CHLOROPLAST organelle found in plant cells and eukaryotic algae conduct Photosynthesis Chloroplasts are green....chlorophyll pigment
STRUCTURE Chloroplast ultrastructure: 1. outer membrane 2. intermembrane space 3. inner membrane (1+2+3: envelope) 4. stroma (aqueous fluid) 5. thylakoid lumen (inside of thylakoid) 6. thylakoid membrane 7. granum (stack of thylakoids) 8. thylakoid (lamella) 9. starch 10. ribosome 11. plastidial DNA 12. 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, ribosomalproteins. Polypeptide components of thephotosystem- involved in capturingsunlight. Catalytically active subunit of enzymeRuBP carboxylase. 4 subunits of chloroplast specific RNApolymerase.
Molecular 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 inmesophyll cells of the developing leaf and canreach values of more than 20,000 cell The dual D-loop model for the initiationof 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
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