Chapter 20: Q20-13TYU. (page 439)

You hope to study a gene that codes for a neurotransmitter protein produced in human brain cells. You know the amino acid sequence of the protein. Explain how you might (a) identify what genes are expressed in a specific type of brain cell, (b) identify (and isolate) the neurotransmitter gene, (c) produce multiple copies of the gene for study, and(d) produce large quantities of the neurotransmitter for evaluation as a potential medication.

Short Answer

Expert verified

(a) Here in the question, the amino acid sequence of the protein is known, so the DNA sequence of the coding gene can be found out. So, DNA probes can be made using information, and through hybridization of probes with the mRNA extracted from the brain cells, the location of genes can be found that are coding for the protein.

(b) To identify the neurotransmitter gene, DNA microarray can be used, which is the glass slide containing a large number of single-stranded DNA fragments that show different genes of an organism in the form of dots.

(c) To produce multiple copies of genes, the polymerase chain reaction is utilized that is a quick technique for making billions of copies of DNA in a few hours.

(d) To produce the large quantities of the neurotransmitter for evolution as a potential medication, the cDNA can be prepared by using reverse transcriptase by using mRNA coding this protein. This cDNA can be cloned and expressed in a bacterium.

Step by step solution

Amino Acids

Amino acids are essential constituents of the proteins that are linked by a covalent linkage to form a linear chain. The property of a protein is determined by the proportion of these amino acids present in it.

Amino acids are 20 in number in all types of organisms. All amino acids are coded by the same types of codons in all types of organisms.

Explanation for an answer (a)

The sequence of amino acids in the neurotransmitter protein is known according to the question. By using this sequence, the genomic sequence can be found out because the amino acids are coded by the sequence present in the gene.

By using probes, a DNA sequence can be prepared, and a fluorescently colored tag is added to it. These probes can be added to the mRNA sample that is expressed in the brain cells. So by using this technique of nucleic acid hybridization, the location of the genes expressing this protein can be found out.

Explanation for the answer (b)

For finding genomic sequences expressing particular proteins, DNA microarray assays are used. A microarray or DNA chip containing the genomic sequences in the form of an array of dots of DNA are attached with cDNA probes that are prepared by reverse-transcribing the mRNA for the neurotransmitter protein.

Explanation for the answer (c)

A PCR or polymerase chain reaction is carried out for the production of the multiple copies of the gene that is studied. As an initiation gene segment, the cDNA produced by the mRNA coding for the protein is taken. The primers specific to this cDNA are used and by using PCR multiple copies of the gene can be prepared.

Explanation for answer (d)

To produce large quantities of neurotransmitter, the cDNA is prepared by mRNA for this protein by reverse transcription, and then it is attached with a suitable vector-like a plasmid. After insertion in a vector, cDNA is replicated and expressed in a bacterial cell. Thus a large amount of protein can be produced.