# DBT JRF 2020 — Question 85

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Easy

## Question

A protein of 100 KDa would have approximately how many amino acids?

## Options

- **A.** 100
- **B.** 1000
- **C.** 900
- **D.** 800

## Answer

Option C

## Explanation

$100 \text{ kDa} = 100{,}000 \text{ Da}$ . Average amino acid MW $\approx 110$ Da. Number of amino acids $= \dfrac{100{,}000}{110} \approx 909 \approx 900$ . Some texts use 120 Da/AA giving $\approx 833$ , but 110 Da is the most commonly accepted average giving ~900 as the standard approximation. This is consistent with the empirical 'rule of thumb': 1 kDa $\approx$ 9–10 amino acids, so 100 kDa $\approx$ 900–1000 amino acids.

Source: https://mypyqbuddy.com/questions/a-protein-of-100-kda-would-have-approximately-6a05a8a02adafec47029326d