# DBT JRF 2020 — Question 47

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

## Question

What are the cellular sites for protein glycosylation?

## Options

- **A.** endoplasmic reticulum and lysosomes
- **B.** endoplasmic reticulum and golgi body
- **C.** endoplasmic reticulum and mitochondria
- **D.** mitochondria and lysosomes

## Answer

Option B

## Explanation

Three established methods for determining protein 3D structure at atomic resolution: (1) X-ray crystallography — protein crystals diffract X-rays; Fourier transform of diffraction pattern gives electron density map → atomic coordinates. Provides high-resolution structures of large proteins/complexes. (2) NMR (Nuclear Magnetic Resonance) spectroscopy — chemical shifts and NOE signals from $^1$ H, $^{13}$ C, $^{15}$ N nuclei in solution reveal inter-atomic distances. Best for proteins <50 kDa; provides dynamics information. (3) Cryo-Electron Microscopy (cryo-EM) — rapid-frozen protein samples imaged by electrons; computational averaging of thousands of particle images reconstructs 3D density maps now routinely at 1.5–3 Å resolution (2017 Nobel Prize in Chemistry). Cryo-EM revolutionised structural biology of large, flexible, and membrane-bound complexes.

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