What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

Why is DNA replication called semiconservative?

Because each newly formed DNA molecule retains one original parental strand and one newly synthesised strand, as demonstrated by Meselson and Stahl.

What are Chargaff's rules?

In DNA, the amount of adenine equals thymine (A=T) and guanine equals cytosine (G=C), so purines equal pyrimidines.

State the central dogma of molecular biology.

Genetic information flows from DNA to RNA by transcription and from RNA to protein by translation.

List the salient features of the genetic code.

It is triplet, non-overlapping, degenerate, unambiguous, commaless, nearly universal, and has start (AUG) and stop codons.

Which experiment proved DNA, not protein, is the genetic material?

The Hershey and Chase experiment using bacteriophages with radioactively labelled DNA and protein proved DNA is the genetic material.

What is the role of DNA ligase in replication?

DNA ligase joins the Okazaki fragments of the discontinuously synthesised lagging strand into a continuous strand.

What is a nucleosome?

A nucleosome is the repeating unit of chromatin consisting of DNA wrapped about 1.65 turns around a histone octamer.

How does the lac operon get switched on?

In the presence of lactose (the inducer), lactose binds the repressor, inactivating it; RNA polymerase then transcribes the structural genes z, y and a.

What were the main goals of the Human Genome Project?

To identify all genes in human DNA, determine the sequence of the base pairs, store the information, develop analysis tools and address ethical issues.

What is the basis of DNA fingerprinting?

It is based on polymorphism in repetitive DNA sequences called VNTRs (variable number of tandem repeats) that differ among individuals.

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

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DNA replication is described as semiconservative because each new molecule has:

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