Question
What is PCR? Explain different steps involved in it.
Mechanism of PCR: At the start of PCR, all the requirements are mixed together in ‘eppendorf tube’ and the following operations are performed sequentially:
Step i: Denaturation
The reaction mixture is heated to a temperature (90–98o C) to separate two strands of desired DNA. This is called denaturation.
Step ii: Annealing
The mixture is allowed to cool (40–60o C) that permits pairing of the primer to the complementary sequences in DNA. This step is called annealing.
Step iii: Primer extension / Polymerization
The temperature (70–75o C) allows thermostable Taq DNA polymerase to use single-stranded DNA as template and adds nucleotides. This is called primer extension. It takes around two minutes duration.
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| Column A | Column B |
| (1) Nutritive tissue of embryo | (a) Perisperm |
| (2) Remnants of nucellus in seed | (b) Cotyledon |
| (3) Nutritive tissue of developing microspores | (c) Endosperm |
| (4) First photosynthetic organ of embryo | (d) Tapetum |
| Column A | Column B |
| (1) Walter Rosen | (a) Popularisation of term biodiversity |
| (2) David Tillman | (b) Rivet Popper Hypothesis |
| (3) Paul Ehrlich | (c) Productivity Stability Hypothesis |
| (4) Edward Wilson | (d) Coined |
| Column (A Type of cancer) | Column B (Organs affected) |
| (1) Carcinoma | ————– |
| (2) Sarcoma | ————– |
| (3) Lymphoma | ————– |
| (4) Adenocarcinoma | ————– |