12th Class Biology Molecular basis of inheritance

  • question_answer 8) Differentiate between the following : (a) Repetitive DNA and Satellite DNA (b) mRNA and tRNA (c) Template strand and coding strand  


          (a) Difference between repetitive and satellite DNA are as follows:                

    Repetitive DNA Satellite DNA
    Repetitive DNA consists of short identical genes which are repeated in tandem several hundred or thousand times. It is of two types. Highly repetitive DNA (satellite DNAs) and moderately repetitive DNA. They are mainly found in telomere, centromere and ends of transposons. The proportion of the DNA of a eukaryotic cell that consists of very large number (approximately 106) of copies of a short nucleotide sequence. It occurs mainly around the centromeres and telomers of the chromosomes. The highly repetitive nature of this DNA fraction gives it a distinctive base composition, and consequently when samples of DNA are centrifuged it forms so-called ‘satellite bands quite separate from the band representing the bulk of the cell’s DNA.
      (b) Differences between mRNA and tRNA are as follows:                
      Features Messenger RNA (mRNA) Transfer RNA (tRNA)
    1. Percentage of cell’s total RNA About 5 About 15
    2. Length of molecule Longest Shortest
    3. Shape of molecule Linear Clover leaf-like, folded into L-shape
    4. Types Numerous About 60
    5. Role Carry information from DNA Carry amino acids to mRNA codons
    6. Life Very short, 2 minutes to 4 hours, degraded Long, used again and again in translation
    7. Function Transfer genetic information from genes to ribosomes to synthesize proteins Transfer amino acid to mRNA
      (c) Difference between template and coding strand are the following:
      Template strand Coding strand
    1. Strand of DNA having 3’-5’ polarity. Strand of DNA having 5’-3’ polarity.
    2. It serves as the template in transcription and produces working copies of RNA molecule and is also known as master strand or sense strand. It does not participate in transcription and is also called non template strand.

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