Structure of cell organelles

1. Nucleus

• It is round protoplasmic body and controls overall functioning of the body.
• Largest cell organelle being 2-10 µm in diameter.
• Consists of two membranes i.e. outer and inner membrane about 15nm wide, known as perinuclear space.
• 8% of surface area of nuclear membrane is occupied by pores.
• Outer membrane consists of rough endoplasmic reticulum.
• DNA is tightly coiled around histone protein and organized into complexes called chromosomes.
• Nucleolus acts as site of rRNA synthesis.

Enzymes present: DNA polymerase and RNA polymerase.

2. Mitochondria

• Powerhouse of cells.
• Sphere, rod or filamentous body.
• 5 µm diameter and 7 µm in length
• Inner membrane has large infoldings called cristae and is site of oxidative phosphorylation and electron transport involved in ATP production.
• Central matrix is the site of Citric acid cycle and fatty acid breakdown.

Enzyme present: ATP synthetase, pyruvate dehydrogenase, Adenine nucleotide translocase, glyceral 3-phosphate dehydrogenase, succinate dehydrogenase, cytochrome c oxidase.

Function

• Oxidative phosphorylation
• Conserve energy for cellular respiration and urea cycle.

3. Golgi bodies ( Dictyosomes)

• They are situated between the endoplasmic reticulum and the plasma membrane.

Function

• Glycosylation
• Acylation
• Sulphation
• Sorting and delivering
• Cell plate formation
• Synthesis of pectin in the cell wall.
• Helps in the formation of primary lysosome

Involved enzymes : Galactosyl transferase and mannosidase.

4. Endoplasmic reticulum

• Interconnected network of membrane vesicles
• Connected with nuclear membrane and is associated with ribosome
• If ribosome present à Rough ER
• If ribosome absent à Smooth ER

Function

• Transport of material
• Provide mechanical strength and support to the cell
• Cell plate formation during cytokinesis

Involved enzymes : Glucose-6-phosphatase and cytochrome-b5-reductase

5. Lysosome

• Contain hydrolytic enzymes and carryout degradation of protein, nucleic acid, lipids and carbohydrate.
• It helps in

1. a) Endocytosis: Degradation of macromolecule
2. b) Autophagy : Degradation of unwanted intercellular constituents

Involved  enzymes : Hydrolases, Acid phosphatase, Nucleases, Proteases, Lipases, Sulfatases, etc.

6. Glyoxysomes ( Only fat storing cells of plants)

• Present in cotyledon of fat storing seed.
• Helps in conversion of stored fat into carbohydrate
• Operate the series of reaction known as glyoxylate cycle

Enzymes involved: Citrate synthetase, Aconitase, Isocitrate lyase, malate synthetase, etc.

7. Chloroplast

• Contains two-unit membrane, outer and inner lipoprotineous membrane with intermembrane space.
• Intermembrane encloses stroma or matrix.
• Thylaknoid vesicles helps in absorbing light energy and converting them to ATP.
• Stroma is the CO₂ reduction site to form starch and glucose.
• Contains DNA which encode some of the chloroplast.

Enzyme involved: DNA polymerase, ribulose-1,5-biphosphate, Carboxylase oxygenase.

8. Vacuole

• Helps in removing waste materials in plant.
• Surrounding membrane tonoplast regulate the entry of ions into vacuole.
• Cell sap contains digestive enzymes that degrade and recycle macromolecular components no longer in use.
• Anthocyanin gives color to flower and fruits.

Function

• Maintain cell turgidity
• Storage function
• Act as lysosome

9. Perioxisomes

• Convert toxic hydrogen peroxide into harmless H₂O and O₂.
• Present in photosynthetic cells of higher plants and non-photosynthetic cells in gymnosperm, pteridophytes.
• Helps in photorespiration.

Involved enzymes: Catalyse, Glycollate oxidase, glutamate, urate oxidase, etc.