Chloroplast GenomeChloroplast Genome

- organelle found in plant cells and eukaryotic algae

- Photosynthesis

ChloroplastChloroplast

Structure of chloroplast

• Lens shaped ,5-10 um long

• Soluble phase –stroma –CO2

• Memrane phase –thylakoids -Photosynthesis

• Other functions –amino acid,nucleic acid,pigments , hormones synthesis and nitrate reduction

Cp Genetics

• Maternal inheritance –Genes for a paricular character are only transmitted through the female parent.

• Rely on nuclear genomes-Not autonomous

• Both nuclear and Cp –code for polypeptides which form the part of same enzyme

• Sexual recombination does not occur

Cp DNA

• Ris and Plaut in 1962

• Ds circular molecule, lack of 5methyl cytosine and not complexed with histones.

• Genome sizes varies Chloroplast genome size ranges 120-217kb with majority of plants fall into 120-160kb. (Pelargonium has a chloroplast genome size 217kb

• 5-10 % OF TOTAL SIZE OF THE GENOME

• contain about 100 genes to synthesize proteins

• cpDNA regions includes Large Single-Copy (LSC) & Small Single-Copy (SSC) regions, and Inverted Repeats (IRA & IRB-codes for rRNA and Trna(20-50 kb)

• Conifers and a group of legumes lack Inverted Repeats. Chloroplast DNA is passed on from one generation to the next with only an occasional mutation altering the molecule;.

Chloroplast genomeChloroplast genome

IRA

IRB

LSC

SSC

chloroplast DNA sequences of four land plants (Nicotiana tabacum(122 genes & 146 genes with IR)Marchantia polymorpha, Oryza sativa and Epifagus virginiana) are available At present, the number of complete chloroplast genome sequences is 122 (from 114 different organisms).

Ribulosebisphosphate carboxylase /oxygenase(large subunit-LSC and small nuclear genome)

Six Subunits of F-ATP synthase Sub units of PI & PII ,cytochrome bf and NADH Contains introns 4 r-RNA (4.5S, 5S 16S AND 23S r-RNA) Ribosomes 70s 30 t-RNA s

Chloroplast genomeChloroplast genome

r-RNA of Ct DNA

IRA

IRB

LSC

SSC

rbcL

matK

atpB-rbcL

trnL intron

trnL-trnF

trnT-trnLrpoC

16S

• 2 RNA Polymerases

• Transcription of plastid gene for subunits of the photosynthetic complex

• It is insensitive to rifampicin

• RNA Polymerase from nuclear encoded is derived from duplication of mt DNA

• It transcribes HK genes

• Plastid gene contain 2 promoters like bacteria

• Polycistronic

• Operon

Mitochondrial DNA

Feature of Mt DNA

• 47% g+c

• organelle found in eukaryotic cells

• cellular respiration – ATP production

• Maternally inherited .

• Mt DNA is circular and DS

• The size of the genome varies

• Large DNA molecules and several small ones

Mt DNA

• It has very less info due to its repetitive sequences

• Lot of junk genes

• In Brassica campestris the main chromosome is 218 kb which is separated into 135kb and 83

• These 135 and 83 exist as separate circles

• The first sequence located is encoding sequences of RNA –78s RNA (26,18,5s RNA)

• Promiscuous DNA

• Mt DNA codes for cytochrome c and f,

• Mt DNA don’t use universal code

• Mt DNA contains Plasmid like genes(ccc)

• The function –SENESENCE

• Encodes translation machinery apparatus(3r-RNA and 10 proteins)

• Promoters are heterogenous

• m-RNA didnt contain correct info.

• RNA editing