Core 13.pptx 6th semester questions utkal

6th semester

1. +3 Botany Honours UTKAL UNIVERSITY NEW CBCS Model syllabus Important Long Questions with Answers 2023–2024 Core – 13 :- PLANT METABOLISM Sure shot 6 th Semester

2. Q1. What are regulatory Enzymes ? Describe role of allosteric Enzymes and Covalent Modification in regulation of metabolism

3. What are regulatory Enzymes ? Regulatory enzymes are enzymes that play a pivotal role in controlling the flux of biochemical reactions within cells. They exert precise control over metabolic pathways, ensuring that cellular processes proceed at appropriate rates and are responsive to changing conditions. Regulatory enzymes typically catalyze irreversible or rate-limiting steps in metabolic pathways, meaning that their activity strongly influences the overall rate of the pathway . These enzymes are subject to various forms of regulation, including allosteric regulation, covalent modification, and transcriptional control. Their activity can be modulated by factors such as substrate concentration, product concentration, cofactors, pH, temperature, and the presence of regulatory molecules . Overall, regulatory enzymes serve as key regulators of metabolism, coordinating the intricate network of biochemical reactions within cells to maintain homeostasis and respond to metabolic demands.

4. Role of allosteric Enzymes Allosteric enzymes play a crucial role in the regulation of metabolic pathways by responding to changes in the concentrations of specific molecules within the cell. Here's a more detailed description of their role : Definition : Allosteric enzymes are proteins that have multiple binding sites, including an active site where the substrate binds to undergo a chemical reaction, and one or more allosteric sites where regulatory molecules, known as effectors, bind. The binding of effectors at allosteric sites induces conformational changes in the enzyme's structure, which in turn modulate its catalytic activity at the active site.

5. Regulation of Enzyme Activity : Allosteric enzymes can be regulated in two main ways: Positive Regulation: Binding of certain effectors at the allosteric site can enhance the enzyme's catalytic activity. This positive regulation often occurs when the cell requires an increase in the flux through a metabolic pathway. For example, in glycolysis, phosphofructokinase-1 (PFK-1) is activated by the allosteric activator fructose-2,6-bisphosphate, leading to an increase in glycolytic activity. Negative Regulation: Conversely, binding of other effectors can inhibit the enzyme's catalytic activity. This negative regulation typically occurs when there is an excess of end products or when the cell needs to conserve resources. For example, in the citric acid cycle, isocitrate dehydrogenase is inhibited by ATP, signaling that the cell has sufficient energy and does not require further ATP production.

6. Rapid Response to Cellular Signals : Allosteric regulation allows cells to respond rapidly to changes in the concentrations of specific metabolites or signaling molecules. When the concentration of a regulatory molecule changes, it binds to the allosteric site of the enzyme, inducing a conformational change and altering enzyme activity within milliseconds to seconds. Fine-Tuning Metabolic Pathways : Allosteric enzymes are often strategically positioned at key regulatory points within metabolic pathways. By modulating the activity of these enzymes, cells can fine-tune the flux through entire metabolic pathways in response to varying metabolic demands or environmental conditions.

7. In summary, allosteric enzymes serve as key regulators of metabolic pathways, allowing cells to quickly and precisely adjust their metabolic activities in response to changing internal and external signals. Their ability to modulate enzyme activity through allosteric interactions plays a critical role in maintaining cellular homeostasis and adapting to fluctuating metabolic requirements.

8. Covalent modification in regulation of metabolism Covalent modification is a crucial mechanism for the regulation of metabolism, allowing cells to dynamically control enzyme activity in response to various signals and metabolic demands. In covalent modification, chemical groups are added to or removed from enzymes, altering their activity, stability, or subcellular localization. Phosphorylation, acetylation, methylation, and glycosylation are common forms of covalent modification involved in metabolic regulation.

9. Here's how covalent modification participates in the regulation of metabolism: Phosphorylation : Definition: Phosphorylation involves the addition of phosphate groups to specific amino acid residues, typically serine, threonine, or tyrosine, on the enzyme molecule. Role in metabolism: Activation: Phosphorylation can activate or enhance enzyme activity. For example, in glycogen metabolism, phosphorylation activates glycogen phosphorylase , promoting glycogen breakdown to release glucose. Inhibition: Conversely, phosphorylation can inhibit enzyme activity. For instance, phosphorylation of glycogen synthase inhibits glycogen synthesis, conserving glucose when cellular energy levels are high. Regulation: Protein kinases catalyze phosphorylation, while protein phosphatases remove phosphate groups, reversing the effects of phosphorylation. The balance between kinase and phosphatase activities regulates enzyme activity dynamically.

10. Acetylation : Definition: Acetylation involves the addition of an acetyl group to lysine residues on proteins, including enzymes. Role in metabolism: Regulation of enzyme activity: Acetylation can modulate enzyme activity by altering protein conformation or interactions with substrates or cofactors. For example, acetylation of enzymes involved in fatty acid metabolism can regulate lipid biosynthesis and oxidation. Cellular localization: Acetylation can also influence the subcellular localization of enzymes, affecting their accessibility to substrates or regulatory factors.

11. Methylation: Definition : Methylation involves the addition of methyl groups to amino acid residues, such as lysine, arginine, or histidine , on proteins. Role in metabolism: Regulation of enzyme activity: Methylation can impact enzyme activity by altering protein-protein interactions or affecting substrate binding. For example, methylation of histones regulates gene expression, indirectly influencing metabolic enzyme levels. Signal transduction: Methylation can also serve as a signal for protein-protein interactions or as a mark for protein degradation pathways, indirectly influencing metabolic processes.

12. Glycosylation : Definition: Glycosylation involves the addition of carbohydrate moieties to proteins. Role in metabolism: Stability and activity: Glycosylation can affect enzyme stability, folding, and activity. For example, glycosylation of lysosomal enzymes ensures their proper targeting and stability within lysosomes, facilitating metabolic processes. Cell-cell interactions: Glycosylation can also modulate cell-cell interactions and signaling pathways, indirectly influencing metabolic regulation.

13. covalent modification plays a fundamental role in the regulation of metabolism by dynamically modulating enzyme activity, stability, subcellular localization, and interactions. These reversible modifications allow cells to respond rapidly and precisely to changes in metabolic conditions, ensuring proper metabolic homeostasis and adaptation to varying physiological states.

14. Q2. What is plant Signal transduction? Explain briefly role of calcium, Nitric oxide (no) and c GMP in plant signal transduction.

15. What is plant Signal transduction? Plant signal transduction is the process by which plants perceive external and internal signals, such as environmental cues, hormones, and developmental signals, and convert them into specific cellular responses. It involves a complex network of molecular events that enable plants to adjust their growth, development, and physiology in accordance with changing conditions.

16. The process of plant signal transduction typically involves several key steps : Reception: External signals are perceived by various receptors located on the plant cell's surface or within the cell. These receptors can be proteins, such as receptor kinases, or small molecules that bind to specific receptors . Transduction: Once a signal is perceived, it is transmitted through the cell via signal transduction pathways. These pathways often involve a series of protein modifications, such as phosphorylation cascades, where the signal is relayed from one protein to another, leading to amplification and propagation of the signal . Response: The signal transduction pathways ultimately lead to specific cellular responses, which can include changes in gene expression, alterations in enzyme activity, modifications in cellular metabolism, adjustments in growth and development, or initiation of defense mechanisms . Feedback Regulation: Plants have mechanisms in place to regulate and fine-tune their responses to signals. Feedback loops, negative regulators, and cross-talk between signaling pathways help to ensure that responses are appropriate and adaptive to the prevailing conditions. Plant signal transduction is critical for plant survival and adaptation to environmental challenges, such as changes in light, temperature, water availability, nutrient availability, and biotic stresses. It allows plants to sense their surroundings, integrate multiple signals, and coordinate appropriate responses to optimize their growth, development, and defense strategies.

17. roles of calcium (Ca^2+) Role: Calcium ions serve as ubiquitous second messengers in plant cells, playing essential roles in mediating a wide range of signaling processes. Signal transduction: Changes in cytosolic calcium levels are often triggered by various stimuli, such as hormonal signals, environmental cues (e.g., light, temperature, and stress), and developmental signals. Function: In response to stimuli, calcium ions are released from intracellular stores or enter the cell through calcium channels. Elevated cytosolic calcium levels then activate calcium-binding proteins, such as calmodulin , calcium-dependent protein kinases (CDPKs), and calcineurin B-like proteins (CBLs), which relay the signal to downstream targets. Effects: Calcium signaling regulates diverse processes in plants, including gene expression, hormone signaling, stomatal movement, ion transport, cell division, and responses to biotic and abiotic stresses.

18. Roles of Nitric Oxide ( N O ): Role: Nitric oxide is a gaseous signaling molecule involved in diverse physiological processes in plants, including growth, development, and stress responses. Signal transduction: Nitric oxide is produced enzymatically by nitric oxide synthase (NOS)-like enzymes or non-enzymatically by reactions involving nitrate reductase , nitrite reductase , and other sources. Function: Once produced, nitric oxide can modulate the activity of various proteins through post-translational modifications, such as S- nitrosylation , or by directly interacting with targets. Effects: Nitric oxide signaling influences numerous processes in plants, including seed germination, root development, stomatal regulation, floral transition, defense responses against pathogens, and tolerance to abiotic stresses like drought, salinity, and heavy metals.

19. Roles of Cyclic Guanosine Monophosphate ( cGMP ): Role: Cyclic guanosine monophosphate is a second messenger involved in signaling pathways that regulate plant growth, development, and stress responses. Signal transduction: cGMP levels in plant cells are dynamically regulated by guanylate cyclases , which produce cGMP from guanosine triphosphate (GTP), and phosphodiesterases , which degrade cGMP . Function: cGMP modulates the activity of various effector proteins, including cyclic nucleotide-gated ion channels (CNGCs), protein kinases, phosphodiesterases , and transcription factors, by binding to their regulatory domains. Effects: cGMP signaling regulates processes such as stomatal movement, root growth, pollen tube elongation, seed germination, and responses to environmental stresses like drought, cold, and pathogens.

20. calcium, nitric oxide, and cyclic guanosine monophosphate are key signaling molecules involved in plant signal transduction, mediating diverse physiological processes and responses to environmental cues. Their dynamic regulation and interactions with downstream targets enable plants to perceive and respond to changes in their surroundings, ultimately ensuring their survival and adaptation in diverse habitats.

21. Q3. With neat sketch explain C3 cycle and it's significance? Compare it with c4 cycle.

22. C3 Cycle (Calvin Cycle) The Calvin cycle is the light-independent stage of photosynthesis that takes place in the stroma of the chloroplast. It is a series of chemical reactions that use the energy from ATP and NADPH produced during the light-dependent reactions to convert carbon dioxide into sugar (glucose ). Here are the steps of the Calvin cycle : Carbon fixation: Carbon dioxide (CO 2 ) diffuses into the stroma from the cytoplasm. An enzyme called RuBisCO (ribulose-1,5-bisphosphate carboxylase/ oxygenase ) fixes CO 2 by attaching it to a five-carbon sugar molecule called ribulose-1,5-bisphosphate ( RuBP ). This reaction produces a six-carbon molecule that is unstable and immediately breaks down into two three-carbon molecules called 3-phosphoglycerate (3-PGA).

23. Reduction: ATP and NADPH provide the energy and electrons to convert 3-PGA into glyceraldehyde-3-phosphate (G3P). G3P is a three-carbon sugar molecule that can be used to make glucose or other organic molecules . Regeneration of RuBP : Some of the G3P is used to regenerate RuBP , which is needed for the carbon fixation step. This regeneration process requires ATP.

24. Significance of C3 Cycle Ubiquitous: The C3 cycle is the predominant photosynthetic pathway used by most plants on Earth. Efficiency: It efficiently fixes carbon dioxide and produces organic compounds, including glucose, which serve as energy sources and building blocks for plant growth and development. Energy Conservation: It conserves energy by using ATP and NADPH generated during the light-dependent reactions. Adaptability: C3 plants perform well in moderate temperatures and under normal environmental conditions.

25. C4 Cycle The C4 cycle is a variation of the Calvin cycle that is found in some plants, such as corn, sugarcane, and sorghum. C4 plants are more efficient at photosynthesis than C3 plants in hot, dry conditions . Here are the steps of the C4 cycle : Carbon fixation: In the mesophyll cells of the leaf, CO2 is fixed into a four-carbon compound called oxaloacetate by the enzyme phosphoenolpyruvate carboxylase (PEPC ). Carbon transfer: The oxaloacetate is then converted to malate or another four-carbon compound and transported to the bundle-sheath cells . Decarboxylation: In the bundle-sheath cells, the four-carbon compound is decarboxylated , releasing CO2. The CO2 is then concentrated around the RuBisCO enzyme, which can then efficiently fix it into 3-PGA . Calvin cycle: The 3-PGA enters the Calvin cycle in the bundle-sheath cells, which is similar to the Calvin cycle in C3 plants . Regeneration : Some of the G3P produced in the Calvin cycle is transported back to the mesophyll cells and used to regenerate PEP, which is needed for the initial carbon fixation step.

26. Significance of C4 Cycle The C4 cycle is an adaptation that allows plants to photosynthesize more efficiently in hot, dry conditions. C4 plants have a higher concentration of CO 2 around RuBisCO , which reduces photorespiration. Photorespiration is a process that wastes energy and fixed carbon.

27. Comparison with C4 Cycle: Anatomical Differences: C3 plants lack specialized anatomy for carbon fixation, while C4 plants have specialized leaf anatomy with two types of photosynthetic cells: mesophyll cells and bundle sheath cells. Initial Carbon Fixation: In C3 plants, carbon fixation occurs directly by Rubisco in mesophyll cells. In C4 plants, carbon dioxide is initially fixed into a 4-carbon compound, oxaloacetate, by phosphoenolpyruvate carboxylase ( PEPCase ) in mesophyll cells. Spatial Separation: In C4 plants, the initial fixation of carbon dioxide and the Calvin Cycle are spatially separated between mesophyll and bundle sheath cells, which minimizes oxygen inhibition of Rubisco . Efficiency in Hot and Dry Conditions: C4 plants are more efficient in hot and dry environments due to their ability to minimize photorespiration and conserve water . Energy Requirement: C4 plants require more energy (ATP) to fix carbon dioxide than C3 plants due to the additional steps involved in the C4 cycle.

28. Q4. What is photorespiration ? Briefly explain its mechanism in plant with neat diagram .

29. Photorespiration Photorespiration is a process which involves loss of fixed carbon as CO2 in plants in the presence of light. It is initiated in chloroplasts. This process does not produce ATP or NADPH and is a wasteful process. Photorespiration occurs usually when there is the high concentration of oxygen . Under such circumstances, RuBisCO , the enzyme that catalyses the carboxylation of RuBP during the first step of Calvin cycle, functions as an oxygenase .

30. Some O 2 does bind to RuBisCO and hence CO 2 fixation is decreased . The RuBP binds with O 2 to form one molecule of PGA (3C compound) and phosphoglycolate (2C compound ) in the pathway of photorespiration. There is neither the synthesis sugar nor of ATP. Rather, it results in the release of CO 2 with the utilisation of ATP . It leads to a 25 percent loss of the fixed CO 2 . Significance of photorespiration: Photorespiration helps in dissipation of energy where stomata get closed during daytime because of water stress. Photorespiration protects the plant from photoxidative damage by dissipating excess of excitation energy .

31. Photorespiration is a process that occurs in Calvin Cycle during plant metabolism. In this process, the key enzyme RuBisCO that is responsible for The fixing of carbon dioxide reacts with oxygen rather than carbon dioxide . It occurs because of the conditions in which carbon dioxide concentration falls down and rubisco does not have enough carbon dioxide to fix and it starts fixing oxygen . Under suitable conditions, C3 plants have sufficient water, the supply of carbon dioxide is abundant and in such conditions, photorespiration is not a problem.

32. Mechanism of photorespiration: Oxygen Fixation: In photorespiration, oxygen (O2) is mistakenly bound by the enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/ oxygenase ) instead of carbon dioxide (CO2) to the RuBP , forming a two-carbon compound called phosphoglycolate . Conversion to Glycolate : Phosphoglycolate is then converted into glycolate in the chloroplast. Peroxisome Reaction: Glycolate moves from the chloroplast to the peroxisome, where it undergoes a series of reactions that release carbon dioxide and produce glycerate . Mitochondrial Involvement: Glycerate moves from the peroxisome to the mitochondria, where it is converted into glycine. Return to Chloroplast: Glycine returns to the chloroplast, where it reacts with another molecule of glycine to form serine, releasing ammonia in the process. Conversion to Glycolate : Serine is then converted back into glycolate , which re-enters the peroxisome to continue the cycle.

33. The correct sequence of organelles in which glycolate and glyoxylate are produced sequentially in photorespiration is: Chloroplast: RUBP reacts with fixed oxygen to produce phosphoglycolate , which is converted to glycolate . Peroxisome: Glycolate is transported to the peroxisome and converted to glyoxylate . Peroxisome: The glyoxylate is converted to glycine by glutamate:glyoxylate aminotransferase.

34. Photorespiration is influenced by high temperature as well as light intensity and accelerating the formation of glycolate and the flow through the photorespiratory pathway . Photorespiration causes a light-reliant acceptance of O2 and discharge of CO2 and is related to the creation and metabolism of a minute particle named glycolate . Photosynthesis and photorespiration are two biological processes (in flourishing plants) that can function simultaneously beside each other as photosynthesis gives off oxygen as its byproduct and photorespiration gives off carbon dioxide as its byproduct, and the said gases are the raw material for the said processes . When the carbon dioxide levels inside the leaf dip to about 50 ppm, RuBisCO begins combining Oxygen with RuBP as an alternative to Carbon dioxide . The final result of this is that as an alternative to manufacturing 2 molecules of 3C- PGA units, merely one unit of PGA is fashioned with a noxious 2C molecule termed phosphoglycolate .

35. To purge themselves of the phosphoglycolate the plant takes some steps. Primarily, it instantly purges itself from the phosphate cluster, transforming those units into glycolic acid. After that, this glycolic acid is transferred to the peroxisome and then transformed into glycine. The conversion of glycine into serine takes place in the mitochondria of the plant cell. The serine produced after that is used to create other organic units. This causes a loss of carbon dioxide from the flora as these reactions charge plant’s energy.