Module 2

Chapter 7: Microbial Metabolism

Metabolism and The Role of Enzymes

  • Metabolism: Pertains to all chemical reactions and physical workings of the cell

  • Anabolism:

    • Any process that results in the synthesis of cell molecules and structures

    • A building process that forms larger macromolecules from smaller ones

    • Requires the input of energy

  • Catabolism:

    • Breaks the bones of larger molecules into smaller molecules

    • Releases energy

  • Metabolism performs these functions:

    • Assembles smaller molecules into larger macromolecules - ATP (energy) is utilized to form bonds (anabolism)

    • Degrades macromolecules into smaller molecules, a process that yields energy (catabolism)

    • Stores energy in the form of ATP (adenosine triphosphate)

Enzymes: Catalyzing the Chemical Reactions of Life

  • Enzymes

    • Chemical reactions of life cannot proceed without them

    • Are catalysts that increase the rate of chemical reactions without becoming part of the products or being consumed in the reactions

Concept Check - 1

Anabolism and catabolism constitute the sum of reactions in the cell known as _____.

A. Binary fission

B. Metabolism

C. Energy balance

D. Mutation

How Do Enzymes Work?

  • Reactants are converted into products by bond formation or bond breakage

    • Substrate: Reactant molecules acted on by an enzyme

  • Speed up the rate of reactions without increasing the temperature

  • Much larger than substrates

  • Have a unique active site on the enzyme that fits only the substrate

Checklist of Enzyme Characteristics

  • Most composed of protein; may require cofactors

  • Act as organic catalysts to speed up the rate of cellular reactions

  • Have unique characteristics such as shape, specificity, and function

  • Enable metabolic reactions to proceed at a speed compatible with life

  • Have an active site for target molecules called substrates

  • Are much larger than their substrates

  • Associate closely with substrates but do not become integrated into the reaction products

  • Are not used up or permanently changed by the reaction

  • Can be recycled, thus functioning in extremely low concentrations

  • Are greatly affected by temperature and pH

  • Can be regulated by feedback and genetic mechanism

Conjugated Enzyme Structure

  • Metallic cofactor

  • Coenzyme

  • Coenzyme and Metallic cofactor

    • All of them made apoenzymes

Cofactors: Supporting the Work of Enzymes

  • The need of microorganisms for trace elements arises from their roles as cofactors for enzymes

    • Iron, copper, magnesium, manganese, zinc, cobalt, selenium, etc.

  • Participate in precise functions between the enzyme and substrate

    • Help bring the active site and substrate close together

  • Coenzymes

    • Organic compounds that work in conjunction with an apoenzyme

    • The general function is to remove a chemical group from one substrate molecule and add it to another substrate molecule

    • Carry and transfer hydrogen atoms, electrons, carbon dioxide, and amino groups

    • Many derive from vitamins

Enzyme-Substrate Interactions

  • A temporary enzyme-substrate union must occur at the active site

    • Fit is so specific that it is described as a “lock-and-key” fit

  • The bond formed between the substrate and enzyme are weak adn easily reversible

  • Products are formed

  • Enzyme is free to interact with another substrate

Concept Check - 2

What is true about enzymes? They _________

A. are proteins

B. speed up reactions

C. are specific to substrates

D. are not consumers in reactions

E. all

Concept Check - 3

Micronutrients such as Cu, Fe, Mn, and Zn, are essential for microbes because they function as ________

A. coenzymes

B. cofactors

C. active site

D. apoenzymes

Concept Check - 4

Apoenzymes are _______ part of a conjugated enzyme

A. protein

B. protein + inorganic adjuncts

C. protein + organic adjuncts

D. Substrates

E. all

Metabolic Pathways

  • Often occur in a multistep series or pathway, with each step catalyzed by an enzyme

  • Products of one reaction are often the reactant (substrate) for the next, forming a linear chain or reaction

  • Many pathways have branches that provide alternate methods for nutrient processing

  • Others have a cyclic form, in which the starting molecule is regenerates to initiate another turn of the cycle

  • Do not stand alone; interconnected and merge at many sites

ATP: Metabolic Money

  • Three-part molecule

    • Nitrogen base (adenine)

    • 5-carbon sugar (ribose)

    • Chain of three phosphate groups bonded to ribose

    • Phosphate groups are bulky and carry negative charges, causing a strain between the last two phosphates

    • The removal of the terminal phosphate releases energy

The Metabolic Role of ATP

  • ATP utilization and replenishment is an ongoing cycle

    • Energy released during ATP hydrolysis powers biosynthesis

    • Activates individual subunits before they are enzymatically linked together

  • Used to prepare molecules for catabolism

  • When ATP is utilized, the terminal phosphate is removed to release energy, and ADP is formed

    • Input of energy is required to replenish ATP

  • In heterotrophs, catabolic pathways provide the energy infusion that generates the high-energy phosphate to form ATP from ADP

Getting Materials and Energy

  • Nutrient processing in bacteria is extremely varied, but in most cases the nutrient is glucose

  • Aerobic respiration

    • Conversions of glucose CO2 with the production of energy (ATP)

    • Utilizes glycosis, the Kerbs cycle, and the electron transport chain (ETC)

    • Relies on free oxygen as the final electron and hydrogen acceptor

    • Characteristics of many bacteria, fungi, protozoa/animals

  • Anaerobic respiration

    • Used by strictly anaerobic organisms and those who are unable to metabolize without oxygen

    • Involves glycolysis, the Kerbs cycle, and the electron transport chain

    • Uses NO 3-, SO4 2-, CO3 3-, and other oxidized compounds as final electron acceptors

  • Fermentation

    • Incomplete oxidation of glucose

    • Oxygen is not required

    • Organic compounds are final electron acceptors

Concept Check - 5

The energy molecule ATP is made up of

A. Proteins

B. Adenine

C. Ribose + Adenine + 3P

D. Adenine + 3P

E. All

Concept Check - 6

Aerobic & Anaerobic - both types of cellular respiration - involve

A. Glycolysis

B. Krebs Cycle

C. Electron Transport System

D. All above

E. Only B, C

Glycolysis

  • Turns glucose into pyruvate, which yields energy in the pathways

The Krebs Cycle: A Carbon and Energy Wheel

  • Takes place in the cytoplasm of bacteria and in the mitochondrial matrix of eukaryotes

    • A cyclical metabolic pathway begins with acetyl CoA

    • Transfer the energy stored in acetyl CoA to NAD+ and FAD by reducing them

    • NADH and FADH2 carry electrons to the electron transport chain

    • 2 ATPs are produced for each molecule of glucose through phosphorylation

Concept Check - 7

Glycolysis is the first step in catabolism that generates

A. Pyruvate

B. ATP

C. NADH

D. All above

E. Only B, C

Concept Check - 8

The Krebs Cycle starts with converting ______ into ______ that runs the wheel of releasing energy molecules.

A. Pyruvate, Acetyl CoA

B. ATP, NADH

C. NADH, Pyruvate

D. Acetyl, CoA, Pyruvate

The Respiratory Chain: Electron Transport

  • A chain of special redox carriers that receives reduced carriers (NADH, FADH2) generated by glycolysis and the Krebs cycle

    • Passes them in a sequential and orderly fashion from one to the next

    • Highly energetic

    • Allows the transport of hydrogen ions outside of the membrane

    • In the final step of the process, oxygen accepts electrons and hydrogen, forming water.

  • Primary

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