cp DNA Chloroplast DNA definition and function

cpDNA or ctDNA: DNA present in chloroplast is called cpDNA

Plastid Genome

Exist in multiple copies

• Each chloroplast has several nucleoid regions containing 8-10 DNA molecules
• ds circular DNA
• Genome size 120-150 kb of DNA
• 46-90 protein coding genes, 2 rRNA  and over 30 tRNA genes.
• Generally lack introns




• Highly conserved throughout plant species

Chloroplast- Function

Chloroplast

Photosynthesis and photorespiration

• Grana: Light reaction or synthesis of ATP and NADPH (code LG: light reaction at grana)
• Stroma: Dark reaction or CO₂ fixation using energy  (ATP and NADPH) synthesised during light reaction
• Thylakoid lumen: H₂O splitting complex. 

Similarity between chloroplast and prokaryotes 

(That supports Endosymbiont theory)

• Circular ds DNA.
• Not covered by a membrane (nucleoid region).
• Not associated with histone proteins.
• Generally introns are absent.
•  Small 70 S ribosomes.
• Protein synthesis initiated by formyl methionyl tRNA (f-met tRNA).
• Replication, transcription and translation similar to bacteria.
• Transcription and translation are similar in chloroplasts and eubacteria: most chloroplast genes are transcribed as polycistronic units, their mRNAs are not capped, no poly(A) tails are added, and they possess a Shine Dalgarno ribosome binding sequence. 
• The RNA polymerase of liverworts contains α and β subunits and the amino acid sequence has great similarity to those of E.coli.
• DNA sequences in cyanobacteria which supports the endosymbiotic theory. Most cpDNA evolves slowly in sequence and structure. 

Endosymbiont theory