Class 12 Biology - WEST-BENGAL
Molecular Basis of Inheritance
The chapter Molecular Basis of Inheritance in Class 12 Biology explores the genetic material DNA, its structure, replication, and how genetic information flows to RNA and proteins. Students will study Hershey-Chase experiments, Meselson and Stahl's semi-conservative replication, transcription, the genetic code, translation, and the Human Genome Project along with DNA fingerprinting. This is a high-weightage chapter for the West Bengal (WBBSE) board examinations, frequently featuring descriptive questions on protein synthesis, replication mechanisms, and numerical problems based on Chargaff's rules and DNA dimensions.
Start Learning FreeKey Concepts
DNA Structure (Watson and Crick Model)
DNA is a double helix consisting of two polynucleotide chains running anti-parallel, held together by hydrogen bonds between complementary nitrogenous bases (A-T and G-C).
Central Dogma of Molecular Biology
Proposed by Francis Crick, it states that genetic information flows in one direction: DNA undergoes replication to form DNA, transcribes to form mRNA, and translates to form proteins.
DNA Replication
The semi-conservative process where DNA makes exact copies of itself with the help of enzymes like DNA polymerase, creating leading and lagging strands.
Transcription
The process of copying genetic information from one strand of DNA into RNA using the enzyme RNA polymerase, guided by promoter and terminator regions.
Genetic Code
The sequence of nucleotides in mRNA that directs the incorporation of amino acids during protein synthesis, possessing properties like being triplet, universal, and degenerate.
Lac Operon
An inducible operon system in E. coli consisting of structural genes regulated by a common promoter and repressor, responsible for lactose metabolism.
Important Formulas
Board Exam Info
In the West Bengal Council of Higher Secondary Education (WBBSE) Class 12 Biology examination, this chapter carries approximately 7-10 marks. Questions typically include long descriptive answers on protein synthesis or DNA replication, short-answer questions on the lac operon or Hershey-Chase experiment, and numerical problems based on Chargaff's rules.
Frequently Asked Questions
Why is DNA considered a better genetic material than RNA?
DNA is chemically more stable due to the presence of deoxyribose sugar (lacking a reactive 2'-OH group) and thymine instead of uracil, making it less prone to mutations compared to RNA.
What is the difference between leading strand and lagging strand in DNA replication?
The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously in short segments called Okazaki fragments, which are later joined by DNA ligase.
How does the lac operon switch on and off?
In the absence of lactose, a repressor protein binds to the operator region and blocks RNA polymerase, keeping the operon off. When lactose (inducer) is present, it binds to the repressor, inactivating it and switching the operon on.
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