2. Points of Discussion
• What is Chloroplast?
• Protein translocation
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
• Chloroplasts are a type of plastid.
• Shape varies.
• Contain their own genome.
• They show maternal inheritence.
• Membrane bound organelle. Inner and Outer
• 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
• 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
• 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.
• 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
• 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).
• 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.