Compare and contrast the structure and function of Chloroplasts and mitochondria

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Compare and contrast the structure and function of

Chloroplasts and mitochondria


The invention of the light microscope in the 17th century was the key event that allowed the English scientist Robert Hooke to first observe and discover the cell. Hooke coined the term 'cell' in 1665, as the honeycomb structures reminded him of monks' chambers he had once seen in monasteries. It was not until the 1830s that the Belgian botanist Matthias Schleiden and Theodor Schwann, a German zoologist, developed the cell theory. The two scientists jointly proposed that every living organism was composed of individual cellular units. Further scientific study led to the discovery of microscopic cell substructures, which were collectively given the name organelles. Organelles were identified as being highly organised internal structures that had specific shapes and functions. It was found that Eukaryotic cells had a larger number of membrane bound organelles and that Prokaryotic cells had very few organelles, and that those present lacked the membrane covering. The typical organelles found to occupy a cell included the cytoskeleton, ribosomes, endoplasmic recticulum, lysomes, Golgi complex, nucleus, peroxisomes, vacuoles and mitochondria. Centrioles are only located in human and animal cells and chloroplasts can only be found inside plant cells. The aim of this essay is to investigate the similarities and differences between the structure and function of mitochondria and chloroplasts.

The structure and function of mitochondria

Mitochondria were first observed with a light microscope by several cytologists in the period between 1850 and 1880. Their black, thread-like appearance prompted C. Benda to name the structures mitochondrion, from the Greek words 'mitos' (thread), and 'chondros', (granule), in the year 1898, (Sadava, David.E. 1993).

Diagram of Mitochondria



The development of improved methods of fixation and the use of transmission electron microscope in 1953 enabled Palade and Sjostrand to describe the basic structural plan of mitochondria. Most eukaryotic cells, whether from protists, fungi, plants, animal or human cells contain mitochondria. The primary function of mitochondrion is to generate energy in the form of ATP, Adenosine triphosphate, so they are often referred to as the powerhouses of the cell. The number of mitochondrion present in each cell ranges from a few hundred to thousands and is dependant on the type of organism and the location of the cell. Cells with high energy requirements, such as myofibrils found in heart muscle, possess the most mitochondria while the less active cells contain far fewer. Mitochondria are relatively large organelles that are usually 0.5 to 1.0 microns in diameter and may vary in length up to 400 microns, (Mader, Sylvia.S. 2001). They are located within the cytoplasm of the cell and are usually sausage shaped, although the size and activity are the primary determinants of the shape. An envelope of two phospholipid membranes named the outer membrane and the inner membrane surrounds each mitochondrion. The outer membrane is smooth and contains transmembrane proteins known as porins that permit the passage of certain solutes, ions and small molecules with molecular weights of up to 10,000 Daltons, (Becker, Wayne.M., et al. 2000). In contrast, the inner membrane acts as a permeability barrier to most solutes, only allowing pyruvate, fatty acids, ADP and ATP to pass through it. The inner membrane has many distinctive folds named cristae that work to greatly increase its surface area. The cristae are covered with tiny spheres, which are attached by short protein stalks to the hydrophobic polypeptides embedded within the membrane, (Jones, Mary., Gregory, Jennifer. 1999). The spheres are known as F1 complexes, each one being an assembly of six polypeptides acting as an ATPase. A group of polypeptides situated inside the inner membrane are referred to as F0 complexes. When the two complexes join together to form an F0F1 complex they function as an ATP synthetase, (Becker, Wayne.M., et al. 2000). An ATP synthetase can initiate and control the flow of positively charged hydrogen ions through the membrane, or gradient, and generally drives the entire process of ATP synthesis. The space between the outer and inner membrane is known as the intermembrane space and contains enzymes and other soluble proteins that are too large to fit the porin channels. Intermembrane space usually has a lower pH than other areas inside the mitochondria because it is the collection site for the hydrogen ions produced by the activity of the electron transport chain. The central fluid filled cavity inside the mitochondria is termed the matrix. Within the matrix there are many enzymes, tiny ribosomes and multiple copies of a circular DNA molecule that has 37 genes. Mitochondrial DNA allows the organelle to self-replicate and can only be inherited from the female parent. The matrix is also the site of the link reaction and the Krebs cycle.

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The structure and function of chloroplasts

The plant anatomist N. Grew first saw chloroplasts in the 17th century with a light microscope. They were found to be unique to green plant cells, (also certain protists), but their role was not understood until the late 19th century, (Sadava, David.E. 1993).

 Diagram of a Chloroplast


The name chloroplast originates from the Greek words chloros and plastos, meaning green and moulded. Chloroplasts contain the green pigment chlorophyll, ...

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