Question

Lactose permease, a protein of \(E\). coli, is composed of a single polypeptide that is 417 amino acids in length. By convention, the amino acids within a polypeptide are numbered from the aminoterminus to the carboxyl-terminus. Are the following questions about lactose permease true or false? A. Because the 64th amino acid is glycine and the 68 th amino acid is aspartic acid, the codon for glycine, 64 , is closer to the \(3^{\prime}\) end of the mRNA than the codon for aspartic acid, 68 . B. The mRNA that encodes lactose permease must be greater than 1241 nucleotides in length.

Short answer

A. False, B. True

Step-by-step solution

Answering Question A

The order of numbering in amino acids of a polypeptide goes from the amino-terminus (1st amino acid) to the carboxyl-terminus. This is the exact opposite of how we number the mRNA from \(5^{\prime}\) end to \(3^{\prime}\) end. So, the 64th amino acid will be closer to the carboxyl-terminus and it will be further from the \(3^{\prime}\) end of the mRNA relative to the 68th amino acid. Thus, the statement in Question A is false.

Answering Question B

The rule of thumb in mRNA is that one codon (group of 3 nucleotides) codes for one amino acid. Given that the lactose permease is a protein which is composed of 417 amino acids, the minimum number of nucleotides that the mRNA which codes for it should have is \(417 \times 3\) which equals to 1251 nucleotides. Thus, the statement in Question B is true, as the mRNA for lactose permease is longer than 1241 nucleotides.

Key concepts

mRNA codons

In the study of genetics and molecular biology, understanding mRNA codons is essential. Codons are sequences of three nucleotides on messenger RNA (mRNA) which encode for specific amino acids during protein synthesis. There are 64 possible codons, corresponding to 20 amino acids plus stop signals which terminate protein synthesis.

Different codons can code for the same amino acid due to 'redundancy' or 'degeneracy' in the genetic code. This means that although there are more codons than amino acids, the cells can still accurately produce proteins. For example, both GGA and GGG codons code for the amino acid glycine. Understanding the exact position and sequence of these codons is critical for decoding the genetic message and predicting the resultant protein's structure and function.

Protein synthesis

Protein synthesis is the process by which cells build proteins. It involves transcription and translation. Transcription is the first step where DNA is used as a template to synthesize mRNA. During translation, which happens at the ribosome, the mRNA's codons are read in sequence to assemble the protein, amino acid by amino acid.

The ribosome matches each mRNA codon with the appropriate transfer RNA (tRNA) molecule that carries the corresponding amino acid. This process continues, adding one amino acid at a time until a stop codon is reached, signaling the end of the protein synthesis. Understanding this biological mechanism is crucial for students as it connects genetics to function within the cell.

Amino acid sequencing

Amino acid sequencing involves determining the precise order of the amino acids in a protein. This sequence defines the protein's three-dimensional structure, which in turn, determines its function. In the context of lactose permease, the sequence starts from the amino-terminus and ends at the carboxyl-terminus, which is important to note because the structure and function of proteins are directionally dependent.

A change in the sequence can affect the protein's function, as seen in many genetic disorders. Hence, understanding how to determine and interpret amino acid sequencing is vital in fields like bioinformatics, genetics, and molecular biology, as it's the basis for understanding how proteins will interact within the body.

Nucleotide length calculation

Nucleotide length calculation is a fundamental task when studying genes and their corresponding proteins. Knowing the length of the mRNA strand is important, for instance, to predict the size of a protein. Since one amino acid is coded by three nucleotides – a triplet called a codon – the math is straightforward: you would multiply the number of amino acids in the protein by three to get the minimum length of mRNA.

For lactose permease, with its 417 amino acids, the minimum mRNA length is calculated as follows: \(417 \times 3 = 1251\) nucleotides. Understanding this calculation allows students to estimate the genetic information required for synthesizing proteins and contributes to grasping the scale and complexity of genetic coding.