Cell Division and Energy Metabolism: Mitosis, Meiosis, and Respiration Stages

Cell Division Processes

Mitosis: Somatic Cell Replication

Mitosis is an equational division resulting in two identical daughter cells. This process covers the growth and repair throughout the life of organisms.

• Homologous chromosomes do not form pairs.
• Results in 2 identical daughter cells.
• Cells can undergo successive mitotic divisions.
• Occurs in somatic cells (all body cells, excluding germ cells).

Meiosis: Gamete and Spore Formation

Meiosis is the process of cell division that occurs in germ cells, resulting in genetically distinct reproductive cells (gametes or spores).

1. First Division: Reductional.
2. Second Division: Equational.

• Homologous chromosomes form pairs.
• Results in 4 daughter cells, genetically different from each other.
• Cells cannot undergo more than one meiosis, but they can undergo mitosis.
• Occurs only in germ cells in sexually mature organisms.

Cellular Metabolism and Energy Production

Glycolysis (Anaerobic Catabolism)

Glycolysis is a simple, anaerobic catabolic process that occurs in the hyaloplasm (cytosol) of all living things. It is the initial step in glucose breakdown.

• Energy Yield: Energy-poor, producing only two ATP molecules per glucose molecule.
• Location: Hyaloplasm (Cytosol).
• Starting Material: Glucose.

Cellular Respiration: Aerobic Energy Generation

Cellular respiration is a vital metabolic process that provides energy (ATP) for cellular work and biosynthesis. It is a catabolic pathway carried out by aerobic eukaryotic animals, plants, and many prokaryotes.

Organic molecules are oxidized, donating electrons to molecular oxygen through intermediaries (NADH and FADH₂). ATP is produced during this electron transfer. The final products are CO₂ and water.

Stage 1: Formation of Acetyl CoA (Pyruvate Oxidation)

Pyruvate, derived from glycolysis in the cytosol, moves into the mitochondria where it is oxidized.

• Pyruvate (CH₃COCOOH) undergoes decarboxylation (releasing CO₂) and oxidation (reducing NAD⁺ to NADH + H⁺).
• Coenzyme A (CoA-SH) is involved.
• The resulting product is Acetyl CoA (CH₃COO-CoA).

Stage 2: The Krebs Cycle (Citric Acid Cycle)

The Krebs Cycle is a cyclic, catalytic, and amphibolic route that occurs in the mitochondrial matrix. It is strictly dependent on aerobic conditions (oxidation).

Acetyl CoA enters the cycle, undergoing a series of decarboxylation, oxidation, and reduction processes.

Products per Acetyl CoA molecule:

• 3 NADH + 3 H⁺
• 1 FADH₂
• 1 GTP (energy rich, equivalent to ATP)

Global Balance (Input/Output per Cycle):

Input: Acetyl CoA + 3 NAD⁺ + 1 FAD + Pᵢ + GDP + H₂O

Output: 3 NADH + 3 H⁺ + 1 FADH₂ + 1 GTP + CoA

Stage 3: Oxidative Phosphorylation

This stage involves the oxidation of the high-energy electron carriers (NADH + H⁺ and FADH₂) generated in previous stages (like the Krebs Cycle).

The carriers are oxidized through gradual oxidation-reduction processes (the Electron Transport Chain). The energy released during this transfer is used to form ATP from ADP and inorganic phosphate (Pᵢ).