Inheritance and Protein Synthesis: From DNA to Gene Expression

The Genetic Code and Protein SynthesisPage 1

DNA functions as a code system where sequences of nucleotides determine protein synthesis. A triplet of nucleotides (codon) codes for one amino acid. Proteins are essential for cellular structure, transport, defense, and enzymatic activity. The process involves transcription of DNA into mRNA in the nucleus, followed by translation in the cytoplasm using ribosomes, where tRNA matches anticodons to mRNA codons to assemble polypeptide chains.

RNA Processing and Genomic InsightsPage 2

Eukaryotic cells perform RNA processing on pre-mRNA, including adding a 5' cap and a poly-A tail for stability and recognition. Splicing removes non-coding introns, leaving coding exons. The Human Genome Project revealed that humans have far fewer genes than previously expected (approx. 20,000-25,000), confirming that a single gene can produce multiple protein variants through alternative splicing and post-translational modification.

Mutations and Genetic DiseasePage 3

Mutations are permanent DNA changes, either spontaneous or caused by environmental mutagens. Point mutations include substitutions (silent, missense, or nonsense) and frameshifts (deletions/insertions). While many are harmless, loss-of-function mutations can cause diseases like sickle cell anemia. Somatic mutations affect the individual, while germinal mutations are heritable.

Cancer BiologyPage 4

Cancer is characterized by uncontrolled cell division resulting from accumulated mutations in regulatory genes. Oncogenes stimulate division, while tumor-suppressor genes (like TP53) stop it. Cancer develops through a multi-step process of deregulated cell cycle progression, often involving both inherited predispositions and environmental factors like radiation or chemicals.

Gene Regulation and EpigeneticsPage 5

Cells regulate gene expression to specialize (differentiation) and save energy. Prokaryotes use operons (e.g., the lac-operon) controlled by repressors and inducers. Eukaryotes use complex transcription factors, RNA interference (miRNA), and epigenetic mechanisms like DNA methylation and histone acetylation. Epigenetics modifies gene accessibility without changing the underlying DNA sequence, often influenced by environmental factors such as diet, as seen in the development of honeybee queens versus workers.