Quiz 8: Homologs

A PCR reaction contains ~1000 molecules of a desired product. How many more cycles are needed before the reactions contains ~1 million molecules of product?

10

In the example given in the previous question, what is happening on the molecular level when the reaction is being incubated at 55 degrees?

Oligonucleotide primers are annealing to the DNA

What is happening on the molecular level when the reaction is being incubated at 94 degrees?

The DNA is denaturing

A typical PCR reaction might involve incubations at 55 degrees, 72 degrees and 94 degrees. What is happening on the molecular level when the reaction is being incubated at 72 degrees?

The DNA polymerase is synthesizing DNA.

In the next lab, you will use a tiny portion of a yeast colony in a PCR reaction. Which of the following statements about yeast colony PCR is true? Check all that apply. a. DNA must first be purified from a yeast colony before it can be used in a PCR reaction. b. Ten micrograms of yeast colony DNA will have far fewer copies of a target gene sequence than ten micrograms of plasmid DNA containing the same target sequence. c. Colonies provide good substrates for PCR reactions, because the cells in the colony should have nearly identical DNA. d. Mis-priming is a greater problem when plasmid DNA is used as a substrate in a PCR reaction than when a yeast colony is used as the source of DNA.

a

The polymerase chain reaction (PCR) is used for many different applications in molecular cloning. Which of the following is not true about PCR reactions? a. PCR requires complete knowledge of the DNA sequence that will be analyzed. b. PCR can be done with damaged DNA, such as that found at a crime scene. c. Not all the molecules produced in a PCR reaction have the same length. d. PCR is often used to construct plasmids.

a

The polymerases used in PCR a. resist denaturation at high temperatures b. require highly purified DNA templates. c. denature and renature in each cycle of PCR d. are able to use RNA templates in RT-PCR

a

Which of the following statements are the annealing step in PCR reactions is true? a. The melting temperature of a hybrid formed between an oligonucleotide with a 50% GC composition and a target DNA increases as its length increases. b. Increasing the annealing temperature in a PCR reaction will decrease the specificity of the reaction. c. Double-stranded primers are used in the annealing step of PCR reactions. d. The melting temperature of a hybrid formed between a 17 bp oligonucleotide and target DNA increases in direct proportion to the number of As and Ts.

a

Which of the following primer sequences would have the highest melting temperature? a. A G A T T C A T A C b. A A T C C G T A T G c. A C G C A T G C C T d. G G T A A T A T G G

c

When an investigator designs primers to amplify an ORF from genomic DNA (as you will do in the yeast colony PCR), the investigator tries to a. design primers with the highest melting temperature b. design primers that are complementary to each other c. design two primers from the Crick strand of DNA for ORFs that are read on the Watson strand d. design primers that are each complementary to a single sequence in the genome

d