Gene Structure, Replication, and Genome Integrity
Genome architecture
Genes are embedded in regulatory landscapes
Genomes are not merely linear gene lists. They contain promoters, enhancers, silencers, insulators, repetitive elements, replication origins, and structural domains that collectively define expression, stability, and inheritance.
Modern view
A genome is a dynamic, folded, and epigenetically annotated system rather than a static sequence string.
Replication and repair
Faithful duplication with controlled error
DNA replication requires polymerase selectivity, proofreading, mismatch repair, and checkpoint coordination. The balance between fidelity and mutability is evolutionarily tuned: excessive errors are deleterious, but zero error would eliminate heritable variation.
Replication fidelity mechanisms
Proofreading
- Corrects misincorporated nucleotides during synthesis
- Depends on polymerase exonuclease activity
Mismatch repair
- Fixes errors after synthesis
- Detects replication-associated mismatches and small loops
Which mechanism primarily corrects errors immediately during DNA synthesis?
Proofreading removes misincorporated nucleotides via exonuclease activity during replication.
Correct answer: Proofreading by DNA polymerase
What is the main role of mismatch repair?
Mismatch repair recognizes and fixes mismatched bases and small insertion-deletion loops missed by proofreading.
Correct answer: To correct replication errors after DNA synthesis
Genome instability and variation
Mutation, recombination, and structural change
Genome variation arises through point mutation, indels, transposition, recombination, copy-number change, and chromosomal rearrangement. These processes can create disease, fuel adaptation, and reveal constraints on genome organization.
Which process can generate large-scale chromosomal rearrangements and novel gene combinations?
Recombination can reshuffle genetic material and produce structural variation.
Correct answer: Recombination
Why is genome instability sometimes evolutionarily beneficial?
Although often harmful, instability can accelerate adaptation by generating diversity.
Correct answer: It increases genetic variation on which selection can act