Study sheet: Metabolism and Energy Balance

📋 Course Outline

1. Metabolism and Chemical Reactions
2. Cellular Compartments and Coordination
3. Anabolism and Catabolism
4. Aerobic and Anaerobic Metabolism
5. ATP Production and Energy Expenditure
6. Metabolic Intermediates and Reserves
7. Fasting Adaptations

📖 1. Metabolism and Chemical Reactions

🔑 Key Concepts & Definitions

• Metabolism : the set of chemical reactions through which the cells of an organism produce and/or use energy, while transforming matter
• Enzyme : a catalyst that facilitates a chemical reaction in a cell without being presented as a reactant

★ Must-know

📌 Anabolism consists of synthesis pathways that build molecules, whereas catabolism consists of degradation pathways that break molecules down.

Further detail

• A molecule is a group of atoms joined by chemical bonds, whereas an atom is the smallest part of a simple body that can chemically combine with another atom.

💡 Memory Hook

Substrates → enzyme-catalyzed reactions → products

📖 2. Cellular Compartments and Coordination

🔑 Key Concepts & Definitions

• Cell : the smallest structural and functional unit constituting all or part of a living organism

★ Must-know

• A eukaryotic cell contains a nucleus, cytoplasm, and membrane-bound organelles such as mitochondria.

📌 Cellular compartmentalization assigns specialized tasks to specialized locations, such as mechanical work to muscle cells and electrical work to nerve cells.

📌 Metabolic regulation maintains relatively constant living conditions in response to internal and external signals while the environment changes continuously.

Further detail

• The plasma membrane delimits the cell and permits regulated exchanges with its environment.

💡 Memory Hook

A coordinated city where each organelle has a specialized workplace

📖 3. Anabolism and Catabolism

🔑 Key Concepts & Definitions

• Anabolism : the synthesis of small molecules and macromolecules from simple nutrients or metabolic intermediates, and it requires an energy supply
• Catabolism : the production of energy through the oxidation and degradation of food-derived nutrients and cellular reserves

📝 Essential Points

• Catabolism produces chemical, electrical, or mechanical energy, with part of the chemical energy stored as ATP.

💡 Memory Hook

Anabolism builds and consumes energy; catabolism breaks down and produces energy

📖 4. Aerobic and Anaerobic Metabolism

★ Must-know

📌 Aerobic metabolism uses oxygen and is suited to prolonged exercise, whereas anaerobic metabolism functions without oxygen during intense, brief exercise.

• Aerobic oxidation of glucose produces water, carbon dioxide, heat, and ATP.

• 🔄 The progression of myocardial infarction is:

  1. arterial occlusion
  2. reduced oxygen delivery
  3. ischemia
  4. necrosis
  5. death or sequelae

Further detail

• The alactic anaerobic system supports intense effort for approximately 20 seconds, whereas the lactic anaerobic system can support effort for approximately 2 minutes and may cause cramps through lactate accumulation.

💡 Memory Hook

Oxygen-supported endurance versus oxygen-limited intensity

📖 5. ATP Production and Energy Expenditure

★ Must-know

• ATP is an energy intermediary used immediately or hydrolyzed when energy is needed.

• Approximately 20–30% of ATP production occurs in the cytosol through carbohydrate oxidation, whereas 70–80% occurs in mitochondria from carbohydrates and lipids.

• Mitochondrial oxidative phosphorylation uses a proton flow generated by oxidation pathways to synthesize ATP, with oxygen contributing to water formation.

• The resting energy expenditure represents 60–70% of total energy expenditure and supports vital functions, resting muscle tone, and active ion transport.

Further detail

• Post-prandial thermogenesis represents 10–15% of total energy expenditure, while physical activity represents 20–25% in sedentary people and 60–70% in high-level athletes.

💡 Memory Hook

Cytosol → mitochondrion → oxidative phosphorylation → ATP

📖 6. Metabolic Intermediates and Reserves

🔑 Key Concepts & Definitions

• Metabolic intermediates : a crossroads where carbohydrate, lipid, and protein pathways interact and connect with energy storage

★ Must-know

• Glycogen is the glucose storage polymer found mainly in muscle and liver, whereas lipids are stored in adipose tissue.

📌 Insulin acts mainly as a storage hormone, promoting the storage or synthesis of carbohydrates, lipids, and proteins after food intake.

Further detail

• ATP supports glycogen synthesis, lipid synthesis, protein detoxification through urea production, and sodium pumping for hydromineral homeostasis.

💡 Memory Hook

A metabolic crossroads linking carbohydrates, lipids, proteins, and storage tissues

📖 7. Fasting Adaptations

★ Must-know

📌 During fasting, the first priorities are to maintain blood glucose for the brain and red blood cells and to preserve muscle protein mass.

• The first fasting phase uses glycogenolysis to release glucose from limited liver and muscle glycogen stores and lasts approximately 48 hours.

• The second fasting phase uses gluconeogenesis to synthesize glucose from amino acids, consumes energy, and threatens muscle protein mass over approximately 1–3 days.

📌 During the lipid phase, fatty acids provide energy through ketone bodies, but lipids do not produce glucose because the relevant metabolic pathway does not exist.

Further detail

• In the final stage of fasting, proteolysis again supplies substrates for gluconeogenesis, and depletion of 54% of the vital metabolic compartment compromises the vital prognosis.

• With water and mineral salts available, survival may be possible for 45–65 days through metabolic regulation, although the duration depends on individual reserves.

💡 Memory Hook

Glycogenolysis → gluconeogenesis → ketone use → final proteolysis

📊 Synthesis Tables

Aerobic and Anaerobic Metabolism

Feature	Aerobic metabolism	Anaerobic metabolism
Oxygen	Uses oxygen	Functions without oxygen
Typical effort	Prolonged exercise	Intense, brief exercise
Main limitation	Not described as limited	Alactic: approximately 20 seconds; lactic: approximately 2 minutes
Metabolic outcome	Water, carbon dioxide, heat, and ATP	Possible lactate accumulation