मराठी

Overview of Molecular Basis of Inheritance

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Maharashtra State Board: Class 12

Key Points: Packaging in Prokaryotes

  • Prokaryotes like E. coli do not have a true nucleus. Their DNA is present in a region called nucleoid.
  • The DNA is very long but the cell is very small, so the DNA must be tightly packed inside the cell.
  • The DNA becomes circular and folded into loops. About 40–50 loops are formed to reduce its size.
  • The DNA is further coiled and supercoiled with the help of HU proteins, DNA gyrase and topoisomerase, so it fits inside the cell.
Maharashtra State Board: Class 12

Key Points: Regulation of gene expression

  • Gene expression is a multistep process by which a gene is regulated and its product (polypeptide/protein) is formed.
  • In eukaryotes, gene expression is regulated at different levels such as transcription, RNA processing, mRNA transport, and translation.
  • Genes are expressed only when needed to perform specific functions, for example β-galactosidase enzyme in E. coli helps in breaking lactose into glucose and galactose.
  • If lactose is absent, E. coli does not produce β-galactosidase, showing that gene expression depends on environmental and metabolic conditions.
  • Some bacterial genes are inducible, meaning they are switched on only in the presence of a substrate; this process is called induction and works by positive control.
Maharashtra State Board: Class 12

Definition: Operon

A long segment of DNA that contains an operator, promoter and a group of structural genes working together is called an operon.

Maharashtra State Board: Class 12

Definition: Operator

A regulatory DNA sequence that controls transcription by allowing or blocking RNA polymerase binding is called an operator.

Maharashtra State Board: Class 12

Definition: Repressor Protein

A protein that binds to the operator and prevents transcription of structural genes is called a repressor protein.

Maharashtra State Board: Class 12

Definition: Regulator Gene

A gene that produces the repressor protein is called a regulator gene.

Maharashtra State Board: Class 12

Definition: Cistron

An individual gene that codes for a single polypeptide chain is called a cistron.

Maharashtra State Board: Class 12

Definition: Polycistronic mRNA

A single mRNA molecule that carries information for more than one cistron is called polycistronic mRNA.

Maharashtra State Board: Class 12

Key Points: Genomics

  • The complete genetic constitution or one complete set of chromosomes of an organism is called the genome, and its study is known as genomics.
  • Genomics involves sequencing, mapping, analysis of genes, and understanding their functions.
  • Genomics is of two types: structural genomics (mapping and sequencing of genomes) and functional genomics (study of gene functions and expression).
  • Comparative genomics is done by sequencing organisms like yeast, fruit fly and mouse to understand human genes.
  • Genomics has applications in medicine, agriculture, biotechnology and forensics, including gene therapy, transgenic crops and production of useful proteins.
 
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