Rough Endoplasmic Reticulum Functions

Cytoplasm

The cytoplasm of the cell is the jelly-like material formed by 80 percent of water. It contains a clear liquid portion called cytosol and various particles of different shapes and sizes. The particles are proteins, carbohydrates, lipids or electrolytes in nature. The cytoplasm also contains many organelles with distinct structures and functions.

The cytoplasm is made up of two zones:

1. Ectoplasm: The peripheral part of cytoplasm situated just beneath the cell membrane
2. Endoplasm: Inner part of cytoplasm interposed between the ectoplasm and the nucleus.

Organelles In Cytoplasm

Cytoplasmic organelles are the cellular structures embedded in the cytoplasm. The organelles are considered as small organs of the cell. Some organelles are bound by limiting membranes and others do not have limiting membranes. Each organelle is having a definite structure and specific function.

Read And Learn More: Medical Physiology Notes

1. Endoplasmic Reticulum:

• The endoplasmic reticulum is a network of tubular and microsomal vesicular structures which are interconnected- ted with one another. It is covered by a limiting membrane which is formed by proteins and bilayered lipids.
• The lumen of the endoplasmic reticulum contains a fluid medium called an endoplasmic matrix. The diameter of the lumen is about 400 to 700Å. The endoplasmic reticulum forms the link between the nucleus and cell membrane by connecting the cell membrane with the nuclear membrane.

Types of Endoplasmic Reticulum: The endoplasmic reticulum is of two types namely, rough endoplasmic reticulum and smooth endoplasmic reticulum. Both types are interconnected and continuous with one another. Depending upon the activities of the cells, the rough endoplasmic reticulum changes to the smooth endoplasmic reticulum and vice versa.

Rough Endoplasmic Reticulum: It is the endoplasmic reticulum with a rough, bumpy or bead-like appearance. The rough appearance is due to the attachment of granular ribosomes to its outer surface. Hence, it is also called the granular endoplasmic reticulum Rough endoplasmic reticulum is vesicular or tubular in structure.

Functions of Rough Endoplasmic Reticulum:

• Synthesis of proteins:
  • The rough endoplasmic reticulum is concerned with the synthesis of proteins in the cell. It is involved with the synthesis of mainly those proteins which are secreted from the cell such as insulin from ẞ cells of islets of Langerhans in the pancreas and antibodies from B lymphocytes.
  • The ribosomes arrange the amino acids into small units of proteins and transport them into the rough (cancer-producing substances) in the liver. endoplasmic reticulum. Here, the carbohydrates are added to the protein units forming the glycosylated proteins or glycoproteins which are arranged in the form of reticular vesicles.
  • These vesicles are transported mainly to the Golgi apparatus for further modification and processing. Some of the vesicles are transported to other cytoplasmic organelles.
• Degradation of worn-out organelles: Rough endoplasmic reticulum also plays an important role in the degradation of worn-out cytoplasmic organelles like mitochondria. It wraps itself around the worn-out organelles and forms a vacuole which is often called the auto-phagosome. Autophagosome is digested by lysosomal enzymes (see below for details).

Smooth Endoplasmic Reticulum: It is the endoplasmic reticulum with a smooth appearance. It is also called agranular reticulum. It is formed by many interconnected tubules. So, it is also called tubular endoplasmic reticulum.

Functions of Smooth Endoplasmic Reticulum:

• Synthesis of nonprotein substances: Smooth endoplasmic reticulum is responsible for the synthesis of nonprotein substances such as cholesterol and steroid. This type of endoplasmic reticulum is abundant in cells that are involved in the synthesis of lipids, phospholipids, lipoprotein substances, steroid hormones, sebum, etc. In most of the other cells, the smooth endoplasmic reticulum is less extensive than the rough endoplasmic reticulum.
• Role in cellular metabolism: The outer surface of the smooth endoplasmic reticulum contains many enzymes which are involved in various metabolic processes of the cell.
• Storage and metabolism of calcium: Smooth endoplasmic reticulum is the major site of storage and metabolism of calcium. In skeletal muscle fibers, it releases calcium which is necessary to trigger muscle contraction.
• Catabolism and detoxification of toxic substances

It is also concerned with catabolism and detoxification of toxic substances like some drugs and carcinogens