Lesson 28 : DNA and RNA Structures and Protein Synthesis


Translation -mRNA codons are read, amino acids are brought to the mRNA strand and polypeptides (proteins) are produced at the ribosomes. Translation ends with the production of a protein.

The three specific parts of translation are:

  1. Initiation - the ribosomal RNA (ribosome) and the mRNA strand become attached.

  2. Elongation - the polypeptide lengthens one amino acid at a time

  3. -the tRNA anti-codons (3 letter code of the tRNA) bond to the mRNA codons (3 letter code of the mRNA) by complementary base pairing at the ribosome. The codons determine the type of amino acid brought to the polypeptide chain.

    -The ribosome is large enough to accomodate two tRNA molecules at a time, one incoming and one outgoing The amino acid on the incoming tRNA forms a peptide bond with the amino acid on the outgoing tRNA.

    -The ribosome then moves laterally, allowing the outgoing tRNA to leave and making space for a new incoming tRNA.

  4. Termination - occurs at the stop codon on the mRNA. The completed polypeptide dissociates from the ribosome
  5. -Translation is shown in the diagram below. The ribosomes (look like snowmen, the mRNA strand is labeled X and the growing polypeptide strand is indicated with individual circles representing each amino acid.


Determine the amino acids coded for by a strand of DNA

  1. Determining codons from a strand of DNA
  2. Consider the following strand of DNA read from left to right:

    T T A T G C T C C T A A

    When complementary base pairing occurs the following strand of mRNA is obtained.

    A A U A C G A G G A U U

    The codons are read three letters at a time from the transcribed mRNA. The codons are:

    A A U A C G A G G A U U

  3. Determining amino acids from mRNA codons
  4. Find the codons in the table of mRNA codons below and the amino acids they code for.

    AAU -Asparagine ACG - Threonine AGG - Arginine AUU -isoleucine

Last modified: Tuesday, 24 January 2012, 9:35 AM