Question

In studies of the amino acid sequence of wild-type and mutant forms of tryptophan synthetase in \(E .\) coli, the following changes have been observed: Determine a set of triplet codes in which only a single-nucleotide change produces each amino acid change.

Short answer

Answer: The set of triplet codes are: 1. GCA (Alanine) -> GTA (Valine) 2. TTC (Phenylalanine) -> TTG (Leucine) 3. CCT (Proline) -> CTT (Leucine)

Step-by-step solution

List the given amino acid changes.

Write down the amino acid changes observed in the studies: 1. Ala -> Val (Alanine to Valine) 2. Phe -> Leu (Phenylalanine to Leucine) 3. Pro -> Leu (Proline to Leucine)

List the codons for the given amino acids.

Look up the triplet codes for the given amino acids from a standard genetic code table: Alanine (Ala): GCA, GCC, GCG, GCT Valine (Val): GTA, GTC, GTG, GTT Phenylalanine (Phe): TTC, TTT Leucine (Leu): CTA, CTC, CTG, CTT, TTA, TTG Proline (Pro): CCA, CCC, CCG, CCT

Find codon combinations with single-nucleotide changes.

Compare the given amino acid's codons and find combinations that differ by only one nucleotide: 1. Ala -> Val: GCA -> GTA (changed nucleotide C -> T at the second position) 2. Phe -> Leu: TTC -> TTG (changed nucleotide C -> G at the third position) 3. Pro -> Leu: CCT -> CTT (changed nucleotide C -> T at the third position)

Determine the triplet codes for the observed changes.

Use the combinations found in the previous step to determine the single nucleotide changes producing each amino acid change: 1. Alanine (Ala) to Valine (Val): GCA -> GTA 2. Phenylalanine (Phe) to Leucine (Leu): TTC -> TTG 3. Proline (Pro) to Leucine (Leu): CCT -> CTT The set of triplet codes where only a single nucleotide change produces each amino acid change is: 1. GCA (Alanine) -> GTA (Valine) 2. TTC (Phenylalanine) -> TTG (Leucine) 3. CCT (Proline) -> CTT (Leucine)

Key concepts

Amino Acid Sequence

Every protein within an organism is made up of a specific sequence of amino acids, which are the building blocks of proteins. These sequences determine the structure and function of proteins. The process starts with the transcription of genetic information from DNA into messenger RNA (mRNA), followed by the translation of mRNA into a chain of amino acids forming a protein.

For instance, the difference in the amino acid sequence of wild-type and mutant forms of enzymes can significantly impact their functionality. A well-known enzyme, tryptophan synthetase of E. coli, is crucial for the synthesis of tryptophan—an essential amino acid. Changes in its amino acid sequence can affect the enzyme's activity and, therefore, E. coli's ability to produce tryptophan.

Triplet Codons

A triplet codon is a sequence of three nucleotides in mRNA that specifies a single amino acid or a stop signal during protein synthesis. There are 64 possible codons, coding for 20 amino acids and three stop signals, which make up the genetic code. The genetic code is nearly universal for all living organisms and is read in a non-overlapping, sequential manner from a fixed starting point.

To understand codons, it's important to recognize that each codon corresponds to a specific amino acid or a stop signal. For example, the codon 'AUG' not only initiates the process of translation but also codes for the amino acid methionine.

Nucleotide Changes

Nucleotide changes, or point mutations, are alterations within a gene at a specific point in the DNA sequence. These changes can result from errors during DNA replication or from the influences of mutagens such as radiation or chemicals.

A single-nucleotide polymorphism (SNP) is the most common form of nucleotide change and can lead to variations within a population, including changes in amino acids coded by the affected codons. Some nucleotide changes can be silent, causing no alteration in the amino acid sequence, while others can be missense mutations that change one amino acid for another—potentially having significant effects on protein function.

Tryptophan Synthetase

Tryptophan synthetase is an enzyme that catalyzes the final two steps of tryptophan biosynthesis in bacteria, fungi, and plants. This enzyme is essential for living organisms because tryptophan is a precursor for various biomolecules, including serotonin and melatonin in humans. The enzyme consists of multiple subunits and requires a specific amino acid sequence to function correctly.

Research on the tryptophan synthetase of E. coli helps scientists understand protein structure and function, including the effects that changes in the amino acid sequence can have on enzyme activity. It also provides insights into the adaptive mechanisms of bacteria.

E. coli Genetics

Escherichia coli, commonly known as E. coli, is a bacterium widely used in molecular biology and genetics research due to its simple genetic makeup and the ease with which it can be manipulated. Its genetics is a well-studied area that has provided vast amounts of information about gene regulation, DNA replication, and protein synthesis.

Studies of E. coli have led to the discovery of important biological concepts such as operons and gene expression control mechanisms. Moreover, E. coli's ability to harbor and express foreign genes makes it a powerful tool for producing proteins, including those with therapeutic importance.

Mutant Forms

Mutant forms of enzymes and other proteins often arise from genetic mutations, which are changes in the organism's DNA sequence. These mutations can lead to changes in the amino acid sequence of a protein, potentially altering its structure and function. Some mutations might confer an adaptive advantage to the organism in certain environments, while others might be detrimental or neutral.

Studying these mutant forms, particularly in model organisms like E. coli, offers a window into understanding the basics of evolutionary biology, the consequences of genetic variations, and the principles underpinning genotype-phenotype relationships.