1. Chapter 8: Microbial Metabolism- the Chemical Crossroads of Life

2. The Metabolism of Microbes
Metabolism: All chemical reactions and physical workings of the cell
Anabolism: also called biosynthesis- any process that results in synthesis of cell molecules and structures (usually requires energy input)
Catabolism: the breakdown of bonds of larger molecules into smaller molecules (often release energy)
Functions of metabolism
Assembles smaller molecules into larger macromolecules needed for the cell
Degrades macromolecules into smaller molecules and yields energy
Energy is conserved in the form of ATP or heat

3. Enzymes Catalyze the chemical reactions of life
Enzymes: an example of catalysts, chemicals that increase the rate of a chemical reaction without becoming part of the products or being consumed in the reaction

5. How do Enzymes Work?
Energy of activation: the amount of energy which must be overcome for a reaction to proceed. Can be achieved by:
Increasing thermal energy to increase molecular velocity
Increasing the concentration of reactants to increase the rate of molecular collisions
Adding a catalyst
An enzyme promotes a reaction by serving as a physical site upon which the reactant molecules (substrates) can be positioned for various interactions

6. Enzyme Structure Most- protein
Can be classified as simple or conjugated
Simple enzymes- consist of protein alone
Conjugated enzymes- contain protein and nonprotein molecules
A conjugated enzyme (haloenzyme) is a combination of a proten (now called the apoenzyme) and one or more cofactors
Cofactors are either organic molecules (coenzymes) or inorganic elements (metal ions)

7. Figure 8.2

9. Apoenzymes: Specificity and the Active Site
Exhibits levels of molecular complexity called the primary, secondary, tertiary, and quaternary organization
The actual site where the substrate binds is a crevice or groove called the active site or catalytic site

10. Figure 8.3

11. Enzyme-Substrate Interactions
For a reaction to take place, a temporary enzyme-substrate union must occur at the active site
“Lock-and-key” fit
The bonds are weak and easily reversible

12. Figure 8.4

13. Cofactors: Supporting the Work of Enzymes
Metallic cofactors
Include Fe, Cu, Mg, Mn, Zn, Co, Se
Metals activate enzymes, help bring the active site and substrate close together, and participate directly in chemical reactions with the enzyme-substrate complex
Coenzymes
Organic compounds that work in conjunction with an apoenzyme to perform a necessary alteration of a substrate
Removes a chemical group from one substrate molecule and adds it to another substrate
Vitamins: one of the most important components of coenzymes

14. Classification of Enzyme Functions
Site of action
Type of action
Substrate

15. Location and Regularity of Enzyme Action
Either inside or outside of the cell
Exoenzymes break down molecules outside of the cell
Endoenzymes break down molecules inside of the cell

16. Figure 8.5

17. Rate of Enzyme Production
Enzymes are not all produced in the cell in equal amounts or at equal rates
Constitutive enzymes: always present and in relatively constant amounts
Regulated enzymes: production is either induced or repressed in response to a change in concentration of the substrate

18. Figure 8.6

19. Synthesis and Hydrolysis Reactions
Figure 8.7

20. Transfer Reactions by Enzymes
Oxidation-reduction reactions
A compound loses electrons (oxidized)
A compound receives electrons (reduced)
Common in the cell
Important components- oxidoreductases
Other enzymes that play a role in necessary molecular conversions by directing the transfer of functional groups:
Aminotransferases
Phosphotransferases
Methyltranferases
Decarboxylases

21. The Role of Microbial Enzymes in Disease
Many pathogens secrete unique exoenzymes
Help them avoid host defenses or promote multiplication in tissues
These exoenzymes are called virulence factors or toxins

22. The Sensitivity of Enzymes to Their Environment
Enzyme activity is highly influenced by the cell’s environment
Enzymes generally operate only under the natural temperature, pH, and osmotic pressure of an organism’s habitat
When enzymes subjected to changes in normal conditions, they become chemically unstable (labile)
Denaturation: the weak bonds that maintain the native shape of the apoenzyme are broken

23. Regulation of Enzymatic Activity and Metabolic Pathways
Metabolic reactions usually occur in a multiseries step or pathway
Each step is catalyzed by an enzyme
Every pathway has one or more enzyme pacemakers that set the rate of a pathway’s progression

24. Figure 8.8

25. Direct Controls on the Action of Enzymes
Competitive inhibition: The cell supplies a molecule that resembles the enzyme’s normal substrate, which then occupies and blocks the enzyme’s active site
Noncompetitive inhibition: The enzyme has two binding sites- the active site and the regulatory site; a regulator molecule binds to the regulatory site providing a negative feedback mechanism

26. Figure 8.9

27. Controls on Enzyme Synthesis
Enzymes eventually must be replaced
Enzyme repression: stops further synthesis of an enzyme somewhere along its pathway
Enzyme induction: The inverse of enzyme repression

28. Figure 8.10

29. The Pursuit and Utilization of Energy
Energy in Cells
Exergonic reaction: a reaction that releases energy as it goes forward
Endergonic reaction: a reaction that is driven forward with the addition of energy

30. Figure 8.11

31. A Closer Look at Biological Oxidation and Reduction
Biological systems often extract energy through redox reactions
Redox reactions always occur in pairs
An electron donor and electron acceptor
Redox pair
Electron donor (reduced) + electron acceptor (oxidized)  Electron donor (oxidized) + electron acceptor (reduced)
This process leaves the previously reduced compound with less energy than the now oxidized one
The energy in the electron acceptor can be captured to phosphorylate to ADP or some other compound, storing the energy in a high-energy molecule like ATP

32. Electron Carriers: Molecular Shuttles
Electron carriers repeatedly accept and release electrons and hydrogens
Facilitate the transfer of redox energy
Most carriers are coenzymes that transfer both electrons and hydrogens
Some transfer electrns only
Most common carrier- NAD

33. Figure 8.12

34. Adenosine Triphosphate: Metabolic Money
ATP
Can be earned, banked, saved, spent, and exchanged
A temporary energy repository
The Molecular Structure of ATP
Three-part molecule
Nitrogen base (adenine)
5-carbon sugar (ribose)
Chain of three phosphate groups
The high energy originates in the orientation of the phosphate groups
Breaking the bonds between two successive phosphates of ATP yields ADP
ADP can then be converted to AMP