Ch 5Molecular Genetics — Class 12 Zoology, concept-first.

Mendel's laws explained the patterns by which traits could seem to vanish in one generation and reappear in the next, and showed that this hereditary information is passed from parents to offspring on…

A gene is the basic physical and functional unit of heredity. Gregor Mendel worked out the rules by which traits pass from parents to offspring in the 1860s, but he never used the word 'gene' -- he ca…

Long before anyone knew genes were made of DNA, cytologists were already watching the physical objects that would turn out to carry them.

Even with Griffith's and Avery's evidence in hand, a considerable number of biologists remained unconvinced that DNA was the genetic material.

Hershey and Chase worked with bacteriophage T2, a virus that infects the bacterium Escherichia coli. When T2 particles encounter a bacterium, they attach to its outer surface, inject some of their own…

Once DNA (and, in certain viruses, RNA) had been identified as the genetic material, the next task was to work out its chemical make-up.

A living cell typically contains roughly ten times as much RNA as DNA, a striking imbalance explained by the sheer variety of jobs RNA performs inside the cell beyond simply storing genetic informatio…

For any molecule to qualify as a cell's genetic material, it must satisfy three demanding properties, and this section compares how well DNA and RNA each measure up.

The DNA inside even a single mammalian cell is astonishingly long relative to the space available to hold it: the distance between two consecutive base pairs along the double helix is a fixed 0.34 nan…

DNA replication is the process by which a cell copies its entire genome, once per cell cycle, during the S (synthesis) phase, so that each of the two daughter cells produced by division receives a com…

Watson and Crick's semi-conservative model remained an elegant but unproven hypothesis until Matthew Meselson and Franklin Stahl devised an ingenious experiment in 1958 specifically designed to distin…

Carrying out replication accurately and quickly enough to keep pace with cell division requires a coordinated team of specialised enzymes.

Francis Crick's central dogma of molecular biology summarises the normal direction genetic information flows within a cell: DNA is transcribed into RNA (transcription), and that RNA is in turn transla…

Every transcription unit on a DNA molecule is defined by three functionally distinct regions arranged in a fixed order: a promoter, the structural gene itself, and a terminator.

Transcription unfolds through the same three stages in essentially every organism: initiation, elongation and termination, though the details differ meaningfully between prokaryotes and eukaryotes.

Once DNA (and RNA) had been established as the genetic material, the next question was how hereditary information is actually written into the sequence of a nucleic acid molecule, and how that written…

Comparing mutations, sudden heritable changes in a gene, against the resulting changes in the amino acid sequence of the corresponding protein has provided some of the strongest confirmation available…

Transfer RNA, tRNA, is the molecule that physically links a codon on an mRNA to the correct amino acid, because a codon's sequence of bases has no chemical affinity of its own for any particular amino…

Translation is the process by which the ribosome polymerises a chain of amino acids, delivered one at a time as charged tRNAs, into a growing polypeptide chain, following the sequence of codons laid o…

The ribosome is the cell's protein-synthesising factory, and the mechanism by which it carries out translation unfolds in the same three phases, initiation, elongation and termination, that also struc…

Having established how DNA is organised into genes, how those genes store hereditary information, and how that information is expressed as protein, the chapter turns to a more fundamental question: ho…

The international Human Genome Project (HGP) was formally launched in 1990 as a large, coordinated international effort and took thirteen years to complete.

The Human Genome Project pursued six explicit goals: to identify every one of the roughly 30,000 genes present in human DNA; to determine the precise sequence of the three billion chemical base pairs…

The completed Human Genome Project produced a long list of striking headline findings about the structure of the human genome.

Being able to map an individual's chromosomes in detail makes it possible to examine that person's DNA directly and identify specific genetic abnormalities, an ability with immediate practical value f…

Every human being shares essentially the same basic chemical structure of DNA, yet there are literally millions of small differences scattered across the sequence of base pairs between any two individ…

These end-of-chapter Evaluation questions test the full sweep of the chapter: the historical search for the genetic material (Griffith, Avery-MacLeod-McCarty, Hershey-Chase), the chemistry and packagi…

Sample papers and previous-year board questions for this subject.