Concept explainers
Another technique described in Chapter 21 is polymerase chain reaction (PCR) (see Figures 21.5 and 21.6), which is based on our understanding of
A. Why is DNA helicase not needed in a PCR experiment?
B. How is the sequence of each primer important in a PCR experiment? Do the two primers recognize the same strand or opposite strands?
C. The DNA polymerase used in PCR experiments is isolated from thermophilic bacteria. Why is this kind of polymerase used?
D. If a tube initially contained 10 copies of double-stranded DNA, how many copies of double-stranded DNA (in the region flanked by the two primers) would be obtained after 27 cycles?
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Genetics: Analysis and Principles
- Which of the followings statements are true about DNA polymerase? 1.) It can only go in one direction, meaning the lagging strand can't be synthesized continuously. 2.) It cannot start a DNA strand from scratch, so another enzyme is needed to create "primers" as a starting point. 3.) It cannot copy epigenetic marks (such as methyl groups) on its own; these must be "copied" onto the daughter DNA strand by other enzymes after DNA replication. 4.) All of the abovearrow_forwardWhich of the following statements regarding Nucleotide Excision Repair (NER) and Base Excision Repair (BER) is true? Only NER involves the action of DNA ligase to seal nicks in the DNA backbone. Both NER and BER involve the creation of an apyrimidinic (AP) site. Both NER and BER involve a single DNA strand cleavage by an endonuclease. Only BER requires DNA polymerase. Both NER and BER can be activated by exposure to visible light.arrow_forwardIn both leading and lagging strand synthesis, DNA replication always proceeds in a certain direction. What direction is this? Explain how oligonucleotide primers in the Polymerase Chain Reaction work (PCR)arrow_forward
- What is/are the attributes that make nucleotide excision repair (NER) and base excision repair (BER) similar and/or different from each other? Select the correct response: The NER pathway is the only one that can remove DNA lesions in the strand regardless of their size which is followed by attaching the correct strand, then sealed by a DNA ligase. They both use the enzyme DNA glycosylases that recognizes the damaged DNA segments and proceed with repairing the faulty base in the strand. They differ NER only repairs purine bases while BER repairs pyrimidine bases. They both remove the damaged parts of the DNA where the BER pathway corrects only the identified damaged bases which are usually non-bulky lesions. The NER pathway, on the other hand, repairs the damage by removal of bulky DNA adducts which is a short-single stranded DNA segment. They both utilize the enzyme photolyase to reverse the damages created by the faulty section of the DNA. They both remove the damaged parts of the…arrow_forwardDiscuss the following statement: “primase is a sloppy enzyme that makes many mistakes. eventually, the rna primers it makes are disposed of and replaced with dna synthesized by a polymerase with higher fidelity. this is wasteful. it would be more energy-efficient if a dna polymerase made an accurate copy in the first place.”arrow_forwardAn investigator obtains a bacterial temperature-sensitive mutation that affects a step in the process of DNA replication at 42°C but not at 30°C. She grows the cells at 30°C and, upon shifting the temperature to 42°C, she discovers that Okazaki fragments accumulate in unusually large quantities. What is the likely target affected by the temperature-sensitive mutation? primase DNA polymerase III DNA helicase DNA Ligase DNA gyrasearrow_forward
- The template (antisense) strands of two complete (double-stranded) DNA molecules have the base sequences shown in the table below. Two replication experiments are done with each molecule: 1. In Experiment #1, samples of each DNA molecule are incubated with radioactive adenine, along with appropriate replication enzymes, ATP, adenine, thymine, and cytosine. Experiment #1 is stopped when each DNA molecule has replicated once. 2. In Experiment #2, all the DNA molecules from #1 are purified, and then incubated with with a similar reaction mixture - except non-radioactive adenine is used this time. Experiment #2 is stopped when each DNA molecule has replicated one more time. Predict the percentage of DNA in each sample that is radioactive after each experiment. Round your answers to the nearest percent. DNA template strand sequence 3'- T C C C T A -5' 3'- G G C C G C -5' % of DNA radioactive after ... Experiment #1 Experiment #2 % % % % X Śarrow_forwardYou are studying a colony of cells and determine that some of these cells have a mutated DNA polymerase I that results in loss of function of this enzyme. A) What will the effect of the mutation in DNA polymerase I be on DNA replication? In your answer make sure to describe what would be observed in the leading and lagging strand and explain your reasoning. B) Will this mutation in DNA polymerase I have an impact on another step in DNA replication? In your answer make sure to indicate whether DNA replication will be impacted or not. If it is not, explain why. If it is impacted, then describe the step that is impacted and name the molecule or enzyme involved.arrow_forwardThere are 6 parts to this question: This is a follow up to the prior question regarding the replication of the DNA strand below. The DNA strand is here for your reference and you do not need to do anything with or to it. TC GATATCGG AGCTATAGCC c) what enzyme separated the parental DNA template strands, d) what bonds were broken? e) what enzyme replicates DNA f) before DNA can be replicated/copied, what must be laid down to allow the enzyme in "e" to replicated the DNA (be specific)? g) our DNA is replicated in many "pieces", what enzyme connects these many "pieces" into one continuous DNA strand that becomes the sister chromatid? h) during what specific phase of the cell cycle does this DNA replication process occur? (This should be a review question from last topics we covered).arrow_forward
- DNA polymerases have exonuclease activity that hydrolyzes DNA in the 3′ to 5′ direction. When an incorrect base is incorporated, it is removed by the exonuclease activity. true or false Endonuclease activity can remove an error in the middle of the DNA strand like DNA polymerase 1 that removes RNA primer. True or false DNA polymerases can recognize errors and engage exonuclease activity to fix the error on the spot. true or fale?arrow_forwardDNA replication is semi-conservative, this statement means that Question 6 options: a) the new DNA molecules that are made are not identical to the original DNA molecule. b) the new DNA molecules that are made are only partially DNA since RNA primers are included. c) the new DNA molecules that are made are composed of one strand of the old DNA molecule and one strand of new DNA. d) of the two new DNA molecules made, one is entirely new DNA and one is entirely old new. e) the new DNA molecules that are made have a mixture of old and new DNA in each strand of the DNA duplex, randomly interspersed.arrow_forwardRecombinant DNA molecules are produced by incubating plasmids that have been broken open by a restriction enzyme together with DNA molecules containing complementary sticky ends in the presence of the enzyme ? 1) exonuclease 2) DNA connectase O 3) DNA ligase 4) DNA polymerase O 5) endonucleasearrow_forward
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