Chloroplast – Its structure and function

History of chloroplast:

Chloroplasts were first established in eukaryotes through an endosymbiotic relationship with a cyanobacterium; they later spread through the evolution of eukaryotic hosts and the subsequent engulfment of eukaryotic algae by formerly nonphotosynthetic eukaryotes. Hugo von Mohl, a German botanist, is commonly credited with discovering and describing Chlorophyll Korner chloroplast granules in 1837, but the first accounts of green granules appeared much earlier.

Define Chloroplast.

A cell organelle that creates energy through photosynthesis is the chloroplast, which is exclusively present in algal and plant cells. The name chloroplast derives from the Greek words khloros, which means “green,” and plates, which means “made.” Chlorophyll, the chemical that absorbs light energy, is present in great concentrations, giving many plants and algae a green hue. The chloroplast is believed to have evolved from previously free-living bacteria, similar to how the mitochondrion did.

Explain the structure of chloroplast.

under the light microscope, Guard cells, which are about 1-2 µm thick and 5-7 µm in diameter and are present in plant leaves, are frequently home to chloroplasts. Oval in shape, chloroplasts feature an inner membrane as well as an outer membrane. The intermembrane gap between the outer and inner membranes is 10-20 nm broad. The stroma, a viscous fluid within the chloroplast, fills the gap inside the inner membrane. This is the location where carbon dioxide is transformed into carbohydrates.

Additional chloroplast structures consist of:

Thylakoid system:

Light energy is transformed into chemical energy in the internal membrane system known as the thylakoid system, which is composed of flattened sac-like membrane structures. Thylakoids include the light-harvesting complex, which also contains pigments like chlorophyll and carotenoids as well as electron transport chains related to photosynthesis.


Stacks of 10 to 20 thylakoids are closely packed together and serve as the locations where light energy is transformed into chemical energy.


It is an absorbent green photosynthetic pigment found on the surface of thylakoids.

DNA Ring:

A circular form of DNA is separate from nuclear DNA.

Chloroplast genome:

Chloroplasts, which also contain DNA like mitochondria, divide in a manner akin to bacterial binary fission in order to replicate independently of nuclear and mitochondrial DNA. The length of the chloroplast genome is between 120 and 200 kb, and it is normally circular (but linear DNA has sometimes been observed).

 Over the course of evolution, the size of the contemporary chloroplast genome has been greatly decreased, and an increasing proportion of chloroplast genes have been transferred to the nuclear genome. Therefore, in order to encode the proteins necessary for chloroplast activity, the nuclear genome is required.

Land plants have generally conserved chloroplast genomes (cpDNA) in terms of size, organization, and gene content. According to a study, land plants and the oldest species of algae share 81% of their genes (Mesostigma viride). rRNA, tRNA, at least three subunits of bacterial RNA polymerases, and a few other protein-coding genes like those for thylakoid proteins and ribosomal proteins are among the 120 genes that make up the typical chloroplast genome.

Chloroplast DNA sequencing is a high-throughput process that uses PacBio or Illumina platforms to sequence the chloroplast genomes of plants. Information on species taxonomy, phylogenetic evolution, geographic lineage inheritance, disease diagnostics, and forensics can be found by comparative genomic analysis.

Explain the function of Chloroplast.

Photosynthesis, the process of turning light energy into energy stored in the form of sugar and other organic molecules that the plant or alga needs as food, is carried out by chloroplasts, a component of plant and algal cells. Two steps comprise photosynthesis. The reactions that are light-dependent take place in the first stage. Adenosine triphosphate (ATP), the energy currency of the cell, and nicotinamide adenine dinucleotide phosphate (NADPH), which transports electrons, are produced in these processes when sunlight is absorbed by chlorophyll and carotenoids.

The light-independent processes sometimes referred to as the Calvin cycle, make up the second stage. In the Calvin cycle, a process known as CO2 fixation transforms inorganic carbon dioxide into an organic molecule in the form of carbohydrates. Energy can be stored in the form of carbohydrates and other chemical compounds.

For plants and photosynthetic algae to develop and survive, chloroplasts are necessary. Chloroplasts capture light energy and transform it into a form that may be used to power activities, much like solar panels do. Some plants, though, no longer contain chloroplasts. Rafflesia, a parasitic plant genus, is one such. Tetrastigma vines, in particular, are where Tetrastigma vines get their nourishment from.

Rafflesia has lost the genes that over a long period of evolutionary time controlled the development of the chloroplast since it no longer requires its chloroplasts because it obtains all of its energy from parasitizing another plant. The only genus of land plants without chloroplasts is Rafflesia.


Rimsha Bashir
Rimsha Bashir

Rimsha Saith is a highly knowledgeable microbiologist with a keen interest in the field. Her expertise and passion are in her writing for Microbiology. As a writer, Rimsha has authored numerous articles that have been well-received by both health and medical students and industries.

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