1. Describe Glycolysis 2. Explain pyruvate oxidation. 3 Number of ATP gained dur
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1. Describe Glycolysis 2. Explain pyruvate oxidation. 3 Number of ATP gained during glycolysis A)1 B) 2 C)4 D) 6 Enzyme inhibitor used in enzyme lab is A) NaF Cofacter used in enzyme lab is A) NaF B) MgSO4 C)Sodium pyruvate D) Pyruvate What was collected at top of inverted tubes in enzyme lab A) ethyl alcohol B) Lactate C)O D) CO 4. B) MgSO4 C) Glucose D) Pyruvate 5. 6. 7. Explain substrate level phosphorylation with an example. 8. Explain alcoholic fermentation. 9. Describe component structure of NAD 10. Why glycolysis can continue in absence of O, in muscles?Explanation / Answer
1. Glycolysis is derived from the Greek words, glycose= sugar or sweet and lysis = dissolution. Glycolysis is defined as the sequence of reactions converting glucose or glycogen to pyruvate or lactate with the production of ATP.
Salient features of Glycolysis:
Net reaction in glycolysis:
Glucose + 2 ADP + 2Pi ------------> 2 Lactate + 2 ATP
2. Pyruvate oxidation
Pyruvate is the key and important metabolite as it occupies a junction point between various metabolic pathways. Pyruvate oxidation refers to conversion of pyruvate to Acetyl Co A which is utilized in various metabolic reactions like citric acid cycle, fatty acid synthesis and substrate for gluconeogenesis.
Pyruvate oxidation involves three steps such as:
i. Removal of carboxyl group from pyruvate releasing a molecule of carbon dioxide.
ii. Reduction of NAD+ to NADH
iii. Transfer of Acetyl group to coenzyme A resulting in the formation of Acetyl CoA
3. Number of ATP gained during glycolysis: Option B. 2
Explanation: Phosphoglycerate kinase (Substrate level phosphorylation)- 2 ATP
Pyruvate kinase (Substrate level phosphorylation)- 2 ATP
Two ATPs are consumed in the reactions catalyzed by hexokinase and phosphofructokinase.
So, the Net ATP gained are 2 under anaerobic conditions while 7 ATP are synthesized if malate shuttle pathway operates.
4. Option A. NaF (Sodium fluoride)
Explanation: Magnesium Sulfate provides Magnesium ions (Mg2+ ions) which is a cofactor for the enzyme enolase, an enzyme necessary for glycolysis. Hence, option B is incorrect
Glucose is a substrate for glycolysis and not used as inhibitor. Hence, option C is also incorrect.
Pyruvate is a product of glycolysis, which is reduced to ethanol and CO2 or lactic acid during anerobic fermentation. Hence, option D is also incorrect.
Sodium fluoride is an inhibitor of the enzyme enolase hence, it is used as inhibitor in the enzyme lab.
5. Option B. MgSO4
Magnesium Sulfate provides Magnesium ions (Mg2+ ions) which is a cofactor for the enzyme enolase, an enzyme necessary for glycolysis. Hence, option B is the correct answer.
Sodium fluoride is an inhibitor of the enzyme enolase hence, it is used as inhibitor in the enzyme lab. Hence, option B is incorrect.
Sodium pyruvate provides pyruvate, hence an incorrect answer.
Pyruvate is a product of glycolysis, which is reduced to ethanol and CO2 or lactic acid during anerobic fermentation. Hence, option D is also incorrect.
CO2 is a byproduct of respiration and fermentation. Hence, amount of CO2 which accumulates in the inverted tube helps in measurement of rate of respiration and/ or fermentation. Thus, option D is the correct answer.
Ethyl alcohol is not collect in the invert tube but it is produced in the test tube itself. Lactate also cannot collected in the inverted tube. Oxygen is utilized in fermentation and respiration.
7. ATP can be synthesized via Oxidative phosphorylation and Substrate level phosphorylation.
Substrate level Phosphorylation: ATP may be directly synthesized during substrate oxidation in the metabolism. The high energy compounds such as phosphoenol pyruvate and 1,3 bisphospho glycerate (intermediates of glycolysis) and succinyl coA (of citric acid cycle) can transfer high energy phosphate to ultimately produce ATP
Example: The enzyme phosphoglycerate kinase acts on 1,3 bisphosphoglycerate resulting in the synthesis of ATP and formation of 3-Phosphoglycerate in glycolysis. This step is a good example of of substrate level phosphorylation, since ATP is synthesized from the substrate without the involvement of electron transport chain. Phosphoglycerate kinase reaction is reversible, a rate example among the kinase reactions.
8. Fermentation refers to production of energy from substrate molecules in the absence of ATP. Alcoholic fermentation is defined as anaerobic respiration (seen in yeasts and some microorganisms) which releases energy from substrate molecules along with Alcohol and CO2 as products.
Overall reaction: Pyruvic acid + NADH-------> Alcohol + CO2 + NAD+
9. Niacin is a pyridine derivative. The amide form of niacin is known as Niacinamide or nicotinamide. Dietary nicotinamide, niacin and tryptophan contribute to the synthesis of the coenzymes- Nicotinamide adenine dinucleotide (NAD+) and Nicotinamide Adenine Dinucleotide Phosphate (NADP+)
Nicotinamide is deaminated in the body to niacin. Niacin then undergoes a series of reactions to produce NAD+ and NADP+. Tryptophan produces quinolinate which then forms nicotinate mononucleotide and ultimately, NAD+ and NADP+
10. In the absence of oxygen, pyruvate (endproduct of glycolysis) is reduced by NADH to lactate in presence of enzyme lactate dehydrogenase. The NADH utilized in this step is obtained from the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase. The formation of lactate allows regeneration of NAD+ which can be reused by glyceraldehyde 3-phosphate dehydrogenase so that glycolysis proceeds even in the absence of oxygen to supply ATP.
The occurence of uninterrupted glycolysis is very essential in skeletal muscle during strenous exercise where oxygen supply is very limited. Glycolysis in the erythrocytes leads to lactate production, since, mitochondria-the centers for aerobic oxidation are absent.
Hence, mild form of lactic acidosis is associated with strenous exercise, shock, respiratory diseases, cancers, low pyruvate dehydrogenase activityk, von Gierke's disease.
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