Chloroplasts are organelles found in plant cells and algae that are responsible for photosynthesis. They have a double membrane and internal thylakoid membranes that form stacks called grana. The thylakoids contain chlorophyll and protein complexes that absorb light energy and convert it chemically during photosynthesis. Chloroplasts have their own DNA and encode approximately 30 proteins involved in photosynthesis, including the important RuBisCO protein. They are similar to mitochondria in that they both generate energy and contain their own genetic material.

1. Chloroplast
 By
 Dr. Harinatha Reddy Aswartha

2. Introduction:
 Chloroplasts, the organelles responsible for photosynthesis, are in
many respects similar to mitochondria.
 Both chloroplasts and mitochondria function to generate metabolic
energy.
 Both have evolved by endosymbiosis, both contain their own
genetic systems, and both replicate by division.

3. The Structure and Function of Chloroplasts:
 Plant chloroplasts are large organelles (5 to 10 Micrometer long).
 Chloroplasts, are bounded by a double membrane called the
chloroplast envelope.
 Chloroplasts have a third internal membrane system, called the
thylakoid membrane.

5.  The thylakoid membrane forms a network of flattened discs
called thylakoids, which are frequently arranged in stacks
called grana.
 Thylakoids exist in the open space of the chloroplast known as
the stroma.

6.  Three membranes divide chloroplasts into three distinct
internal compartments:
 (1) the intermembrane space between the two membranes of
the chloroplast.
 (2) the stroma, which lies inside the envelope but outside the
thylakoid membrane.
 (3) the thylakoid lumen.

7.  The outer membrane of the chloroplast envelope, like that of
mitochondria, contains porins and is therefore freely permeable to
small molecules.
 The chloroplast stroma is also equivalent in function to the
mitochondrial matrix:

8. The Chloroplast Genome:
 The genomes of chloroplasts consist of circular DNA molecules
present in multiple copies per organelle.
 However, chloroplast genomes are larger and more complex than
those of mitochondria, ranging from 120 to 160 kb and containing
approximately 150 genes.

9.  The chloroplast genome also encodes approximately 30 proteins
that are involved in photosynthesis.
 Ribulose 1,5 bisphosphate carboxylase (Rubisco) is encoded by
chloroplast DNA.

10.  Starch granules are very common in chloroplasts.
 The chloroplast stroma contains many proteins, though the
most common and important protein is RuBisCO.

11.  The thylakoid membranes are important protein complexes which
carry out the light reactions of photosynthesis.
 Photosystem II and photosystem I contain light-harvesting
complexes with chlorophyll and carotenoids that absorb light
energy and convert to chemically.

12. Chlorophylls:
 Chlorophyll a is found in all chloroplasts, as well as their
cyanobacterial ancestors. Chlorophyll a is a blue-green
pigment.
 Chlorophyll b found only in the chloroplasts of plants, green
algae.
 Chlorophyll c is mainly found in secondary endosymbiotic
chloroplasts that originated from a red alga,