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 )