Question

How Many Different mRNA Sequences Can Specify One Amino Acid Sequence? Write all the possible mRNA sequences that can code for the simple tripeptide segment Leu-Met-Tyr. Your answer will give you some idea of the number of possible mRNAs that can code for one polypeptide.

Short answer

There are 12 possible mRNA sequences coding for the tripeptide Leu-Met-Tyr.

Step-by-step solution

Understanding Genetic Code

Each amino acid is coded by a sequence of three nucleotides called a codon. Different codons can code for the same amino acid, a property known as 'degeneracy' of the genetic code.

Identifying Codons for Leucine (Leu)

Leucine is coded by six different codons: UUA, UUG, CUU, CUC, CUA, and CUG.

Identifying Codons for Methionine (Met)

Methionine is coded by a single codon: AUG. This simplifies our calculation for methionine in the sequence.

Identifying Codons for Tyrosine (Tyr)

Tyrosine is coded by two codons: UAC and UAU.

Calculating Total Possible Combinations

To find the number of different mRNA sequences that can code for the amino acid sequence Leu-Met-Tyr, multiply the number of codons for each amino acid: 6 (Leu) x 1 (Met) x 2 (Tyr). This yields 12 possible mRNA sequences.

Listing All Possible mRNA Sequences

- UUA-AUG-UAC - UUA-AUG-UAU - UUG-AUG-UAC - UUG-AUG-UAU - CUU-AUG-UAC - CUU-AUG-UAU - CUC-AUG-UAC - CUC-AUG-UAU - CUA-AUG-UAC - CUA-AUG-UAU - CUG-AUG-UAC - CUG-AUG-UAU

Key concepts

Amino Acids

Amino acids are the building blocks of proteins, which are essential molecules that perform a variety of functions in living organisms. There are 20 different standard amino acids used by cells to build proteins, each with unique properties. They encode specific functions due to their distinct side chains, which impact how they interact with each other and their environment.

In terms of the genetic code, amino acids are specified by sequences of three nucleotides in DNA or RNA, known as codons. For example, in the exercise provided, the amino acid sequence of Leucine (Leu), Methionine (Met), and Tyrosine (Tyr) is considered for its potential diversity of mRNA sequences.

• Leucine is represented by six possible codons, showing it's highly flexible within the genetic code.
• Methionine, meanwhile, has only one codon (AUG), which is unique because it's also the start codon in protein synthesis.
• Tyrosine can be encoded by two different codons, providing some variation in the genetic code.

mRNA Sequences

Messenger RNA (mRNA) is a type of RNA that serves as a template for protein synthesis. It is synthesized based on the sequence of nucleotides in the DNA and is crucial for conveying the genetic information needed to form proteins.

Once DNA is transcribed into mRNA, this sequence reflects the future protein's blueprint. Each group of three nucleotide bases on mRNA corresponds to one amino acid in the chain. For instance, in our tripeptide of Leucine-Methionine-Tyrosine, the DNA is transcribed into various mRNA sequences. These mRNA sequences are read in sets of three bases called codons, which specify the realization of different amino acids, allowing for multiple mRNA versions that can produce the same protein sequence.

• It is the mRNA that ultimately guides the synthesis of proteins during a process known as translation.
• This demonstrates how genetic coding is translated into a physical amino acid sequence by reading the sequences of mRNA codons.

Codons

Codons are vital units of the genetic language composed of triplet nucleotide sequences found in mRNA. Each codon directs the incorporation of a specific amino acid into a growing polypeptide chain during protein synthesis. The genetic code is considered degenerate because several codons can encode the same amino acid.

In the exercise's example, codons for Leucine (Leu) exemplify this degeneracy, where six different codons (UUA, UUG, CUU, CUC, CUA, and CUG) can be used to code for Leucine. Methionine (Met), on the other hand, uses a single codon (AUG), while Tyrosine (Tyr) can be translated from two possible codons (UAC, UAU). This variability allows for robustness in genetic coding and potential error corrections in DNA.

• Codons play a critical role in ensuring that proteins are synthesized accurately and efficiently.
• This diversity ensures the protein synthesis machinery can tolerate some mutations without altering protein function.
• Understanding how different codons translate into amino acids helps illustrate the genetic code's complexity and redundancy.

Polypeptide Synthesis

Polypeptide synthesis is the process by which cells construct proteins from amino acids, following the instructions encoded in the mRNA sequence. It is a central activity in biology that involves transcription and translation.

Transcription is the initial step where DNA's genetic code is copied into mRNA. Translation is where this mRNA is used as a guide to assemble amino acids into a polypeptide chain on ribosomes, the molecular machines responsible for protein assembly. Each codon on the mRNA correlates with specific transfer RNA (tRNA) molecules, which carry the corresponding amino acids and participate in forming the protein sequence.

• During translation, the mRNA sequence is read step by step, codon by codon, ensuring each amino acid is added correctly to the growing chain.
• Proteins begin to fold into their specific structures as they are synthesized, which determines their functionality in the organism.
• Without the precise process of polypeptide synthesis, cells could not produce the proteins necessary for life and biological functions.