1. Biology, 9th ed,Sylvia Mader
Chapter 06
Chapter 06
Metabolism
Metabolism

2. Outline Forms of Energy Metabolic Reactions Metabolic Pathways
Laws of Thermodynamics
Metabolic Reactions
ATP
Metabolic Pathways
Energy of Activation
Enzymes

3. Forms of Energy Kinetic: Potential: Energy of motion Mechanical
Stored energy
Chemical

4. Energy
Energy is capacity to do work; cells must continually use energy to do biological work.
Kinetic energy is energy of motion; all moving objects have kinetic energy.
Potential energy is stored energy.
Ex. Water behind a dam has potential energy that can be converted to kinetic energy.

5. Flow of Energy

6. Laws of Thermodynamics
First Law:
Law of conservation of energy
Energy cannot be created or destroyed, but
Energy CAN be changed from one form to another
Second Law:
Law of ENTROPY
When energy is changed from one form to another, there is a loss of usable energy
Waste energy goes to increase disorder

7. Laws of Thermodynamics
Second law: (Law of ENTROPY)
Energy conversions result in heat and therefore the entropy of the universe is always increasing.
It takes a constant input of usable energy from the food you eat to keep you organized.

8. Carbohydrate Synthesis

9. Carbohydrate Metabolism

10. Cells & Energy

11. Metabolic Reactions and Energy Transformations
Biology, 9th ed,Sylvia Mader
Chapter 06
Metabolic Reactions and Energy Transformations
Metabolism
Metabolism:
Sum of cellular chemical reactions in cell
Reactants participate in reaction
Products form as result of reaction
Free energy is the amount of energy available to perform work
Exergonic Reactions - Products have less free energy than reactants
Endergonic Reactions - Products have more free energy than reactants
Animation

12. Living systems require free energy and matter to maintain order, grow and reproduce.

13. Gibbs Free Energy (G) “Available energy”
Energy that can do work under cellular conditions
Concept from Thermodynamics

14. Life requires a highly ordered system.

15. Order is maintained by constant input of free energy into the system.

16. Loss of order or free energy flow results in death.

17. An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics.

19. Thermodynamics: the laws of energy transformations.

20. The First Law of Thermodynamics
According to the first law of thermodynamics:
Energy cannot be created or destroyed
Energy can be transferred and transformed

21. The Second Law of Thermodynamics: spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe.

22. Increased disorder and entropy are offset by biological processes that maintain or increase order.

23. Metabolic Reactions and Energy Transformations
Catabolic pathways
release energy by breaking down complex molecules to simpler compounds.
Ex: Cellular respiration - degrades glucose to carbon dioxide & water; provides energy for cellular work.
Anabolic pathways
consume energy to build complicated molecules from simpler ones.
Ex: Photosynthesis - synthesizes glucose from carbon dioxide & water

24. Catabolic pathways break down complex molecules into simpler compounds.

25. Catabolic pathways are spontaneous ( G < 0) and release energy: exergonic.
Exergonic Reactions

26. Anabolic pathways build complicated molecules from simpler ones and consume energy.

27. Anabolic pathways are nonspontaneous ( G > 0) and consume energy: endergonic.
Endergonic Reactions

28. Catabolic & Anabolic Reactions
Cats – break things
Anna – builds things
Cells need both types of reactions; both require enzymes

29. The ATP Cycle *High energy compound used to drive metabolic reactions
*Constantly being generated from adenosine diphosphate (ADP)

30. Adenine and ribose (together = adenosine), and
The ATP Cycle
ATP Composed of:
Adenine and ribose (together = adenosine), and
3 phosphate groups

31. The ATP Cycle Coupled reactions
Energy released by an exergonic reaction captured in ATP
That ATP used to drive an endergonic reaction

32. Coupled Reactions
Figure 6.4

33. Work-Related Functions of ATP
ATP - needed to perform cellular work
Chemical Work - Energy needed to synthesize macromolecules
Transport Work - Energy needed to pump substances across plasma membrane
Mechanical Work - Energy needed to contract muscles, beat flagella, etc

34. See Biochemical Pathway Animation
Enzymes
See Biochemical Pathway Animation
Enzymes
Protein molecules that function as catalysts
The reactants of an enzymatically accelerated reaction are called substrates

35. Enzymes: Energy of Activation
Reactants often “reluctant” to participate in reaction
Energy must be added to at least one reactant to initiate the reaction
Energy of activation
Enzyme Operation:
Enzymes operate by lowering the energy of activation
Accomplished by bringing the substrates into contact with one another

37. Energy of Activation
Energy of activation (Ea) is energy that must be added to cause molecules to react.

38. Lower Ea

39. Energy of Activation

40. Enzyme-Substrate Complex
Induced fit model
The active site complexes with the substrates
Causes active site to change shape
Shape change forces substrates together or apart… initiating or breaking bonds
Enzymes Animation

41. Induced Fit Model

43. Synthesis Reaction

44. Degradation or Decomposition reaction

45. Factors Affecting Enzyme Activity
Substrate concentration
Enzyme activity increases with substrate concentration
More collisions between substrate molecules and the enzyme
Temperature
Enzyme activity increases with temperature
Warmer temperatures cause more effective collisions between enzyme and substrate
However, hot temperatures destroy enzyme pH
Most enzymes are optimized for a particular pH

46. Factors Affecting Enzyme Activity: Temperature

47. Denaturation is when a protein unravels and loses its normal structure and function
Generally irreversible
Denaturation
Figure 5.23 Denaturation and renaturation of a protein
Normal protein
Denatured protein

48. Factors Affecting Enzyme Activity: pH

49. Factors Affecting Enzyme Activity
Cells can affect presence/absence of enzyme
Cells can affect concentration of enzyme
Cells can activate or deactivate enzyme
Enzyme Cofactors - Non-protein molecules that assist enzymes. (often metal ions, Fe2+)
Coenzymes are organic cofactors, like some vitamins
Phosphorylation – some require addition of a phosphate

50. Enzyme Cofactors (& Coenzymes)
This enzyme is DNA polymerase. It makes copies of DNA. The purple things are magnesium (Mg), a mineral. Mg is a cofactor for DNA polymerase. This is why you need some Mg in your diet.
Groove
Groove
Some enzymes need cofactors to work; these are non-protein groups that attach to the enzyme. Ex. Minerals such as zinc or Mg
Many vitamins (because they are organic are important because they are called coenzymes

51. Factors Affecting Enzyme Activity: Activation by Phosphorylation

52. Factors Affecting Enzyme Activity
Reversible enzyme inhibition
When a substance known as an inhibitor binds to an enzyme and decreases its activity
Competitive inhibition – substrate and the inhibitor are both able to bind to active site
Noncompetitive inhibition – the inhibitor binds not at the active site, but at the allosteric site
Feedback inhibition – The end product of a pathway inhibits the pathway’s first enzyme

53. Competitive Inhibition
In competitive inhibition, another molecule is similar to enzymes substrate, competes with true substrate for enzyme’s active site, resulting in decreased product formation.

54. Noncompetitive Inhibition
In noncompetitive inhibition, a molecule binds to allosteric site, a site other than active site, hereby changing the three-dimensional structure of enzyme and ability to bind to its substrate.

55. Allosteric Enzymes Allosteric Enzymes- 2 binding sites
Active Site – substrate binds to
Allosteric Site – allosteric affector binds
Allosteric Activator – molecule binds to allosteric site and ACTIVATES enzyme.
Creates active form of enzyme.
Allosteric Inhibitor - molecule binds to allosteric site and INHIBITS enzyme.
Creates inactive form of enzyme.

56. Factors Affecting Enzyme Activity: Feedback Inhibition
See Feedback Inhibition Animation

57. See Biochemical Pathway Animation
Enzymes
See Biochemical Pathway Animation
Each reaction in a metabolic pathway requires a unique and specific enzyme
End product will not appear unless ALL enzymes present and functional
E E2 E3 E4 E5 E6
A  B  C  D  E  F  G

58. “A” is Initial Reactant
Metabolic Pathways
Reactions are usually occur in a sequence
Such linked reactions form a metabolic pathway
Begins with a particular reactant,
Proceeds through several intermediates, and
Terminates with a particular end product
AB C D E FG
“G” is End Product
“A” is Initial Reactant
Intermediates

59. amanitin (mushroom toxin)
Enzyme Inhibitors
amanitin (mushroom toxin)
This enzyme is RNA polymerase. It reads the information in the genetic code in DNA.
Groove
active site
Inhibition is when the wrong molecule (an inhibitor) binds, blocking the active site; substrate can’t bind
Many poisons are inhibitors of essential enzymes (e.g. death cap mushroom, arsenic, cadmium)

60. Irreversible Inhibition
Materials that irreversibly inhibit an enzyme are known as poisons
Cyanides inhibit enzymes resulting in all ATP production
Penicillin inhibits an enzyme unique to certain bacteria
Heavy metals irreversibly bind with many enzymes
Nerve gas irreversibly inhibits enzymes required by nervous system