Fundamentals of Genetics: DNA, Proteins, and Applications

Posted on Nov 29, 2024 in Biology

What is Genetics?

The unit of inheritance is called a gene. Genes are transmitted according to defined rules or laws. They are located on chromosomes, structures composed of a substance in the cell nucleus. Sex is determined by genes or chromosomes in most living organisms.

Key Genetic Terms:

  • Genotype: Genetic constitution of an individual character or a whole set of genes.
  • Phenotype: The external expression characteristic of the individual.
  • Alleles: Each variant of a gene. For each gene, an individual has a pair of alleles, represented by letters.
  • Homozygous: An individual with two identical alleles.
  • Heterozygous: An individual with two different alleles.
  • Locus: The specific chromosome location where each gene is located.

Mendelian Laws:

  • 1st Law or Principle of Uniformity: The first filial generation, resulting from crossing two inbred lines, is uniform, showing the character of one of the parents.
  • 2nd Law or Principle of Segregation: In the second generation, the non-manifested type from the first reappears because factors segregate in the gametes and reunite in the offspring.
  • 3rd Law or Principle of Independent Assortment: Different factor traits follow the above rules, without one influencing the proportions obtained in the other.

DNA:

In every cell of every living thing, there is a molecule, a substance trapped in the nucleus, containing information like a library. This DNA molecule carries the instructions to develop the basic characteristics of life.

Nucleic Acids:

  • A nitrogenous base (adenine, cytosine, guanine, thymine, and uracil).
  • A pentose (ribose or deoxyribose).
  • A phosphate group.

There are two types of nucleic acids: Ribonucleic Acid (RNA) and Deoxyribonucleic Acid (DNA).

Amino Acids:

Proteins are polymers, chains of basic units called amino acids. There are 20 different amino acids involved in forming long protein chains.

Protein Synthesis:

  • Transcription: Information stored in DNA is transferred to messenger RNA (mRNA). mRNA consists of the complementary base of a DNA strand fragment, but with uracil instead of thymine.
  • Translation: A chain of amino acids is formed, determined by the nucleotide sequence of mRNA.

The Genetic Code:

The genetic code is the correspondence between nucleotides and amino acids. It is universal; all living things share the same code.

Recombinant DNA Technology:

Transgenic organisms develop from a cell into which DNA from another living being has been introduced. Recombinant organisms are genetically engineered viruses or bacteria.

Gene Cloning:

  1. A gene of interest is located on an animal cell chromosome, and a vector is selected.
  2. Genetic material is isolated from animal cells and bacteria.
  3. Chromosomal DNA is fragmented using restriction enzymes.
  4. The isolated gene binds to the plasmid through ligase enzymes.
  5. The new recombinant DNA is introduced into bacteria. After several generations, a clone of cells carrying the gene (e.g., for insulin) is produced.

Drug Production:

Interferon, a natural protein produced by human cells in small quantities, can be produced in large amounts by cloning the encoding gene into bacteria. Human insulin is obtained from bacterial cultures containing the corresponding human gene.

Gene Therapy:

  • Introduce the desired gene into cells.
  • Fill the cells in the body.
  • Ensure genes reach their target.
  • Monitor gene expression.

This can be done ex vivo (cells extracted, cultivated, and reintroduced) or in vivo (genes introduced via vectors).

Clinical Diagnosis:

Gene identification allows for early diagnosis, essential for preventing or managing diseases. DNA probes can detect diseases before symptom onset.

Drug Production (Advanced):

  1. Clone the human factor VIII gene into cow embryo cell DNA.
  2. Insert the recombinant DNA into cow embryo cells and implant the embryo.
  3. Obtain transgenic cows carrying the factor VIII gene, from whose milk the factor can be extracted.

Applications in Agriculture and Livestock:

  • In agriculture, genetic engineering creates clones of genetically identical plants.
  • In livestock, transgenic animals incorporating human genes open possibilities for medical research.

Environmental Applications:

  • Bioremediation: Genetically engineered organisms can degrade oil and its derivatives.
  • Bioadsorption: Engineering bacteria to fix toxic ions on their cell surfaces.
  • Enriching activated sludge in water treatment plants to retain toxic ions.

Human Genome Project:

The human genome contains fewer than 30,000 genes. Differences with other species are less than expected.

Applications:

  • GH: Gene therapy.
  • Genetic diagnosis.
  • Pre-transplant genetic testing.
  • Understanding human evolution.

Assisted Reproduction:

  • Artificial Insemination: Introducing semen into the uterus.
  • In Vitro Fertilization: Fertilization in the laboratory, followed by embryo implantation.

Cloning:

  • Cloning single cells or tissues for research or therapeutic purposes.
  • Cloning for medical purposes: obtaining a genetically identical organism.

Cloning Applications:

  • Research in animal reproduction.
  • Transgenic breeding.
  • Endangered animal conservation.
  • Therapeutic applications.

Bioethics:

Bioethics is the application of ethics to life sciences. It promotes education and the creation of independent bioethics committees.