Chapter 24: Nutrition, Metabolism, and Energy Balance

Metabolism

The sum of all chemical reactions in the body

Anabolism

Building larger molecules from smaller ones

Catabolism

Breaking down molecules to release energy

Cellular respiration

Process that releases energy by breaking down glucose and other food molecules in the presence of oxygen

ATP

Main energy source cells use for most of their work

Glycolysis

Breakdown of glucose by enzymes, releasing energy and pyruvic acid.

Citric acid cycle

Completes breakdown of glucose by oxidizing a derivative of pyruvate to carbon dioxide

Oxidative phosphorylation

Production of ATP using energy derived from redox reactions of an electron transport chain

Oxidation

Loss of electrons (or hydrogen), often involves gaining oxygen

Reduction

Gain of electrons (or hydrogen)

Coenzymes

Organic molecule that helps catalysis by donating or accepting electrons or functional groups

NAD+

Becomes NADH after gaining electrons

FAD

Becomes FADH2 after gaining electrons

Substrate-level phosphorylation

Phosphate group is transferred directly from a substrate to ADP to make ATP

Oxidative phosphorylation

Uses energy from electrons transported via NADH/FADH₂ through electron transport chain to drive ATP production via ATP synthase

Aerobic pathway

Requires oxygen; citric acid cycle, electron transport chain

Anaerobic pathway

Does not require oxygen; glycolysis

Glycolysis substrates

Glucose

Glycolysis products

2 pyruvic acid, 2 ATP (net), 2 NADH

Pyruvic acid

Product of glycolysis that can be used in aerobic respiration or converted to lactic acid

Lactic acid

Produced in muscle cells from reduction of pyruvate (under anaerobic conditions) to regenerate NAD+ so glycolysis can continue

NADH

Energy-carrying coenzyme produced by glycolysis and Krebs cycle; carries energy to electron transport chain, where it is stored in ATP

FADH2

Stores energy for harvest by the electron transport chain

Citric acid cycle substrates

Acetyl CoA

Citric acid cycle products

3 NADH, 1 FADH2, 1 ATP, 2 CO2, keto acids

Acetyl CoA

Entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme.

Citric acid

Six-carbon compound formed in the Krebs cycle

Keto acids

Organic acids containing a ketone functional group and a carboxylic acid group

CO2

Produce in citric acid cycle

Electron transport chain

Series of electron carrier proteins that shuttle high-energy electrons during ATP-generating reactions

ATP synthase

Enzyme that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP

Glycogenesis

Formation of glycogen from glucose

Glycogenolysis

Breakdown of glycogen into glucose

Gluconeogenesis

Formation of glucose from non-carbohydrate sources

Beta oxidation

Fatty acids broken down in mitochondria into acetyl CoA, which enters the citric acid cycle

Lipogenesis

Formation of triglycerides (fats) from glucose or amino acids

Lipolysis

Breakdown of triglycerides into glycerol and fatty acids

Ketogenesis

Occurs in liver when there is excess acetyl CoA, produces ketone bodies

Ketone bodies/ketones

Used as fuel by brain and muscles during prolonged fasting/starvation

Degradation of amino acids

Produce molecules used for energy in citric acid cycle or converted to glucose

Protein synthesis

Formation of proteins using information contained in DNA and carried by mRNA

Transamination

Amino group is transferred to form glutamic acid

Ammonia

Produced as a metabolic waste product of protein and nucleic acid metabolism

Urea

Waste product formed in the liver, filtered out of the blood by kidneys, and excreted in urine