Problem 11 - Biology

Question

A genomic library (a) represents all the DNA in a specific chromosome (b) is made using reverse transcriptase (c) is stored in a collection of recombinant bacteria (d) is a DNA copy of mature mRNAs (e) allows researchers to amplify a tiny sample of DNA.

Step-by-Step Solution

Answer

The correct answer is (c) is stored in a collection of recombinant bacteria.

Step 1: Understanding Genomic Libraries

A genomic library is a collection of bacteria that collectively contain a complete set of the DNA fragments from a particular organism's genome. It is different from a cDNA library that represents only the expressed genes as mRNA transcripts.

Step 2: Evaluating Each Option

Evaluate each option: (a) A genomic library consists of DNA cloned from the entire genome, not just a specific chromosome. (b) Reverse transcriptase is used in cDNA libraries, not genomic libraries. (c) A genomic library is stored in a collection of recombinant bacteria, as each bacterium contains a different DNA fragment. (d) A DNA copy of mature mRNAs refers to cDNA. (e) Amplifying DNA refers to PCR, not a genomic library.

Step 3: Identifying the Correct Answer

Option (c), which states that a genomic library is stored in a collection of recombinant bacteria, accurately describes the nature of a genomic library where each bacterium contains a part of the whole genome.

Key Concepts

cDNA Library

A cDNA library is a special type of DNA library. It is created using mRNA transcripts from express genes within a cell. Unlike genomic libraries, it doesn't contain introns, promoters, or intervening sequences found in genomic DNA, as these parts are not transcribed into mRNA.
The creation of a cDNA library involves several steps:

• Isolation of mRNA from cells.
• Use of reverse transcriptase to synthesize complementary DNA (cDNA).
• Cloning of these cDNA into vectors for storage and amplification.

Researchers use cDNA libraries to study gene expression, analyze gene function, and produce recombinant proteins. Since it represents only genes that are actively expressed, it provides valuable insights into cellular function at specific times or conditions.

Recombinant Bacteria

Recombinant bacteria are the backbone of many molecular biology techniques. They are bacteria genetically engineered to carry foreign DNA or genes from different organisms. These are crucial for constructing DNA libraries, such as genomic or cDNA libraries.
The process typically involves:

• Inserting the desired DNA fragment into a bacterial plasmid—a circular DNA molecule.
• Introducing this plasmid into bacteria (often E. coli) via a method like transformation.
• Allowing bacteria to multiply, thereby replicating the inserted DNA along with its genome.

Recombinant bacteria are used in biotechnology to produce proteins, enzymes, and hormones that are important for research and medical therapies.

Reverse Transcriptase

Reverse transcriptase is an enzyme that plays a pivotal role in the creation of cDNA libraries. It is responsible for synthesizing DNA molecules from an RNA template, a process termed reverse transcription.
This enzyme is originally found in retroviruses, where it helps with their replication by converting viral RNA genomes into DNA. In a lab setting, reverse transcriptase works as follows:

• It binds to mRNA templates derived from cells.
• It synthesizes a complementary DNA strand, called cDNA.
• This cDNA is then used for cloning, sequencing, or other analyses.

Using reverse transcriptase allows researchers to generate DNA that corresponds only to expressed genes, making it easier to focus studies on actively functional parts of the genome.

PCR (Polymerase Chain Reaction)

PCR, or Polymerase Chain Reaction, is a revolutionary technique used to amplify minute amounts of DNA. It is not associated with creating genomic libraries but is crucial for various genetic analyses and manipulation tasks.
The procedure requires only a small DNA sample and can produce millions of copies within a few hours. PCR involves three main steps:

• Denaturation: Heating the DNA to separate the strands.
• Annealing: Cooling the DNA so that primers can bind to each target sequence.
• Extension: Taq polymerase extends the primers to form a new DNA strand.

These cycles are repeated multiple times to accumulate millions of DNA copies. PCR is invaluable in research, forensics, and medical diagnostics, enabling scientists to study small DNA samples comprehensively.