Week 13 Quiz

In the double helix, each rung of the twisted ladder is a base pair. Which base does adenine pair with?

Select one.

• Guanine, the other base with a double ring
• Thymine, held to it by two hydrogen bonds
• Cytosine, held to it by three hydrogen bonds
• Uracil, the base that pairs with it in DNA

What holds the two bases of one rung of the DNA ladder together across the middle of the helix?

Select one.

• Covalent bonds that share electrons between the rails
• Ionic bonds from one base handing an electron to the other
• Hydrogen bonds, two for A–T and three for G–C
• Peptide bonds like the ones that link amino acids

In the Chargaff example (illustrative), one model DNA sample is 30% adenine. Using Chargaff's rules, what percent of its bases are guanine?

Select one.

• 30%
• 20%
• 40%
• 70%

Which strand is the complementary partner of the DNA strand 5′-AATGC-3′?

Select one.

• 3′-TTACG-5′
• 5′-AATGC-3′
• 3′-UUACG-5′
• 3′-GGCAT-5′

True or false: the two strands of one DNA double helix are identical copies of each other.

True or false.

• True
• False

A model-kit packet offers a rung that joins adenine to guanine. Why could that rung not fit in a real double helix?

Select one.

• Adenine and guanine are both pyrimidines, so the rung would be too narrow
• The rung would need four hydrogen bonds instead of three
• Guanine is found only in RNA, never in DNA
• Both are purines with a double ring, so the rung would be too wide

Meselson and Stahl (1958) grew bacteria on heavy nitrogen, moved them to light nitrogen, and sorted the DNA by density. After one round of copying, all the DNA formed one band of in-between density. Which model did that single band rule out?

Select one.

• The conservative model
• The semiconservative model
• The dispersive model

During DNA replication, which enzyme unzips the double helix by breaking the hydrogen bonds between the base pairs?

Select one.

• DNA polymerase, which adds nucleotides
• DNA ligase, which seals the backbone
• Helicase, starting at an origin of replication
• Catalase, which splits hydrogen peroxide

Which of these statements place the history of DNA correctly? Select all that apply.

Select every option that applies.

• Griffith (1928) discovered transformation in bacteria
• Avery, MacLeod, and McCarty (1944) showed that the transforming substance is DNA
• Hershey and Chase (1952) showed that protein, not DNA, is the genetic material
• The 1962 Nobel Prize went to Crick, Watson, and Wilkins
• Franklin shared the 1962 Nobel Prize with Watson and Crick

DNA and RNA are both nucleic acids built from nucleotides. Which base does DNA use where RNA uses uracil?

Select one.

• Adenine
• Guanine
• Cytosine
• Thymine