Summary of "MOLECULAR BASIS OF INHERITANCE in ONE SHOT || All Concepts, Tricks & PYQ || Ummeed NEET"
Summary of the YouTube Video: "Molecular Basis of Inheritance in ONE SHOT || All Concepts, Tricks & PYQ || Ummeed NEET"
Main Ideas, Concepts, and Lessons Conveyed
1. Introduction to Molecular Basis of Inheritance
- The chapter is highly conceptual and important for NEET exams.
- Over 100 questions from this chapter have appeared in the last 10 years.
- The chapter builds on prior knowledge of genetics and inheritance principles.
- Focus is on DNA and RNA as genetic materials and their molecular structures.
2. Genetic Material: DNA and RNA
- DNA is the primary genetic material in most organisms; RNA serves as genetic material in some viruses (e.g., Tobacco Mosaic Virus, coronaviruses).
- DNA is more stable than RNA due to:
- Presence of deoxyribose sugar (lacking 2' OH group).
- Thymine instead of uracil.
- RNA is less stable and mutates faster, which suits viruses needing rapid evolution.
- Nucleic acids are polymers of nucleotides, each nucleotide consisting of:
- Nucleoside = nitrogenous base + sugar; Nucleotide = nucleoside + phosphate.
- DNA is double-stranded, antiparallel, with complementary base pairing (A-T with 2 hydrogen bonds, G-C with 3 hydrogen bonds).
- DNA diameter ~20 Å; one helical turn = 10 base pairs, length ~34 Å.
- DNA length in a human cell is about 2.2 meters, tightly packed inside the nucleus.
3. DNA Packaging
- Prokaryotic DNA is naked but associated with positively charged proteins forming nucleoid.
- Eukaryotic DNA is wrapped around Histone proteins forming nucleosomes (histone octamer: 2 each of H2A, H2B, H3, H4).
- DNA wrapped around nucleosomes looks like "beads on a string".
- Linker histone H1 connects nucleosomes.
- Further packing forms chromatin fibers and chromosomes.
- Chromatin exists as:
- Heterochromatin: tightly packed, transcriptionally inactive.
- Euchromatin: loosely packed, transcriptionally active.
4. Experiments Proving DNA as Genetic Material
- Griffith’s Transformation Experiment (1928): demonstrated a "transforming principle" converting non-virulent bacteria to virulent.
- Avery, MacLeod, and McCarty (1944): identified DNA as the transforming principle by selectively destroying proteins, RNA, or DNA.
- Hershey and Chase (1952): used radioactive labeling of DNA (P32) and protein (S35) in bacteriophages to prove DNA enters bacteria and carries genetic information.
- These experiments established DNA as the genetic material, not protein.
5. Properties of Genetic Material
- Must replicate accurately.
- Chemically and structurally stable (DNA > RNA).
- Must allow mutation (DNA mutates slowly, RNA faster).
- Must express itself (DNA transcribed to RNA, RNA translated to protein).
- DNA is the storage medium; RNA acts as a transmission medium.
- RNA world hypothesis: RNA was the first genetic material due to multifunctionality and catalytic properties (ribozymes).
6. Central Dogma of Molecular Biology
- DNA → DNA (Replication)
- DNA → RNA (Transcription)
- RNA → Protein (Translation)
- Exceptions like reverse transcription in retroviruses (RNA → DNA).
- Replication is semi-conservative (Meselson-Stahl experiment).
- DNA replication:
- Origin of replication (ORI) sites where replication begins.
- Prokaryotes have single ORI; eukaryotes have multiple ORIs.
- Leading strand synthesized continuously; lagging strand synthesized discontinuously (Okazaki fragments).
- Enzymes involved: helicase, DNA polymerase III (synthesis), DNA polymerase I (removes RNA primers), ligase (joins Okazaki fragments), topoisomerase (relieves supercoiling).
- DNA synthesis occurs 5’ to 3’ direction.
7. Transcription
- Only one DNA strand (template strand) is transcribed into RNA.
- RNA polymerase binds at promoter, synthesizes RNA 5’ to 3’.
- In prokaryotes, a single RNA polymerase does all transcription; sigma factor helps initiation; rho factor helps termination.
- In eukaryotes, three RNA polymerases exist:
- RNA Pol I: rRNA
Category
Educational
