GN 301 Module 3: The Genetic Code and Translation

Amino Acids and Proteins

• There are 20 different amino acids
• Amino acids are joined by peptide bonds to make proteins

==tRNA== contains the amino acid to the site of the ribosome. A 3 base long sequence called the anticodon binds to the codons of mRNA in translation

==mRNA== contains the codon, which are 3 bases that specify an amino acid for protein synthesis

==Properties of the genetic code==

• universal
• degenerate
• start-stop function
• polarity
• triplet code

How many amino acids have exactly 1 codon? Which are they?

• 2 amino acids (Met and Trp)

How many amino acids have exactly 4 codons? Which are they?

• 5. 1) Val, 2) Pro, 3) Thr, 4) Ala, 5) Gly (Ser and arg have other rows that are split up)

What is the highest number of codons for one amino acid? Which are they?

• 6 codons. (Leu, Ser, Arg)

Is there a pattern to the degeneracy of the code?

• Yes. The pattern of degeneracy allows one to organize the codons into "families" and "pairs.”

Translation

==Initiation:== the ribosome gets together with the mRNA and the first tRNA so translation can begin

==Elongation:== amino acids are brought to the ribosome by tRNAs and linked together to form a chain.

peptide bonds join amino acids

• The ribosome translocates one codon after amino acids bind
• mRNA is read from 5’ to 3’

==Termination:== when a stop codon in the mRNA (UAA, UAG, or UGA) enters the A site.

Translation Example:

Determine the sequence of the protein translated from this mRNA.

5’ – G G G C A A ==A U G== A C A G U U C C G G A A ==U A A== G G C U G A – 3’
Met, Thr, Val, Pro, Glu, STOP

Central Dogma Practice Problems:

The template strand of DNA is given below.

3’ – A T T A C G C C G G T T A G A C T T T – 5’

What is the process of forming mRNA called? Transcription

What is the sequence of the mRNA formed from this strand? (Write it out so you can use it later)

3’ – A T T A C G C C G G T T A G A C T T T – 5’

5’ - U A A U G C G G C C A A U C U G A A A - 3’ <<<(complementary, so U replaces T)

What is the process of making protein from mRNA called?

• transcription

Where does translation take place?

• in the ribosomes

What is the role of tRNA in translation?

• brings proper amino acids to ribosomes

What is the sequence of the protein made from this mRNA sequence? (Hint: First find the start codon and split the RNA into codons and then translate each codon)

5’ - U A ==A U G== C G G C C A A U C ==U G A== A A - 3’
Met, Arg, Pro, Ile, STOP