CBSE Class 12 Biology || Molecular Basis of Inheritance Part 2 || Full Chapter || By Shiksha House

Best for NEET・2 minutes read

Human DNA is 99.9% identical, with a 0.1% difference making individuals unique, comprising deoxyribonucleic acid and nucleotide chains forming the double helix structure. Scientists like Watson and Crick confirmed DNA as the primary genetic material through experiments, leading to advancements in understanding DNA replication and gene expression.

Insights

  • The 0.1% difference in DNA among individuals is what makes each person unique, despite the 99.9% genetic similarity shared by all human beings.
  • The discovery that DNA is the hereditary material in living organisms, confirmed through experiments ruling out proteins and RNA as transforming substances, revolutionized genetics and paved the way for significant advancements in medical research.

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Recent questions

  • What is DNA composed of?

    Nucleic acid, nucleotide chains, nitrogenous bases, sugars.

  • Who proposed the double helix model for DNA?

    James Watson and Francis Crick.

  • What is the Human Genome Project?

    Project to sequence 3 billion base pairs in human genome.

  • How is DNA replicated?

    Enzymes like helicases, DNA polymerase, ligase, specific points.

  • What is transcription in gene expression?

    RNA polymerase produces mRNA from DNA.

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Summary

00:00

"DNA: The Key to Human Uniqueness"

  • DNA in all human beings is 99.9% identical, with the 0.1% difference making individuals unique.
  • DNA is composed of deoxyribonucleic acid, a type of nucleic acid made up of poly nucleotide chains formed by nucleotides.
  • The length of DNA is determined by the number of nucleotides or pairs of nucleotides present, with base pairs being the building blocks.
  • In 1953, James Watson and Francis Crick proposed the double helix model for DNA structure based on x-ray diffraction data.
  • DNA strands have complementary base pairs, allowing for accurate replication and synthesis of new daughter strands.
  • A poly nucleotide chain in DNA consists of nitrogenous bases, phosphate groups, and pentose sugars like deoxyribose.
  • DNA double helix structure includes two antiparallel poly nucleotide chains with bases paired by hydrogen bonds.
  • The DNA double helix structure is stable, with purines always pairing with pyrimidines and a right-handed coiled structure.
  • The packaging of DNA in prokaryotes involves large loops held by positively charged proteins, while eukaryotes have DNA wrapped around histones.
  • The Human Genome Project aimed to sequence the 3 billion base pairs in the human genome, identifying genes and variations for medical advancements.

23:06

"DNA: The Genetic Material and Replication"

  • Scientists conducted experiments to identify the transforming principle in bacteria, discovering that DNA from the S strain bacteria caused transformation.
  • Proteins and RNA were ruled out as transforming substances, leading to the conclusion that DNA is the hereditary material in living organisms.
  • Experiments by Avery, McLeod, and McCarty confirmed DNA as the primary genetic material, with Watson and Crick proposing a scheme for DNA replication.
  • Meselson and Stahl's experiment on E. coli bacteria proved the semi-conservative DNA replication scheme.
  • Further experiments in higher organisms like plants and human cells confirmed semi-conservative DNA replication.
  • DNA replication involves enzymes like helicases, DNA polymerase, and DNA ligase, starting at specific points called origins of replication.
  • DNA polymerase catalyzes the replication process with high accuracy and speed, requiring energy from deoxyribonucleoside triphosphates.
  • Replication bubbles form as DNA strands separate, with leading and lagging strands replicated differently due to the enzyme's directionality.
  • Okazaki fragments on the lagging strand are joined by DNA ligase, ensuring fidelity in DNA replication.
  • Transcription, the first stage of gene expression, involves RNA polymerase, producing messenger RNA from DNA in a process unique to each organism type.

49:19

Genetic Code Deciphered: Polyadenylation and Translation

  • Adenylate residues are added to the three prime end of HN RNA in a template-independent manner, forming a poly A tail, known as polyadenylation.
  • HN RNA is transformed into mRNA after polyadenylation, allowing it to be transported out of the nucleus for protein synthesis during translation.
  • In 1962, James Watson and Francis Crick won the Nobel Prize for deciphering DNA's double helix structure, revealing nucleotides' composition and the genetic blueprint.
  • George Gamow proposed a genetic code based on combinations of three nucleotides coding for amino acids, later confirmed by Marshall Nirenberg and Heinrich Mathei through experiments with E. coli extracts.
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