Glyoxylate Cycle and it's significance ppt

Glyoxylate cycle presentation

1. Glyoxylate Bhavleen (BSc Biochemistry H.) Submitted by Cycle and it’s significance Amity University Punjab Department of Biological Sciences Dr Krishna Kumar Rai Submitted to Carbohydrates: Structure & Metabolism BCH 10 5 Course

2. OVERVIEW The glyoxylate cycle is a specialized anabolic pathway found in certain organisms, including plants, fungi, and bacteria. A variation of TCA where it allows acetyl CoA derived from breakdown of storage lipds (fatty acids, alcohols, esters) to synthesize carbohydrates. In plants, it is important during seed germination and early growth stages . In bacteria and yeasts, it allows them to grow on C2 compounds such as acetate and ethanol. Originally discovered by Hans Kornberg in 1957 resulting in a Nature paper Synthesis of Cell Constituents from C2-Units by a Modified Tricarboxylic Acid Cycle. Links 3 metabolic pathways Fatty acid β-oxidation - TCA - Gluconeogenesis -

3. Is it present in animals? Madsen was the first to report that the glyoxylate cycle is not present in animal tissue. The only clade of animals where the glyoxylate shunt was detected is that of the nematodes at the early stages of embryogenesis. Irreversible nature of PDH complex Absence of enzymes like isocitrate lyase and malate synthase Tetrahymena Saccharomyces

4. LOCATION In plants and fungi - Glyoxysomes In bacteria, algae, protists - cytosol Spherosome (synthesis and storage of lipids)

5. STEPS Acetyl CoA produced from fatty acid oxidation condenses with oxaloacetate to give citrate. The enzyme involved is Citrate synthase . Citrate is then converted into isocitrate by the action of enzyme Aconitase . At this stage isocitrate bypasses the citric acid cycle and cleaved by isocitrate lyase to succinate and glyoxalate. The reaction is a reversible aldolcleavage, similar to the aldolase reaction in glycolysis/gluconeogenesis Isocitrate Lyase Reaction Succinate enters the kreb’s cycle, in the mitochondria and is converted to malate which is further converted to OAA ->gluconeogenesis

6. STEPS Another molecule of acetyl CoA combines with glyoxalate to form malate. Water is also required. This reaction is catalyzed by enzyme Malate synthase . It is an aldol condensation and hydrolysis rxn. Malate enters citric acid cycle. It is then converted into oxaloacetate by enzyme called Malate dehydrogenase . This reaction is mechanistically similar to the citrate synthase r xn , which couples a condensation reaction with the hydrolysis of a thioester bond. Malate Synthase Reaction

7. STEPS Oxaloacetate is the pecursor of gluconeogenesis. It is 1st converted into phosphoenolpyruvate by enzyme P E P Carboxykinase and thus to glucose by gluconeogenesis Finally, glucose and fructose phosphates are converted into sucrose After the conversion of fats into carbohydrates is completed, the glyoxysomes disappear from the cells.

8. Relation with TCA cycle The glyoxylate cycle operates alongside the TCA cycle, utilizing intermediates produced by the TCA cycle, such as isocitrate and succinate. This cycle bypasses the decarboxylation steps that take place in the citric acid cycl e a llowing simple carbon compounds to be used in the later synthesis . Two molecules of acetyl-CoA enter per turn the glyoxylate cycle; compared with one in the citric acid cycle. 2 acetyl-CoA + 2 NAD + + FAD → OAA + 2 CoA + 2 NADH + FADH 2 + 2 H +

9. REGULATION Transcription factors and regulatory elements in the promoter regions of genes coding enzymes respond to various environmental signals and metabolic cues. Enzyme activity within the glyoxylate pathway can be modulated through post-translational modifications such as phosphorylation . Regulation of isocitrate dehydrogenase activity determines the partitioning of isocitrate between the glyoxylate and citric acid cycles. This is decided by the energy status of the cell. Hormones like gibberellic acid and abscisic acid play role in regulation of storage reserve mobilization.

10. Significance The glyoxylate cycle allows the efficient conversion of fatty acids from stored lipids into carbohydrates, providing energy and carbon skeletons for seedling growth. Those micro-organisms which can grow on ethyl alcohol or acetate as a sole source of energy and carbon make use of this cycle in synthesizing longer carbon chains. Pathogenic fungi and parasites can utilize the glyoxylate cycle to adapt to host environments and enhance their virulence.

11. 30-04-2024 THANK YOU by- Bhavleen

12. REFERENCES Lehninger Principles of Biochemistry - EIGHTH EDITION KEGG PATHWAY: Glyoxylate and dicarboxylate metabolism - Reference pathway www.kegg.jp Organizational Cell Biology - ‘ The Glyoxylate Cycle and Glyoxylate Metabolism ’ P.B. Lazarow, in Encyclopedia of Cell Biology, 2016 Luis F. de Figueiredo, Stefan Schuster, Christoph Kaleta, David A. Fell, Can sugars be produced from fatty acids? A test case for pathway analysis tools, Bioinformatics, Volume 25, Issue 1 Wu, WL., Hsiao, YY., Lu, HC. et al. Expression regulation of MALATE SYNTHASE involved in glyoxylate cycle during protocorm development in Phalaenopsis aphrodite (Orchidaceae). Sci Rep 10, 10123 (2020) Cihan Erkut, Vamshidhar R Gade, Sunil Laxman, and Teymuras V Kurzchalia, The glyoxylate shunt is essential for desiccation tolerance in C. elegans and budding yeast. 2016 Apr 18