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RNA and Protein Synthesis

  • RNA (Ribonucleic Acid) is a polynucleotide, similar to DNA, one of whose roles is protein synthesis. RNA is structurally different from DNA, in that
    • It is usually single stranded.
    • It contains the Nitrogenous Base Uracil instead of Thymine.
    • Its Nucleotides contain Ribose sugar, as opposed to Deoxyribose sugar.
  • DNA contains Genes, which code for specific Polypeptide Chains. RNA reads the instructions (Transcription) and assembles the Polypeptide Chain (Translation).
  • During Transcription, the DNA molecule 'opens up', exposing the gene to be read. Free RNA nucleotides, which are complementary using the base paring rules C-G and A-U (since Uracil is similar to Thymine) bond to the exposed bases on the Template Strand.
  • The RNA backbone then forms creating an mRNA (messenger RNA) molecule which is identical to the Coding Stand (opposite to the Template Strand). The mRNA then 'peels away' from the DNA strand.
http://alevelnotes.com/content_images/i52_transcription.png
  • The mRNA strand leaves the nucleus through a nuclear pore and attaches to a Ribosome, which is composed of rRNA (ribosomal RNA).
  • tRNA (Transfer RNA) carries amino acids. When the tRNA carrying the correct amino acid in the sequence collides with the Ribosome, the amino acid joins with the previous amino acid, forming a Peptide Bond.
  • This produces a polypeptide chain, whose Primary Structure is dictated by the sequence of bases in the gene. Primary Structure gives rise to Secondary and Tertiary Structures.