Dr.S.KARTHIKUMAR Associate Professor Department of Biotechnology Kamaraj College of Engineering and Technology, K.Vellakulam-625701, TN, India Email: skarthikumar@gmail.com

1. Chloroplasts
Chloroplasts

2. Introduction
• Plants – Producers
• Contains plastids - manufacturing and storing of food
• Three types of plastids –
• Chromoplasts- They are the colour plastids, found in all flowers, fruits and are mainly
responsible for their distinctive colours.
• Chloroplasts- They are green coloured plastids, which comprise green-coloured pigments
within the plant cell and are called chlorophyll.
• Leucoplasts- They are colourless plastids and are mainly used for the storage of starch, lipids
and proteins within the plant cell.
• Chloroplast is an organelle that contains the photosynthetic pigment chlorophyll that captures
sunlight and converts it into useful energy, thereby, releasing oxygen from water. “

3. Structure

4. Structure
• oval or biconvex
• size - 4-6 µm in diameter and 1-3 µm in thickness
• double-membrane organelle with the presence of outer, inner and intermembrane space
• Grana are made up of stacks of disc-shaped structures known as thylakoids or lamellae
• Stroma is the homogenous matrix which contains grana and is similar to the cytoplasm in cells in
which all the organelles are embedded. Stroma also contains various enzymes, DNA, ribosomes,
and other substances

5. • Membrane Envelope
• It comprises inner and outer lipid bilayer membranes. The inner membrane separates the stroma from the
intermembrane space.
• Intermembrane Space
• The space between inner and outer membranes.
• Thylakoid System (Lamellae)
• The system is suspended in the stroma. It is a collection of membranous sacs called thylakoids or lamellae.
The green coloured pigments called chlorophyll are found in the thylakoid membranes. It is the sight for the
process of light-dependent reactions of the photosynthesis process. The thylakoids are arranged in stacks
known as grana and each granum contains around 10-20 thylakoids.
• Stroma
• It is a colourless, alkaline, aqueous, protein-rich fluid present within the inner membrane of the chloroplast
present surrounding the grana.
• Grana
• Stack of lamellae in plastids is known as grana. These are the sites of conversion of light energy into
chemical energy.
• Chlorophyll
• It is a green photosynthetic pigment that helps in the process of photosynthesis.

6. Functions of Chloroplast
• to synthesise food by the process of photosynthesis
• To absorbs light energy
• To produces NADPH and molecular oxygen (O2) by photolysis of water and
converts it into chemical energy
• To produces ATP
• Stroma contains soluble enzymes known as rubisco (ribulose
bisphosphate carboxylase-oxygenase), accountable for upto 50% of
the total leaf proteins.

7. Chloroplast DNA
• Chloroplast DNA is comparatively large, circular in nature,
commonly denoted as ctDNA.
• The presence of DNA in chloroplast was first identified in 1962.
• The size of chloroplast DNA is usually 140 kb in higher plants
and less than 190 kb in lower eukaryotic plants.
• However, the size of the ctDNA is generally between 120 and 155
kb.
• The size of the chloroplast genome can be comparable to
bacteriophage T4 (165 kb)
• Unlike nuclear DNA, it does not contain 5-methyl cytosine and
is not associated with histones.
• G + C ratio to approximately 37 per cent

9. • DNA replication in plastid is semi conservative.
• In chloroplasts of maize and pea, DNA replication begins at two
sites about 7000 base pairs apart and proceeds in both the
directions.
• Chloroplasts contain introns.
• They fall into two classes. One of the intron classes is located in
tRNA genes and another class in protein coding region.
• Several photosynthetic related genes that encode proteins are
located in thylakoid membrane

10. • Several evidences confirmed that chloroplast DNA contains 45
genes coding for RNA and 27 genes coding for proteins.
• These proteins are mainly involved in chloroplast gene
expression.
• The genes coding for proteins of the thylakoid membrane and
another 10 gene products are committed for electron transport
process.

11. • A restriction map
for maize
chloroplast DNA
(139 kb) reveals
that plastome
contains unique
22,000 base pair
inverted repeated
sequence,
containing the
rRNA genes

12. • Ribosomes of chloroplast show sedimentation coefficient of 70 S
Svedberg units, i.e., 70 S.
• The ribosomes of cytoplasm exhibits 80 S.
• The 70 S ribosomes are made up of 23 S and 16 S.
• Presence of 70 S ribosomes in chloroplast have a resemblance to
prokaryotic ribosome, clearly strengthens the hypothesis of its
prokaryotic origin.
• Plastid contains tRNA synthetase enzymes. The presence of
plastid tRNA is able to charge all of the 20 protein amino acids.
Synthesis of protein in chloroplast utilizes normal genetic code.

13. • genes are transcribed as a polycistronic RNA, which is a
precursor RNA undergoes modification to produce mature
tRNA and rRNA
• Post-transcriptional processing of rRNA such as intron splicing,
generation of a number of RNA fragments, the ligation of RNA
sequence takes place.
• Information on the synthesis and processing of chloroplast
mRNA is meagre.
• They seem to be devoid of 5′ cap and do not contain long region
of polyadenylic acid at the 3′ end.
• Some reports suggested that chloroplast mRNA may contain
short runs of oligo A.
• There are two putative promoter regulatory sequences
(TTGATA and TATGA)

14. THANK YOU