PCR involves a heating step, followed by a cooling step, and then DNA synthesis. What is the primary reason for why this cooling step is necessary?
(a) Cooling the reaction ensures the integrity of the covalent bonds holding the nucleotides together in the DNA strand.
(b) Cooling the reaction gives the DNA polymerase an opportunity to rest from the previous cycle so that it will be ready for the next round of synthesis.
(c) Transcription takes place during the cooling step.
(d) Cooling the reaction brings the temperature down to a level that is compatible with the short primers forming stable hydrogen bonds with the DNA to be amplified.
Choice (d) is correct. During PCR, the reaction is heated to a temperature that will break the hydrogen bonds holding the strands together but should not be harmful to the covalent bonds holding the nucleotides together [choice (a)]. The DNA polymerase used in PCR is a thermostable enzyme that can tolerate the high temperatures used in PCR [choice (b)]. Transcription involves the production of RNA from DNA and does not occur during PCR [choice (c)].
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Hemophilia in humans results from an X linked recessive gene. Which of these statements regarding the inheritance of this trait is true?
A. Heterozygous females will exhibit a milder form of hemophilia. B. All daughters of an affected mother will have hemophilia. C. Carrier females will always pass the hemophilia allele to their sons. D. Males who inherit the recessive allele from their fathers will exhibit hemophilia. E. All sons of an affected mother will have hemophilia.
Spiders are ________
A) herbivores B) filter feeders C) carnivores D) omnivores
________ isolating mechanisms lead to reproductive isolation by preventing the formation of hybrid zygotes.
Fill in the blank(s) with the appropriate word(s).
Outline a procedure for producing a useful new recombinant product
What will be an ideal response?