2. Introduction:
ο Chloroplasts, the organelles responsible for photosynthesis, are in
many respects similar to mitochondria.
ο Both chloroplasts and mitochondria function to generate metabolic
energy.
ο Both have evolved by endosymbiosis, both contain their own
genetic systems, and both replicate by division.
3. The Structure and Function of Chloroplasts:
ο Plant chloroplasts are large organelles (5 to 10 Micrometer long).
ο Chloroplasts, are bounded by a double membrane called the
chloroplast envelope.
ο Chloroplasts have a third internal membrane system, called the
thylakoid membrane.
4.
5. ο The thylakoid membrane forms a network of flattened discs
called thylakoids, which are frequently arranged in stacks
called grana.
ο Thylakoids exist in the open space of the chloroplast known as
the stroma.
6. ο Three membranes divide chloroplasts into three distinct
internal compartments:
ο (1) the intermembrane space between the two membranes of
the chloroplast.
ο (2) the stroma, which lies inside the envelope but outside the
thylakoid membrane.
ο (3) the thylakoid lumen.
7. ο The outer membrane of the chloroplast envelope, like that of
mitochondria, contains porins and is therefore freely permeable to
small molecules.
ο The chloroplast stroma is also equivalent in function to the
mitochondrial matrix:
8. The Chloroplast Genome:
ο The genomes of chloroplasts consist of circular DNA molecules
present in multiple copies per organelle.
ο However, chloroplast genomes are larger and more complex than
those of mitochondria, ranging from 120 to 160 kb and containing
approximately 150 genes.
9. ο The chloroplast genome also encodes approximately 30 proteins
that are involved in photosynthesis.
ο Ribulose 1,5 bisphosphate carboxylase (Rubisco) is encoded by
chloroplast DNA.
10. ο Starch granules are very common in chloroplasts.
ο The chloroplast stroma contains many proteins, though the
most common and important protein is RuBisCO.
11. ο The thylakoid membranes are important protein complexes which
carry out the light reactions of photosynthesis.
ο Photosystem II and photosystem I contain light-harvesting
complexes with chlorophyll and carotenoids that absorb light
energy and convert to chemically.
12. Chlorophylls:
ο Chlorophyll a is found in all chloroplasts, as well as their
cyanobacterial ancestors. Chlorophyll a is a blue-green
pigment.
ο Chlorophyll b found only in the chloroplasts of plants, green
algae.
ο Chlorophyll c is mainly found in secondary endosymbiotic
chloroplasts that originated from a red alga,
