2526AY_SBMS2102_Lect 1_Review Questions

According to the Central Dogma of Molecular Biology, what is the standard flow of genetic information?

• Protein → RNA → DNA

• RNA → DNA → Protein

• DNA → Protein → RNA

• DNA → RNA → Protein

• RNA → Protein → DNA

Which of the following correctly describes the structure of a standard B-form DNA double helix?

• It is a left-handed helix with the bases on the outside.

• It is a right-handed helix with the sugar-phosphate backbones on the inside.

• It is a right-handed helix with the bases on the inside and antiparallel strands.

• It is a left-handed helix with parallel strands.

• The two strands are connected by phosphodiester bonds.

In a nucleic acid chain, what type of bond connects the 3' carbon of one sugar to the 5' carbon of the next sugar?

• Hydrogen bond

• Glycosidic bond

• Peptide bond

• phosphodiester bond

• Disulfide bond

When placed in an electrical field during gel electrophoresis, why does DNA migrate towards the positive electrode (anode)?

• Because the nitrogenous bases are positively charged.

• Because the sugar-phosphate backbone is negatively charged.

• Because the DNA is denatured into single strands.

• Because the agarose gel is positively charged.

• Because the intercalating dye gives it a positive charge.

A researcher measures the absorbance of a nucleic acid sample and finds the A260/A280 ratio to be 1.8. What does this value typically indicate?

• The sample is 'pure' RNA.

• The sample is heavily contaminated with protein.

• The sample is 'pure' double-stranded DNA.

• The sample is contaminated with phenol from the extraction.

• The sample contains only free nucleotides.

During the thermal denaturation (melting) of a DNA molecule, which bonds are broken?

• The phosphodiester bonds along the sugar-phosphate backbone.

• The N-glycosidic bonds connecting the base to the sugar.

• The hydrogen bonds between complementary base pairs.

• The covalent bonds within the deoxyribose sugar ring.

• All of the above bonds break simultaneously.

Who first proposed the 'Triplet Hypothesis,' deducing that the genetic code must be composed of nucleotide triplets?

• Marshall Nirenberg

• Severo Ochoa

• George Gamow

• Philip Leder

• Francis Crick

In the landmark 'Poly-U' experiment by Nirenberg and Matthei, what was concluded from adding a synthetic poly(U) RNA to a cell-free system?

• The codon CCC codes for proline.

• The codon UUU codes for phenylalanine.

• The codon AAA codes for lysine.

• The codon AUG is the start codon.

• The genetic code is degenerate.

In a traditional nucleic acid extraction using phenol:chloroform, where do the denatured proteins primarily partition after centrifugation?

• In the upper aqueous phase with the DNA/RNA.

• In the lower organic (phenol) phase.

• At the interphase between the aqueous and organic layers.

• They precipitate out and form a pellet at the bottom.

• They remain dissolved in the aqueous phase but are inactive.

For what purpose is a low pH (acidic) condition used during a phenol-chloroform extraction?

• To precipitate both DNA and RNA simultaneously.

• To specifically keep DNA in the aqueous phase while RNA moves to the organic phase.

• To denature RNases more effectively.

• To specifically keep RNA in the aqueous phase while DNA partitions into the organic phase.

• To cause all proteins to precipitate.