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.
5. 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.
7. • 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.
8. 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
9. • 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.
10. • 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:
1) Those that encode for the components of
chloroplast protein biosynthetic apparatus:
RNA pol subunits,
structural components of chloroplast ribosome
subunits
Set of tRNAs
11. 2) Those specifying the components of the
photosynthetic machinery:-
PS I
PS II
ETC
• The chloroplast genomes of higher plants are
about one-20th to one-30th 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.
12. • 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.
