GRE Subject Test: Biology : Understanding Recombinant DNA
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Example Questions
Example Question #2 : Genetic Manipulation
Which term describes DNA that has been altered by genes from a different organism, typically from a different species?
DNA-DNA hybridization
DNA sequencing
DNA replication
DNA fingerprinting
Recombinant DNA
Recombinant DNA
Recombinant DNA are segments of DNA from one organism artifically manipulated or inserted into the DNA of another organism, using a technique known as gene splicing. This technique permits isolation and examination of properties and actions of specific genes.
DNA sequencing is the process of determining the chemical composition of a DNA molecule (in particular, the order in which the molecule's nucleic acids are arranged). DNA fingerprinting is the use of enzymes to cut DNA samples into a unique set of restriction fragments that can be used as a genetic identified for a single individual. DNA-DNA hybridization is a technique by which DNA from two species is separated into single strands and then allowed to re-form. DNA replication is the copying of the double-stranded DNA molecule, producing two identical DNA double helices.
Example Question #3 : Genetic Manipulation
A scientist seeks to synthesize a rare human protein in lab. To accomplish this, she utilizes recombinant techniques to insert the DNA of a eukaryotic gene for the protein into bacterial plasmids. These plasmids are transformed into bacteria for expression. She is disappointed to discover that the gene product from the bacteria is not the correct protein. What corrective step could she take in the procedure to fix this issue?
Use cDNA for the gene instead of DNA
Use a different genus bacteria
Ligate the gene directly into the chromosome
Use archaea instead of bacteria
Insert mRNA into the plasmid instead of DNA
Use cDNA for the gene instead of DNA
The corrective step would be to use cDNA in the plasmid rather than DNA from the gene. cDNA (complementary DNA) is the DNA copy of the mature mRNA created by the reverse transcriptase enzyme. This would allow the introns to be spliced out from the sequence of the strand. This must be done since prokaryotes lack the equipment necessary for splicing. Simply inserting the DNA gene into the plasmid would result in a translated product with introns present. cDNA avoids this problem.
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