substrate(s) • The enzyme and substrate form an enzyme-substrate complex during the reaction. • The enzyme is not changed by the reaction (active site returns to its original state), and it is free to act again. 0 http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

11. 0 Enzymatic reaction Substrates are combined into alarger product Substrate is broken down intosmaller products

12. Induced fit model 0 • Because the enzyme must undergo a slight change in shape to fit with the substrate, this is known as theinduced fit model.

13. 0 Factors Affecting Enzymatic Speed • Substrate concentration • Temperature and pH • Enzyme concentration • Enzyme inhibition • Competitive inhibitors • Non-competitive inhibitors • Enzyme co-factors

14. Substrate concentration: • Enzyme activity increases as substrate concentration increases because there are more collisions between substrate molecules and the enzyme. • When active sites on enzymes are filled almost continuously with substrate, rate of activity cannot increase further.

15. 0 • Temperature and pH: • As the temperature rises, enzyme activity increases because more collisions occur between enzyme and substrate. • If the temperature is too high, enzyme activity levels out and then declines rapidly because the enzyme isdenatured. • When enzyme is denatured, its shape changes and it can no longer bind to substrate. • Each enzyme has an optimal pHand temperature at which the rate of reaction is highest.

16. 0 Rate of an enzymatic reaction as a function of temperature and pH

17. Enzyme Concentration: • A cell regulates which enzymes are present or active at any one time and the quantity of enzyme present by turning on of off genes • Another way to control enzyme activity is toactivate or deactivate the enzyme, such as through phosphorylation(removal of phosphate group). 0

18. 0 • Enzyme Inhibition: • Occurs when an active enzyme is prevented from combining with its substrate. • When the product of a metabolic pathway is in abundance, it binds competitively with the enzyme’s active site, a simple form of feedback inhibition. • Other metabolic pathways are regulated by the end product binding to an allosteric site(another area of enzyme). • Poisons such as cyanide are often enzyme inhibitors; penicillin is an enzyme inhibitor for bacteria.

19. 0 Feedback inhibition

20. 0 When there is a sufficient amount of the end product, some of the product binds to theallosteric site on the enzyme, the active site changes shape, the reactant cannot bind, and the end product is no longer produced. http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter8/animations.html

21. Competitive inhibitors: • Have a similar shape to the substrate & fit into the active site of the enzyme • Don’t take part in the reaction • Block active site so substrate can’t enter 0 Animation • Non-competitive inhibitors: • Do not have the same shape as the substrate & do not compete for the active site • Bind at some other point on the enzyme molecule, which still changes the shape of the active site so enzyme-substrate complex cannot be formed. http://www.stolaf.edu/people/giannini/flashanimat/enzymes/allosteric.swf

22. 0 • Enzyme Cofactors • Presence of enzyme cofactorsmay be necessary for some enzymes to carry out their functions. • Inorganic metal ions, such as copper, zinc, or iron function as cofactors for certain enzymes. • Organic molecules, termedcoenzymes, must be present for other enzymes to function. • Some coenzymes are vitamins; certain vitamin deficiencies result in a lack of certain enzymatic reactions.

23. 0 The ATP cycle

24. ATP (adenosine triphosphate) • The energy currency of cells. • A nucleotide made of the following: • Adenine • Ribose (a sugar) • Three phosphate groups • Constantly regenerated from ADP (adenosine diphosphate) after energy is expended by the cell. • Pneumonic devices – ATP – a triple phosphate • - ADP – a double phosphate 0 http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn2.swf

25. Advantages of ATP: 1) It can be used in many types of reactions. 2) When ATP → ADP + P, energy released is sufficient for cellular needs and little energy is wasted. 3) ATP is coupled to endergonic reactions (requires an input of energy) in such a way that it minimizes energy loss. 0

26. Overview of Cellular Respiration • Makes ATP molecules • Releases energy in several reactions • Glycolysis • Transition reaction • Citric acid cycle (Kreb’s cycle) • Electron transport system • An aerobic process that requires O2 0

27. Cellular respiration takes the potential chemical energy in the bonds of glucose and transforms it into the potential chemical energy in the bonds of ATP. • ATP molecules store usable chemical energy to drive life processes through coupled reactions.

28. It is an oxidation-reduction reaction, or redox reactionfor short. • Oxidationis the loss of electrons; hydrogen atoms are removed from glucose. • Reduction is the gain of electrons; oxygen atoms gain electrons. • Remember OIL RIG(oxidation is loss, reduction is gain) 0

29. 0 • Enzymes involved: • NAD+ • Nicotinamide adenine dinucleotide • Accepts 2 electrons & 1 H+ to become NADH • FAD • Flavin adenine dinucleotide (sometimes used instead of NAD+) • Accepts 2 electrons & 2 H+ to become FADH2

30. 0 The NAD+ cycle

31. 0 Phases of Cellular Respiration • Four phases: • Glycolysis • Transition reaction • Citric acid cycle (Kreb’s cycle) • Electron transport system • (If oxygen is not available, fermentationoccurs in the cytoplasm instead of proceeding to cellular respiration.)

32. 0 The four phases of complete glucose breakdown

33. 0 • Glycolysis • Occurs in the cytoplasm (outside the mitochondria) • Glucose  2 pyruvate molecules. • Universally found in all organisms • Does not require oxygen. http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html

37. 0 • Energy-Investment Steps • Requires 2 ATP to start process and activate glucose • Glucose splits into two C3 molecules (PGAL) • Each C3 molecule undergoes the same series of reactions.

38. Energy-Harvesting Steps • PGAL is oxidized by the removal of electrons by NAD+; phosphate group is attached to each PGAL as well (phosphorylation) • Removal of phosphate from 2 PGAP by 2 ADP produces 2 ATP, and 2 PGA molecules 0

39. Removal of water results in 2 PEP molecules • Removal of phosphate from 2 PEP by 2 ADP produces 2 ATP molecules and 2 pyruvate molecules 0

40. 0 Glycolysis summary • Inputs: • Glucose • 2 NAD+ • 2 ATP • 4 ADP + 2 P • Outputs: • 2 pyruvate • 2 NADH • 2 ADP • 2 ATP (net gain) • When oxygen is available, pyruvate enters the mitochondria, where it is further broken down • If oxygen is not available, fermentation occurs

41. 0 • Inside the Mitochondria • Structure of mitochondia: • Has a double membrane, with an intermembrane space between the two layers. • Cristae are folds of inner membrane • The matrix, the innermost compartment, which is filled with a gel-like fluid. • The transition reaction and citric acid cycle occur in the matrix; the electron transport system is located in the cristae.

42. 0 Mitochondrion structure and function

43. Transition Reaction • Is the transition between glycolysis and the citric acid cycle. • Pyruvate (made during glycolysis) is converted to acetyl CoA, and CO2 is released • NAD+ is converted to NADH + H+ • The transition reaction occurs twice per glucose molecule. 0

44. 0 Transition reaction inputs and outputs per glucose molecule • Inputs: • 2 pyruvate • 2 NAD+ • Outputs: • 2 acetyl groups • 2 CO2 • 2 NADH http://www.science.smith.edu/departments/Biology/Bio231/krebs.html

45. Citric Acid Cycle (aka Kreb’s Cycle) • Occurs in the matrix of the mitochondria. • C2 acetyl group (produced during transition reaction) joins a C4 molecule, and C6 citrate results. • Each acetyl group gives off 2 CO2 molecules. • NAD+ accepts electrons in three sites and FAD accepts electrons once. • Substrate-level phosphorylationresults in again of one ATP per every turn of the cycle; it turns twice per glucose, so a net of 2 ATP are produced. • The citric acid cycle produces four CO2 per molecule of glucose. 0

47. 0 Citric acid cycle

48. 0 Citric acid cycle inputs and outputs per glucose molecule • Inputs: • 2 acetyl groups • 6 NAD+ • 2 FAD • 2 ADP + 2 P • Outputs: • 4 CO2 • 6 NADH • 2 FADH2 • 2 ATP

49. 0 • Electron Transport System (ETS) • Located in the cristae of mitochondria • Series of protein carriers pass electrons from one to the other. • NADH and FADH2 carry electrons picked up during glycolysis, transition reaction, & citric acid cycle • NADH and FADH2enter the ETS.

50. 0 • As a pair of electrons is passed from carrier to carrier, energy is released and is used to form ATP molecules byoxidative phosphorylation (term used to describe production of ATP as a result of energy released by ETS). • Oxygen receives electrons at the end of the ETS, which combines with hydrogen to form water: • ½ O2 + 2 e- + 2 H+→ H2O