Chapter 18: Metabolic Pathways and Energy Production

Flashcards covering key concepts from Chapter 18 on metabolism, ATP, glycolysis, coenzymes (NAD+/NADH, FAD/FADH2, CoA), and the citric acid cycle and electron transport chain.

What is metabolism?

All chemical reactions in cells that provide energy and substances needed for continued growth; includes catabolic and anabolic processes.

What are catabolic and anabolic reactions?

Catabolic reactions break down complex molecules to release energy; anabolic reactions build large molecules using energy.

Define a metabolic pathway.

A series of linked enzyme-catalyzed reactions that produce energy or cellular compounds.

Name the three main metabolic pathways involved in glucose oxidation.

Glycolysis, the citric acid cycle (Krebs), and the electron transport chain (oxidative phosphorylation).

What are the three stages of catabolism?

Stage 1 digestion in the digestive tract; Stage 2 intracellular degradation to two- and three-carbon compounds (pyruvate and acetyl-CoA); Stage 3 oxidation in mitochondria producing CO2, H2O, and ATP.

Where is most ATP energy produced in the cell?

In the mitochondria during the citric acid cycle and electron transport chain.

What is ATP and what energy is released by hydrolysis?

ATP is the energy-currency of the cell; hydrolysis to ADP and Pi releases about 7.3 kcal per mole.

What cellular processes require ATP?

Muscle contraction, movement of substances across membranes, nerve impulse transmission, and synthesis of large molecules.

What are NAD+ and NADH?

NAD+ is the oxidized coenzyme that accepts 2H to form NADH + H+; NADH is the reduced form that acts as an electron carrier.

What is FAD and FADH2?

FAD is a coenzyme that accepts 2H to form FADH2; it participates in oxidation that forms C=C bonds (e.g., succinate to fumarate).

What is Coenzyme A and its reactive feature?

CoA is derived from pantothenic acid; its thiol (-SH) forms a thioester with an acetyl group to make acetyl-CoA.

What is acetyl-CoA and why is it important?

Acetyl-CoA is an acetyl group bound to CoA; it is the entry molecule to the citric acid cycle.

Where does glycolysis occur and is it aerobic or anaerobic?

Glycolysis occurs in the cytoplasm and is an anaerobic process; it does not require oxygen.

What are the energy-investing and energy-generating phases of glycolysis?

Energy-investing phase (reactions 1-5) consumes 2 ATP; energy-generating phase (reactions 6-10) produces 4 ATP and 2 NADH; net gain is 2 ATP per glucose.

What are the end products of glycolysis from one glucose?

Two pyruvate molecules, with net production of 2 ATP and 2 NADH.

What happens to pyruvate under aerobic conditions?

Pyruvate is converted to acetyl-CoA by pyruvate dehydrogenase, releasing CO2 and generating NADH; acetyl-CoA enters the citric acid cycle.

What happens to pyruvate under anaerobic conditions?

Pyruvate is reduced to lactate; NAD+ is regenerated for glycolysis.

In the citric acid cycle, what are the end products and electron carriers produced?

CO2 is released; NADH and FADH2 are produced; energy is captured for ATP via the electron transport chain.

What is the role of the electron transport chain?

NADH and FADH2 donate electrons to the chain; energy is used to pump protons and synthesize ATP; O2 is the final electron acceptor forming water.

Where are mitochondria and their compartments located and what do they do?

Mitochondrion has outer membrane, inner membrane, intermembrane space, and matrix; enzymes for oxidation reside in the matrix and inner membrane; the ETC is located in the inner membrane and ATP is produced from the energy of electron transfer.

What is the function of the cytosol in metabolism?

The aqueous solution of electrolytes and enzymes that catalyze many reactions; site of the glycolysis steps 1–5.

Which vitamins form NAD+ and FAD?

NAD+/NADH are derived from niacin (vitamin B3); FAD/FADH2 are derived from riboflavin (vitamin B2).