1. Essential Concepts of Metabolism
Chapter 5
Microbiology 130

2. Metabolism: An Overview
Anabolism
Catabolism-
- electron transfer
Oxydation-
Reduction-

3. How do microbes obtain energy?
Autotrophs- self feeders, use CO2 to sysnthesis organic compounds
- Photoautotrophs- use sunlight for energy
- Chemoautotrophs- use inorganics such as sulfides and nitrites for energy
Heterotrophs- other feeders, use organic molecules,
- Photoheterotrophs-obtain chemical energy from light
- Chemoheterotrophs- obtain energy from ready made organic compounds

4. What Is Energy? Capacity to do work Forms of energy Potential energy,
Kinetic energy
Chemical energy
What Can Cells Do With Energy?
Cells use energy for:
Chemical work
Mechanical work
Electrochemical work

5. One-Way Flow of Energy The sun is life’s primary energy source
Producers trap energy from the sun and convert it into chemical bond energy
All organisms use the energy stored in the bonds of organic compounds to do work

6. Endergonic Reactions Energy input required
Product has more energy than starting substances
glucose, a high energy product
+ 6O2
ENERGY IN 6 6
low energy starting substances 6 6

7. Exergonic Reactions Energy is released
Products have less energy than starting substance
glucose, a high energy starting substance
+ 6O2
ENERGY OUT
low energy products 6 6

8. three phosphate groups
The Role of ATP
Cells “earn” ATP in exergonic reactions
Cells “spend” ATP in endergonic reactions
base
three phosphate groups
sugar

9. ATP/ADP Cycle
When adenosine triphosphate (ATP) gives up a phosphate group, adenosine diphosphate (ADP) forms
ATP can re-form when ADP binds to inorganic phosphate or to a phosphate group that was split from a different molecule
Regenerating ATP by this ATP/ADP cycle helps drive most metabolic reactions

10. Participants in Metabolic Reactions
Energy carriers
Enzymes
Cofactors
Transport proteins
Reactants
Intermediates
Products

11. Chemical Equilibrium
At equilibrium, the energy in the reactants equals that in the products
Product and reactant molecules usually differ in energy content
Therefore, at equilibrium, the amount of reactant almost never equals the amount of product

12. Chemical Equilibrium

13. Redox Reactions
Cells release energy efficiently by electron transfers, or oxidation-reduction reactions (“redox” reactions)
One molecule gives up electrons (is oxidized) and another gains them (is reduced)
Hydrogen atoms are commonly released at the same time, thus becoming H+

14. Electron Transfer Chains
Arrangement of enzymes, coenzymes, at cell membrane
As one molecule is oxidized, next is reduced
Function in aerobic respiration and photosynthesis

15. Uncontrolled vs. Controlled Energy ReleaseH2
1/2 O2
Explosive release of energy as
heat that cannot be harnessed
for cellular work
H2O

16. Metabolic Pathways
Defined as enzyme-mediated sequences of reactions in cells
Biosynthetic (anabolic) – ex: photosynthesis
Degradative (catabolic) – ex: aerobic respiration

17. Enzyme Structure and Function
Enzymes are catalytic molecules
They speed the rate at which reactions approach equilibrium

18. Four Features of Enzymes
1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster.
2) Reactions do not alter or use up enzyme molecules.

19. Four Features of Enzymes
3) The same enzyme usually works for both the forward and reverse reactions.
4) Each type of enzyme recognizes and binds to only certain substrates.

20. Activation Energy
For a reaction to occur, an energy barrier must be surmounted
Enzymes make the energy barrier smaller
activation energy
without enzyme
starting
substance
activation energy
with enzyme
energy
released
by the
reaction
products

21. How Catalase Works

22. Induced-Fit Model Substrate molecules are brought together
Substrates are oriented in ways that favor reaction
Active sites may promote acid-base reactions
Active sites may shut out water

23. Factors Influencing Enzyme Activity
Temperature pH
Salt concentration
Allosteric regulators
Coenzymes and cofactors

24. Enzyme Helpers Cofactors Coenzymes Metal ions NAD+, NADP+, FAD
Accept electrons and hydrogen ions; transfer them within cell
Derived from vitamins
Metal ions
Ferrous iron in cytochromes

25. Allosteric Activation
allosteric activator
enzyme active site
vacant
allosteric binding site
active site cannot bind substrate
active site altered, can bind substrate

26. Allosteric Inhibition
allosteric inhibitor
allosteric binding site vacant; active site can bind substrate
active site altered, can’t bind substrate

27. END PRODUCT (tryptophan)
Feedback Inhibition
enzyme 2
enzyme 3
enzyme 4
enzyme 5
A cellular change, caused by a specific activity, shuts down the activity that brought it about
enzyme 1
END PRODUCT (tryptophan)
SUBSTRATE

28. Effect of Temperature
Small increase in temperature increases molecular collisions, reaction rates
High temperatures disrupt bonds and destroy the shape of active site

29. Effect of pH

30. Producing the Universal Currency of Life
All energy-releasing pathways
require characteristic starting materials
yield predictable products and by-products
produce ATP

31. Main Types of Energy-Releasing Pathways
Anaerobic pathways
Evolved first
Don’t require oxygen
Start with glycolysis in cytoplasm
Completed in cytoplasm
Aerobic pathways
Evolved later
Require oxygen
Completed in mitochondria

32. Energy-Releasing Pathways

33. Main Pathways Start with Glycolysis
Glycolysis occurs in cytoplasm
Reactions are catalyzed by enzymes
Glucose 2 Pyruvate
(six carbons) (three carbons)

34. The Role of Coenzymes
NAD+ and FAD accept electrons and hydrogen from intermediates during the first two stages
When reduced, they are NADH and FADH2
In the third stage, these coenzymes deliver the electrons and hydrogen to the transfer chain

35. Anaerobic Pathways Do not use oxygen
Produce less ATP than aerobic pathways
Two types of fermentation pathways
Alcoholic fermentation
Lactate fermentation

36. Fermentation Pathways
Begin with glycolysis
Do not break glucose down completely to carbon dioxide and water
Yield only the 2 ATP from glycolysis
Steps that follow glycolysis serve only to regenerate NAD+

37. Alcoholic Fermentation

38. Yeasts Single-celled fungi Carry out alcoholic fermentation
Saccharomyces cerevisiae
Baker’s yeast
Carbon dioxide makes bread dough rise
Saccharomyces ellipsoideus
Used to make beer and wine

39. Lactate Fermentation Carried out by certain bacteria
Electron transfer chain is in bacterial plasma membrane
Final electron acceptor is compound from environment (such as nitrate), not oxygen
ATP yield is low

40. Lactate Fermentation

41. Carbohydrate Breakdown and Storage
Glucose is absorbed into blood
Pancreas releases insulin
Insulin stimulates glucose uptake by cells
Cells convert glucose to glucose-6-phosphate
This traps glucose in cytoplasm where it can be used for glycolysis

42. Glycolysis Occurs in Two Stages
Energy-requiring steps
ATP energy activates glucose and its six-carbon derivatives
Energy-releasing steps
The products of the first part are split into three-carbon pyruvate molecules
ATP and NADH form

43. Energy-Requiring Steps

44. Energy-Releasing Steps

45. Net Energy Yield from Glycolysis
Energy requiring steps:
2 ATP invested
Energy releasing steps:
2 NADH formed
4 ATP formed
Net yield is 2 ATP and 2 NADH

46. Overview of Aerobic Respiration
C6H O2  6CO2 + 6H20
glucose oxygen carbon water dioxide

47. Overview of Aerobic Respiration

48. Second-Stage Reactions
Occur in the mitochondria
Pyruvate is broken down to carbon dioxide
More ATP is formed
More coenzymes are reduced

49. Two Parts of Second Stage
Preparatory reactions
Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide
NAD+ is reduced
Krebs cycle
The acetyl units are oxidized to carbon dioxide
NAD+ and FAD are reduced

50. Preparatory Reactions
pyruvate + coenzyme A + NAD+
acetyl-CoA + NADH + CO2
One of the carbons from pyruvate is released in CO2
Two carbons are attached to coenzyme A and continue on to the Krebs cycle

51. Using Glycogen
When blood levels of glucose decline, pancreas releases glucagon
Glucagon stimulates liver cells to convert glycogen back to glucose and to release it to the blood
(Muscle cells do not release their stored glycogen)

52. Energy Reserves
Glycogen makes up only about 1 percent of the body’s energy reserves
Proteins make up 21 percent of energy reserves
Fat makes up the bulk of reserves (78 percent)

53. Energy from Fats Most stored fats are triglycerides
Triglycerides are broken down to glycerol and fatty acids
Glycerol is converted to PGAL, an intermediate of glycolysis
Fatty acids are broken down and converted to acetyl-CoA, which enters Krebs cycle

54. Energy from Proteins Proteins are broken down to amino acids
Amino acids are broken apart
Amino group is removed, ammonia forms, is converted to urea and excreted
Carbon backbones can enter the Krebs cycle or its preparatory reactions

55. Reaction Sites

56. Evolution of Metabolic Pathways
When life originated, atmosphere had little oxygen
Earliest organisms used anaerobic pathways
Later, noncyclic pathway of photosynthesis increased atmospheric oxygen
Cells arose that used oxygen as final acceptor in electron transfer

57. Processes Are Linked Aerobic Respiration Reactants Sugar Oxygen
Products
Carbon dioxide
Water
Photosynthesis
Processes Are Linked

58. Life Is System of Prolonging Order
Powered by energy inputs from sun, life continues onward through reproduction
Following instructions in DNA, energy and materials can be organized, generation after generation
With death, molecules are released and may be cycled as raw material for next generation