DNA Molecular Structure and Genetic Engineering Principles

The Molecular Structure of DNA

The molecular structure of DNA was discovered by J. Watson and F. Crick in 1953. The double helix of DNA consists of two strands twisted together in the form of a helical spring. Each strand forms a chain that acts as the rails of a ladder, joined to the other strand through molecular steps.

Nucleotides and Base Pairing

Nucleotides: Each nucleotide consists of a specific nitrogenous base: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). In the DNA structure, Adenine always pairs with Thymine (A-T), and Guanine always pairs with Cytosine (G-C).

DNA Polymerase and Replication

DNA polymerase: This is the primary enzyme involved in DNA replication. It adds complementary nucleotides to the template strand to extend the new DNA chain. Primers: These are small nucleic acid sequences that act as a starting point for the addition of nucleotides to copy the template strand.

Creating Transgenic Organisms

The process of developing a transgenic organism follows these steps:

1. DNA is extracted and the specific gene fragment is located.
2. The DNA gene fragment is copied.
3. The DNA gene is modified.
4. The exogenous gene enters the nucleus of the target cell.
5. The cell incorporates the transgene into a chromosome.

The Process of Gene Cloning

Gene cloning via thermal cycling involves three main stages:

1. Denaturation: The DNA to be cloned is heated to 90°C to separate the strands.
2. Hybridization: The temperature is lowered to 50°C to favor the binding of primers (small sequences).
3. Extension: The temperature is increased to 60°C, and a heat-resistant DNA polymerase adds nucleotides to produce the chain extension.

Transgenic Foods and the Human Genome

Transgenic foods: These are products derived from Genetically Modified Organisms (GMOs).

Characteristics of the Human Genome

• Contains approximately 3.2 billion base pairs.
• Only 2% of the human genome contains genes that code for protein synthesis.
• A very high percentage consists of non-coding DNA (formerly referred to as "junk DNA"), the exact function of which is not fully understood.
• It contains approximately 25,000 genes, though the function of almost half remains unknown.

Genetic Disorders and Medical Intervention

Genetic disorders: These are conditions where a gene or chromosome deviates from its normal function due to a mutation.

• Chromosomal disorders: These affect specific chromosomes (e.g., Down Syndrome).
• Monogenic disorders: These result from changes in a single gene.

Gene Therapy

Gene therapy consists of the insertion of a functional copy of a gene into the cellular tissue of a patient to restore normal function and replace a defective gene.