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