1. Chapter 6 Biology in Focus AP Bio 2014 Ms. Eggers
Energy & Enzymes
Chapter 6 Biology in Focus
AP Bio 2014
Ms. Eggers

2. Chapter 6 vocabulary terms
Energetics
Metabolism
Catabolic pathways
Anabolic pathways
Bioenergetics
Kinetic energy
Thermal energy
Potential energy
Chemical energy
Thermodynamics
First law of thermodynamics
Entropy
Second law of thermodynamics
Spontaneous reaction
Free energy
Exergonic
Endergonic
Energy coupling
ATP/phosphorylated intermediate
Enzymes
Enzyme
Catalyst
Activation energy
Substrate
Enzyme-substrate complex
Active site
Induced fit
Cofactors
Coenzyme
Competitive inhibitors
Noncompetitive inhibitors
Allosteric regulation
Cooperativity
Feedback inhibition

3. Part 1: Metabolism & Energetics Sections 6.1 - 6.3

4. Metabolism, anabolic and catabolic defined

5. Examples of metabolic pathways

6. Metabolism is WICKED COMPLEX - these are just the reactions involved in starch and sucrose metabolism

7. Forms of Energy Kinetic energy Potential energy Energy of motion
Thermal energy
Potential energy
Chemical energy
Stored in the covalent bonds of organic molecules such as carbohydrates and fats

8. The Laws of Thermodynamics
1st Law of Thermodynamics
Energy can be transferred but it can neither be created nor destroyed
2nd Law of Thermodynamics
Every energy transfer increases the entropy of the universe
Entropy: a measure of the disorder or randomness
Heat is the most randomly ordered form of energy so in terms of biology, the second law really means that no conversion of chemical energy is perfect – heat is always generated and lost.

9. A SPONTANEOUS process occurs without any input of energy AND always results in an INCREASE in ENTROPY

10. Free-energy DG = Gfinal – Ginitial
Measures the portion of a system’s energy that is available to do work
DG is the change in free energy between the final state and the initial state
DG = negative value = can occur spontaneously
DG = positive value = can NOT occur spontaneously
DG = Gfinal – Ginitial
A system must LOSE free energy from its initial state to its final state in order for it to occur spontaneously

11. More on Free-energy (G)
Free energy is also a measure of the “instability” of a system – losing free energy makes a system more stable
A system at maximum stability is at EQUILIBRIUM
If a system is moving TOWARD equilibrium, it will occur spontaneously (ie diffusion) AND can do work
At equilibrium, DG = 0

13. Exergonic versus endergonic reactions
An exergonic reaction RELEASES free energy
DG is negative
Can occur spontaneously
Makes things LESS ordered
Catabolic reactions
An endergonic reaction requires an input of energy
DG is positive
Will not occur spontaneously
Makes things MORE ordered Anabolic reactions

14. Endergonic Exergonic
Plant and animal cells break down glucose and convert the energy to usable ATP
Plants use an input of the sun’s energy to assemble glucose from CO2 and H2O

15. ATP: the cell’s battery
Pushing endergonic reactions – those that build molecules (anabolic reactions) – requires chemical work
An endergonic reaction MUST be coupled to an exergonic reaction

16. ATP = adenosine triphosphate

17. Coupling ATP hydrolysis to an endergonic process
Coupling ATP to an endergonic reaction can involve a phosphorylated intermediate (a)
Or can be indirect as in (b)

18. Part 2: Enzymes Sections 6.4 & 6.5

19. In chemistry, a “spontaneous” reaction doesn’t necessarily occur readily…
Example: a log – the log contains A LOT of chemical potential energy and once the log is lit it will burn and release that energy in the form of heat and light energy BUT without the small input of energy from a match, that log would sit there NOT burning for a LONG time

20. Exergonic reactions often require…
Activation energy = free energy of activation, or EA
The breakdown of glucose releases energy – and is therefore considered “spontaneous”, but those covalent bonds are quite stable…

21. Enzymes are chemical catalysts
Enzymes speed up the occurrence of chemical reactions by reducing the “height” of the activation energy barrier
Enzymes reduce EA

22. The name game…what is the name of the enzyme that breaks down lactose?
Proteases- A protease is any enzyme that can break down a long protein into smaller chains called peptides (a peptide is simply a short amino acid chain).
Peptidases - Peptidases break peptides down into individual amino acids. Proteases and peptidases are often found in laundry detergents -- they help remove things like blood stains from cloth by breaking down the proteins.
Amylases - Amylases break down starch chains into smaller sugar molecules. Your saliva contains amylase and so does your small intestine. Maltase, lactase, and sucrase finish breaking the simple sugars down into individual glucose molecules.
Lipases - Lipases break down fats.
Hydrolases – Hydrolases catalyze hydrolysis reactions.
Transferases – Transferases transfer different functional groups on a molecule.
Nucleases – The various nucleases act on nucleic acids.
You get the picture… add –ase to the end

23. Another enzyme example: maltase
Maltose is made of two glucose molecules bonded together.
The maltase enzyme is a protein that is perfectly shaped to accept a maltose molecule and break the bond. Then the two glucose molecules are released.
A single maltase enzyme can break in excess of 1,000 maltose bonds per second, and will only accept maltose molecules.

24. Substrate specificity
The molecule that an enzyme acts on is called its substrate (sometimes the term ligand will be used)
When the enzyme binds the substrate, it is called an enzyme-substrate complex.
The substrate is bound by the enzyme in a specific region called the active site.

29. Reaction rates – effect of varying enzyme concentration and substrate concentration

30. Enzymes have a unique 3-dimensional shape that is held together primarily by ionic and hydrogen bonds: Many factors can affect enzyme function
Temperature pH
Cofactors
Enzyme inhibitors
Regulators – negative feedback

31. Reaction rates – the effect of temperature

32. At low temperatures things are moving too slow, some temperature is “just right”, and at high temperatures, the enzyme denatures

33. Reaction rates – the effect of pH

34. Other factors affecting enzyme activity
Cofactors = non-protein helpers
Metals such as iron, zinc & copper
Coenzymes = organic molecule ‘helpers’ – many vitamins are coenzymes

35. The protein portion of an enzyme is called the apoenzyme
The protein portion of an enzyme is called the apoenzyme. A cofactor is the non-protein part of an enzyme. The complete enzyme (apoprotein + cofactor) is termed the holoenzyme.

36. Enzyme inhibitors
Competitive inhibitors block the substrates from entering the active sites
Noncompetitive inhibitors bind at spots away from the active site but change the shape of the protein so it can no longer bind the substrate

37. Enzyme Inhibitors

38. How are enzymes regulated?
Allosteric regulation is kind of like noncompetitive inhibition – but purposeful…

39. Another kind of allosteric regulation -- cooperativity
Cooperativity can amplify the response of an enzyme to a substrate (eg hemoglobin)

40. Feedback inhibition – shutting enzymes off

41. Animated tutorials & resources