Q: A solution is prepared by dissolving 5 grams of NaCl (molar mass = 58.44 g/mol) in enough water to make 500 mL of solution. What is the molarity ($$M) of $$the solution? Use the formula $$M = \frac{\text{moles of solute}}{\text{liters of solution}}.$$

$$M = \frac{5}{58.44 \times 0.5} = 0.171 M$$

Question 1

Which of the following best explains why buffers are essential in biological laboratory experiments involving enzymes?

Accepted Answer

Buffers maintain a stable pH, preventing drastic changes that could denature enzymes.

Question 2

A solution is prepared by dissolving 5 grams of NaCl (molar mass = 58.44 g/mol) in enough water to make 500 mL of solution. What is the molarity ($$M) of $$the solution? Use the formula $$M = \frac{	ext{moles of solute}}{	ext{liters of solution}}.$$

Accepted Answer

$$M = \frac{5}{58.44 	imes 0.5} = 0.171 M$$

Question 3

Which of the following statements correctly distinguishes between covalent and ionic bonds?

Accepted Answer

Covalent bonds involve the sharing of electrons, while ionic bonds involve the transfer of electrons.

Question 4

During agarose gel electrophoresis, DNA samples are loaded into wells at one end of the gel. Given that DNA is negatively charged, toward which electrode will the DNA migrate, and why?

Accepted Answer

DNA migrates toward the positive electrode because opposite charges attract.

Question 5

Which of the following best describes the Central Dogma of molecular biology?

Accepted Answer

DNA is transcribed into RNA, which is then translated into protein.

Question 6

A student is performing a Lowry protein assay and obtains an absorbance (optical density) of 0.250 for an unknown sample. Using the standard curve below, estimate the protein concentration in $$\mu g/mL if $$the best-fit line is $$y = 0.0011x + 0.099$$, where $$y is $$absorbance and $$x is $$protein concentration. Solve for $$x.$$

Accepted Answer

$$x = \frac{0.250 - 0.099}{0.0011} = 137.27\ \mu g/mL$$

Question 7

Which of the following is NOT a reason why expected results may not be obtained in a restriction digestion experiment?

Accepted Answer

The DNA was loaded into the gel without adding loading dye.

Question 8

Which of the following best describes the function of restriction enzymes in molecular biology?

Accepted Answer

They cut DNA at specific recognition sequences, often palindromic.

Question 9

In a transformation experiment, why is it important to include both +DNA (with plasmid) and –DNA (without plasmid) samples on both LB and LB/amp plates?

Accepted Answer

To distinguish between antibiotic resistance due to transformation and spontaneous mutation, and to serve as positive and negative controls.

Question 10

Which of the following is a critical difference between prokaryotic and eukaryotic cells?

Accepted Answer

Eukaryotic cells have a nucleus, while prokaryotic cells lack a nucleus.

Question 11

Which of the following is NOT a component required for a standard PCR reaction?

Accepted Answer

RNA ligase

Question 12

Which of the following best describes the purpose of the 'milk step' in an ELISA assay?

Accepted Answer

To block non-specific binding sites, reducing background signal.

Question 13

A scientist is preparing a 10% (w/v) NaCl solution. How many grams of NaCl are needed to make 250 mL of this solution?

Accepted Answer

25 grams

Question 14

Which of the following best explains why DNA fragments of different sizes separate during agarose gel electrophoresis?

Accepted Answer

Smaller DNA fragments move more easily through the gel matrix, traveling farther than larger fragments.

Question 15

Which of the following is a function of RNA polymerase?

Accepted Answer

Synthesizing RNA from a DNA template during transcription.

Question 16

Which of the following best describes the structure of a DNA molecule?

Accepted Answer

A double helix with a sugar-phosphate backbone and nitrogenous bases paired in the center.

Question 17

Which of the following is an example of a non-covalent interaction important in protein folding?

Accepted Answer

Hydrogen bonds

Question 18

Which of the following best describes the role of quality control (QC) in a biotechnology laboratory?

Accepted Answer

QC ensures that all products meet safety and efficacy standards through systematic testing and documentation.

Question 19

Which of the following is a plausible reason for obtaining incorrect results in an ELISA experiment?

Accepted Answer

The wells were not washed thoroughly between steps, leading to high background signal.

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