Biology · Biotechnology: Principles and Processes · NEET
There are four core tools. (1) Restriction enzymes (restriction endonucleases) act as molecular scissors and cut DNA at fixed sequences. (2) DNA ligase acts as glue and joins two DNA pieces. (3) Vectors (like plasmids or bacteriophages) carry the foreign DNA into a host. (4) A competent host cell takes up the recombinant DNA and multiplies it. Some books also list polymerising enzymes (like Taq polymerase used in PCR) as helping tools.
This confuses many students. PCR (Polymerase Chain Reaction) is a process used to make many copies of a gene, but the enzyme it uses, Taq polymerase, is counted among the enzyme tools. So the machine/technique is a process, while the enzyme inside it is a tool. In NEET, if the question asks for a 'tool', pick the enzyme; if it asks for a 'step' or 'process', pick amplification/PCR.
A naked piece of DNA cannot enter a cell easily and cannot copy itself once inside. A vector solves both problems. It has an origin of replication (ori) so it can multiply inside the host, and it carries the foreign gene along. So the vector is like a delivery van plus a photocopier for the gene.
Yes, in a way. A restriction enzyme cuts the sugar-phosphate backbone of DNA at a specific palindromic site, while DNA ligase joins two cut ends back together by sealing the backbone. When the same restriction enzyme cuts both the vector and the foreign DNA, they get matching sticky ends, and ligase then pastes them into one recombinant molecule.
Normally a cell membrane does not let large DNA molecules pass through. A 'competent' host cell is one that has been specially treated (for example with divalent calcium ions and a brief heat shock) so that its membrane can take up the recombinant DNA. Without making the host competent, transformation would fail.
Match the following enzymes with their functions: (a) Restriction endonuclease (i) Joins the DNA fragments (b) Restriction exonuclease (ii) Extends primers on genomic DNA template (c) DNA ligase (iii) Cuts DNA at specific position (d) Taq polymerase (iv) Removes nucleotides from the ends of DNA
Which of the following enzyme(s) are NOT essential for gene cloning? A. Restriction enzymes B. DNA ligase C. DNA mutase D. DNA recombinase E. DNA polymerase
A foreign DNA and plasmid cut by the same restriction endonuclease can be joined to form a recombinant plasmid using
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Remember four core tools: restriction enzymes, DNA ligase, vectors, and competent host cells. Also link the enzymes group to include Taq polymerase (for PCR).
Restriction enzymes, also called restriction endonucleases, are the molecular scissors because they cut DNA at specific palindromic sequences.
DNA ligase is the molecular glue. It joins two DNA fragments by sealing the sugar-phosphate backbone.
A plasmid is one type of vector. Vectors are the carrier tool, and plasmids like pBR322 are the most common example used to carry foreign DNA into a host.
The host cell is also counted as a tool. A competent host cell is required to take up the recombinant DNA and multiply it, so it is part of the toolkit.
