Question

Compare the structural formulas of the aromatic amino acids phenylalanine and tyrosine. Compare also the codons for these two amino acids.

Short answer

Question: Compare the structural formulas and codons of the aromatic amino acids phenylalanine and tyrosine. Answer: Phenylalanine has a phenyl group (C6H5) side chain, while tyrosine has a phenol group (C6H4OH) side chain, which is a phenyl group with an additional hydroxyl group (OH). The codons for phenylalanine are UUU and UUC, while for tyrosine, they are UAU and UAC. The difference in the codons is in the second nucleotide, where phenylalanine has uracil (U) and tyrosine has adenine (A). This variation in codon sequence leads to different side chains and properties in the resulting protein.

Step-by-step solution

Define Aromatic Amino Acids

Aromatic amino acids are a subclass of amino acids that contain an aromatic side chain. These amino acids are important for both their roles in protein synthesis and as precursors for other biomolecules. The term "aromatic" refers to the presence of a ring structure in the side chain, which is the distinguishing feature of these amino acids.

Structural Formulas of Phenylalanine and Tyrosine

Now, let's look at the structural formulas of these two aromatic amino acids: Phenylalanine: \[\mathrm{H}_2\mathrm{N-CH}\left(\mathrm{COOH}\right)-\mathrm{CH}_{2}-\mathrm{C}_{6}\mathrm{H}_{5}\] Tyrosine: \[\mathrm{H}_2\mathrm{N-CH}\left(\mathrm{COOH}\right)-\mathrm{CH}_{2}-\mathrm{C}_{6}\mathrm{H}_{4}-\mathrm{OH}\]

Compare the Structural Formulas

Comparing the structural formulas of phenylalanine and tyrosine, we can see that they both have a similar backbone, consisting of the amino group (NH2), carboxyl group (COOH), and a carbon atom between them. The difference lies in their side chains: phenylalanine has a phenyl group (C6H5) attached to its backbone, while tyrosine has a phenol group (C6H4OH), which is a phenyl group with an additional hydroxyl group (OH).

Define Codons

Codons are sequences of three nucleotides in DNA or RNA that specify which amino acid will be added to the growing polypeptide chain during protein synthesis. The genetic code is made up of 64 different codons, each corresponding to an amino acid or a stop signal for translation.

Identify the Codons for Phenylalanine and Tyrosine

The codons for phenylalanine and tyrosine are as follows: Phenylalanine: UUU and UUC Tyrosine: UAU and UAC

Compare the Codons for Phenylalanine and Tyrosine

Comparing the codons for phenylalanine and tyrosine, we see that they only differ in the second nucleotide. Phenylalanine codons have uracil (U) in the second position, while tyrosine codons have adenine (A) in the second position. This small change in the codon sequence leads to a change in the amino acid, resulting in a different side chain and therefore different properties for the protein.

Key concepts

Structural Formulas

Aromatic amino acids play a crucial role in biochemistry due to their unique structures and the presence of an aromatic ring. Among them, phenylalanine and tyrosine are two significant examples, each with a distinct structural formula. The backbone of these amino acids is similar: they both possess an amino group \(\mathrm{NH_2}\), a carboxyl group \(\mathrm{COOH}\), and a connecting carbon atom known as the alpha carbon.

However, the difference lies in their side chains. Phenylalanine's side chain is a simple phenyl group \(\mathrm{C_6H_5}\) making it hydrophobic, which affects how it interacts within proteins. On the other hand, tyrosine features a phenol group \(\mathrm{C_6H_4OH}\). This includes a hydroxyl group (OH) attached to the aromatic ring, introducing polar characteristics and allowing for hydrogen bonding. Such differences might seem minor, but they crucially affect the amino acids' roles and functions in proteins.

Understanding these structural formulas is important as it lays the foundation for grasping how these molecules behave in biological systems and contribute to protein structure and function.

Codons

Codons, the language of genetic instructions, are sequences of three nucleotides in DNA and RNA that dictate which amino acid will be incorporated during protein synthesis. The genetic code comprises 64 codons, and each one specifies a particular amino acid or a signal to stop translation.

For phenylalanine, the codons are UUU and UUC. These codons both include uracil (U) as the second nucleotide. In contrast, tyrosine is specified by the codons UAU and UAC, where adenine (A) is in the second position.

• Phenylalanine: UUU, UUC
• Tyrosine: UAU, UAC

This tiny difference in nucleotide sequence - switching from U to A in the second position - significantly alters the amino acid being coded, thereby affecting the protein's characteristics. Codons modify not just the protein composition, but also its shape and functionality, thereby reinforcing the intricate nature of genetic coding.

Protein Synthesis

Protein synthesis is a fundamental biological process where cells create new proteins, guided by the sequence of codons within an organism's genetic material. It involves two main stages: transcription and translation. During transcription, the DNA sequence of a gene is transcribed into messenger RNA (mRNA), which carries the genetic code out of the nucleus and into the cytoplasm.

In the cytoplasm, translation occurs. Ribosomes read the mRNA code in groups of three nucleotides, or codons, pairing them with transfer RNA (tRNA) that brings corresponding amino acids. Each tRNA has an anticodon that determines which amino acid it delivers based on complementarity to the mRNA codon. For example, mRNA codons UUU and UUC will pair with tRNA carrying phenylalanine, while UAU and UAC pair with tRNA carrying tyrosine.

Through this process, the sequence of amino acids dictated by mRNA gradually forms into a polypeptide chain, ultimately folding into a functional protein. Understanding protein synthesis, including the roles of codons and the impact of the amino acids phenylalanine and tyrosine, highlights the precise orchestration required to sustain life.