Chapter 5: Microbial Metabolism

Metabolism

The buildup and breakdown of nutrients within a cell through chemical reactions.

Purpose of Metabolism

Provides energy and creates substances needed to sustain life.

Catabolism

Breakdown of large molecules into smaller molecules while releasing energy.

Anabolism

Building of larger molecules from smaller molecules while using energy.

Catabolism vs Anabolism

Catabolism breaks molecules down and releases energy while anabolism builds molecules and requires energy.

ATP Role in Metabolism

Stores energy released by catabolism and provides energy for anabolic reactions.

Metabolic Pathway

Sequence of enzyme-controlled chemical reactions occurring in a cell.

Enzymes and Metabolic Pathways

Enzymes determine and control the steps of metabolic pathways.

Activation Energy

Energy required for a chemical reaction to occur.

Catalyst

Substance that speeds up a chemical reaction without being permanently changed.

Enzyme

Biological catalyst that speeds up chemical reactions.

Substrate

Specific reactant on which an enzyme acts.

Active Site

Region of an enzyme where the substrate binds.

Enzyme-Substrate Complex

Temporary combination formed when a substrate binds to an enzyme active site.

Enzymatic Action

Substrate binds to the active site and is changed into products while the enzyme remains unchanged.

Enzyme Reuse

An enzyme is unchanged after a reaction and can act on additional substrate molecules.

Enzyme Naming

Many enzyme names end in the suffix ase.

Transferase

Enzyme that transfers functional groups.

Hydrolase

Enzyme that catalyzes hydrolysis reactions.

Cofactor

Nonprotein substance that helps an enzyme function.

Inorganic Cofactor

Nonprotein enzyme helper such as a metal ion.

Coenzyme

Organic cofactor that assists an enzyme.

Electron Carrier Coenzymes

NAD plus; NADP plus; and FAD can carry electrons.

Apoenzyme

Inactive protein portion of an enzyme.

Holoenzyme

Complete active enzyme formed from an apoenzyme plus its required cofactor.

Factors Affecting Enzyme Activity

Temperature; pH; substrate concentration; and inhibitors affect enzyme activity.

Temperature and Enzymes

Increasing temperature can increase enzyme activity until high heat causes denaturation.

pH and Enzymes

Extreme pH can denature enzymes and reduce their activity.

Denaturation

Loss of a protein normal shape that causes loss of function.

Substrate Concentration Effect

Increasing substrate concentration increases reaction rate until all enzyme active sites are occupied.

Maximum Enzyme Reaction Rate

Point at which all available enzyme active sites are filled and adding more substrate no longer increases the rate.

Enzyme Inhibitor

Substance that decreases or prevents enzyme activity.

Competitive Inhibitor

Inhibitor that competes with the substrate for the enzyme active site.

Competitive Inhibition Effect

Blocks the substrate from binding by occupying the active site.

Noncompetitive Inhibitor

Inhibitor that binds somewhere other than the active site.

Noncompetitive Inhibition Effect

Changes the shape of the active site and prevents normal enzyme function.

Allosteric Site

Site on an enzyme separate from the active site where some inhibitors can bind.

Competitive vs Noncompetitive Inhibition

Competitive inhibitors bind the active site while noncompetitive inhibitors bind elsewhere and change active site shape.

Feedback Inhibition

End product of a pathway inhibits an enzyme that acts earlier in the pathway.

Purpose of Feedback Inhibition

Prevents unnecessary production of an end product and conserves cellular resources.

Oxidation

Removal or loss of electrons from a molecule.

Reduction

Gain of electrons by a molecule.

Redox Reaction

Reaction in which oxidation and reduction occur together.

OIL RIG

Oxidation is loss of electrons and reduction is gain of electrons.

Electron Carrier

Molecule that accepts and transports high-energy electrons.

NAD Plus

Oxidized electron carrier that can accept electrons and become NADH.

NADH

Reduced electron carrier that carries high-energy electrons.

FAD

Oxidized electron carrier that can accept electrons and become FADH2.

FADH2

Reduced electron carrier that carries high-energy electrons.

Phosphorylation

Addition of a phosphate group to a molecule.

ATP Formation

ATP is generated when ADP gains a phosphate with an input of energy.

Substrate-Level Phosphorylation

Formation of ATP by directly transferring a high-energy phosphate to ADP.

Carbohydrate Catabolism

Breakdown of carbohydrates to release energy.

Three Main Stages of Carbohydrate Catabolism

Glycolysis; Krebs cycle; and electron transport chain.

Glycolysis

Oxidation of glucose to pyruvic acid while producing ATP and NADH.

Location of Glycolysis

Glycolysis occurs before the Krebs cycle and electron transport chain.

Glycolysis Preparatory Stage

Stage in which two ATP are used and glucose is split into two three-carbon molecules.

ATP Used in Glycolysis

Two ATP are invested during the preparatory stage.

Glucose Splitting in Glycolysis

One six-carbon glucose is split into two three-carbon molecules.

Glyceraldehyde 3-Phosphate

Three-carbon intermediate produced during glycolysis.

Glycolysis Energy-Conserving Stage

Stage in which two glyceraldehyde 3-phosphate molecules are oxidized to pyruvic acid.

ATP Produced in Glycolysis

Four ATP are produced during the energy-conserving stage.

NADH Produced in Glycolysis

Two NADH are produced per glucose molecule.

Pyruvic Acid Produced in Glycolysis

Two pyruvic acid molecules are produced per glucose molecule.

Net ATP from Glycolysis

Two ATP are gained per glucose because four are produced after two are used.

Overall Products of Glycolysis

Two pyruvic acid; two NADH; and a net gain of two ATP per glucose.

Cellular Respiration

Process that uses oxidation and an electron transport chain to generate ATP.

Final Electron Acceptor in Respiration

Comes from outside the cell and accepts electrons at the end of the electron transport chain.

Aerobic Respiration

Respiration that uses oxygen as the final electron acceptor.

Anaerobic Respiration

Respiration that uses a final electron acceptor other than oxygen.

Aerobic vs Anaerobic Respiration

Aerobic respiration uses oxygen while anaerobic respiration uses another final electron acceptor.

Oxidative Phosphorylation

Production of ATP using energy released through the electron transport chain and chemiosmosis.

Preparatory Step Before Krebs Cycle

Pyruvic acid is converted into acetyl CoA before entering the Krebs cycle.

Decarboxylation

Removal of carbon dioxide from a molecule.

Pyruvate Oxidation

Pyruvic acid is oxidized and loses carbon dioxide before forming acetyl CoA.

Acetyl CoA

Two-carbon compound attached to coenzyme A that enters the Krebs cycle.

NADH During Acetyl CoA Formation

NADH is produced when pyruvic acid is converted to acetyl CoA.

Krebs Cycle

Cyclic pathway that oxidizes acetyl CoA and produces electron carriers; ATP; and carbon dioxide.

Citric Acid Cycle

Another name for the Krebs cycle.

Beginning of Krebs Cycle

Two-carbon acetyl group combines with four-carbon oxaloacetic acid.

Citric Acid

Six-carbon molecule formed at the beginning of the Krebs cycle.

Oxaloacetic Acid

Four-carbon molecule regenerated at the end of the Krebs cycle.

Krebs Cycle Products

NADH; FADH2; ATP; and carbon dioxide are produced during the cycle.

Main Purpose of Krebs Cycle

Produces reduced electron carriers that can supply electrons to the electron transport chain.

Carbon Dioxide in Krebs Cycle

Carbon atoms are removed and released as carbon dioxide.

Electron Transport Chain (ETC)

Series of carrier molecules that pass electrons through oxidation and reduction reactions.

ETC Electron Movement

Electrons move from higher energy to lower energy through a series of carriers.

NADH Role in ETC

Donates high-energy electrons to the electron transport chain.

FADH2 Role in ETC

Donates high-energy electrons to the electron transport chain.

ETC Location in Prokaryotes

Located in the plasma membrane.

ETC Location in Eukaryotes

Located in the inner mitochondrial membrane.

Energy Released by ETC

Used to pump protons across a membrane.

Chemiosmosis

Process in which movement of protons through ATP synthase provides energy to make ATP.

Proton Gradient

Difference in hydrogen ion concentration across a membrane.

Proton Motive Force

Stored energy created by a proton concentration gradient across a membrane.

ATP Synthase

Membrane enzyme that uses proton movement to produce ATP from ADP and phosphate.

Proton Movement Through ATP Synthase

Protons move from high concentration to low concentration through ATP synthase.

Chemiosmosis Steps

Electrons move through the ETC; protons are pumped; a gradient forms; and protons return through ATP synthase.

Final Electron Acceptor in Aerobic Respiration

Molecular oxygen.

Oxygen at End of ETC

Oxygen accepts electrons and combines with protons to form water.