Chloroplast dna

1. CHLOROPLAST- DNA ( cpDNA ) PRESENTED BY: Noopur Joshi ( M.Sc . I Semester) DEPARTMENT: Biotechnology

2. INTRODUCTION TO CHLOROPLAST Chloroplasts are the most widely distributed plastids and one of the most important of all. Their shapes vary from filamentous, saucer shape to discoid or club shaped. Generally, they measure 2-3µm in thickness & 5-10µm in diameter, however this measure changes with the specie. Their no. in a cell remains constant for a specie but may also vary with the specie and within the specie.

3. CHLOROPLAST AS A SEMI-AUTONOMOUS ORGANELLE

4. RIBOSOMES OF CHLOROPLAST: Are smaller than the cytoplasmic ribosomes . Are of 70S type and resemble to those of bacterial ribosomes . They consist of two ribosomal RNAs; 23S rRNA and 16S rRNA . Polysomes have also been reported to be found in the chloroplast. Aminoacyl-tRNAs , aminoacyl-tRNA synthetases and methionyl-tRNA are also found in chloroplast.

5. cpDNA : Salient Features

6. Ris and Plant(1962),first reported DNA molecules in the chloroplast of Chlamydomonas . The DNA molecule here is genreally double helical, Average length: 45µm i.e. about 135,000 bp Replication of chloroplast DNA has been followed with ³H-thymidine. Genetic maps of chloroplast DNA have been successfully made by the use of restriction enzymes.

7. The chloroplast DNA ( cpDNA ) codes for following: Choloroplast mRNA Chloroplast rRNA Chloroplast tRNA Chloroplast ribosomal protiens Certain structural proteins of thyllakoid membranes. The larger subunits of C Dase enzyme which weighs about 55,000D

8. In higher plants, cpDNAs range in size from 120-160kb . In algae: 85-292kb choloroplast genomes are found where the cpDNa is circular. In 2 species of green algae of genus Acetabularia , the cpDNAs appear to be huge; about 2000kb. The large single chloroplast of Chlamydomonas reinhardtii contains about 200 copies of the cpDNA .

9. All the chloroplast genomes analyzed till now contain the same set of genes, but with these arranged very differently on the cpDNAs Genes present on cpDNAs can be grouped into 2: Those that encode for the components of chloroplast protein biosynthetic apparatus: RNA pol subunits, structural components of chloroplast ribosome subunits Set of tRNAs

10. 2) Those specifying the components of the photosynthetic machinery:- PS I PS II ETC The chloroplast genomes of higher plants are about one-20 th to one-30 th the size of the genomes of the prokaryotic genomes, from whcich they are believed to have evolved( cyanobacteria ). THUS, chloroplasts have lost much of the genetic information of their ancestors, and have become dependent much on nuclear genes of the host cell for many essential components.

11. Comparative studies of chloroplast genomes have provided information about the evolutionary relationship of plant and algal species. J.D.Palmer has distinguished 6 major lines of chloroplast evolution. The chloroplast genomes present in different evolutionary lines contain nearly the same genes but in different arrangementson the cpDNA molecules.

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