Quiz Genomic Libraries & Cdna Libraries

Gene libraries made from genomic DNA are called genomic libraries because they contain a collection of DNA fragments that represent the entire genome of an organism. These libraries are created by cutting the genomic DNA into smaller fragments and inserting them into a vector, such as a bacterial plasmid. On the other hand, cDNA libraries are made from complementary DNA, which is synthesized from mRNA using the enzyme reverse transcriptase. These libraries only contain the expressed genes in a particular cell or tissue. Therefore, the given statement is true as it correctly states that gene libraries made from genomic DNA are called genomic libraries, while those made from cDNA are known as cDNA libraries.

The explanation for the given correct answer is that cDNAs are synthesized from mRNA molecules through the process of reverse transcription. This means that cDNAs only contain the coding sequences of genes, excluding introns and non-coding regions. Therefore, cDNAs represent the transcribed parts of the genome, making the statement TRUE.

Engineered plasmids are commonly used as vectors for cloning because they are small, circular DNA molecules that can be easily manipulated in the laboratory. They can carry foreign DNA fragments and be introduced into host cells, where they replicate independently. This allows for the production of multiple copies of the desired DNA sequence. Additionally, engineered plasmids often contain selectable markers, such as antibiotic resistance genes, which enable the identification and selection of cells that have successfully taken up the plasmid. Overall, the extensive use of engineered plasmids in cloning is well-documented and widely recognized in the field of molecular biology.

Special nucleic acid linkers are indeed added to create sticky ends for cloning. Sticky ends are single-stranded overhangs that are created when a DNA molecule is cut by a restriction enzyme. These sticky ends can then be joined with complementary sticky ends from another DNA molecule, allowing for the insertion of a specific DNA fragment into a vector for cloning purposes. Nucleic acid linkers are short DNA sequences that are designed to have complementary sticky ends, facilitating the cloning process. Therefore, the statement is true.

All of the options listed (plasmid, phage, cosmid, BAC) can be used to construct genomic libraries. Genomic libraries are collections of DNA fragments that represent the entire genome of an organism. Plasmids, phages, cosmids, and BACs are all commonly used vectors in molecular biology that can carry and replicate DNA fragments. Therefore, all of these options are correct as they can be utilized for constructing genomic libraries.

Alkaline phosphatase is used to dephosphorylate the vector. Dephosphorylation of the vector is necessary to prevent self-ligation and promote the ligation of the insert into the vector. This enzyme removes phosphate groups from the vector's ends, making them unable to ligate to each other.

mRNA can be isolated from lysed eukaryotic cells by adding magnetic beads that have oligo(dT) covalently attached. This is because the poly(A) tail of mRNA consists of a string of adenine nucleotides. The oligo(dT) sequence specifically binds to the poly(A) tail, allowing for the isolation and purification of mRNA from the cell lysate. The other options, oligo(dA), oligo(dG), and oligo(dC), do not specifically bind to the poly(A) tail and therefore would not be effective in isolating mRNA.

The statement is false because cDNA libraries from eukaryotic mRNA do have gene sequences. cDNA libraries are created by reverse transcribing mRNA into complementary DNA (cDNA), which contains the gene sequences. These libraries are valuable tools for studying gene expression and identifying specific genes of interest. Therefore, the correct answer is false.

cDNA libraries are not made using prokaryotic mRNA. Instead, cDNA libraries are made using eukaryotic mRNA. This is because cDNA libraries are constructed by reverse transcribing the mRNA into complementary DNA (cDNA), which is then inserted into a vector for cloning. Prokaryotes do not have introns, so their mRNA does not require reverse transcription to remove introns. Therefore, prokaryotic mRNA is not used to create cDNA libraries.

The statement is false because not all mRNAs in eukaryotes are polyadenylated. While most mRNAs do undergo polyadenylation, there are exceptions to this rule. Some mRNAs may have alternative methods of 3'-end formation or may not have a poly(A) tail at all. Therefore, it is incorrect to say that most mRNAs are polyadenylated.