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

What are restriction enzymes and what do they recognise?

They are molecular scissors that recognise specific palindromic sequences in DNA and cut the strands at defined sites, producing fragments often with sticky ends.

What is a palindromic sequence?

A palindromic sequence reads the same on both strands when read in the same orientation (5' to 3'), the recognition site for many restriction enzymes.

Why is DNA ligase called molecular glue?

Because it joins (seals) the sticky ends or fragments of DNA by forming phosphodiester bonds, sealing the recombinant molecule.

List the essential features of a good cloning vector.

An origin of replication, a selectable marker, recognition (cloning) sites for restriction enzymes, and a small size.

What are the three steps of a PCR cycle?

Denaturation (strand separation by heating), annealing (primer binding) and extension (synthesis of new strands by Taq polymerase).

Why is Taq polymerase used in PCR?

Taq polymerase, isolated from Thermus aquaticus, is thermostable and remains active at the high temperatures used during denaturation in PCR.

How are DNA fragments separated and visualised in gel electrophoresis?

They are separated by size as they move through an agarose gel under an electric field and are visualised by staining with ethidium bromide under UV light.

What does making a cell "competent" mean?

It means treating the cell (e.g., with divalent cations like calcium) so its membrane becomes permeable, allowing recombinant DNA to enter.

What is biolistics or the gene gun method?

It is a method of introducing foreign DNA into cells by bombarding them with high-velocity microparticles of gold or tungsten coated with DNA.

Why is downstream processing important?

Downstream processing involves separation, purification, formulation and quality control of the product after biosynthesis, making it suitable for marketing as a finished product.

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Chapter 9: Biotechnology: Principles and Processes — Class 12 Biology

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Chapter 9: Biotechnology: Principles and Processes

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Restriction enzymes are often called:

Summary

This chapter introduces biotechnology, the use of living organisms or their components to produce useful products, and the principles and tools underlying recombinant DNA (genetic engineering) technology. The two core techniques are genetic engineering (altering DNA and introducing it into hosts) and maintaining sterile conditions for the large-scale growth of microbes and cells. Key tools of recombinant DNA technology include restriction enzymes (molecular scissors that cut DNA at specific palindromic sequences producing sticky ends), DNA ligase (molecular glue), cloning vectors (plasmids, bacteriophages) with features such as origin of replication, selectable markers and recognition sites, and host organisms. Separation and isolation of DNA fragments is achieved by gel electrophoresis. The process of recombinant DNA technology is described step by step: isolation of the gene of interest, cutting and joining DNA, amplification using the Polymerase Chain Reaction (PCR), insertion into a vector, transfer into a competent host (transformation), selection of transformants, and obtaining the foreign gene product. Methods of introducing recombinant DNA, including microinjection, biolistics (gene gun) and disarmed Agrobacterium, are covered. Bioreactors for scaling up production, downstream processing, and quality control are explained, highlighting the industrial application of these principles.

Principles of biotechnologyTools of recombinant DNA technologyRestriction enzymes and vectorsGel electrophoresis and PCRProcesses of recombinant DNA technologyBioreactors and downstream processing

Key terms

Restriction enzyme

An enzyme that recognises specific palindromic DNA sequences and cuts the DNA, used as molecular scissors.

Cloning vector

A DNA molecule (e.g., plasmid) used to carry and replicate a foreign gene inside a host cell.

PCR

Polymerase Chain Reaction, a technique to amplify a specific DNA segment in vitro using primers and Taq polymerase.

Gel electrophoresis

A technique to separate DNA fragments according to size by their migration through a gel in an electric field.

Transformation

The process of introducing recombinant DNA into a competent host cell.

Bioreactor

A vessel in which raw materials are biologically converted into specific products using microbes or cells on a large scale.

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An enzyme that recognises specific palindromic DNA sequences and cuts the DNA, used as molecular scissors.

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