Ground Rules of Metabolism

1. Ground Rules of Metabolism Chapter 6 Part 1

2. Impacts, Issues:A Toast To Alcohol Dehydrogenase • In the liver, alcohol dehydrogenase helps break down toxic alcohols, but at the expense of liver function and energy metabolism over time

3. Energy Dispersal • Only source of biological energy is the sun • First law of thermodynamics is key • Energy is neither created nor destroyed, but it can be transferred from one form to another • Cells utilize energy by storing and releasing it • Second law of thermodynamics • Entropy (a measure of dispersal of energy in a system) increases spontaneously • The entropy of two atoms decreases when a bond forms between them (endergonic reaction)

4. Motion: A Form Of Energy

5. One Way Flow of Energy for Earth • The total amount of energy available in the universe to do work is always decreasing • Each time energy is transferred, some energy escapes as heat (not used for doing work) • In fact, most sunlight energy ends up as heat • On Earth, energy flows from the sun, through producers, then consumers • Living things need a constant input of energy • But most of the potential energy falling on the earth ends up as heat and is lost

6. Energy Conversion • Only about 10 percent of the energy in “food” goes toward building body mass, most is lost in energy conversions • So, food chains are short because of the energy loss at each stage

7. Energy Flow

8. Energy In, Energy Out • Reaction • A chemical change that occurs when atoms, ions, or molecules interact • Reactants - Atoms, ions, or molecules that start a reaction (the left side of the equation) • Product - Atoms, ions, or molecules remaining at the end of a reaction (right side of the equation) • reactant + reactant  product(s)

9. Chemical Reaction Example

10. Reactions Require Or Release Energy • We can predict whether a reaction requires or releases energy by comparing the bond energies of reactants with those of products • Endergonic (“energy in”) • Reactions that require a net input of energy • Exergonic (“energy out”) • Reactions that end with a net release of energy

11. Endergonic And Exergonic Reactions

12. Why World Doesn’t Go Up In Flames • Activation energy • The minimum amount of energy needed to get a reaction started • Some reactions require a lot of activation energy, others do not

13. Activation Energy

14. ATP – The Cell’s Energy Currency • ATP (adenosine triphosphate) • A nucleotide with three phosphate groups • Transfers a phosphate group and energy to other molecules • Cell constantly has ATPADP + energy release + P and ADP + extra energy + P  ATP • Phosphorylation • A phosphate-group transfer • ADP binds phosphate in an endergonic reaction to replenish ATP (ATP/ADP cycle)

15. ATP

16. 6.1-6.2 Key Concepts:Energy Flow For Life • Energy tends to disperse spontaneously; each time energy is transferred, some of it disperses • Organisms maintain their organization only by continuously harvesting energy • ATP couples reactions that release usable energy with reactions that require energy

17. 6.3 Enzymes Make Substances React • Enzyme • A catalyst that makes a specific reaction occur much faster than it would on its own (note that reaction would occur anyway, the catalyst just speeds it up) • Enzymes are not consumed or changed by participating in a reaction • Most are proteins, some are RNA Substrate • The specific reactant acted upon by an enzyme

18. How Enzymes Work • Enzymes lower the activation energy required to bring on the transition state, when substrate bonds break and reactions run spontaneously • Active sites • Locations on the enzyme molecule where substrates bind and reactions proceed • Complementary in shape, size, polarity and charge to the substrate

19. Active Site Of An Enzyme

20. Mechanisms Of Enzyme-Mediated Reactions • Binding at enzyme active sites may bring on the transition state by four mechanisms • Helping substrates get together • Orienting substrates in positions that favor reaction • Inducing a fit between enzyme and substrate (induced-fit model – like “lock and key”) • Shutting out water molecules

21. Temperature, pH, And Salinity • Raising the temperature boosts reaction rates by increasing a substrate’s energy -- but very high temperature denatures enzymes • Each enzyme has an optimum pH range • In humans, most enzymes work at pH 6 to 8 • Higher or lower pH gives lowered reactions • Salt levels affect the hydrogen bonds that hold enzymes in their three-dimensional shape

22. Enzymes And Temperature Low temp of extremities such as face, tail, ears results in dark color as tyrosinase level affects expression of melanin.

23. Enzymes And pH This carnivorous plant gets nitrogen from the trapped insects, an advantage in the nitrogen lacking environ that it lives in.

24. Help From Cofactors • Cofactors • Atoms or molecules (other than proteins) that are necessary for enzyme function • Example: Iron atoms in catalase • Coenzymes • Organic cofactors such as vitamins • May become modified during a reaction

25. Catalase And Cofactors • Catalase is an antioxidant that neutralizes free radicals (atoms or molecules with unpaired electrons that attack biological molecules) • Catalase works by holding a substrate molecule close to one of its iron atoms (cofactors) • Iron pulls on the substrate’s electrons, bringing on the transition state • That’s why “antioxidants” are so strongly pushed for human health including slowing aging effects

26. 6.3 Key Concepts:Summary OfHow Enzymes Work • On their own, reactions proceed too slowly to sustain life • Enzymes tremendously increase the rate of metabolic reactions • Environmental factors such as temperature, salt, and pH influence enzyme function

27. Ground Rules of Metabolism Chapter 6 Part 2

28. Types Of Metabolic Pathways • A metabolic pathway is any series of enzyme-mediated reactions by which a cell builds, rearranges, or breaks down organic substances • Anabolic pathways build molecules • Catabolic pathways break apart molecules • Cyclic pathways regenerate a molecule from the first step

29. Controls Over Metabolism • Concentrations of reactants or products can make reactions proceed forward or backward • Feedback mechanisms can adjust enzyme production, or activate or inhibit enzymes • Regulatory molecules can bind to an allosteric site to activate or inhibit enzymes by processes such as Feedback inhibition

30. Allosteric Control – “lock and key”

31. Feedback Inhibition Controls Production

32. Redox Reactions • Oxidation-Reduction Reactions • A molecule that gives up electrons is oxidized • A molecule that accepts electrons is reduced • Coenzymes can accept molecules in redox reactions (also called electron transfers)

33. ATP Synthesis • Coenzymes deliver electrons to electron transfer chains for ATP synthesis to store energy • Electron transfer chain • A series of redox reactions in membrane-bound enzymes or molecules that release energy in small, controlled steps • Those controlled steps give a maximum harvest of the available energy

34. Uncontrolled And Controlled Reactions

35. Overview: Energy Pathways

36. 6.4 Key Concepts:TheNature Of Metabolism • Metabolic pathways are energy-driven sequences of enzyme-mediated reactions • They concentrate, convert, or dispose of materials in cells • Controls over enzymes that govern key steps in metabolic pathways can shift cell activities fast

37. 6.5 Night Lights • Bioluminescence • Light emitted from metabolic reactions in some living organisms • Bioluminescence is thus a visible evidence of metabolism in these organisms

38. Enzymes And Bioluminescence • Bioluminescent organisms emit light when enzymes (luciferases) convert chemical bond energy in luciferins to light energy luciferin + ATP → luciferin-ADP + Pi luciferin-ADP + O2→ oxyluciferin + AMP + CO2 + light

39. Key Players In Metabolic Reactions