Q: Which formula correctly calculates specific activity?

$$\text{Specific Activity} = \frac{\text{Target Protein Activity}}{\text{Total Protein}}$$

Question 1

Which of the following best defines 'specific activity' in the context of protein purification?

Accepted Answer

The amount of enzyme activity per unit of total protein.

Question 2

During a protein purification procedure, a biochemist measures the following: total protein = 200 mg, target protein activity = 4,000 units. What is the specific activity?

Accepted Answer

$$\frac{4,000}{200} = 20$$ units/mg

Question 3

If a purification step increases the specific activity of an enzyme from 10 units/mg to 100 units/mg, what is the relative purity increase?

Accepted Answer

$$\frac{100}{10} = 10$$

Question 4

A biochemist purifies an enzyme and obtains the following data after a chromatography step: total protein = 5 mg, target protein activity = 500 units. What is the specific activity?

Accepted Answer

$$\frac{500}{5} = 100$$ units/mg

Question 5

Why does specific activity increase as a protein sample becomes more purified?

Accepted Answer

Because the proportion of target protein relative to total protein increases.

Question 6

Which purification step would be considered most effective in increasing purity if it results in the largest increase in specific activity?

Accepted Answer

The step with the largest increase in specific activity compared to the previous step.

Question 7

A scientist performs two purification steps. After step 1: total protein = 100 mg, target activity = 1,000 units. After step 2: total protein = 10 mg, target activity = 800 units. What is the fold increase in specific activity from step 1 to step 2?

Accepted Answer

$$\frac{800/10}{1,000/100} = \frac{80}{10} = 8$$

Question 8

If a purification step results in a decrease in specific activity, what does this most likely indicate?

Accepted Answer

The target protein was lost or denatured during the step.

Question 9

In a purification table, which value is most useful for determining the purity of the target protein?

Accepted Answer

Specific activity

Question 10

A biochemist notes that after a final purification step, the specific activity of an enzyme is $$1,000$$ units/mg, while the initial crude extract had a specific activity of $$10$$ units/mg. What is the relative purity?

Accepted Answer

$$\frac{1,000}{10} = 100$$

Question 11

Which of the following best explains why specific activity is a better measure of protein purity than total protein?

Accepted Answer

Specific activity accounts for both the amount of target protein and the total protein present.

Question 12

A researcher purifies an enzyme and finds that after a certain step, the specific activity does not increase. What is the most likely explanation?

Accepted Answer

The step did not remove any impurities.

Question 13

If a purification step results in a large decrease in total protein but only a small decrease in target protein activity, what happens to the specific activity?

Accepted Answer

It increases.

Question 14

Which formula correctly calculates specific activity?

Accepted Answer

$$	ext{Specific Activity} = \frac{	ext{Target Protein Activity}}{	ext{Total Protein}}$$

Question 15

A scientist is comparing two flasks: Flask A has 100 mg total protein and 1,000 units of target activity; Flask B has 10 mg total protein and 500 units of target activity. Which flask has higher specific activity?

Accepted Answer

Flask B: $$\frac{500}{10} = 50$$ units/mg

Question 16

During a purification process, which step is considered least effective in increasing purity?

Accepted Answer

The step with the smallest increase in specific activity.

Question 17

If a biochemist suspects that the enzyme is lost after a purification step, which data should they examine to confirm this?

Accepted Answer

A significant decrease in target protein activity.

Question 18

A purification table shows the following for a step: total protein = 2 mg, target activity = 200 units, specific activity = 100 units/mg. If the next step yields total protein = 1 mg and target activity = 150 units, what is the new specific activity?

Accepted Answer

$$\frac{150}{1} = 150$$ units/mg

Question 19

Why is it important to measure both total protein and target protein activity during purification?

Accepted Answer

To calculate specific activity and assess the purity of the sample.

Specific Activity and Protein Purification in Biochemistry

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