Lesson 4.2:Protein Synthesis

4.2.4 Protein Synthesis Reading

Transcription and Translation

Transcription is the process of creating mRNA from the DNA in the nucleus. mRNA is made in a similar way to DNA replication.The DNA double helix is unwound and unzipped and the RNA nucleotides are added.The same base pairing rules are used except uracil (U) pairs with adenine (A) instead of thymine, and mRNA strand that is created is only single stranded.

DNA_transcription by National Human Genome Research Institute / Public Domain

Each gene that is transcribed into mRNA contains triplets of bases called codons that code for a specific amino acid. The code in the mRNA determines the order of amino acids in the protein.

Rna-codons-protein by NIH / Public Domain

The chart below shows the how the genetic code is read.Start at the center of the chart for the first base of a three base codon and work towards the outside.For example the mRNA codon GCC would code for alanine (Ala).Notice an amino acid may have more than one codon.

Codons_aminoacids_table by Onie / CC BY-SA 3.0

During translation the mRNA goes to the ribosome and tRNA reads the code and brings in the correct amino acids to make the protein.Three codons: UGA, UAA, and UAG are called stop codons and indicate that protein synthesis is complete.

Peptide syn by Frank Boumphrey / CC BY-SA 3.0

Quick write:

What is the purpose of transcription?

What is the purpose of translation?

Go on to the next section for a Protein synthesis presentation. You may want to look at the assignments in section 4.2.6 first, because the presentation will be helpful in completing the review worksheet.