Protein Synthesis and Codons Practice

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Protein synthesis is the process where a sequence of DNA is used to build a protein from individual amino acids. The first step in this process is called TRANSCRIPTION, where a coding region of DNA is converted to messenger RNA (mRNA). During transcription, mRNA is made from the DNA sequence following the base pair rule, except RNA does not contain the base Thymine, but instead has Uracil. The mRNA then leaves the nucleus and goes to a ribosome in the cell's cytoplasm. The ribosome reads the message three bases at a time, called a CODON. Each codon will specify a single amino acid. The amino acids are joined together and folded into a protein, a process called TRANSLATION

Key Points

Biologists use a codon chart or a codon wheel to determine the amino acids. Amino acids are usually abbreviated on these charts as three letter words, like Cys and Ser.

codon chart codon wheel


1. Use the codon chart to write the amino acid that corresponds to each codon found in mRNA:

C C C ______________________      A G U ______________________

C A G ______________________      U A C ______________________

G A A ______________________      C G U ______________________

U U U ______________________      C C A ______________________


2. Write the CODON that corresponds with each amino acid. There may be more than one. The full names are written, but the codon chart only shows the first three letters.

proline ______________________      glycine ______________________

valine ______________________       phenylalanine ______________________

histidine ______________________   arginine ______________________


3. A single codon is used to signal the beginning of protein synthesis. It is commonly called the START CODON.

Locate the start codon on the chart. What are the three bases of this codon? ________

4. There are three codons that signal the end of synthesis, these are called STOP codons.

What are the three stop codons? ________________________________


5. For each sequence of DNA is shown. Write the complementary RNA sequence underneath the letters, then use the codon chart to determine the amino acid sequence:

DNA →   T A C   C A T   G G A   A G T   A C T


Amino Acids →



DNA →   T T C   A A T   G G T   C T A   G G G


Amino Acids →



DNA →   A C A   T T T   C A G   A C C   G T C


Amino Acids →

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