Question

Francis Crick proposed the "adaptor hypothesis" for the function of tRNA. Why did he choose that description?

Short answer

Answer: The adaptor hypothesis, proposed by Francis Crick, describes the function of tRNA as an adaptor molecule that enables the correct translation of genetic information on mRNA into a specific sequence of amino acids in a protein. The term "adaptor" was chosen because tRNA acts as a molecular bridge that connects the genetic information on the mRNA (in the form of codons) with the appropriate amino acids to be incorporated into the polypeptide chain, ensuring accurate translation and proper functioning of cells.

Step-by-step solution

Understanding tRNA

Transfer RNA (tRNA) is a type of RNA molecule that plays a critical role in the process of protein synthesis. It is responsible for carrying amino acids to the ribosome, where they are incorporated into the growing polypeptide chain. The tRNA molecule is structured in such a way that one end carries the amino acid and the other end has an anticodon, which is a sequence of nucleotides complementary to the codon sequence on the messenger RNA (mRNA).

Protein synthesis and tRNA's role

In the process of protein synthesis, or translation, the genetic information on the mRNA is decoded in order to build the polypeptide chain. The information stored in the mRNA is in the form of codons, which are groups of three nucleotides that correspond to specific amino acids. Each of these codons is matched with a tRNA molecule carrying the appropriate amino acid. The tRNA anticodon pairs with the mRNA codon, ensuring the correct amino acid is incorporated into the growing polypeptide chain.

The "adaptor hypothesis"

Francis Crick proposed the "adaptor hypothesis" to describe the function of tRNA. According to this hypothesis, tRNA serves as an adaptor molecule that allows the correct translation of the information on the mRNA into a specific sequence of amino acids in a protein. In other words, tRNA acts as a molecular "bridge" connecting the genetic information on the mRNA with the amino acids to be incorporated into the polypeptide chain.

Reason behind the description

Crick chose the term "adaptor" because tRNA effectively adapts the information encoded in the mRNA by recognizing the codon sequence and bringing the corresponding amino acid to the ribosome. This adaptability allows the accurate translation of the genetic code into proteins, which is essential for the proper functioning of cells. The term "adaptor" highlights the critical role tRNA plays in ensuring the accurate translation of genetic information into proteins.

Key concepts

Protein Synthesis

Protein synthesis is a fundamental process in cellular biology where cells build proteins. The process is known as translation and occurs within a cellular structure called the ribosome. As the central dogma of molecular biology suggests, DNA is transcribed into messenger RNA (mRNA), which then travels to the ribosome to be translated into a protein. During translation, ribosomes read the sequence of mRNA in sets of three nucleotides, known as codons. Each codon corresponds to a specific amino acid, the building blocks of proteins.

Proteins perform a plethora of functions within organisms, from catalyzing metabolic reactions as enzymes to providing structural support in cells and tissues. Therefore, accurate protein synthesis is crucial for maintaining the health and function of cells. It involves multiple stages including initiation, elongation, and termination, each regulated by various factors to ensure the correct amino acid sequence is produced.

To help with the visualization of this process, one might compare it to a construction site where ribosomes are the machines, mRNA provides the blueprints, and tRNA brings in the correct building materials - amino acids - to assemble the structure, which in this analogy is the protein.

Genetic Information Translation

The translation of genetic information from a language of nucleic acids to a language of proteins is a vital biological process. Just as a translator converts text from one language to another, the cellular translation machinery interprets the genetic code contained within mRNA to produce a corresponding protein sequence. The genetic code is nearly universal to all living organisms, with specific triplet codons in the mRNA corresponding to specific amino acids.

The process begins when mRNA, which has been transcribed from DNA, engages with the ribosome. Transitioning from nucleotide sequences to a chain of amino acids requires accuracy to produce functional proteins. Mistakes in this process can lead to the incorporation of the wrong amino acids, which can disrupt protein function and lead to diseases.

As this translation proceeds, a start codon signals the beginning of a protein-coding sequence, while subsequent codons specify the order in which amino acids are to be added. Finally, a stop codon signals that the protein is complete, and it is then released to perform its specific role in the cell. It's much like following a recipe, where every ingredient must be added in the correct order and amount for the final dish to turn out as expected.

mRNA and tRNA Interaction

The interaction between mRNA and tRNA is central to the translation of genetic code into functional proteins. mRNA and tRNA come together within the ribosome. mRNA brings the template, which is a sequence of codons, each codon being a set of three nucleotides. tRNA molecules, on the other hand, are adaptors which have a specific amino acid attached to one end and an anticodon on the other end that complements the mRNA codon.

As the ribosome moves along the mRNA strand, tRNAs enter the ribosome matched to the codons being read. This ensures that the amino acids are added in the proper sequence for the growing polypeptide chain. This specific pairing is critical as incorrect pairings could result in dysfunctional proteins. The concept mirrors a lock and key mechanism, where the anticodon of the tRNA must fit perfectly with the codon of the mRNA, much like a key fits into a lock to open a door.

The synchronization of this process is a marvel of cellular biology, with each component working in concert to translate the genetic information quickly and accurately. Ultimately, these interactions culminate in the synthesis of a new protein, ready to take on roles from enzyme activity to cellular scaffolding, showcasing the precision and efficiency of cellular machinery.