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What is the primary role of glycolysis in intermediary metabolism?
What is the primary role of glycolysis in intermediary metabolism?
Which glucose transporter is primarily found in muscle and adipose tissue and is stimulated by insulin?
Which glucose transporter is primarily found in muscle and adipose tissue and is stimulated by insulin?
In anaerobic glycolysis, what is the end product of glucose conversion due to the lack of oxygen?
In anaerobic glycolysis, what is the end product of glucose conversion due to the lack of oxygen?
What characterizes the first five reactions of glycolysis?
What characterizes the first five reactions of glycolysis?
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What mechanism allows glucose to be transported against its concentration gradient?
What mechanism allows glucose to be transported against its concentration gradient?
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What is the primary role of hexokinase I-III in glucose metabolism?
What is the primary role of hexokinase I-III in glucose metabolism?
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Which characteristic distinguishes glucokinase (hexokinase IV) from hexokinases I-III?
Which characteristic distinguishes glucokinase (hexokinase IV) from hexokinases I-III?
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How does fructose 6-phosphate affect glucokinase activity?
How does fructose 6-phosphate affect glucokinase activity?
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What is the significance of phosphofructokinase-1 (PFK-1) in glycolysis?
What is the significance of phosphofructokinase-1 (PFK-1) in glycolysis?
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What factor leads to glucokinase being released from the GKRP complex?
What factor leads to glucokinase being released from the GKRP complex?
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Study Notes
Unit II: Intermediary Metabolism
- Glycolysis is a metabolic pathway occurring in all tissues
- Glucose is broken down to generate ATP and other metabolic intermediates
- It's the central pathway for carbohydrate metabolism, converting various sugars into glucose
- Pyruvate is the end product of glycolysis in the presence of oxygen (aerobic)
- In the absence of oxygen (anaerobic), pyruvate is converted to lactate.
Chapter 8: Glycolysis
- Glycolysis is a metabolic pathway occurring in all tissues
- Glucose is transformed into energy (ATP) and other metabolic intermediates
- Glucose metabolism is a central hub, converting dietary and catabolic sugars into glucose
- Pyruvate is the end product of aerobic glycolysis in cells with mitochondria and sufficient oxygen
- In anaerobic conditions where there's limited oxygen or no mitochondria, glucose is converted into pyruvate, and NADH reduces it to lactate, producing energy
IV. Transport of glucose into cells
- Glucose requires specific transporters to cross cell membranes.
- There are 14 glucose transporter families (GLUTs)
- GLUT transporters are characterized by their unique tissue distribution and regulation.
- GLUT-1 is high in erythrocytes and blood brain barrier, with varying levels in other tissues
- GLUT-2 is present in liver, kidney, and pancreatic beta cells.
- GLUT-3 is primarily found in neurons.
- GLUT-4 is insulin-dependent and found in muscle and adipose tissue.
B. Na+-monosaccharide cotransporter system
- Sodium-dependent glucose transporters (SGLTs) move glucose against its concentration gradient.
- These transporters are crucial in the absorption of glucose from the gut and certain other tissues.
- They are located in the intestinal tract, renal tubules, and choroid plexus.
V. Reactions of glycolysis
- Glycolysis occurs in two stages: an energy investment phase and an energy generation phase.
- In the initial (energy investment) phase, glucose is phosphorylated at the expense of ATP investment.
- The subsequent phase (energy generation) results in the generation of ATP via substrate-level phosphorylation.
A. Phosphorylation of glucose
- Glucose phosphorylation is a crucial step for trapping glucose inside the cell, preventing its diffusion back out.
- Hexokinase is the primary enzyme responsible for glucose phosphorylation, with four isozymes (I-IV)
- Hexokinases I-III have high affinity for glucose.
- Hexokinase IV (glucokinase) is found in the liver and pancreatic beta cells.
- Glucokinase is importantly regulated by glucose concentration
- Hexokinase IV has a higher Km (lower affinity) for glucose than the other isozymes.
2. Hexokinase IV (Glucokinase)
- Glucokinase functions as a glucose sensor for insulin secretion in pancreatic beta cells.
- It also regulates glucose metabolism in hepatocytes (liver cells).
- The enzyme's high Km ensures it's only active at high glucose concentrations.
- It is also important in regulating glucose homeostasis.
- It plays a key role during a high carbohydrate meal
- It is involved in controlling hyperglycemia
b. Regulation by fructose 6-phosphate and glucose
- Glucokinase activity isn't allosterically inhibited by G-6-P like other hexokinases.
- It is regulated indirectly by fructose 6-phosphate.
- The regulatory protein, GKRP, regulates the activity of glucokinase in the liver.
c. Regulation by fructose 6-phosphate
- Phosphofructokinase-1 (PFK-1) is the key regulatory enzyme in glycolysis.
- The activity of PFK1 is modulated by different compounds.
- PFK-1 is inhibited by high ATP and citrate concentrations, reflecting high energy levels in the cell.
- PFK-1 is activated by high AMP and fructose 2,6-bisphosphate (F-2,6-BP).
2. Regulation by fructose 2,6-bisphosphate
- Fructose 2,6-bisphosphate (F-2,6-BP) is a potent allosteric regulator of PFK-1 and plays a central role in the regulation of glycolysis and gluconeogenesis.
- F-2,6-BisP is synthesized from fructose-6-phosphate by phosphofructokinase 2 (PFK-2.)
VII. Alternate fates of pyruvate
- Pyruvate can be oxidized to acetyl-CoA, entering the citric acid cycle.
- It can also be carboxylated to oxaloacetate, a precursor for gluconeogenesis.
- In certain microorganisms, pyruvate can be reduced to ethanol.
K. Reduction of pyruvate to lactate
- Lactate is the end product of anaerobic glycolysis in certain tissues, such as exercising muscles and red blood cells.
- The conversion of pyruvate to lactate is catalyzed by lactate dehydrogenase (LDH)
3. Lactic acidosis
- Lactic acidosis occurs when the production of lactate exceeds the body's capacity to utilize or remove it.
- This can be caused by various factors, including circulatory collapse, tissue hypoxia, and certain diseases.
- High levels of lactate in blood indicate a disruption in cellular metabolism and require medical attention.
L. Energy yield from glycolysis
- Glycolysis produces a small amount of ATP but most of the energy is stored in pyruvate or lactate.
- The citric acid cycle is required to release the energy stored in these compounds.
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Description
Test your understanding of glycolysis, the crucial metabolic pathway responsible for converting glucose into energy. This quiz covers both aerobic and anaerobic processes involved in glucose metabolism and the generation of ATP. Dive into the details of how various sugars are converted and the implications of pyruvate formation.
