Exam 4: Glycolysis, TCA (CAC), ETC, & Gluconeogenesis

What is the primary purpose of Stage 1 in glycolysis?

To trap glucose in the cell and modify it for cleavage into two phosphorylated 3-carbon compounds.

What molecule is produced from the cleavage of fructose-1,6-bisphosphate?

Two molecules of glyceraldehyde-3-phosphate.

How many ATP molecules are invested during Stage 1 of glycolysis?

2 ATP molecules.

What is the net production of ATP during glycolysis?

2 ATP molecules.

What are the three simultaneous reactions involved in glycolysis?

Glucose is oxidized to pyruvate, NAD+ is reduced to NADH, and ADP is phosphorylated to ATP.

What must happen to NADH for ATP synthesis to continue after glycolysis?

NADH must be reoxidized to NAD+.

What are the two main fates of pyruvate in anaerobic conditions?

Conversion into ethanol or lactate.

What is the process called when pyruvate is converted to ethanol?

Ethanol fermentation.

Which enzyme catalyzes the decarboxylation of pyruvate in alcoholic fermentation?

Pyruvate decarboxylase.

What is produced when pyruvate is converted to lactate?

Lactic acid.

What enzyme catalyzes the conversion of pyruvate to lactate?

Lactate dehydrogenase.

What is the role of galactokinase in galactose metabolism?

It phosphorylates galactose to galactose 1-phosphate.

How is fructose metabolized in the liver?

By the fructose 1-phosphate pathway.

What is the first step in the metabolism of fructose?

Phosphorylation of fructose to fructose 1-phosphate by fructokinase.

What is the role of phosphofructokinase in glycolysis?

It is the key regulator of glycolysis and is allosterically inhibited by ATP.

What effect does AMP have on phosphofructokinase?

AMP stimulates phosphofructokinase, reversing the inhibitory effect of ATP.

What is the function of pyruvate carboxylase?

It requires thiamine pyrophosphate and catalyzes the decarboxylation of pyruvate.

What is the significance of maintaining redox balance in fermentation?

It allows glycolysis to continue by regenerating NAD+.

What is the final product of lactic acid fermentation?

Lactate.

What is the role of triose kinase in fructose metabolism?

It phosphorylates glyceraldehyde to glyceraldehyde 3-phosphate.

What is the role of galactose 1-phosphate uridyl transferase?

It converts galactose 1-phosphate into UDP-galactose and glucose 1-phosphate.

What is the role of phosphoglucomutase in galactose metabolism?

It converts glucose 1-phosphate into glucose 6-phosphate.

What is the relationship between glycolysis and ATP generation?

Glycolysis degrades glucose to generate ATP and provides building blocks for biosynthetic reactions.

What happens to pyruvate in the presence of oxygen?

It is metabolized to CO2 and H2O through the citric acid cycle.

What is the primary control mechanism for glycolysis in skeletal muscle?

The energy charge of the cell, specifically the ATP to AMP ratio.

What is the significance of the enzyme's regulatory site in phosphofructokinase?

ATP binding to the regulatory site lowers the enzyme's affinity for fructose 6-phosphate.

Why is NADH oxidized in fermentation?

To regenerate NAD+ and maintain glycolysis.

What enzyme generates ATP from ADP and produces AMP during high energy demands in muscles?

Adenylate kinase

What inhibits hexokinase in muscles?

Glucose 6-phosphate

What is the role of fructose 1,6-bisphosphate in glycolysis?

It stimulates pyruvate kinase.

How does ATP affect pyruvate kinase activity in muscles?

ATP allosterically inhibits pyruvate kinase.

What happens to glycolysis during muscle contraction?

The ATP/AMP ratio decreases, activating phosphofructokinase and increasing glycolysis.

What are the key regulators of phosphofructokinase in the liver?

Citrate (inhibitor) and fructose 2,6-bisphosphate (activator).

What is the primary function of the liver regarding glucose?

It maintains blood glucose concentration by storing glucose as glycogen or releasing it when supplies are low.

What activates phosphofructokinase in the liver after a carbohydrate-rich meal?

Fructose 2,6-bisphosphate.

What enzyme is primarily responsible for phosphorylating glucose in the liver?

Glucokinase (hexokinase IV).

What is the main site of gluconeogenesis?

The liver, although it can also occur in the kidneys.

What are the major noncarbohydrate precursors for gluconeogenesis?

Lactate, amino acids, and glycerol.

How is pyruvate formed from lactate in gluconeogenesis?

By lactate dehydrogenase in the liver.

What must gluconeogenesis bypass compared to glycolysis?

The three irreversible steps of glycolysis.

What is the effect of high glucose levels on fructose 6-phosphate concentration in the liver?

It increases the concentration of fructose 6-phosphate, which activates phosphofructokinase.

What happens to pyruvate kinase in the liver when blood glucose is low?

It is phosphorylated and inhibited.

What is the role of ATP in the regulation of phosphofructokinase in the liver?

ATP can regulate phosphofructokinase, but its effect is less critical than in muscles.

What is the relationship between fructose 2,6-bisphosphate and ATP in regulating phosphofructokinase?

Fructose 2,6-bisphosphate reduces the sensitivity of phosphofructokinase to ATP inhibition.

What is the primary fuel source for the brain and red blood cells?

Glucose.

What is gluconeogenesis?

The synthesis of glucose from pyruvate.

What is the significance of gluconeogenesis during fasting or starvation?

It provides glucose as the primary fuel for the brain and red blood cells.

What is the effect of high ATP concentration on glycolysis?

It inhibits phosphofructokinase and pyruvate kinase.

What is the effect of muscle contraction on the ATP/AMP ratio?

It decreases the ATP/AMP ratio, activating glycolysis.

What is the role of glucokinase in the liver?

It phosphorylates glucose when blood glucose levels are high.

How does fructose 6-phosphate influence phosphofructokinase activity?

High concentrations activate phosphofructokinase through fructose 2,6-bisphosphate.

What is the relationship between glycolysis and gluconeogenesis?

Gluconeogenesis is not a complete reversal of glycolysis.

Where are the enzymes for gluconeogenesis primarily located?

In the cytoplasm, except for pyruvate carboxylase (in mitochondria) and glucose 6-phosphatase (in the endoplasmic reticulum).

What is the first step in gluconeogenesis?

The carboxylation of pyruvate to form oxaloacetate, catalyzed by pyruvate carboxylase.

What is formed from oxaloacetate in gluconeogenesis?

Phosphoenolpyruvate (PEP) is formed from oxaloacetate by phosphoenolpyruvate carboxykinase.

What is the role of fructose 1,6-bisphosphatase in gluconeogenesis?

It catalyzes the hydrolysis of fructose 1,6-bisphosphate to fructose 6-phosphate, an irreversible step.

What is the final step in gluconeogenesis?

The generation of free glucose from glucose 6-phosphate, catalyzed by glucose 6-phosphatase.

How does gluconeogenesis differ from glycolysis in terms of energy?

Gluconeogenesis is energetically unfavorable and requires the hydrolysis of 6 nucleotide triphosphates, while glycolysis generates only 2 ATP.

What regulates the activity of gluconeogenesis and glycolysis?

They are reciprocally regulated based on the concentrations of glucose, lactate, ATP, and AMP.

What happens when glucose is abundant in the cell?

Glycolysis predominates when glucose is abundant.

What happens when glucose is scarce in the cell?

Gluconeogenesis is favored when glucose is scarce.

What is the key regulatory site in gluconeogenesis?

The interconversion of fructose 1,6-bisphosphate and fructose 6-phosphate.

How does AMP affect glycolysis and gluconeogenesis?

High AMP stimulates glycolysis and inhibits gluconeogenesis.

What effect do high levels of ATP and citrate have on glycolysis?

They inhibit phosphofructokinase, promoting gluconeogenesis instead.

What is the Cori cycle?

A series of reactions where lactate produced by muscles is converted into glucose by the liver.

What is the fate of lactate produced by active skeletal muscle?

It is transported to the liver, where it is converted back to pyruvate and then to glucose.

What role does fructose 2,6-bisphosphate play in glucose metabolism?

It stimulates phosphofructokinase and inhibits fructose 1,6-bisphosphatase.

What happens to fructose 2,6-bisphosphate when blood glucose concentration is low?

It is dephosphorylated to form fructose 6-phosphate, which no longer activates phosphofructokinase.

What is the role of pyruvate carboxylase in gluconeogenesis?

It catalyzes the conversion of pyruvate to oxaloacetate.

What is the significance of the interconversion of phosphoenolpyruvate and pyruvate?

It is a regulatory point where glycolysis and gluconeogenesis are reciprocally controlled.

How does lactate serve as an energy source for other organs?

Lactate can be converted back to pyruvate and metabolized through the citric acid cycle in well-oxygenated cells.

What is the primary purpose of gluconeogenesis?

To synthesize glucose from non-carbohydrate precursors, especially during fasting or intense exercise.

What are the two main enzymes involved in converting pyruvate to phosphoenolpyruvate?

Pyruvate carboxylase and phosphoenolpyruvate carboxykinase.

What is the role of NADH in the conversion of oxaloacetate to phosphoenolpyruvate?

NADH is generated during the reoxidation of malate to oxaloacetate in the cytoplasm.

What is the energetic cost of synthesizing glucose from pyruvate?

It requires the hydrolysis of 6 high-energy phosphate bonds.

What is the consequence of simultaneous high activity in both glycolysis and gluconeogenesis?

It would lead to the hydrolysis of four nucleoside triphosphates per reaction cycle, which is energetically wasteful.

What process captures energy from glucose as ATP?

Glycolysis

What is the main purpose of cellular respiration?

To generate ATP by completely oxidizing pyruvate into CO2 and water.

Where does cellular respiration occur?

In the mitochondria.

What are the two main parts of cellular respiration?

Citric acid cycle and oxidative phosphorylation.

What is another name for the citric acid cycle?

Krebs cycle or tricarboxylic acid cycle.

What does the citric acid cycle produce from acetyl CoA?

CO2, ATP, NADH, and FADH2.

What type of reactions occur in the citric acid cycle?

Oxidation, reduction, condensation, dehydration, hydration, and hydrolysis.

What is the role of activated carriers in cellular metabolism?

To degrade and release free energy upon degradation.

What is the function of Coenzyme A (CoA)?

To carry acyl groups, such as the acetyl group.

What are the fates of pyruvate in the absence of oxygen?

It is converted to lactic acid or ethanol.

What is the link between glycolysis and the citric acid cycle?

The irreversible conversion of pyruvate into acetyl CoA.

What is produced during the decarboxylation of pyruvate?

Acetyl CoA and CO2.

What is the role of the pyruvate dehydrogenase complex?

To oxidatively decarboxylate pyruvate to form acetyl CoA.

What are the three steps in the synthesis of acetyl CoA from pyruvate?

Decarboxylation, oxidation, and transfer to CoA.

What coenzymes are involved in the pyruvate dehydrogenase complex?

Thiamine pyrophosphate (TPP), lipoic acid, flavin adenine dinucleotide (FAD), CoA, and NAD+.

What is the significance of the thioester bond formed during acetyl CoA synthesis?

It is energy-rich and facilitates the transfer of the acetyl group.

What is the rate-limiting step in the synthesis of acetyl CoA?

The decarboxylation of pyruvate catalyzed by pyruvate dehydrogenase.

What happens to the high-energy electrons captured during the citric acid cycle?

They are transferred to oxygen to form water during oxidative phosphorylation.

How many molecules of CO2 are produced in one turn of the citric acid cycle?

Two molecules of CO2.

What is produced alongside ATP during the citric acid cycle?

Reduced coenzymes NADH and FADH2.

What is the role of NAD+ in cellular respiration?

To accept electrons and become NADH, a carrier of high-energy electrons.

What is the function of FAD in the citric acid cycle?

To accept electrons and form FADH2.

What is the main energy currency produced during cellular respiration?

ATP.

What is the importance of the citric acid cycle in metabolism?

It serves as a central metabolic hub and provides precursors for biosynthesis.