Biochemistry: Energy and Mitochondria

What is Energy?

• Energy is required for living things to maintain order, grow and reproduce
• Bioenergetics is the branch of biochemistry focusing on how cells transform energy
• Chemical energy is stored in the bonds of molecules and can be released and transformed by metabolic pathways
• Free Energy (G) is the chemical energy available to do work

Why Life Requires a Highly Ordered System?

• Living organisms require a highly ordered system to maintain life

Mitochondria

• Mitochondria are often referred to as the “powerhouses of the cell”
• Discovered by Rudolph Albert von Kolliker in 1857

Mitochondria Structure

• Two separate membranes: an inner and outer membrane
• Three compartments: intermembrane space, cristae space, and matrix

Outer Membrane

• Acts as a molecular sieve allowing only small molecules to diffuse through

Inner Membrane

• Folds to form cristae that divide the organelle into three compartments
• Where the third stage of cellular respiration, the Electron Transport Chain, takes place

Intermembrane Space

• Located between the inner and outer membrane
• Involved in regulating respiration and metabolic functions

Cristae

• High curvature structures in the inner mitochondrial membrane (IMM) that are crucial for ATP production

Matrix

• Space enclosed by the inner membrane
• The second stage of cellular respiration, the Krebs Cycle, takes place in the matrix

Antoine Lavoisier

• Related chemistry to the science of bodies, physiology, and the study of metabolism and respiration

Coupled Reactions

• A class of organic reactions that involve the joining of two chemical species
• Increase entropy

Krebs Cycle

• Also known as the Citric Acid Cycle
• Second stage of cellular respiration
• Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions
• Discovered by British biochemist, Hans Adolf Krebs, in 1937

Tricarboxylic Acid (TCA) Cycle/Krebs Cycle

• The three-carbon pieces are pulled apart bit by bit to release the energy stored in the covalent bonds
• Most of the CO2 is formed in this process
• Citric acid is formed in the initial reactions of the cycle

Two Types of Organisms

• Autotrophs make their own food
• Heterotrophs obtain food from other organisms

Food-Making Processes of Autotrophs

• Photosynthesis: captures energy from sunlight to produce carbohydrates
• Chemosynthesis: captures energy from small inorganic chemicals in the environment, can occur without oxygen

Adenosine Triphosphate (ATP)

• The energy currency of the cell
• Composed of adenine, ribose, and three phosphate groups

Hydrolysis of ATP

• Endergonic (requires energy)
• Active transport
• Cell movements
• Anabolism

Synthesis of ATP

• Exergonic (releases energy)
• Cell respiration
• Catabolism

Catabolism

• The metabolic breakdown of complex molecules into simpler ones and the release of energy

Cellular Respiration

• Cells trap and release chemical bond energy step by step in a series of chemical reactions
• Breaks down glucose and produces ATP
• Food is the raw material that provides energy for body function
• Cells use food to synthesize new molecules for life processes

Aerobic Respiration

• Chemical process in which oxygen is used to make energy from carbohydrates
• Oxygen is the final electron acceptor

Anaerobic Respiration

• Type of cellular respiration that does not use oxygen to produce energy

Equation for Aerobic Respiration

• 6O2 + C6H12O6 → 6CO2 + 6H2O + energy (ATP)
• Oxygen + glucose → carbon dioxide + water + energy

Equation for Anaerobic Respiration

• C6H12O6 → 2C3H6O3 + energy (ATP)
• Glucose → lactic acid + energy

Major Stages of Aerobic Respiration

• Glycolysis
• Krebs cycle
• Electron Transport Chain

Glycolysis

• Breakdown of a glucose molecule into two three-carbon molecules (pyruvate)
• Occurs in the cytoplasm of the cell

Nicotinamide Adenine Dinucleotide (NAD+)

• The oxidized form of NAD+ undergoes reduction by reacting with 2H (two hydrogen ions and two electrons)

Krebs Cycle

• Second stage of cellular respiration
• Pyruvic acid is broken down into carbon dioxide
• Occurs in the mitochondrial matrix
• Also known as the Citric Acid Cycle

Electron Transport Chain

• The third and final stage of aerobic respiration
• Occurs in the inner mitochondrial membrane
• Produces the most ATP