Lecture 1.2 - Energy reactions in cells

Carrier Molecules

• The total concentration of carrier molecules in cells is constant and consists of both oxidized and reduced forms.
• Carrier molecules are complex and contain components from vitamins (B vitamins).
• They are converted to reduced form by adding two H atoms (H+ + e-), and H+ dissociates into solution.
• NADPH is a carrier molecule.

Bioenergetics

• Bioenergetics is the study of energy changes (transfer and utilization) in biochemical reactions.
• Reactions are classified as exergonic (energy releasing) and endergonic (energy consuming).
• Free energy (G) is the energy available to do work and is related to enthalpy and entropy changes.
• Free energy change (ΔG) is the energy change as the system moves from its initial state to equilibrium.
• Exergonic reactions are spontaneous and release energy, while endergonic reactions require more energy to take place.

ATP-ADP-AMP

• ATP is produced by the energy released in exergonic reactions.
• ATP is a high-energy molecule due to the chemical bond energy of its terminal phosphate group.
• The concentration of ADP and ATP is limited, making it necessary to cycle.
• ATP is stable in the absence of specific catalysts, enabling controlled flow of energy.

Cellular Metabolism

• Cell metabolism refers to the chemical reactions that occur within cells.
• Many reactions take place in the body, but only a few reaction types are organized into metabolic pathways.
• Metabolic pathways are distinct but integrated and occur in all cells, some cell types, or specific compartments.
• Anabolism and catabolism are interconnected and make up metabolism.

Catabolic Metabolism

• Products of catabolic metabolism include:
  • Building block materials (sugars, amino acids, fatty acids)
  • Organic precursors (acetyl CoA)
  • Biosynthetic reducing power (NADH, NADPH)
  • Energy for cell function and synthesis of cell components (ATP)

Biological Oxidation

• Biological oxidation is the release of chemical bond energy of fuel molecules through oxidation reactions.
• Oxidation involves the removal of electrons (e-) or H atoms (H+ + e-).
• Oxidation reactions are accompanied by reduction reactions, forming REDOX reactions.

H-Carrier Molecules

• H-carrier molecules, such as NAD+, transfer electrons and protons from fuel molecules during oxidation.
• H-carrier molecules cycle between oxidative and reductive processes.
• They act as carriers of reducing power for ATP production and biosynthesis.

Clinical Relevance

• Creatine phosphate is a high-energy reserve that can rapidly produce ATP for muscle contraction under anaerobic conditions.
• Creatine kinase (CK) is a marker of myocardial infarction (heart attack).
• CK is released from cardiac myocytes when damaged, and its levels appear in blood after a few hours.
• CK is diagnostic of MI and rises approximately 6 hours after MI, remaining elevated for 36-48 hours.
• Creatinine levels are indicative of skeletal muscle mass and kidney function.
• Increased creatinine levels in urine suggest muscle wasting, while high blood levels and low urine levels indicate reduced kidney function.