CELL ORGANELLES - 2

PLASTIDS

• present in the plant cells
• bear some specific pigments -- specific colours to the plants.
• Based on the type of pigments plastids can be classified into chloroplasts, chromoplasts and leucoplasts.

• The chloroplasts contain chlorophyll and carotenoid pigments -- trap light energy essential for photosynthesis.
• In the chromoplasts, fat soluble carotenoid pigments like carotene, xanthophylls and others are present.

• The leucoplasts -- no pigments --colourless 
• store nutrients 1. amyloplasts - store carbohydrates
• 2. elaioplasts store oils and fats, 3. aleuroplasts store proteins.

• Chloroplasts of the green plants are found in the mesophyll cells of the leaves.

• The chloroplasts are double membrane bound.
• The space limited by the inner membrane of the chloroplast -- stroma.
• A number of organised flattened membranous sacs -- thylakoids.
• Thylakoids are arranged in stacks like the piles of coins called grana.
• There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.
• The membrane of the thylakoids enclose a space -- lumen.
• stroma -- enzymes, double stranded DNA molecules, ribosomes.

RIBOSOMES

• Ribosomes are the granular structures composed of ribonucleic acid (RNA) and proteins.
• The eukaryotic ribosomes are 80S
• ‘S’ stands for the sedimentation coefficient - indirectly is a measure of density and size.

CYTOSKELETON

• An elaborate network of filamentous proteinaceous structures -- in the cytoplasm.
• Function- provides mechanical support, motility, and maintains the shape of the cell.