C
CraftExam
medium difficulty7 min

Steps in Recombinant DNA Technology

The steps in recombinant DNA technology are the ordered procedures used to isolate a desired gene, insert it into a vector, introduce it into a host, select transformants, express the gene and process the product.

In one line: I-C-A-L-T-S-E-D: isolate, cut, amplify, ligate, transform, select, express, downstream.

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Understand it

  • Recombinant DNA technology is sequence-dependent.
  • DNA is first isolated and cut with restriction enzymes to obtain the desired fragment.
  • The same or compatible enzyme can cut vector DNA so that the insert can be joined by ligase.
  • PCR may amplify the gene to produce many copies.
  • The recombinant vector is introduced into competent host cells by transformation.
  • Cells containing the recombinant DNA are selected using markers, then grown so the inserted gene can replicate or express its product.
  • Finally, downstream processing purifies and tests the product.
  • If the order is confused, the biological logic of cloning breaks down.

Example

To produce a recombinant protein in bacteria, the gene of interest is isolated, amplified, inserted into a plasmid, introduced into bacterial cells, selected, expressed and processed.

Rule to remember

Sequence rule: isolate DNA, cut DNA, amplify if needed, ligate into vector, transform host, select transformants, express gene, then perform downstream processing.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

In a case study where bacterial colonies grow on a selective medium, infer that the medium helps identify cells carrying a marker linked to the vector.

Method you can reuse

Isolate DNA containing the gene of interest; cut source DNA and vector DNA with restriction enzymes; amplify the gene by PCR when required; join the gene into the vector using DNA ligase; introduce recombinant DNA into competent host cells; select transformed cells using markers; culture selected cells for expression; purify and check the product through downstream processing.

Visual tip

A process diagram should label gene of interest, restriction digestion, vector, recombinant DNA, host cell, transformant, expression and downstream product recovery.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why is selection needed after transformation?

Think first, then show answer
Selection is needed because not every host cell takes up the recombinant vector. Selectable markers help identify cells that carry the desired vector so only useful transformants are grown further.

Common wrong answer

Recombinant DNA is made simply by injecting a gene into any cell.

Don't mix this up

Students often place PCR after transformation as a routine step; amplification is generally used before cloning when many copies of the gene are needed.

Exam tip

For long answers, write steps in order and use action verbs: isolate, cut, amplify, ligate, transform, select, express, purify.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Commonly asked as a long answer sequence, case-study interpretation, flowchart completion, or reason-based question on PCR, transformation and selection.

Answer plan

Start with a one-line definition, then write the ordered steps with enzyme/vector/host terms, add PCR and selection where relevant, and finish with expression plus downstream processing.
  1. 1

    Enough for 1 mark

    The steps in recombinant DNA technology are the ordered procedures used to isolate a desired gene, insert it into a vector, introduce it into a host, select transformants, express the gene and process the product.

  2. 2

    Add for 2 marks

    Example: To produce a recombinant protein in bacteria, the gene of interest is isolated, amplified, inserted into a plasmid, introduced into bacterial cells, selected, expressed and processed.

  3. 3

    Add for 3 marks

    DNA is first isolated and cut with restriction enzymes to obtain the desired fragment.

Practice

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