Genetic Code

Objectives

• Describe the characteristics of the genetic code

RNA uses uracil instead of thymine.

The four bases (A, C, G, U) are combined into groups of three called codons.

Each codon codes for one amino acid unless it is a stop signal.

There are 20 common amino acids but 64 possible codons

AUG codes for methionine and is also the start codon that begins translation, the second part of the central dogma of molecular biology.

The start codon establishes the reading frame.

Each codon is read until a stop (termination) codon is reached.

Stop Codons

• UAG
• UGA
• UAA

The genetic code is...

• universal.
• unambiguous.
• redundant.

During translation, the mRNA is read one codon at a time by a ribosome.

tRNA brings amino acids to the ribosome in the correct sequence.

Each tRNA molecule has an anticodon that is complementary to the codon for the amino acid it carries.

As tRNA brings amino acids to the ribosome, polypepitide bonds are formed.