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Molecular Basis of Inheritance — Revision Notes

Punjab Board · Class 12 · Biology

Molecular Basis of Inheritance revision notes for Punjab Board Class 12 Biology: 4 topics in quick points. Includes Structure of DNA, Packaging of DNA.

45 questions33 flashcards5 concepts

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A detailed labeled diagram showing the components of a DNA nucleotide: a deoxyribose sugar, a phosphate group, and one of the four nitrogenous bases (Adenine, Guanine, Cytosine, or Thymine). Emphasize
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Key Topics to Revise

1

Structure of DNA

  • DNA (Deoxyribonucleic Acid) is a long polymer of deoxyribonucleotides.
  • Each nucleotide has three components: a nitrogenous base, a pentose sugar (deoxyribose), and a phosphate group.
  • Nitrogenous bases: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine). Uracil replaces Thymine in RNA.
2

Packaging of DNA in the Nucleus

  • Total length of DNA in a human cell (~2.2 metres) must fit into a nucleus of ~10⁻⁶ m — this requires extraordinary packaging.
  • In prokaryotes (e.g., E. coli): DNA is organised in 'nucleoid' region with the help of positively charged proteins. DNA forms large loops held by these proteins.
  • In eukaryotes: DNA is packaged around histone proteins.
3

Search for Genetic Material – Key Experiments

  • DNA was first identified in the nucleus by Friedrich Miescher in 1869 and called 'Nuclein'.
  • GRIFFITH'S EXPERIMENT (1928): Used Streptococcus pneumoniae (pneumococcus). S-strain (smooth, virulent, has polysaccharide coat) kills mice; R-strain (rough, non-virulent, no coat) does not kill mice.
  • Heat-killed S-strain does not kill mice. BUT mixture of heat-killed S + live R kills mice — and live S bacteria were recovered from dead mice.
4

Properties of Genetic Material and RNA World

  • Criteria for a molecule to be genetic material: (1) Ability to replicate, (2) Chemical and structural stability, (3) Ability to mutate slowly for evolution, (4) Ability to express as 'Mendelian Charac
  • Both DNA and RNA can replicate (due to complementarity), but only DNA satisfies all four criteria optimally.
  • RNA is less stable because of the reactive 2'-OH group at every nucleotide. DNA lacks this group, making it more stable.

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Full Notes

Key Concepts

DNA is a polymer of deoxyribonucleotidesThe journey to identify DNA asWhile both DNA and RNA canHuman DNA would stretch approximately 2DNA replication is the process by

Frequently Asked Questions

What are the important topics in Molecular Basis of Inheritance for Punjab Board Class 12 Biology?
Key topics in Molecular Basis of Inheritance include Structure of DNA, Packaging of DNA in the Nucleus, Search for Genetic Material – Key Experiments, Properties of Genetic Material and RNA World. Study these first, then practise questions on each for the Punjab Board Class 12 board exam.
How should I revise Molecular Basis of Inheritance for the Punjab Board Class 12 board exam?
Learn the core ideas first, then work through the 45 practice questions on Molecular Basis of Inheritance. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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