Question

Write a short note on Endoplasmic reticulum with a neat labeled diagram.

Answer 1

Endoplasmic Reticulum is three-dimensional networks of intracellular membranes. It is present in all eukaryotic cells. In young meristematic cells, ER is very much developed. In spermatocytes, ER is represented by a few vacuoles. Cells actively synthesising proteins like liver, fibroblast and pancreatic cells have abundant ER.

1. ER is formed of three types of elements.

• Cisternae :
  

- They are sacs like unbranched structures.

- It lies in stacks or piles parallel to each other. These cisternae in the stack are interconnected with each other.

- Cisternae contain transmembrane Glycoprotein Ribophorin 2, they bind with larger subunits of the ribosome.

- Cytosolic spaces are present between Cisternae.

• Tubules :
  

- These are irregular branched tubular structures.

- They form a network along with other elements.

• Vesicles :
  

- These are oval, rounded vacuole-like elements.

- It is often isolated in the cytoplasmic matrix.

2. There is two type of ER :

• Smooth ER or Smooth Endoplasmic Reticulum: Ribosome is not present in SER. It is generally peripheral in position & connected with the plasma membrane.
  
• Rough ER (RER) or Rough Endoplasmic Reticulum: RER is present in the Ergastoplasm. RER is generally internal in position & are connected with the nuclear envelope.
  

3. Functions of ER :

• It provides mechanical support and acts as endoskeleton or cytoskeleton of the cell.

• Sarcoplasmic Reticulum relates Ca++ which helps in muscle contraction.

• The Ca++ plays an important role in the fusion of vesicles in cell plate formation and also helps in the movement of chromosomes.

• RER in association with Golgi complex give rise to Lysosomes.

• ER keeps various cell organelles in their position.