DNA Repair Mechanisms

Study Notes

Base alterations, such as cytosine deamination, can lead to abnormal bases like uracil.
Enzymes called glycosylases recognize and remove abnormal bases, creating an apyrimidinic site.
Double-strand breaks in DNA are induced by radiation or free radicals; traditional repair mechanisms are ineffective for these breaks.
Repair proteins can re-ligate DNA ends, potentially causing harmful errors, mutations, cancer, or immunodeficiency diseases.

Genetic diversity exists within and between populations, influencing traits like skin color and disease susceptibility.
Variation arises from mutation, recombination, and natural selection.
Natural selection favors alleles providing selective advantages.
Genetic variations can alter phenotypes by affecting gene expression, protein function, or efficacy.

SNPs are single base pair changes, primarily from replication errors.
More frequent in noncoding regions due to selective pressure on coding domains.
Synonymous SNPs do not change amino acids, whereas nonsynonymous SNPs can lead to missense (amino acid substitution) or nonsense mutations (premature stop codon).
Nonsense mutations are more likely to be pathogenic; missense mutation effects depend on amino acid positioning and substitution nature.
SNPs in noncoding regions may influence gene expression, especially if located in regulatory areas.

Secondary structures, such as α-helices and β-sheets, form through intramolecular hydrogen bonding, minimizing steric repulsion.
Tertiary structure refers to the three-dimensional arrangement of a polypeptide, often revealing structural domains.

Glycosylation involves attaching carbohydrates, significant in eukaryotic proteins, particularly on cell surfaces.
γ-Carboxylation and β-hydroxylation are PTMs influencing blood coagulation by mediating calcium ion binding.
Sulfation, the addition of sulfate groups, enhances protein-protein interactions, while amidation, the conversion of a carboxyl group to an amide, stabilizes certain peptides.

Physicians often prescribe medications based on clinical signs and empirical data, with variability in drug effectiveness (30-60%).
Only 25% of cancer patients benefit significantly from treatments; many experience adverse effects without improved outcomes.
Genetic and environmental factors lead to inter-individual variability in drug responses, with genetics explaining 20-95% of pharmacokinetic differences.
Proteins play vital roles in drug absorption, metabolism, and action; genetic variations can alter protein function, stability, and structure, affecting drug efficacy or toxicity.