Cell Organelles: Golgi body, Ribosome, Lysosomes, Centrosome and Micro bodies | Biology Grade XI

Science Notes

Cell Organelles: Golgi body, Ribosome, Lysosomes, Centrosome and Micro bodies

a) Golgi body:

It is also known as lipochondria or dictyosome. It arises from ER and is formed by four structures. It lies near cell membrane.

  • Cisternae: They are curved with dilated ends and are parallel to each other.
  • Vesicles:   They lie on convex side of cisternae.
  • Vacuoles:They are larger sac like structures lie on concave side of cisternae.
  • Tubules: They formed net with cisternae vesicles and vacuoles.
  • Functions of Golgi body: It forms new cell membrane, It forms cell wall components, It secrets hormones, It stores proteins and fats. It forms vesicles and lysosomes.

b) Ribosome

They are small dense granular particles of RNA and proteins. It is also known as ribonucleioproteins. They are found freely in cytoplasm and found on the surface of endoplasmic reticulum and within some cell organelles. It is not bounded by any membrane. Each particle of ribosome consists of two subunits i.e. One larger and another smaller cap like subunit over larger subunit. There are two types of ribosome

70S type

80 S type

It is smaller in size and the number of protein is 55

The ratio of RNA and protein is 2:1 Molecular weight is 2.7×106 Dalton

When it break down then it gives 50S and 30S subunits

It is found in prokaryotic cells (1 dalton = 1.6*10-24)

It is larger in size

the no of proteins is 82

The ratio of RNA and protein is 1:1 Molecular weight is 4.5*106

when it breaks down it gives 60S and 40S subunits

it is found in eukaryotic cells

Function of Ribosome: It is the site of protein synthesis, it also stores protein, and therefore ribosome is called protein Factory.

c) Lysosomes:

The lysosomes are vesicles like structures bounded by single membrane; the lysosome contains several enzymes that digest extra cellular and intra cellular substances. Lysosomes digest cell organelles causing death of cell. Therefore, it is called suicidal bag. There are four types of lysosomes

  • Primary lysosomes: The newly formed lysosomes containing inactive enzymes are called primary lysosomes.
  • Secondary lysosomes: These are formed by fusion of primary lysosomes with active enzymes, which digest unnecessary particles.
  • Tertiary lysosomes: Lysosome containing undigested food is called tertiary lysosome or residual body.
  • Auto lysosome: Lysosome which digests cell organelles is called auto lysosome.

Function of Lysosome:

It digests dead cells, it digests extra and intra cellular particles, it ingest particles.

d) Centrosome:

The centrosome is globose body, which consists of two star shaped structures called centrioles. Each centriole consists of nine rows of triplet fibrils and remains surrounded by cytoplasmic area called centrosphere. When centrosome is present at the base of flagella or cilia then it is called basal body.

Function of Centrosome:

During cell division, it produces spindle fibers; the basal bodies control the movement of cilia and flagella.

e) Micro bodies

They are small vacuole like structures, which are of following types.

  • Sphaerosomes: They are small lysosomes like structures. They contain enzymes like lysosomes, which digest lipid and other substance. They may also act as lysosomes usually present in plant cells.
  • Glyoxisomes: They are sphaerosomes like structures, which contain rod like enzymes, which digest lipid and decompose aminoacids.
  • Peroxisomes: These are microbodies, which contains two types of enzymes. The enzyme Catalases catalyses the decomposition of Hydrogen Peroxide to Water and Oxygen and The enzyme Oxidases oxidize organic compounds.

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