Question

Predict the amino acid sequence produced during translation by the following short hypothetical mRNA sequences (note that the second sequence was formed from the first by a deletion of only one nucleotide): Sequence 1: 5'-AUGCCGGAUUAUAGUUGA-3' Sequence 2: 5'-AUGCCGGAUUAAGUUGA-3' What type of mutation gave rise to sequence \(2 ?\)

Short answer

Answer: A frameshift mutation led to the formation of sequence 2. The amino acid sequence of sequence 1 is Methionine-Proline-Aspartic acid-Tyrosine-Serine-Stop, and the amino acid sequence of sequence 2 is Methionine-Proline-Aspartic acid-Stop.

Step-by-step solution

Translate sequence 1 into the amino acid sequence

For sequence 1 (5'-AUGCCGGAUUAUAGUUGA-3'), we will divide it into codons and use the genetic code to find the respective amino acids. The codons are AUG, CCG, GAU, UAU, AGU, UGA. Using the genetic code chart, we find: AUG = Methionine (M) CCG = Proline (P) GAU = Aspartic acid (D) UAU = Tyrosine (Y) AGU = Serine (S) UGA = Stop codon The resulting amino acid sequence for sequence 1: Methionine-Proline-Aspartic acid-Tyrosine-Serine-* (Stop codon) Step 2:

Translate sequence 2 into the amino acid sequence

For sequence 2 (5'-AUGCCGGAUUAAGUUGA-3'), we will divide it into codons and use the genetic code to find the respective amino acids. The codons are AUG, CCG, GAU, UAA, GUU, GA. Using the genetic code chart, we find: AUG = Methionine (M) CCG = Proline (P) GAU = Aspartic acid (D) UAA = Stop codon GUU = Valine (V) GA = Incomplete codon (Codon should have 3 nucleotides) The resulting amino acid sequence for sequence 2: Methionine-Proline-Aspartic acid-* (Stop codon) Step 3:

Determine the type of mutation in sequence 2

Since sequence 2 is formed by deleting one nucleotide from sequence 1, it causes a frameshift mutation. A frameshift mutation occurs when the addition or deletion of a nucleotide changes the reading frame, causing the translation process to interpret the new sequence in a completely different way. In this case, deleting one nucleotide leads to a premature stop codon after the Aspartic acid, causing the synthesis of a shorter protein than the original sequence 1.

Key concepts

Understanding the Genetic Code

The genetic code is the set of rules by which information encoded in genetic material (DNA or mRNA sequences) is translated into proteins by living cells. Proteins are made up of amino acids, and the genetic code determines how sequences of nucleotides correspond to specific amino acids.

Essentially, the genetic code is like the language that the cell's machinery uses to translate mRNA sequences into amino acid chains, which fold to become functional proteins. It is a universal code shared by almost all organisms, reflecting the shared evolutionary heritage of life.

Decoding Amino Acid Sequences

Proteins are the workhorses of our cells, and their functions are determined by their unique amino acid sequences. Each protein's function is shaped by its specific sequence of amino acids, creating a three-dimensional structure that determines its activity within the cell.

The sequence of amino acids in a protein is derived from the sequence of codons in an mRNA molecule. During protein synthesis, ribosomes translate the mRNA sequence into an amino-acid sequence, following the genetic code, resulting in a polypeptide chain. Once the chain is completed, it folds into a functional protein ready to perform its task in the cell.

The Process of mRNA Translation

mRNA translation is a pivotal process in cellular biology, wherein the ribosome reads mRNA sequences codon by codon to synthesize proteins. Each group of three nucleotides, called a codon, corresponds to one amino acid. During translation, tRNA molecules bring the appropriate amino acids to the ribosome, which then attaches them to the growing polypeptide chain.

The accuracy of mRNA translation is crucial for the proper function of proteins. If the mRNA sequence is altered, it can lead to changes in the resulting protein, potentially affecting its function. This delicate process ensures that genetic instructions are accurately converted into the enzymes and structural proteins necessary for life.

Codons: The Building Blocks of Proteins

Codons are the three-nucleotide segments of mRNA that specify which amino acid will be added next during protein synthesis. There are 64 possible codons, but only 20 standard amino acids, meaning that several codons can code for the same amino acid. This 'redundancy' is known as the degeneracy of the genetic code.

Understanding codons is crucial when analyzing mutations. For instance, in this exercise, the deletion of just one nucleotide shifts the reading frame, resulting in a frameshift mutation. Such a mutation can alter codons throughout the sequence, leading to a completely different translation from the original mRNA, usually with detrimental effects to the protein's function.