Metabolism, Energy, and Nutrient Breakdown Overview

Metabolism

Metabolism is the sum of all chemical reactions involved in catabolism (breaking down molecules) and anabolism (building molecules).

Excess energy from catabolism

It is stored as glycogen or fat for future use.

Body needs more energy than it takes in

It catabolizes stored energy such as glycogen or fat.

Catabolic hormones

Cortisol, glucagon, epinephrine, and cytokines.

ATP composition

Adenine, ribose, and three phosphate groups.

ATP breakdown

It becomes ADP and an inorganic phosphate (P), releasing energy.

Energy from catabolism

40% is transferred to ATP; 60% is given off as heat.

Carbohydrates breakdown

Into glucose; stored as glycogen in the liver or muscles.

Fats breakdown

Into glycerol and fatty acids; stored in adipocytes.

Proteins breakdown

Into amino acids; used for protein synthesis in cells and energy during starvation.

Primary use of nucleic acids

For nucleic acid metabolism: replication, transcription, and translation in cells.

Anabolism

The process of using energy to build small molecules into larger ones (biosynthesis).

Reactions requiring ATP

Anabolic reactions.

Anabolic hormones

Growth hormone, insulin-like growth factor, insulin, testosterone, and estrogen.

Oxidation

Oxidation is losing electrons; reduction is gaining electrons.

Redox reactions

Catalyzed by enzymes that trigger removal of hydrogen atoms and electrons.

Main coenzymes in redox reactions

NAD becomes NADH and FAD becomes FADH2.

Carbohydrates composition

Carbon, hydrogen, oxygen. Monosaccharides (e.g., glucose) and polysaccharides (e.g., starch, glycogen).

Glucose uptake

In response to insulin.

Glycolysis production

4 ATP, 2 NADH, and 2 pyruvate (net gain: 2 ATP).

Pyruvate with oxygen

With oxygen: enters Krebs cycle. Without oxygen: converts to lactic acid.

Anaerobic respiration

Respiration without oxygen; produces 1 ATP, oxidizes NADH to NAD+, and forms lactic acid.

Cori cycle

Converts lactic acid back into pyruvate or glucose in the liver.

Aerobic respiration

Respiration with oxygen; final electron acceptor is oxygen (forms water).

Krebs cycle location

Inner mitochondrial matrix; acetyl CoA enters.

Krebs cycle

Produces 1 ATP, 3 NADH, and 1 FADH2 per pyruvate.

Carbon atoms from pyruvate

Converted into carbon dioxide.

Electron Transport Chain (ETC)

Powered by electrons from NADH and FADH2.

ATP production in the ETC

H+ gradient powers ATP synthase, generating ATP.

ATP produced per glucose

Net 36 ATP.

Gluconeogenesis

Creating glucose from non-carbs (pyruvate, lactate, amino acids); occurs during fasting/starvation.

Lipid metabolism

Oxidation of fatty acids for energy; stimulated by cholecystokinin.

Lipolysis

Breaking down fat stores to form acetyl CoA for energy.

Energy yield of fats

Fats provide more than twice the energy per gram compared to carbs or protein.

Ketogenesis

Formation of ketone bodies from excess acetyl CoA during fasting or low carbs.

Diabetic ketoacidosis

Excess ketone bodies create CO₂ and acetone, acidifying the blood.

Lipogenesis

Formation of lipids (fatty acids, cholesterol, etc.) from excess acetyl CoA.

Excess protein in the body

Converted to glucose, triglycerides, or decomposed into waste.

Urea cycle

Converts toxic ammonium and CO₂ into urea in the liver for excretion.

Absorptive state

Occurs during digestion; insulin levels are elevated.

Postabsorptive state

Fasting state (e.g., overnight); glucagon levels rise.

Starvation state

Glucose is preserved for the brain; ketones become fuel; proteins are eventually broken down.

Body temperature control

The hypothalamus controls sweating (cooling) and shivering (heating).

Thermoneutrality

When the body doesn't expend energy to maintain temperature.

Heat loss percentages

Conduction - 3%, Convection - 15%, Radiation - 60%, Evaporation - 20%.

Basal Metabolic Rate (BMR)

Energy used at rest, postabsorptive, in a neutral environment.

Daily energy use percentages

70% organ function, 20% physical activity, 10% thermoregulation.

Overweight and obesity definitions

Overweight = 10% excess intake/day; Obesity = 20% or more excess intake/day.

Macronutrient energy requirement

Protein requires the most energy to break down.

Body Mass Index (BMI)

Height-to-weight ratio; doesn't account for body composition or overall health.

Vitamins

Organic compounds aiding biochemical reactions; B vitamins are most involved.

Minerals

Inorganic compounds from the diet; help in ionic form with body functions (e.g., calcium, phosphate, sodium).