Overview
This lecture discusses the relationship between biomolecular structure and function, focusing on how mutations, gene duplications, and evolutionary processes shape proteins and genetic material in organisms.
Structure-Function Relationship in Biology
- Structure determines function at both the molecular and organismal level.
- Examples: DNA double helix enables heredity, protein structure defines enzyme activity.
- Evolution selects for structures that best fulfill required biological functions.
Evolution and Genetic Relationships
- Modern birds evolved from dinosaur ancestors; structure changed with function (e.g., flight).
- DNA comparisons (e.g., hippo and whale, human and chimp) reveal evolutionary relationships not obvious from appearance (morphology).
- Molecular biology can challenge or refine conclusions drawn from morphology alone.
Mutations and Their Impact
- Mutations can occur during DNA replication or from environmental damage.
- Most mutations are repaired, but germline mutations may be inherited.
- Many mutations accumulate outside protein-coding regions and are neutral.
- Some mutations in coding regions can drastically alter protein function (e.g., single nucleotide changes affecting enzyme activity).
Gene Duplication and Evolution
- Gene duplication allows for evolutionary innovation:
- Two working copies can be advantageous.
- One copy may diverge and acquire new function.
- Duplicated useless genes may become lost.
- Gene duplication is a major driver of molecular evolution.
Paralogs and Orthologs
- Paralogs are similar genes within the same organism from gene duplication (e.g., alpha- and beta-globin in humans).
- Orthologs are similar genes in different species that arose from a common ancestor (e.g., mouse and human beta-globin).
Structure-Function Patterns and Exceptions
- Similar structure usually suggests similar function (e.g., ribonucleotide reductase in bacteria and mice).
- Similar structures can have different functions due to evolutionary divergence (e.g., membrane channel vs. green fluorescent protein).
- Different structures may perform the same function (e.g., different transcription factors regulating gene expression).
- Experimental evidence is needed to confirm function even when structures appear similar.
Key Terms & Definitions
- Morphology — Physical appearance or structure of an organism.
- Mutation — A change in DNA sequence that can affect structure and function.
- Germline — Cells that give rise to gametes and can pass mutations to offspring.
- Gene Duplication — The creation of an extra copy of a gene, enabling evolutionary diversity.
- Paralog — Gene copies within the same species arising from duplication.
- Ortholog — Genes in different species that evolved from a common ancestral gene.
Action Items / Next Steps
- Review lecture notes and Chapter 1 for structure-function relationships.
- Be prepared to analyze examples of paralogs and orthologs in future lessons.
- Understand exceptions to structure-function rules for upcoming discussions.