Genetics and Molecular Biology: Laws, DNA, and Mutations

Mendelian Genetics and DNA Principles

Mendelian Inheritance Laws

• First Law (Law of Uniformity): When two homozygous individuals for a character cross, the descendants of the first generation are phenotypically and genotypically identical.
• Second Law (Law of Segregation): Crossing two individuals of the first filial generation yields a non-uniform progeny due to the separation of implied alleles during gamete formation.
• Third Law (Law of Independent Assortment): Traits with more than one factor are transmitted independently of one another, generating new combinations not present in the parents.

DNA Structure and Replication

DNA is the molecule that contains the biological information characteristic of living beings.

DNA Replication

Fundamental for cell division and ensures that all cells in a multicellular organism maintain the same identity.

• Initiation: An enzyme intervenes to separate the DNA double helix by breaking the hydrogen bonds between complementary nitrogenous bases.
• Elongation: Synthesis of complementary strands begins on each original DNA strand via DNA polymerase III, which requires an RNA primer to begin.
• Termination: Each newly synthesized strand winds with its template strand, forming two identical double helices.

DNA Error Correction

DNA has self-repair mechanisms. Mismatched nucleotides are removed by nucleases:

• Endonucleases: Detect errors and cut the damaged DNA strand.
• Exonucleases: Remove the incorrect fragment.
• DNA Polymerases: Synthesize the correct replacement segment.
• DNA Ligases: Seal the new segment into the DNA strand.

Molecular Biology: Transcription and Translation

Transcription

The process of copying the genetic message from its original DNA form into an mRNA molecule to direct protein synthesis. This is catalyzed by the DNA-dependent RNA polymerase enzyme.

The Genetic Code

The mRNA copy directs ribosomes in protein synthesis. The genetic code is the relationship between the nucleotide sequence of mRNA and the amino acid sequence of a protein.

• It consists of 64 different base triplets called codons.
• It features a linear sequence of nitrogenous bases with no spaces between consecutive codons.
• It is universal.

Translation

Once transcribed, the mRNA molecule contains the necessary information for protein synthesis. Amino acids are joined by peptide bonds on ribosomes, aided by aminoacyl-tRNA molecules.

Mutations and Genetic Alterations

Mutations are alterations in the nucleotide sequence of DNA, leading to changes in the corresponding protein amino acid sequence.

Types of Mutations

• Gene Mutations: Chemical changes in DNA affecting single genes, often visible only microscopically. Causes include replication errors or physical/chemical mutagenic agents. Types include base substitution, deletion, insertion, and segment translocation.
• Chromosomal Mutations: Affect chromosome structure and can be detected microscopically. Types include structural alterations, gene loss, or changes in gene order.
• Genomic Mutations: Involve changes in chromosome number. Types include euploidy (changes in entire sets) and aneuploidy (changes in specific chromosome numbers).

Genetic Engineering and Biotechnology

Genetic Engineering

The deliberate artificial alteration of a living organism's genome by directly modifying its DNA.

Cloning Stages

1. Isolation and obtention of the desired gene.
2. Selection of a cloning vector.
3. Formation of recombinant DNA.
4. Inclusion of recombinant DNA into a host cell.
5. Expression verification and selection of host cells carrying the gene.

Microbiology: Bacteria

Microorganisms are a diverse group of complex living beings capable of growth, relation, and reproduction, either as single cells or simple aggregates.

Bacterial Characteristics

Bacteria are prokaryotic microorganisms that reproduce asexually by binary fission or budding.

• Gram-Negative Bacteria: Present a murein cell wall with a Gram-negative structure and diverse metabolism.
• Gram-Positive Bacteria: Have a Gram-positive murein cell wall and typically exhibit a chemoorganotrophic metabolism.