Chloroplasts

Presentation by DebashishChakrabartyM.Sc 1st Sem (SLS)-CUG

CHLOROPLASTS

Points of Discussion

• What is Chloroplast?• Structure• Endosymbiosis• Genome• Protein translocation• Division• Functions

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 tosynthesize carbohydrates. In this process O2 isreleased.

• Chloroplasts are a type of plastid.• Shape varies.• Contain their own genome.• They show maternal inheritence.

STRUCTURE

• Membrane bound organelle. Inner and Outermembrane.

• Inter membrane space is present between Innerand 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.

ENDOSYMBIOTIC THEORY

• According to this theory several organelles ofeukaryotes originated as symbioses betweenseparate single celled organisms.

• Cyanobacteria is considered the ancestor ofchloroplasts.

• The new cellular resident provided the food forhost, hence weren’t eliminated.

• Can be divided into Three lineages:-Glaucophyte, Red algal and Green chloroplast.

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.

PROTEIN TRANSLOCATION

• The vast majority of chloroplast proteins areimported from the cytosol.

• The outer and inner envelope membranescontain distinct translocation complexes (Toc andTic complexes, respectively).

• Chaperones aid in the unfolding of thepolypeptides in the cytosol and folding of theproteins in the chloroplast.

• Most proteins destined for the chloroplast aresynthesized with a removable N-terminal signalsequence (termed the transit peptide).

PROTEIN TRANSLOCATION

PROTEIN TRANSLOCATION INTO THYLAKOIDS

CHLOROPLAST DIVISION

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.

LIGHT REACTION

DARK REACTION

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