Question

Which of the following are non-membrane bound organelles?

• A. Nucleolus
• B. Ribosomes
• C. Centrosome
• D. All of these

Answer 1

The correct option is D All of these

Nucleolus is a dense spherical structure in the nucleoplasm. It is not bound by a membrane. It is composed of DNA, RNA and proteins (basic histone proteins and non histone proteins). It is the site of ribosome assembly. It forms a thin thread-like network of nucleoprotein fibres.
Ribosomes are non-membrane bound organelles. In prokaryotes, 70S ribosomes are found. They are made up of RNA and proteins. They are the site of protein synthesis, because of which they are called the protein factories of the cell. They consist of 2 subunits- 50S larger subunit and 30S smaller subunit. Ribosomes form a chain called polyribosome or polysome.
There are a few structures in the eukaryotic cell which are made up of cytoskeletal elements, such as centrosome and centriole. Centrosomes are found in animal cells only and are made up of 2 units called centrioles. Centrosomes are non-membrane bound.