Molecular Biology and Genetics – Explorations: An Open Invitation to Biological Anthropology, 2nd Edition

Introduction to Biological Molecules and Cells

All living organisms are composed of four essential biomolecules: proteins, lipids, carbohydrates, and nucleic acids. These molecules organize into cells, the fundamental units of life. Cells are classified as prokaryotes or eukaryotes; the latter possess membrane-bound organelles, such as the nucleus (containing DNA) and mitochondria (responsible for energy production via ATP).

DNA Structure, Replication, and Mutations

DNA is a double-stranded helix composed of nucleotides (A, T, C, G) with a sugar-phosphate backbone. In the nucleus, it is organized around histones into chromatin and chromosomes. DNA replication is a semi-conservative process requiring enzymes like helicase and DNA polymerase to produce identical copies. Errors during this process result in mutations, which introduce genetic variation.

Cell Division: Mitosis and Meiosis

Somatic cells undergo mitosis to produce two identical diploid daughter cells for growth and repair. In contrast, germ cells undergo meiosis—a two-stage division process—to create four haploid gametes. Meiosis includes genetic recombination, which increases diversity by shuffling genetic material between homologous chromosomes.

Protein Synthesis

Protein synthesis occurs in two major steps: transcription and translation. During transcription, DNA is copied into mRNA within the nucleus; this mRNA undergoes splicing to remove introns. In translation, ribosomes read the mRNA in triplets called codons, matching them with tRNA-carried amino acids to assemble proteins. These proteins fold into specific shapes to perform essential biological functions.

Mendelian and Complex Inheritance

Mendelian genetics describes traits controlled by a single gene, characterized by dominant and recessive alleles that segregate predictably, as illustrated by Punnett squares and pedigrees. However, many human traits are polygenic (controlled by multiple genes) or display complex inheritance patterns like incomplete dominance. Environment, lifestyle, and epigenetics—regulatory changes that do not alter the DNA sequence itself—also significantly influence phenotypes.

Genetic Testing and Bioethics

Advancements in biotechnology, such as PCR and next-generation sequencing, have made genetic testing widespread. Clinical testing provides medical guidance for hereditary risks, while direct-to-consumer (DTC) services offer health and ancestry information. While these tools offer insights, they raise significant ethical concerns regarding privacy, psychological impacts of information, and the potential for improper interpretation without professional genetic counseling.