Lecture Notes on DNA and Mutations

DNA Length and Replication

DNA is a fascinating molecule, particularly for its length.
In a human cell, if DNA is stretched out, it measures 2 meters.
During a lifetime, humans produce about 2 x 10^13 kilometers of DNA, roughly equivalent to 2 light years.
Every day, 10 billion new immune system cells are created, resulting in 20 million kilometers of DNA.
Collectively, York University's 50,000 students and staff could produce DNA stretching across the Milky Way galaxy.

DNA is densely packed in a tiny nucleus of 6 microns in diameter.
Nucleosomes: DNA wraps around histone proteins, forming nucleosomes, the first level of packaging.
The structure unwinds into successive levels of chromatin packing.

DNA undergoes frequent chemical changes; most are repaired.
Mutations: Occur when DNA repair mechanisms fail, affecting the genome (6 billion nucleotides).
Each cell may have 1-5 mutations, often in non-coding regions (98.5% of DNA).

Point Mutation: Involves a single nucleotide; can be caused by replication errors or mutagens (e.g. smoking).
- Silent Mutation: No change in amino acid sequence due to codon redundancy.
- Missense Mutation: Alters amino acid sequence but not necessarily protein function.
- Nonsense Mutation: Introduces a stop codon, truncating the protein.
Frameshift Mutation: Caused by insertions or deletions, altering the reading frame, often more severe.

DNA repair involves removal and resynthesis of damaged bases.
Proteins such as MSH2, MSH6, MLH1, PMS2, and exonuclease Exo-1 are involved in correcting mutations.

Selective Advantage: Mutations can drive evolution, providing advantages based on environmental context.
Genetic Diseases: Mutations can cause diseases like sickle cell anemia (missense mutation).
Cancer: Accumulation of mutations, failure in DNA repair can lead to cancer.

Evolution is driven by DNA mutations and their selection for or against in changing environments.
Mutations contribute to diversity and adaptability of species.
Darwin noted adaptability is key to survival, not just strength or intelligence.

Mutations can lead to beneficial adaptations or harmful conditions.
DNA repair is crucial for minimizing mutation-related damage.
Understanding mutations helps in studying evolution, genetic diseases, and potential therapies.