Understanding DNA, Cell Reproduction, and Genetics

Posted on Oct 31, 2024 in Biology

DNA and Genetic Information

DNA Structure

Deoxyribonucleic acid (DNA) carries an individual’s genetic information. It consists of four nitrogenous bases: adenine, cytosine, guanine, and thymine.

A pentose sugar with five carbons binds to the nitrogenous base. Three bases form a triplet or codon.

Triplets and Genetic Traits

Triplets determine traits like eye color. The nitrogenous bases pair up: adenine with thymine, and guanine with cytosine.

Amino Groups

  • Polar or hydrophobic R groups
  • Uncharged polar R groups
  • Positively charged R groups
  • Negatively charged R groups

DNA Composition

DNA is composed of:

  • Deoxyribose sugar
  • Phosphate group
  • Nitrogenous base

RNA and Protein Synthesis

RNA has two main functions:

  • Transcription: Obtaining genetic information from DNA.
  • Translation: Interpreting the information and building a protein based on the encoded instructions.

DNA information is organized into triplets (codons) that are read during translation.

Cell Reproduction

The Cell Cycle

The cell cycle is the time it takes for a cell to reproduce.

Phases of the cell cycle:

  1. G1 phase: The cell grows.
  2. S phase: The cell replicates its DNA.
  3. G2 phase: The cell completes growth and prepares for division.
  4. M phase: Mitosis (cell division) occurs.

When a cell is not reproducing, it is in the interphase stage. The genetic code consists of 64 triplets (codons) that code for 20 amino acids. Each codon specifies a particular amino acid. There is a start codon and three stop codons. The genetic code is universal for all living organisms.

Mitosis

Mitosis is the process of eukaryotic cell reproduction.

  1. Prophase: The nuclear membrane disappears, and chromosomes become visible.
  2. Metaphase: Chromosomes align in the center of the cell.
  3. Anaphase: Chromosomes move towards opposite poles of the cell as the centromeres split.
  4. Telophase: Chromosome division is complete.

Cytokinesis

After mitosis, cytokinesis divides the cytoplasm and organelles into the daughter cells.

Asexual Reproduction

Asexual reproduction involves a single individual dividing to produce offspring.

Types of Asexual Reproduction

  • Cell Fusion: One cell divides into two identical daughter cells.
  • Sporulation: Primarily occurs in mosses and ferns.
  • Budding: A bud of cells forms, creating offspring identical to the parent.
  • Vegetative Reproduction: Some plants reproduce through small body parts.
  • Parthenogenesis: An unfertilized egg develops into an embryo.

Meiosis and Sexual Reproduction

Meiosis

In an embryo, all cells are diploid. Sex cells undergo meiosis, a cell division process that reduces the number of chromosomes by half (haploid).

Sexual Reproduction

Sexual reproduction involves the union of two gametes (male and female) to form an individual with characteristics from both parents.

Types of Fertilization

  • External Fertilization: No contact between male and female; typically occurs in water.
  • Internal Fertilization: The male deposits sperm inside the female, ensuring fertilization.

Reproductive Strategies

  • Oviparous: Eggs develop outside the mother’s body.
  • Viviparous: The embryo develops inside the mother and receives nutrients from her.
  • Ovoviviparous: The embryo develops inside an egg within the mother, feeding on the egg’s contents (e.g., some snakes).
  • Marsupials: The embryo develops partially inside the mother and completes development in a pouch.

Androgyny

Androgynous organisms have both male and female reproductive organs and can produce both eggs and sperm. Cross-fertilization occurs when two individuals exchange gametes.

Genetics and Inheritance

Genetic Terminology

  • Locus: The specific location of a gene on a chromosome.
  • Alleles: Different forms of a gene at the same locus.
  • Homozygous: Having identical alleles for a gene.
  • Heterozygous: Having different alleles for a gene.
  • Dominant Allele: The allele that is expressed.
  • Recessive Allele: The allele that is masked by the dominant allele.
  • Codominant Alleles: Both alleles are fully expressed.
  • Diploid: Having two sets of chromosomes (one from each parent).
  • Haploid: Having one set of chromosomes.
  • Genotype: The genetic makeup of an individual.
  • Genome: The complete set of genes in an organism.
  • Hybridization: Crossbreeding between different species or varieties.

Mendel’s Laws

  • First Law (Law of Segregation): Alleles for a trait separate during gamete formation.
  • Second Law (Law of Independent Assortment): Alleles for different traits are inherited independently.

Other Inheritance Concepts

  • Polygenic Inheritance: Traits influenced by multiple genes.
  • Chromosome Theory of Inheritance: Genes are located on chromosomes.

Mutations

Mutations are changes in the normal structure of genes or chromosomes.

  • Gene Mutations: Alterations in the chemical structure of a gene.
  • Chromosome Mutations: Changes in chromosome morphology.
  • Genomic Mutations: Affect the number of chromosomes (e.g., extra or missing chromosomes).

Biotechnology and Bioethics

Biotechnology

Biotechnology involves using biological knowledge and techniques for various applications.

Bioethics

Bioethics addresses ethical issues related to scientific and technological advancements in biology and medicine.