Genetics and Molecular Biology Concepts

Gene Function and Mutations

• "Knocking out a gene" refers to making a gene defective to observe effects on morphology, like penis development.
• This process is often linked to studying null or loss of function alleles.
• Experimental Methodology:
• Scientists irradiated a type of red mold called Edgrassa to induce random mutations in its genetic material.
• Observing mutated organisms helps understand gene function in metabolic pathways.

Metabolic Pathway Focus

• Researchers aimed to connect mutations with specific proteins by focusing on a simplified metabolism, e.g., the arginine synthesis pathway.
• Pathway Steps:
• Precursor → Ornithine → Citrulline → Arginine.
• Each transformation thought to be facilitated by a different enzyme.

Experimental Strategy:

• Mutants unable to perform ariginine synthesis grown without arginine.
• Mutants that survive likely retained a functional synthesis pathway, while non-surviving ones indicated a defect.

One Gene - One Enzyme Hypothesis

• Scientists hypothesized that each gene corresponds to a single enzyme related to the arginine synthesis pathway.
• Further experiments involved growing mutant cells with different metabolites to observe growth and infer enzyme functionality along the pathway.

Advanced Understanding of Genetic Information

• This principle expanded to understand that one gene corresponds not just to one enzyme but to one polypeptide/protein.
• DNA → RNA → Protein model (the central dogma of molecular biology).
• Key Players:
• Francis Crick explained how genes function as codes, and how RNA acts as an intermediary between DNA and protein synthesis.
• mRNA (messenger RNA) transports genetic information from DNA to ribosomes for protein synthesis.

Transcription and Translation Process

• Transcription: The process of creating RNA from a DNA template using RNA polymerase.
• Translation: Converting RNA sequences into protein.
• Understanding genotypes (DNA sequence) links to phenotypes (observable traits), produced mainly by proteins.

Codon and Genetic Code

• George Gamow concluded that a triplet base code (3 nucleotides) specifies amino acids, forming codons.
• Example of redundancy: Multiple codons may represent the same amino acid, contributing to genetic code versatility.
• Reading Frame: Codons are read one at a time—addition or deletion of nucleotides affects the translation frame in specific ways.

Key Features of the Genetic Code

• Codons are unambiguous, non-overlapping, and mostly universal across organisms.
• Some genes produce RNA products that do not code for proteins (e.g., rRNA, tRNA) and serve other roles in the cell.
• Rare cases exist where RNA can reverse transcribe into DNA, characteristic of certain viruses.

Practical Applications of the Genetic Code

• The redundancy allows approximation of potential DNA sequences from known amino acids, though not exact due to multiple codons for the same amino acid.
• In studying proteins across different organisms, similarities in genetic coding enable understanding of biological function and relationships.