Tag: structure and function of cell organelles

Catalases and oxidases are found in peroxisomes. Peroxisomes contain oxidative enzymes, such as catalase, D-amino acid oxidase, and uric acid oxidase. A major function of the peroxisome is the breakdown of very long chain fatty acids through $\beta$-oxidation. 

Glyoxysomes are specialized peroxisomes found in plants, particularly in the fat storage tissues of germinating seeds and also in filamentous fungi. As in all peroxisomes, in glyoxysomes the fatty acids are hydrolyzed to acetyl-CoA by peroxisomal-oxidation enzymes. Besides peroxisomal functions, glyoxysomes possess additionally the key enzymes of glyoxylate cycle which accomplish the glyoxylate cycle bypass. Thus, glyoxysomes contain enzymes that initiate the breakdown of fatty acids and additionally possess the enzymes to produce intermediate products for the synthesis of sugars by gluconeogenesis. The seedling uses these sugars synthesized from fats until it is mature enough to produce them by photosynthesis. Glyoxysomes also participate in photorespiration and nitrogen metabolism in root nodules.

Glyoxysomes are specialized peroxisomes found in plants, particularly in the fat storage tissues of germinating seeds and also in filamentous fungi. As in all peroxisomes, in glyoxysomes the fatty acids are hydrolyzed to acetyl-CoA by peroxisomal oxidation enzymes. Besides peroxisomal functions, glyoxysomes possess additionally the key enzymes of glyoxylate cycle which accomplish the glyoxylate cycle bypass. Thus, glyoxysomes contain enzymes that initiate the breakdown of fatty acids and additionally possess the enzymes to produce intermediate products for the synthesis of sugars by gluconeogenesis. The seedling uses these sugars synthesized from fats until it is mature enough to produce them by photosynthesis. Glyoxysomes also participate in photorespiration and nitrogen metabolism in root nodules.

In plants the glyoxylate cycle occurs in special peroxisomes which are called as glyoxysomes. The glyoxylate cycle, is an anabolic pathway occurring in plants, bacteria, protists, and fungi. The glyoxylate cycle centers on the conversion of acetyl-CoA to succinate for the synthesis of carbohydrates. This cycle allows seeds to use lipids as a source of energy to form the shoot during germination. The seed cannot produce biomass using photosynthesis because of lack of an organ to perform this function. The lipid stores of germinating seeds are used for the formation of the carbohydrates that fuel the growth and development of the organism.

Spherosomes, also referred to as lipid bodies or oleosomes, are vesicles that stores triacylglycerol in the form of oil (during seed development). They are surrounded by a phospholipid monolayer - derived from ER. It is the cell organelle responsible for synthesis of cutin and wax. 

Endomembrane system is a membrane system of a eukaryotic cell that involves flow of membrane from one component to another by means of small membrane vesicles. 

The nucleus is the double membrane bound organelle of eukaryotic cells that serve to house genetic material. The cell wall is the rigid structure present outside the cell membrane of plants, fungi, algal and microbial cells. Being rigid in composition, it provides mechanical support, help maintains the cell shape and prevent lysis of the cell. Lysosomes, present in the cytoplasm, are the suicidal bags of cell that digest and remove the wear and tear organelles and molecules from the cell. Photorespiration is oxidation of RuBP, rather than carboxylation, by enzyme RUBISCO and formation of 2-phosphoglycolate. Dephosphorylation of 2 phosphoglycolate forms glycolate which in turn enters peroxisomes and is then transaminated to glycine. Condensation of two glycine molecules to form serine and carbon dioxide by enzyme glycine decarboxylase takes place in mitochondria. Serine again enters peroxisomes and is converted to hydroxypyruvate and then to glycerate. The glycerate reenters the chloroplasts and is phosphorylated to enter Calvin cycle. Thus, the correct answer is option A.

Sphaerosomes are detected with the help of Sudan black. Sphaerosomes are vesicles that store triacylglycerol in the form of oil and surrounded by phospholipid monolayer. It is produced by an endoplasmic reticulum. It is also responsible for the synthesis of cutin and wax.

Glycolate cycle, also known as C$ _2$ cycle, is a complex metabolic pathway, that takes place in chloroplasts, mitochondria and peroxisomes of plant cells and is responsible for the formation of the amino acids, serine and glycine from non-phosphorylated intermediates of the carbon reduction cycle of photosynthesis.