Q: If the average human chromosome contains $$1 \times 10^8$ base pairs and each base pair has a mass of about 660 daltons, what is the approximate mass of DNA in one chromosome (in grams)? (1 dalton = 1.66$$ \times $$10^{-24} g)$$

$$1 \times 10^8$ \times 660 \times 1.66 \times 10$$^{-24}$$ = 1.1 \times 10$$^{-13}$$ g

Question 1

Which of the following best describes the effect of a competitive inhibitor on the kinetic parameters of an enzyme-catalyzed reaction, as observed in a Lineweaver–Burk plot?

Accepted Answer

It increases $$K_M$$ and leaves $$V_{max}$$ unchanged.

Question 2

Given the following initial rate data for an enzyme-catalyzed reaction: $$[S]$$ (μmol/L): 5, 10, 30, 100, 200; $$v$$ (μmol/L·min): 22, 39, 65, 110, 135. What is the most accurate way to estimate $$V_{max}$$ and $$K_M$$ from this data?

Accepted Answer

By plotting $$1/v$$ versus $$1/[S]$$ and determining the intercepts.

Question 3

An enzyme contains an active site aspartic acid with a $$pK_a = 5.0. $$Which of the following best describes the expected shape of the enzyme activity versus pH curve?

Accepted Answer

A bell-shaped curve with maximum activity near pH 5.

Question 4

A Lineweaver–Burk plot for an enzyme in the presence of an uncompetitive inhibitor shows which of the following changes compared to the uninhibited reaction?

Accepted Answer

Both $$V_{max}$$ and $$K_M$$ decrease.

Question 5

If a person with type AB blood receives a transfusion, which of the following statements is correct?

Accepted Answer

They can receive blood from any major blood type but can only donate to AB individuals.

Question 6

Which of the following best explains why an enzyme that binds the transition state more tightly than the substrate increases the reaction rate?

Accepted Answer

It stabilizes the transition state, lowering the activation energy.

Question 7

A DNA molecule is being transcribed. Which strand is referred to as the 'sense' strand?

Accepted Answer

The nontemplate strand, because its sequence matches the mRNA (except T for U).

Question 8

In a Michaelis–Menten experiment, the $$y-$$intercept of a Lineweaver–Burk plot is $$0.00246$$ $$(	ext{μmol}^{-1} 	ext{min}). If $$the enzyme concentration is $$3$$ nmol mL$$^{-1}$$, what is the value of $$V_{max}$$?

Accepted Answer

$$V_{max} = \frac{1}{0.00246} = 406$$ μmol min$$^{-1}$$

Question 9

Which of the following best describes the effect of Tamiflu as a competitive inhibitor of neuraminidase?

Accepted Answer

It increases the apparent $$K_M$$ without affecting $$V_{max}.$$

Question 10

If the average human chromosome contains $$1 	imes 10^8$ base pairs and each base pair has a mass of about 660 daltons, what is the approximate mass of DNA in one chromosome (in grams)? (1 dalton = 1.66$$ 	imes $$10^{-24} g)$$

Accepted Answer

$$1 	imes 10^8$ 	imes 660 	imes 1.66 	imes 10$$^{-24}$$ = 1.1 	imes 10$$^{-13}$$ g

Question 11

Which of the following best describes the compaction ratio achieved by forming nucleosomes and wrapping them into a 30-nm fiber, if the fiber contains about six nucleosomes per 10 nm of length?

Accepted Answer

The compaction ratio is significantly increased compared to naked DNA, due to tight packing of nucleosomes.

Question 12

Which of the following is a deoxyribonucleotide?

Accepted Answer

Deoxycytidine 5'-monophosphate

Question 13

How many unique tripeptides can be formed from three different amino acids (A, B, and C), using each amino acid only once per tripeptide?

Accepted Answer

6

Question 14

In a DNA renaturation experiment, which phase of the renaturation curve corresponds to highly repetitive sequences?

Accepted Answer

The initial, fastest phase of renaturation.

Question 15

Which of the following best describes the effect of an uncompetitive inhibitor on a Lineweaver–Burk plot?

Accepted Answer

Parallel lines with increased $$y-$$intercept and $$x-$$intercept.

Question 16

If you wish to mutate a histidine codon (CAC) to a proline codon (CCC) using site-directed mutagenesis, which oligonucleotide sequence would you design?

Accepted Answer

A 21-mer containing the CCC codon in place of CAC, flanked by the original sequence.

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