Problem 5 - Campbell Biology

Question

Which of the following is true of cDNA produced using human brain tissue as the starting material? (A) The procedure to make it requires amplification by the polymerase chain reaction. (B) It is produced from pre-mRNA using reverse transcriptase. (C) It can be labeled and used as a probe to detect genes expressed in the brain. (D) It includes the introns of the pre-mRNA.

Step-by-Step Solution

Answer

C

Step 1: Identify Key Concept of cDNA

Complementary DNA (cDNA) is synthesized from an mRNA template using the enzyme reverse transcriptase. cDNA lacks introns.

Step 2: Analyze Each Option

Review each option carefully: (A) Incorrect. Amplification by PCR is not necessary to make cDNA but can be used in subsequent steps. (B) Incorrect. It is produced from mature mRNA, not pre-mRNA. (C) Correct. cDNA can be labeled and used as a probe to study gene expression. (D) Incorrect. cDNA does not include introns; they are removed in mRNA processing.

Step 3: Select Best Answer

Based on the analysis of the options, the correct answer is (C). cDNA can be labeled and used as a probe to detect genes expressed in the brain.

Key Concepts

reverse transcriptase

cDNA synthesis is a crucial process in molecular biology, allowing scientists to create complementary DNA (cDNA) from an mRNA template. This process involves an enzyme called reverse transcriptase. Reverse transcriptase is essential because it reverses the usual direction of genetic information flow. Typically, DNA is transcribed to mRNA, which is then translated into proteins. However, reverse transcriptase goes the other way, turning RNA back into DNA.

Here's a simplified breakdown of the reverse transcriptase role:

• It binds to the mRNA template.
• It synthesizes a DNA strand complementary to the mRNA.
• This results in cDNA, which can then be used for further genetic analysis.

Reverse transcriptase was first discovered in retroviruses and has since become a vital tool in biotechnology and research. It allows scientists to study gene expression patterns and understand how genes behave in different tissues, such as human brain tissue.

gene expression

Gene expression is the process through which a gene's DNA sequence is converted into functional products, like proteins. When studying gene expression, scientists often look at the mRNA levels, as it indicates which genes are actively being expressed. Using cDNA synthesis, researchers can create a snapshot of mRNA in a cell at a given time, reflecting the genes being actively transcribed.

How does gene expression relate to cDNA?

• cDNA provides a way to study mRNA without the instability issues of RNA itself.
• By converting mRNA to cDNA, researchers can amplify and analyze gene expression patterns.
• This is particularly useful for tissues like the brain, where specific gene expression profiles can give insights into neurological functions and disorders.

Therefore, understanding which genes are expressed in brain tissue can help in diagnosing, studying, and treating brain-related diseases.

mRNA template

mRNA, or messenger RNA, serves as the template in cDNA synthesis. mRNA is a single-stranded molecule that carries genetic information from DNA to the ribosomes, where proteins are made. For cDNA synthesis, the mRNA template is crucial because it already has introns (non-coding regions) removed.

What's the significance of mRNA in cDNA synthesis?

• mRNA contains the coding sequence needed to create proteins.
• cDNA synthesized from mRNA represents the expressed genes, providing a clearer understanding of gene activity.
• Using mRNA makes the process straightforward as it directly reflects functional genes.

By using an mRNA template, scientists can efficiently produce cDNA that represents only the expressed portions of the genome. This makes it easier to study gene expression accurately without the complications of non-coding regions.