LECTURE                    THE THREE MAJOR KINDS OF RNA AND THEIR FUNCTION

The main points of this lecture are:

  • there are 3 major forms of RNA
  • mRNA which is the "message"
  • rRNA which is the machinery/enzyme
  • tRNA which brings in the amino acids and "translates"

  •  
    1. mRNA is messenger RNA 

    - it is the actual linear "message" that is TRANSLATED into protein
    - the base sequence specifies which proteins will be made during translation

    2. rRNA is ribosomal RNA

    -  the RNA that is the "machinery" that makes proteins
    - it is structural in that proteins and the rRNA are assembled together into a globular structure like an enzyme
    - it is composed of 2 subunits

    3. tRNA is transfer RNA

    - There are 32 different tRNAs and each one binds a SPECIFIC  one of the 20 amino acid
    - it holds the amino acid in a physical position so it can be added onto the developing protein polymer chain 
    - each tRNA is the product of a separate gene or section of DNA  containing 73-93 nucleotides
    each has a "loop and stem" structure
    -  the stems are hydrogen bonded to give structure
    the paired and H bonded stems can form sections of double helix 
    -  the unpaired regions form 3 loops
    -  each tRNA carries (at its 3' end) the amino acid specific to that tRNA
    - the middle loop has the 3 unpaired bases that form the anticodon base 
    - it is the anticodon that pairs with the complementary codon on the mRNA molecule and brings the correct amino acid into alignment to be added to the growing polypeptide chain.

    REVIEW QUESTIONS:
    What are the 3 kinds of RNA?
    What is their function and how are they different from each other?
    Describe what the different RNAs look like.