Chloroplasts are organelles found in plants and algae that carry out photosynthesis. They have an inner and outer membrane, with an intermembrane space between them. Inside is the stroma, which contains thylakoids that are arranged in stacks called grana. Chloroplasts contain their own genome and divide independently. According to the endosymbiotic theory, chloroplasts originated from cyanobacteria that were engulfed by other cells but not destroyed. Chloroplasts import most proteins from the cytosol through translocation complexes in the inner and outer membranes. They perform photosynthesis through light and dark reactions, using solar energy to fix carbon dioxide and produce oxygen and carbohydrates.

1. Presentation by Debashish
Chakrabarty
M.Sc 1st Sem (SLS)-CUG
CHLOROPLASTS

2. Points of Discussion
• What is Chloroplast?
• Structure
• Endosymbiosis
• Genome
• Protein translocation
• Division
• Functions

3. What is a Chloroplast ?
• Chloroplasts are the organelles present within
plants and algae which carry out photosynthesis.
Where solar energy is utilized to fix CO2 to
synthesize carbohydrates. In this process O2 is
released.
• Chloroplasts are a type of plastid.
• Shape varies.
• Contain their own genome.
• They show maternal inheritence.

4. STRUCTURE
• Membrane bound organelle. Inner and Outer
membrane.
• Inter membrane space is present between Inner
and outer membrane.
• Inner membrane encloses a matrix called stroma.
• Another membrane bound structure called
Thylakoids are present within the stroma.
• Thylakoids are arranged as stacks to form the
granum.
• Stroma lamellae connects the granum.

7. ENDOSYMBIOTIC THEORY
• According to this theory several organelles of
eukaryotes originated as symbioses between
separate single celled organisms.
• Cyanobacteria is considered the ancestor of
chloroplasts.
• The new cellular resident provided the food for
host, hence weren’t eliminated.
• Can be divided into Three lineages:-
Glaucophyte, Red algal and Green chloroplast.

9. GENOME
• Contains their own genome, called ctDNA.
• Earlier thought to be circular but now considered
mostly linear, size is 120kbp to 170kbp.
• Distributed in several clusters called nucleoid.
• Most of the genes have been transferred to the
host nucleus.
• Proteins contain parts both from nuclear and
chloroplast encoded genes.

10. PROTEIN TRANSLOCATION
• The vast majority of chloroplast proteins are
imported from the cytosol.
• The outer and inner envelope membranes
contain distinct translocation complexes (Toc and
Tic complexes, respectively).
• Chaperones aid in the unfolding of the
polypeptides in the cytosol and folding of the
proteins in the chloroplast.
• Most proteins destined for the chloroplast are
synthesized with a removable N-terminal signal
sequence (termed the transit peptide).

11. PROTEIN TRANSLOCATION

12. PROTEIN TRANSLOCATION INTO THYLAKOIDS

13. CHLOROPLAST DIVISION

14. FUNCTIONS
• Main function is photosynthesis.
• 2 phases light reaction and dark reaction.
• Photosystems are involved in light reaction, that
synthesize ATP and NADPH. O2 is released.
• Dark reaction utilizes the product of light
reactions to fix CO2.
• Starch synthesis occurs within the stroma.
• Some of the intermediates are transported to
cytosol for sucrose synthesis.

15. LIGHT REACTION

16. DARK REACTION

17. THANK YOU