Question

In the genetic code of human nuclear DNA, one of the codons specifying the amino acid tyrosine is UAC. If one nucleotide is changed and the codon is mutated to UAG, what type of mutation will occur? (A) Silent mutation (B) Missense mutation (C) Nonsense mutation (D) Frameshi mutation

Short answer

The type of mutation is a nonsense mutation.

Step-by-step solution

Understand the Original Codon

The original codon is UAC, which specifies the amino acid tyrosine.

Evaluate the Mutated Codon

The mutated codon is UAG. Determine which amino acid UAG codes for or if it has a different function.

Identify the Function of the Mutated Codon

UAG is one of the stop codons in genetic code. Stop codons signal the end of translation.

Determine the Type of Mutation

Since the codon UAG signals a stop, it changes the codon from specifying an amino acid to signaling termination. This type of mutation is known as a nonsense mutation.

Key concepts

nonsense mutation

A nonsense mutation occurs when a DNA sequence changes in such a way that it introduces a premature stop codon.
A stop codon signals the end of protein synthesis during translation.
For example, in the given exercise, the original codon UAC, which codes for the amino acid tyrosine, mutates to UAG.
UAG is a stop codon, which halts the translation process prematurely.
This can lead to truncated, usually non-functional proteins, impacting cellular functions.
Here are some potential consequences of nonsense mutations:

• Incomplete or faulty proteins.
• Possible loss of protein function.
• Diseases and genetic disorders, such as some cancers or muscular dystrophy.

genetic code

The genetic code is a set of rules used to translate information encoded within genetic material (DNA or mRNA sequences) into proteins.
Each set of three nucleotides, known as a codon, corresponds to a specific amino acid or a stop signal during translation.
The genetic code is nearly universal among all organisms, which means the same codons typically code for the same amino acids across different species.
Here are key features of the genetic code:

• It is redundant, meaning multiple codons can code for the same amino acid.
• It is unambiguous, meaning each codon specifies only one amino acid.
• It has start and stop signals for initiating and terminating protein synthesis.

DNA codons

DNA codons are triplet sequences of nucleotides in mRNA that determine which amino acid will be added next during protein synthesis.
Each codon consists of three bases from the nucleotides adenine (A), cytosine (C), guanine (G), and uracil (U) (in RNA) or thymine (T) (in DNA).
For example, the codon UAC codes for the amino acid tyrosine, while UAG is a stop codon.
Understanding DNA codons is crucial for interpreting the genetic information and translating it into functional proteins.
Some critical points about DNA codons:

• There are 64 possible codons (4 bases^3 combinations).
• AUG is a universal start codon, coding for methionine and signaling the start of translation.
• Three stop codons (UAG, UAA, UGA) signal the end of protein synthesis.