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Transcription and Translation. GENE EXPRESSION - How the genes are expressed is a function of the protein produced. DNA (gene). Ribosome. tRNA & rRNA. Protein. m RNA. Trait (expression). There are two processes that make this happen…. Transcription. Translation.

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gene expression how the genes are expressed is a function of the protein produced
GENE EXPRESSION - How the genes are expressed is a function of the protein produced.

DNA (gene)





Trait (expression)

there are two processes that make this happen
There are two processes that make this happen…



mRNA strand is usedat the ribosome to help join amino acids to form a protein.

  • mRNA strand is builtfrom the code on the DNA strand (gene)


Let’s watch a video of transcription…

requirements for transcription
Requirements for Transcription
  • PREDICT: What do you think the RNA polymerase will do?
steps in transcription
Steps in transcription

These stages are catalyzed by the enzyme RNA polymerase

each triplet code on a dna molecule is transcribed into a triplet codon on the mrna molecule
Each triplet codeon a DNA molecule is transcribed into a triplet codonon the mRNA molecule.
  • If the DNA codes for a polypeptide is


  • What would the codons on the complimentary strand of mRNA codons look like?

A-U-G – G-G-C – A-U-C – G-A-A – U-G-A

  • DNA codes:


  • mRNA codons:

A-U-G – G-U-A – G-G-G – U-U-U – U-G-A

think think think
  • What does each letter in the code or codon stand for represent?

That’s right….a nucleotide

  • What do the particular codes and codons represent?

Amino Acids….good job!

  • Because each base triplet on the mRNA stands for an amino acid, each mRNA molecule must contain how many times the number of nucleotides as the number of amino acids making up the protein product.

3X….Wow! You guys are on a roll!

engage your brain the intersection of science and math
Engage your BRAIN….The intersection of science and math
  • An mRNA strand with 66 nucleotides codes for a polypeptide how many amino acids in length?

22…you all are Math whizzes

  • A protein 300 amino acid units in length was synthesized from an mRNA strand how many nucleotides in length?

900…Woo Hoo!

  • A DNA strand 700 nucleotides in length will be transcribed into an mRNA strand how many nucleotides in length.

700…Ah! This one is tricky!

how do we read mrna codons
How do we read mRNA codons?
  • There are 4 different bases in DNA (A, C, G, T) which can combine in different triplets to form 64 possible triplet codes (43).
  • When these codes are transcribed into mRNA, there are 64 triplet codons which can be formed.
  • Only 20 amino acids are used so sometimes more than one codon represents an amino acid.
  • We can use the chart to the right to determine the exact sequence of amino acids that will make up a protein.
How many different mRNA codons are there on the chart?

43 = 4 x 4 x 4 = 64

different codons (using A, G, C and U in triplets)

  • How many different amino acids are there?

Only 20

  • Which amino acids only have ONE triplet code assigned to them?

Methionine and Trytophan

  • With the exception of Methionine and Tryptophan,

more than one nucleotide triplet codes for each amino acid.

  • Give an example of an amino acid which has more than one codon.

valine, alanine, isoleucine, threonine, and many more

  • What do you notice about the codons that code for the same amino acid?

They are very similar and usually only the last nitrogen base is different.

What is the DNA code for the mRNA start codon, methionine?


  • What are the DNA codes for the stop codons UAA, UAG and UGA?


  • After transcription has taken place, the mRNA moves out of the nucleus to link with a ribosome in the cytoplasm. Translation will take place here…..


Let’s Watch a video on Translation…