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Discovery and Characteristics of Chloroplast DNA

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Chloroplast DNA (cpDNA) is crucial for photosynthesis in plants and certain protists. Discovered biochemically in 1959, cpDNA is a circular molecule with a size of 120,000 to 170,000 base pairs. It encodes around 100 genes, mainly for photosynthesis and protein synthesis. The chloroplast genome has reduced over time due to endosymbiotic gene transfer to the nuclear genome, yet it remains essential for the organelle's function. Proteins required by chloroplasts are mostly encoded by nuclear genes and targeted to the organelle through specific translocon complexes.

Discovery and Characteristics of Chloroplast DNA

Chloroplasts are essential organelles found in plant cells and certain protists, where they perform photosynthesis. Each chloroplast contains its own DNA, known as chloroplast DNA (cpDNA), which is separate from the nuclear DNA of the cell. The existence of cpDNA was first confirmed biochemically in 1959 and later visualized using electron microscopy in 1962. These discoveries, coupled with the identification of chloroplast ribosomes and the organelle's ability to synthesize proteins, have led to the recognition of chloroplasts as semi-autonomous organelles with their own genetic systems. The first complete chloroplast genome was sequenced in 1986, and since then, the genomes of many species, primarily land plants and green algae, have been sequenced. It is important to note that the sequencing efforts have been less extensive for other algal groups, such as glaucophytes and red algae, which may affect our understanding of the diversity of cpDNA structures and gene content.
Bright green leaf in the foreground with visible vein network, solar reflections and natural blurred background.

Molecular Structure and Replication of Chloroplast DNA

Chloroplast DNA is generally found as a single, circular molecule, although linear and branched forms can also occur. The size of cpDNA varies from 120,000 to 170,000 base pairs, corresponding to a physical length of about 30–60 micrometers and a mass of roughly 80–130 million daltons. The cpDNA molecule often contains two inverted repeats that separate the genome into a large single-copy region and a small single-copy region. These repeats, while not identical, are conserved across many plant species, suggesting they play a role in the genome's stability. The replication of cpDNA is complex and not entirely understood, but it is believed to involve the double displacement loop (D-loop) mechanism, and in some cases, homologous recombination, particularly in species with linear cpDNA molecules.

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00

______ are vital components in plant cells and some protists, responsible for ______.

Chloroplasts

photosynthesis

01

The first complete ______ genome was sequenced in the year ______, paving the way for further genomic studies.

chloroplast

1986

02

cpDNA size range in base pairs

Chloroplast DNA varies from 120,000 to 170,000 base pairs.

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