AP BIOLOGY

THE MOLECULAR BASIS OF INHERITANCE

STRUCTURE OF NUCLEIC ACIDS

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
What is a start codon?
A
This always reads:AUG, This begins every polypeptide chain, This codes for methionine, If a missense mutation occurs in this codon, the protein will never be translated
B
This is a set of 3 nucleotides on mRNA
C
This is a set of 3 nucleotides on tRNA
Explanation: 

Detailed explanation-1: -The codon AUG is called the START codon as it the first codon in the transcribed mRNA that undergoes translation. AUG is the most common START codon and it codes for the amino acid methionine (Met) in eukaryotes and formyl methionine (fMet) in prokaryotes.

Detailed explanation-2: -The standard start codon for translation of a gene is “AUG, ” which encodes the amino acid methionine (Met or M), and establishes the reading frame for the ribosome to follow, adding corresponding amino acids in a polypeptide chain.

Detailed explanation-3: -The start codon marks the site at which translation into protein sequence begins, and the stop codon marks the site at which translation ends.

Detailed explanation-4: -At the start of the initiation phase of translation, the ribosome attaches to the mRNA strand and finds the beginning of the genetic message, called the start codon (Figure 4). This codon is almost always AUG, which corresponds to the amino acid methionine.

Detailed explanation-5: -The start codon in all mRNA molecules has the sequence AUG and codes for methionine. Next, the large ribosomal subunit binds to form the complete initiation complex. During the elongation stage, the ribosome continues to translate each codon in turn.

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