Cell Division, Genetics, and Chemical Reactions Explained

Posted on Mar 22, 2025 in Biology

Cell Division: Interphase and Mitosis

Interphase is when DNA duplication occurs.

Interphase Stages:

  • G1: Synthesis of RNA and proteins, increasing cell cytoplasm.
  • S: DNA replication results in two chromatids.
  • G2: Additional growth and preparation for mitosis.

Mitosis: Somatic Cell Division

Mitosis is an equational division that occurs in somatic cells. It is divided into four stages:

  1. Prophase: A long step involving the disappearance of the nuclear envelope (carioteca), centriole duplication, spindle formation, and visible duplicated chromosomes.
  2. Metaphase: Chromosomes align at the middle of the cell, forming the equatorial plate.
  3. Anaphase: Sister chromatids segregate and move to opposite poles of the cell. Double chromosomes become single chromosomes.
  4. Telophase: Cellular restructuring occurs, the nuclear envelope reorganizes, the cell divides, and the spindle disappears.

Meiosis: Germ Cell Division

Meiosis occurs in germ cells and consists of two divisions: meiosis I (reductional) and meiosis II (equational).

Key Features of Meiosis:

  • Reduces the number of chromosomes by half.
  • Forms gametes (in animals) and spores (in plants).
  • Results in four cells (n) different from the original cell.
  • Increases the genetic variability of organisms.

Gametogenesis:

  • Spermatogenesis: Sperm production occurs in the testes of males.
  • Oogenesis: Egg production occurs within the ovaries.

Mutations and Genetics

Mutations are the primary source of variability in living organisms.

While some mutations can lead to better adaptation, others cause defects, diseases, or even death.

Types of Mutations:

  • Gene Mutations: Alterations in the nucleotide sequence of DNA can form defective genes, leading to conditions like cancer or hemophilia.
  • Chromosome Mutations: Structural and numerical stability of chromosomes is critical for harmonious organism development. Any structural or numerical change can modify individual characteristics.

Numerical Chromosome Alterations:

Changes in the normal number of chromosomes due to errors during meiosis.

  • Nullisomy (2N-2): Loss of two chromosomes from the karyotype, often lethal.
  • Trisomy (2N+1): An extra chromosome is present in a pair, resulting in three copies instead of two.

Basic Genetics Concepts

  • Gene: A DNA sequence on a chromosome responsible for a specific trait.
  • Character/Trait: A characteristic determined by a gene.
  • Dominant Gene: The predominant gene (A).
  • Recessive Gene: The non-dominant gene (a).
  • Homozygous: Having the same alleles for a gene (AA) or (aa).
  • Heterozygous: Having different alleles for a gene (Aa).
  • Locus: The specific location of a gene on a chromosome.
  • Allelic Genes: Genes that determine the same characteristics on homologous chromosomes (Aa).


Chemical Reactions

Chemical reactions are represented by chemical equations:

aA + bB → cC

Acid-Base Neutralization Reactions

Neutralization occurs through the union of H+ (acid) with OH– (base) to form H2O.

The acid anion and the base cation form a salt.

ACID + BASE → SALT + H2O

  • Total Neutralization: All H+ and OH– are neutralized.
  • Partial Neutralization: Some H+ or OH– remain.
  • Partial Neutralization of Acid: H+ remains.

Classification of Salts

  • Hydroxysalt: A salt with two or more anions and one hydroxide anion.
  • Double Salt: A salt with more than one cation or more than one anion, but is not a hydroxysalt.

Water Solubility:

Salts can be soluble or insoluble.

General Rule: Salts with cations from Group 1, NH4+, or nitrate anions (NO3–) are generally soluble.

Nomenclature:

  • OSO → ITO
  • ICO → ATO
  • HYDRIC → ETO

Major Salts

  • Sodium chloride (NaCl)
  • Sodium nitrate (NaNO3)
  • Sodium carbonate (Na2CO3)
  • Sodium bicarbonate (NaHCO3)
  • Sodium fluoride (NaF)
  • Calcium carbonate (CaCO3)
  • Calcium sulfate (CaSO4)

Reactions and Classification of Oxides

  • Acidic Oxides: Formed by nonmetals reacting with H2O to form acids.
  • Nonmetal Oxide + H2O → Acid
  • Nonmetal Oxide + Base → Salt + H2O
  • Basic Oxides: Formed by metals (Group 1A, 2A, Ag+, transition metals) reacting with H2O to form bases.
  • Metal Oxide + H2O → Base
  • Metal Oxide + Acid → Salt + H2O
  • Amphoteric Oxides: React as both a base and an acid.
  • Neutral Oxides: Do not react with water, acids, or bases.

Inorganic Chemical Reactions

Evidence of Chemical Reactions:

  • Color change
  • Temperature change
  • Gas release
  • Change of state

Reaction Types:

  • Synthesis/Combination: A + B → C
  • Decomposition/Analysis: A → B + C
  • Single Replacement/Displacement: A + BC → AC + B
  • Double Replacement/Metathesis: AB + CD → AD + CB

Expect the formation of:

  • Gas
  • Weak electrolyte
  • Solid (precipitate)