BI10.1-7 | Molecular Biology — Summary & Reflection

REFLECT

Now that you've learned about the molecular machinery of life, take a moment to connect these concepts:

1. Concrete experience: Think about the COVID-19 RT-PCR test. You (or someone you know) probably had a nasal swab taken. That swab collected cells containing viral RNA. Trace the molecular steps: How does RT-PCR detect viral RNA? Why is it called "reverse transcription" PCR?

1. Reflective observation: Consider the gout case from the beginning. The patient's uric acid was 11.2 mg/dL. Now you know that uric acid comes from purine degradation via xanthine oxidase. Why does allopurinol help? What would happen to hypoxanthine and xanthine levels in a patient taking allopurinol?

1. Abstract conceptualisation: The central dogma says DNA → RNA → Protein. But retroviruses (like HIV) use reverse transcriptase to go RNA → DNA. How does this challenge the original dogma? What implications does this have for HIV treatment?

1. Active experimentation: If you were designing a gene therapy for sickle cell disease using CRISPR, what specific DNA sequence would you target? What change would you make?

Connections across subjects:
- You're currently studying Cerebellum in Anatomy — these topics connect because they both relate to the nervous system.
- You're currently studying Cranial nerve nuclei & Cerebral hemispheres in Anatomy — these topics connect because they both relate to the nervous system.
- You're currently studying Histology & Embryology (Neuroanatomy) in Anatomy — these topics connect because they both relate to the nervous system.

KEY TAKEAWAYS

Key Takeaways — Molecular Biology (BI10.1-BI10.7):

1. Nucleotides are the building blocks of DNA and RNA, each containing a nitrogenous base (purine or pyrimidine), a pentose sugar, and a phosphate group. Nucleotides also serve as energy carriers (ATP), signalling molecules (cAMP), and coenzyme components (NAD+, FAD).

1. Purine synthesis occurs via two pathways: de novo (energy-expensive, building from scratch to IMP) and salvage (recycling free bases via HGPRT and APRT). The salvage pathway is critical for brain and bone marrow.

1. Purine degradation produces uric acid as the end product. Xanthine oxidase catalyses the final steps. Enzyme defects cause Lesch-Nyhan syndrome (HGPRT deficiency) and SCID (ADA deficiency). Allopurinol treats gout by inhibiting xanthine oxidase.

1. The central dogma — DNA replication (semi-conservative, by DNA polymerase), transcription (by RNA polymerase, with mRNA processing), and translation (ribosome reads codons, tRNA delivers amino acids) — describes the information flow in cells.

1. DNA repair mechanisms (mismatch, base excision, nucleotide excision, double-strand break repair) protect genomic integrity. Defects cause Lynch syndrome (MMR), xeroderma pigmentosum (NER), and BRCA-related cancers.

1. Gene regulation operates at multiple levels: transcriptional (promoters, enhancers, operons), epigenetic (DNA methylation, histone modification), post-transcriptional (miRNA, mRNA stability), and translational.

1. Molecular technologies — recombinant DNA technology (recombinant insulin, vaccines), PCR (COVID testing, TB diagnosis), microarray (gene profiling), FISH (chromosomal analysis), and CRISPR-Cas9 (gene editing) — are transforming diagnostics and therapy.