Ultrastructure of chloroplast

Chloroplast is essential pigment for photosynthesis.

1. ULTRASTRUCTURE OF CHLOROPLAST By: Mr. Porwal Nikhil Balbhim Arts, Science & Commerce College, Beed . MH

2. CHLOROPLAST ENVELOPE OR PERISTOMIUM Outermost, protective covering of chloroplast Double layered made up of outer and inner membrane Outer and Inner membrane made up of lipid and protein ( lipoproteinaceous ) Both membranes are smooth, continuous and selectively permeable Each membrane is 40 – 60 A° (4 – 6 nm) in thickness Space between two membrane is called periplastidal space or intermembrane space which is 100 – 300 A° (10 – 30 nm) width It is filled with watery fluid called as periplastidal fluid. Lack of chlorophyll pigment and cytochromes Help in transport of substance in and out of chloroplast

3. STROMA: Internally, Chloroplast contain colourless, proteinaceous , gel like colloidal fluid called stroma or matrix Contains all three enzymes needed for dark reaction of photosynthesis mainly Rubisco Also contain 70S type of ribosome, lipophilic granules made up of Vit . K, DNA and RNA Starch grain also present DNA of chloroplast (ct DNA) is naked, double stranded and circular molecules also called plastidome Self replicating and show transcription Presence of nucleic acid makes the chloroplast semiautonomous, self replicating, self regulating organelle It is the site of dark reaction i . e. second phase of photosynthesis it acts as site for synthesis of carbohydrates

4. GRANA: Small, dark, cylindrical, granular sacs are present in stroma called as grana Chloroplast have 40 – 100 grana Each granum consist of stack of 2 – 100 disclike , flat, membranous sacs called thyalkoids Thylakoids are placed one above the other like a stack of coins. Thylakoid membranes are called grana lamellae or fret membrane Space present in grana thylakoids is called loculus Thylakoid contains photosynthetic pigment molecules, carrier compounds and enzymes necessary for light reaction Grana is the site for light reaction i.e 1 st phase of photosynthesis Acts as site for synthesis of ATP, release of O2, trapping of light energy Grana lamellae contains both the pigment systems PS – I and PS – II

5. INTERGRANA LAMELLAE OR STROMA LAMELLAE: Grana are connected with each other by colourless, membranous structures called intergranna lamellae or fret lamellae The sapce present in the stroma lamellae is called fret channel They contains CO2 fixing enzymes and helps in fixation of atmospheric CO2 Stroma lamellae contains only PS – I and helps in transport of materials QUANTASOMES: Many small, rounded, flat structures present in thylakoid are called quantasomes or oblate particles Term coined by Parks and Biggins in 1964 They measures about 180 x 110 x 120 Aº Each quantasome contains about 230 – 250 photosynthetic pigment molecules (160 chl.a + 70 chl.b and 50 carotenoids ) Chlorophyll a acts as reaction centre and present in the centre

6. PHOTOSYNTHETIC APPARATUS IN PROKARYOTES: Chloroplast is absent They bear membranous sacs called thylakoids Thylakoids forms photosynthetic apparatus called as chromatophores Lie freely in cytoplasm or may connected with plasmamembrane Pigments are evenly distributed on or inside thylakoid membrane