Fundamental Biological Processes

Posted on May 17, 2025 in Biology

Metabolic Phases

Phase Degraded (Catabolism)

A set of reactions aimed at obtaining energy and precursor molecules. The degradative and catabolic processes are energy-producing chemical reactions and are exergonic. The major catabolic pathways:

  • Glycolysis: The pathway that degrades glucose to produce pyruvate.
  • β-Oxidation: A set of reactions that occur in the oxidation of fatty acids to give rise to acetyl coenzyme A.
  • Transamination and Deamination: The set of processes that take place in amino acid degradation by removing the amine group from the carbon skeleton.

Phase Synthesis (Anabolism)

A set of reactions aimed at the synthesis of complex molecules from precursor molecules and energy. Anabolic processes are synthetic and consume energy, and thus are endergonic reactions. The major anabolic routes are:

  • Photosynthesis: Consists of obtaining organic molecules from light energy and inorganic molecules.
  • Gluconeogenesis: The route of synthesis of glucose from precursors. This route is produced independently of photosynthesis.
  • Fatty-acid synthesis: A set of reactions in which fatty acids are obtained from acetyl-CoA.
  • Synthesis of amino acids: A set of processes to synthesize amino acids from pyruvate, and so on.

Both phases are closely related. ATP is the energy-rich molecule that is produced or consumed in these processes.

Metabolic functions are:

  • Obtaining chemical energy from the degradation of biomolecules.
  • The collection of molecules essential for the synthesis of biomolecules, such as monosaccharides.
  • The synthesis of biomolecules such as carbohydrates, etc.

Oogenesis

The process of formation and maturation of eggs. It takes place inside the ovaries from diploid cells called oogonia. The oogonia divide by mitosis and grow in size, becoming primary oocytes (2n). They start the first division of meiosis and result in two cells of different size. The larger one is the secondary oocyte (n), and the other is the first polar body. Both undergo meiosis. The secondary oocyte gives rise to one large cell which is the egg cell and a second polar body. Only the single-cell egg cell is valid for the female gamete.

G1 Stage

The stage between cell division and initiation of duplication of chromosomes. Activity recovers. Major morphological and functional changes may be seen.

Cell Size Increase

Each daughter cell grows to the size of the parent cell. In animal cells, the increase in size is produced by the synthesis of membrane fragments. In plant cells, the presence of a rigid wall increases cell turgor.

  • The process begins with a softening of the cell wall; the cell incorporates water into the cytoplasm.
  • This causes the expansion of the cytoplasm and increased turgor.
  • The cytoplasm presses onto the softened wall, which yields and allows cell growth.
  • Once the expansion is complete, the cell wall is reinforced with new deposits of cellulose.

Increase in Cellular Structures

  • The doubling of mitochondria and chloroplasts in plants.
  • The ER becomes enlarged and gives rise to the Golgi apparatus, lysosomes, and new vacuoles.
  • It synthesizes proteins that constitute the ribosomes and the cytoskeleton.
  • All enzyme proteins required to control these processes are synthesized.

Restoring Cell Shape

The fibrous structures are “dismantled” and the cytoskeleton is organized as usual. The G1 phase has a very variable duration, ranging from a few hours to several days.

Spermatogenesis

The process of sperm formation. It takes place in the testes from diploid germ cells called spermatogonia, which divide by successive mitosis as the organism reaches sexual maturity. The spermatogonia of the last generation experience an increase in size and become primary spermatocytes (2n). Each primary spermatocyte undergoes the first meiosis, giving rise to two secondary spermatocytes (n). Each of these will undergo a second division to produce two haploid spermatids (n). This is the maturation phase. Spermatids, which are immobile and rounded cells, undergo a number of profound changes and are transformed into sperm.