chloroplast DNA

CHLOROPLAST DNACHLOROPLAST DNA

SUMYYA SADIQM.Phil II

CHLOROPLASTCHLOROPLAST

organelle found in plant cells and eukaryotic algae

conduct Photosynthesis Chloroplasts are green....chlorophyll

 pigment

STRUCTURE

Chloroplast ultrastructure:1. outer membrane2. intermembrane space3. inner membrane (1+2+3: envelope)4. stroma (aqueous fluid)5. thylakoid lumen (inside of thylakoid)6. thylakoid membrane7. granum (stack of thylakoids)8. thylakoid (lamella)9. starch10. ribosome11. plastidial DNA12. plastoglobule (drop of lipids)

Chloroplast genome Chloroplast DNA (cpDNA) is also known as

plastid DNA (ptDNA). Circular double stranded DNA molecule Ct genomes are relatively larger 140kb in higher plants. 200kb in lower eukaryotes. Multiple copies of genome per organelle. Vary in size , But are large enough to code 50-100

proteins as well as rRNAs & tRNAs

cpDNA regions includes Large Single-Copy (LSC) & Small Single-Copy (SSC) regions, and Inverted Repeats (IRA & IRB).

Variation in length mainly due to presence of inverted repeat (IR)

Conifers and a group of legumes lack Inverted Repeats.

GENOME SEQUENCING:

GENOME SEQUENCING Two of the first ct

genome sequenced

- liverwort, Marchantia polymorpha.

- tobacco, Nicotiana tabacum.

Tobacco DNA is larger , contains 150 genes

and that of liverwort is 134.

BASIC GENES:

Gene for rRNAs, tRNAs, ribosomal proteins. Polypeptide components of the photosystem- involved in capturing sunlight. Catalytically active subunit of enzyme RuBP carboxylase. 4 subunits of chloroplast specific RNA polymerase.

Molecular Systematics on cpDNAMolecular Systematics on cpDNA

cpDNA regions can be amplified by means of PCR.

The resulted PCR products may be subjected to RFLP or DNA sequencing.

Common cpDNA regions used in systematic study:

rbcL (1400bp), trnL-trnF (250-800bp), atpB-rbcL (1000bp), trnL intron (300bp), matK (2600bp), trnT-trnL (400-800bp), 16S (1400bp), rpoC (3600bp) etc.

Chloroplast replication

Molecular mechanism is unknow Independent of nuclear replication plastome copies are greatly amplified in mesophyll cells of the developing leaf and can reach values of more than 20,000 cell The dual D-loop model for the initiation of chloroplast DNA replication

1:Unidirectional elongation of nascent strand initiated from both origins

2:Unidirectional fork movement toward each other

3: Fusion of D-loops to Cairn type intermediates

4: Bidirectional, semi-discontinuous replication

5: Resulting daughter molecules.

ENZYMES INVOLVED IN CtDNA REPLICATION

These include : DNA polymerase(s), DNA unwinding activity (helicase), Primase and/or RNA polymerase, Single stranded DNA binding protein Topoisomerase I and II, Origin recognition protein(s).

PROPERTIES of ctDNA:i. Non- mendelian inheritanceii. Self replicationiii. Somatic segregation in plantsiv. Inherited independently of nuclear

genesv. Conservative rate of nucleotide

substitution enables to resolve plant phylogenetic relationships at deep levels of evolution. eg. familial level; mono- dicotyledonous