Molecular Basis of Inheritance
Class 12 Biology · Biology · Chapter 5
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Summary
This chapter explores DNA as the genetic material and the molecular events of inheritance. The structure of DNA, given by Watson and Crick, is an antiparallel double helix with complementary base pairing (A-T, G-C) following Chargaff's rules, with sugar-phosphate backbones. Experiments by Griffith (transformation), Avery, MacLeod and McCarty, and Hershey and Chase established DNA as the genetic material. DNA packaging into nucleosomes and chromatin is described. DNA replication is semiconservative, demonstrated by Meselson and Stahl, and uses enzymes such as DNA polymerase, helicase and ligase at the replication fork, with leading and lagging strand synthesis. The central dogma describes the flow of genetic information from DNA to RNA to protein. Transcription synthesises RNA using RNA polymerase, with post-transcriptional processing (capping, tailing, splicing of introns) in eukaryotes. The genetic code is triplet, degenerate, non-overlapping, unambiguous and nearly universal, with start and stop codons. Translation assembles polypeptides on ribosomes using tRNA and mRNA. Gene regulation is illustrated by the lac operon in bacteria. The chapter concludes with the Human Genome Project, its goals, methods and findings, and DNA fingerprinting based on variable number tandem repeats (VNTRs), used in forensics and parentage testing.
DNA structure and the genetic materialDNA replicationTranscription and RNA processingGenetic code and translationGene regulation: lac operonHuman Genome Project and DNA fingerprinting
Key terms
Semiconservative replication
DNA replication in which each new double helix contains one parental (old) strand and one newly synthesised strand.
Transcription
The process of synthesising RNA from a DNA template using RNA polymerase.
Translation
The process of synthesising a polypeptide from the genetic information in mRNA on ribosomes.
Genetic code
The set of triplet nucleotide codons in mRNA that specify amino acids during protein synthesis.
Lac operon
A cluster of genes in E. coli regulated together for lactose metabolism, a model of prokaryotic gene regulation.
DNA fingerprinting
A technique that identifies individuals based on differences in repetitive DNA sequences (VNTRs).
Extra questions & answers
Try one from this chapter
DNA replication is described as semiconservative because each new molecule has: