Question

The RNA transcript of a region of T4 phage DNA contains the sequence \(5^{\prime}\) -AAAUGAGGA-3'. In theory, this sequence is capable of encoding three different polypeptides. What are they?

Short answer

Polypeptides: 1) Met-Arg-Gly.

Step-by-step solution

Identify Codons in the RNA Sequence

The given RNA sequence is \(5'\) -AAAUGAGGA- \(3'\). To decode the sequence, first, identify the codons. A codon is a sequence of three nucleotides. In this sequence, the possible codons are: \(\begin{align*} &AAA, UGA, GGA. \end{align*}\)

Find the Amino Acids for Each Codon

Using the genetic code, translate each of the codons to the corresponding amino acids: \(\begin{align*} &AAA \text{ codes for Lysine (Lys)}, \ &AUG \text{ is a start codon and codes for Methionine (Met)}, \ &UGA \text{ is a stop codon and does not code for an amino acid}, \ &AGG \text{ codes for Arginine (Arg)}, \ &GGA \text{ codes for Glycine (Gly)}. \end{align*}\)

Determine Potential Polypeptides

List the possible combinations of amino acids from the sequence: - Starting from the first codon: Lysine (Lys), Stop (no polypeptide as UGA is a stop codon) - Starting from the second codon: Methionine (Met), Arginine (Arg), Glycine (Gly) - Starting from the third codon: Arginine (Arg), Glycine (Gly) (Since we started mid-sequence, this does not account for a start codon and is invalid in this context)

Key concepts

Genetic Code

The genetic code is the set of instructions within RNA that guides cells in constructing proteins. It is often compared to a dictionary where specific sequences of nucleotides correspond to particular amino acids, which are the building blocks of proteins. The genetic code is universal, meaning it is the same across almost all living organisms.
Each combination of three nucleotides forms a 'word' known as a codon. There are 64 possible codons made from the four nucleotides: Adenine (A), Uracil (U), Cytosine (C), and Guanine (G). These codons either specify an amino acid or signal a specific action such as the start or stop of protein synthesis.

RNA Sequence

An RNA sequence is a string of nucleotides that is read and translated into proteins. RNA stands for ribonucleic acid, which is a crucial molecule in the process of decoding genetic information from DNA. An RNA molecule is similar to DNA but has a few key differences, including the use of uracil (U) instead of thymine (T).
In our example RNA sequence, 5'-AAAUGAGGA-3', reading occurs from the 5' (five-prime) end to the 3' (three-prime) end. This direction is important because it determines how the sequence is divided into codons, each consisting of three nucleotides.

Amino Acids

Amino acids are organic compounds that combine to form proteins. There are 20 different amino acids that can be arranged in various sequences to produce a vast array of proteins necessary for life.
Each amino acid is encoded by one or more codons. For instance, Lysine is encoded by the codon AAA, Methionine (which also serves as a start signal) is encoded by AUG, Arginine by AGG, and Glycine by GGA. It's important to note that certain codons, like UGA, act as stop signals which indicate the end of protein synthesis.

Codons

Codons are triplets of nucleotides in an RNA sequence that carry the genetic instructions for the addition of specific amino acids during protein synthesis. They're the fundamental units that translate genetic information into functional proteins.
Each codon serves a specific role:

• Some, like AUG, signal the start of translation, marking the starting point for the ribosome.
• Others, such as UGA, act as stop signals, indicating when the protein synthesis should be completed.
• The remaining codons specify the addition of one of the 20 amino acids to the growing polypeptide chain.

In building proteins, the proper identification and interpretation of codons is crucial for ensuring that cells create the intended proteins correctly and efficiently.