What is the Genetic Code?
The genetic code is a set of rules that translates sequences of mRNA codons into amino acids.
- Codons: Groups of three nucleotide bases (e.g., AUG, GCU) in mRNA.
- Amino Acids: The building blocks of proteins. There are 20 different amino acids.
- Degeneracy: Multiple codons can code for the same amino acid. For example, GCU, GCC, GCA, and GCG all code for alanine.
- Remember: The genetic code is read in triplets.
- Each codon specifies one amino acid or a stop signal.
How to Use the Genetic Code Table
- A genetic code table helps you determine which amino acid corresponds to a specific mRNA codon.
- Locate the First Base: Find the first base of the codon in the leftmost column.
- Find the Second Base: Move across the top row to find the second base.
- Identify the Third Base: Use the rightmost column to find the third base.
- Read the Amino Acid: The intersection of these three bases gives you the amino acid.
- Don’t forget to start translation at AUG and stop at the first stop codon.
- Ignoring these signals can lead to incorrect sequences.
Example question
Translate this mRNA Sequence: CUCAUCGAAUAACCC
Solution
- CUC: Leucine
- AUC: Isoleucine
- GAA: Glutamic acid
- UAA: Stop (translation ends here)
Connecting DNA, mRNA, and Amino Acids
- To understand how DNA sequences relate to amino acids, remember these steps:
- DNA to mRNA: Transcription creates an mRNA strand complementary to the DNA template strand.
- mRNA to Amino Acids: Translation uses the genetic code to convert mRNA codons into amino acids.
- Don't confuse DNA and mRNA bases.
- Remember: DNA uses thymine (T), while mRNA uses uracil (U).
- How does the universality of the genetic code support the idea of a common evolutionary ancestor?
- What ethical considerations arise from using this knowledge in genetic engineering?
Can you explain why AUG is both a start codon and codes for methionine? How does this dual role impact protein synthesis?
