Genetics Ch. 20 Homework

Which of the following DNA sequences is one strand of a restriction enzyme recognition sequence?

5′ GGATCC 3′

X-Gal is included in the growth medium on which cells transformed with bacterial plasmids are grown. The reason X-Gal is included is to

identify bacteria that contain a recombinant plasmid.

Within a six-base DNA recognition sequence, an enzyme that cuts between the 3rd and 4th bases from the 5′ end will generate blunt ends.

True.

What is the function of restriction endonucleases in bacteria?

They provide a defense mechanism against infection by viruses.

Restriction endonucleases cut DNA at specific recognition sequences and then bond two strands covalently with the same "sticky ends."

False.

BamHI cuts the sequence 5′ G|GATCC 3′. Which of the following sequences would not be recognized by this enzyme?

3′ TCTTAAG 5′.

Why are filters overlaid with X‑ray film when screening a cDNA library?

To visualize probe hybridization events.

Chromosome walking is used mainly to isolate a gene when the sequence of the gene is known.

False.

The role of the primers in PCR is _______.

to define the target region and provide a 3′ end that can be extended by taq polymerase.

If there are five molecules of DNA containing the target region at the beginning of a PCR reaction, how many copies of the target will be present after three rounds of amplification?

40.

Immediately after the primers have annealed to the target sequence, _______.

the temperature is raised so that taq polymerase can extend the primers.

Which of the following molecules is not required for a PCR reaction?

Ligase.

The thermostability of Taq polymerase is required during the annealing phase of PCR.

False.

What is the purpose of raising the temperature to 90-95°C at the beginning of each cycle of PCR?

To separate the double-stranded DNA.

Phage λ can carry larger DNA fragments than plasmids.

True.

Which of the following elements is not found in a plasmid?

Lambda arms.

A DNA fragment is introduced into the lacZ gene of a plasmid, which also contains a tetracycline resistance gene. What is the appearance of bacteria transformed with this plasmid if they are spread on plates containing tetracycline and Xgal?

White colonies that are resistant to tetracycline.

Which enzyme(s) will produce a DNA fragment that contains the entire vgp gene (shown in red) and has "sticky ends"?
Select all that apply.

HindIII BamHI

Which of the following statements about ddNTPs is true?

They have a hydrogen at the 3′ carbon of the sugar.

DNA fragments that are 600 bp long will migrate more quickly through a sequencing gel than fragments that are 150 bp long.

False.

Which of the following statements about manual Sanger sequencing is true?

The DNA sequence obtained is complementary to the template strand.

How are dideoxynucleotides (ddNTPs) structurally different from deoxynucleotides (dNTPs)?

ddNTPs lack a 3′-hydroxyl group.

How does this structural difference make ddNTPs valuable in chain-termination methods of DNA sequencing?

Once ddNTPs are incorporated in DNA, they terminate the chain elongation, thereby allowing multiple fragments of DNA to be formed and analyzed to reveal the base sequence of original DNA.

If you performed a PCR experiment starting with only one copy of double-stranded DNA, approximately how many DNA molecules would be present in the reaction tube after 25 cycles of amplification?

33554432