# DBT JRF 2020 — Question 95

Exam: DBT JRF 2020 · Section: B · Topic: Cell Biology · Difficulty: Easy

## Question

A supramolecular complex that serves to degrade damaged or unneeded proteins in the cell is called as

## Options

- **A.** ribosome
- **B.** proteasome
- **C.** flagella
- **D.** lysosome

## Answer

Option B

## Explanation

The 26S proteasome is the major cytoplasmic/nuclear ATP-dependent protease complex responsible for regulated protein degradation in eukaryotes. Structure: 20S catalytic core particle (barrel-shaped stack of 4 heptameric rings: $\alpha_7\beta_7\beta_7\alpha_7$ ; the $\beta$ -rings contain the protease active sites with threonine residues) + 19S regulatory particle (RP, 'cap') on one or both ends. Function: (1) Recognises ubiquitylated proteins (polyubiquitin chain via K48 linkage = degradation signal); (2) 19S deubiquitylates and unfolds the substrate (ATP-dependent); (3) Translocates unfolded polypeptide into 20S barrel for proteolytic degradation (chymotryptic, tryptic, and caspase-like activities); (4) Releases short peptides (for MHC-I antigen presentation) and amino acids for recycling. Lysosomes degrade proteins via bulk autophagy/endocytosis using acid proteases; not the same as the proteasome.

Source: https://mypyqbuddy.com/questions/a-supramolecular-complex-that-serves-to-degrade-damaged-6a05a8a02adafec470293277