Chapter 4: Energy and Metabolism

Energy

The capacity to do work or cause change.

Kinetic Energy

Energy associated with motion.

Potential Energy

Stored energy based on an object's position, arrangement, or structure.

Chemical Energy

Potential energy associated with the arrangement of atoms and electrons in chemical substances.

Metabolism

The total of the chemical reactions occurring in an organism.

Enzyme

A biological catalyst that speeds up chemical reactions by lowering activation energy.

Biological Catalyst

A substance that speeds up a biological reaction without being consumed in the reaction.

Activation Energy

The minimum energy needed to start a chemical reaction.

How Do Enzymes Work?

Enzymes lower activation energy, allowing reactions to occur faster without being consumed.

Substrate

The reactant an enzyme acts on.

Active Site

The region of an enzyme where the substrate binds and the reaction occurs.

Enzyme Specificity

The ability of an enzyme to recognize and act on particular substrates.

Denaturation

A change in a protein's shape that can cause it to lose its function.

How Can Heat Affect Enzymes?

High temperatures can disrupt an enzyme's structure and reduce or destroy its activity.

How Can pH Affect Enzymes?

Extreme pH can alter an enzyme's shape and interfere with its function.

Competitive Inhibition

An inhibitor competes with the substrate for the enzyme's active site.

Noncompetitive (Allosteric) Inhibition

An inhibitor binds away from the active site, changing enzyme activity or shape.

Competitive vs. Noncompetitive Inhibition

Competitive inhibitors block the active site; noncompetitive inhibitors bind elsewhere and alter enzyme function.

ATP (Adenosine Triphosphate)

The main energy

ATP Structure

ATP consists of adenine, ribose sugar, and three phosphate groups.

ATP Hydrolysis

The reaction that removes ATP's terminal phosphate, forming ADP and inorganic phosphate and releasing usable free energy.

Why Is ATP Useful to Cells?

ATP transfers energy to power cellular processes, including active transport and biosynthesis.

Cellular Respiration

The process of harvesting energy from organic molecules to produce ATP.

Aerobic Cellular Respiration

Cellular respiration that uses oxygen as the final electron acceptor.

Glycolysis

The pathway in the cytoplasm that splits glucose into two pyruvate molecules, producing a net 2 ATP and NADH.

Where Does Glycolysis Occur?

In the cytoplasm (cytosol) of the cell.

Products of Glycolysis

Two pyruvate molecules, a net 2 ATP, and 2 NADH per glucose molecule.

Citric Acid Cycle (Krebs Cycle)

A series of reactions that oxidize acetyl

Where Does the Citric Acid Cycle Occur?

In the mitochondrial matrix in eukaryotic cells.

Acetyl

CoA

Pyruvate Oxidation

The process that converts pyruvate into acetyl

Oxidative Phosphorylation

ATP production using the electron transport chain and chemiosmosis.

Electron Transport Chain

A series of membrane proteins that pass electrons along and use the released energy to pump protons.

Where Does the Electron Transport Chain Occur?

In the inner mitochondrial membrane in eukaryotic cells.

Final Electron Acceptor in Aerobic Respiration

Oxygen, which accepts electrons and hydrogen ions to form water.

Chemiosmosis

The movement of protons down their electrochemical gradient through ATP synthase to drive ATP production.

ATP Synthase

A membrane protein complex that uses the flow of protons to produce ATP.

Why Is Oxygen Needed in Aerobic Respiration?

Oxygen accepts electrons at the end of the electron transport chain, allowing electron flow to continue.

Overall Equation of Aerobic Cellular Respiration

Glucose + oxygen → carbon dioxide + water + usable energy (ATP).

Main Stages of Cellular Respiration

Glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation.

Where Is Most ATP Produced During Aerobic Respiration?

During oxidative phosphorylation, through the electron transport chain and chemiosmosis.

Fermentation

An anaerobic process that regenerates NAD⁺ so glycolysis can continue producing ATP.

Why Is Fermentation Important?

It regenerates NAD⁺ when oxygen is unavailable or aerobic respiration cannot proceed.

Lactic Acid Fermentation

A process in which pyruvate is reduced to lactate, regenerating NAD⁺ from NADH.

Where Does Lactic Acid Fermentation Occur?

In certain bacteria and in animal cells, including muscle cells under conditions where glycolysis outpaces oxygen

Alcohol Fermentation

A process in which pyruvate is converted into ethanol and carbon dioxide while NAD⁺ is regenerated.

Where Does Alcohol Fermentation Occur?

In yeast and certain microorganisms.

Lactic Acid vs. Alcohol Fermentation

Lactic acid fermentation produces lactate; alcohol fermentation produces ethanol and carbon dioxide.

Obligate Anaerobes

Organisms that cannot tolerate oxygen and must live without it.

Facultative Anaerobes

Organisms that can grow with oxygen but can also use anaerobic pathways when oxygen is unavailable.

Obligate Anaerobes vs. Facultative Anaerobes

Obligate anaerobes cannot tolerate oxygen; facultative anaerobes can function with or without it.