en:gene [Chapters]

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====== GENE ======



  * Molecular structure of a gene
    * mainly two types based on function 
      * structural genes 
        * based on sequence 
          * Introns ( non coding sequences ) 
            * 
          * Exons ( coding sequences )
          * flanking regions ( terminal rregions at ends )
            * at 5' end 
              * promoter region 
                * "TATA" box
                  * GGGCGGG sequence 
                * "CAT" box
                  * CCAAT
            * Transcription factors bind to this region
            * at 3' end 
              * Translation termination codon followed by a 
                * poly (A) cap codon 
      * Regulatory genes ( control genes )

  * DNA
    * Genic dna 
      * single of low copy number 
    * Extragenic dna 
      * highly repetitive DNA sequences 
      * B- extragenic DNA 
        * Tandemly repeated DNA sequences 
          * Satellite dna 
          * Minisatellite dna 
            * highly variable DNA sequences 
              * DNA finger printing 
          * Microsatellite dna 
        * Interspersed repetitive DNA sequence
          * short 
          * long 
  * do not act as genes
    * Junk dna 




  * Single copy genes 


  * Chain initiation 
  * chain termination 

  * Genetic code 
    * 3 bases of DNA ( 3 alphabets of DNA ) 
      * codons 
        * each codon codes for a single amino acid 
        * triplet code 
        * initiation codon 
          * AUG
        * termination codon
          * UAA or UAG  
  * Transcription ( Copying ) 
    * RNA polymerase binds to 
      * promoter region 
    * begins from 5' to 3" end 
    * synthesis of mRNA
      * it is single stranded 
      * Structure of mRNA
        * all sequences of structural genes are transcribed ( exons and introns )
          * by process of SPLICING
            * then introns are excised 
            * exons are joined to form mature RNA which is shorter 
        * It has two ends 
          * 5" end 
            * methylguanine cap  
          * 3' end 
            * poly (A) tail   
  * Translation 
    * mRNA 
      * Provides the coding sequence for ( बहुजीवर्थाणु / जीवार्थसूत्र   - polypeptide chain) 
    * Ribosome 
    * tRNA 
    * Process
      * initiation 
        * 5" cap of mRNA
        * initiation complex formed by
          * attachment of elongation factors 
        * then moves along the 3' end 
        * encounters AUG codon which is the start codon 
          * signals the start of  
      * elongation 
      * termination 
        * encounter of stop codon on mRNA 
        * release factor binds with ribosome 

  * mutation 
    * change occurs in structure of gene 
      * gene mutation or point mutation ( utparivartan )