Glycolysis and Gluconeogenesis Overview

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Questions and Answers

What is one of the primary roles of glucose in metabolism?

It serves solely as a precursor for water synthesis.

It is an energy-rich fuel for ATP generation via glycolysis. (correct)

It acts exclusively as a structural component in cells.

It can only be stored in its monomeric form.

How is the amount of glucose in the blood primarily regulated?

By external supplementation of glucose only.

Primarily by the breakdown of triglycerides.

Through uncontrolled release of insulin.

Via several processes that involve the production and consumption of glucose. (correct)

Which statement accurately describes glucose as an osmolyte?

It serves exclusively as a waste product in metabolism.

It can exist only in liquid form and cannot be polymerized.

It can be stored in polymeric forms like glycogen and starch. (correct)

It is not involved in cellular osmoregulation.

Which of the following represents a high-energy, long-term energy storage system in organisms?

Triglycerides Signup and view all the answers

What is the significance of the negative ΔG value in the glucose metabolism equation?

It shows that the reaction is energetically favorable and releases energy. Signup and view all the answers

What is the primary product of glycogen degradation through phosphorolysis?

Glucose-1-phosphate Signup and view all the answers

Which metabolite is a known activator of hexokinase activity?

AMP Signup and view all the answers

Which of the following enzymes converts phosphoenolpyruvate to pyruvate?

Pyruvate Kinase Signup and view all the answers

Which molecule inhibits phosphofructokinase-1 (PFK-1) activity?

ATP Signup and view all the answers

Which of the following statements about the glycolysis regulation is true?

ATP inhibits PFK-1. Signup and view all the answers

What is the consequence of decreased NADPH levels in relation to glutathione?

Increased levels of oxidized glutathione Signup and view all the answers

How does low NADPH levels affect individuals with G-6-PD deficiency?

They fail to maintain reduced glutathione Signup and view all the answers

What is believed to be the mechanism by which Plasmodium is killed?

Increased levels of H2O2 Signup and view all the answers

Which substance is crucial for reducing oxidative stress by maintaining reduced glutathione levels?

NADPH Signup and view all the answers

What happens to H2O2 levels when NADPH levels decrease?

They increase significantly Signup and view all the answers

What compound inhibits the HMP pathway?

High NADPH concentration Signup and view all the answers

What is reduced glutathione primarily composed of?

Amino acids Signup and view all the answers

Which enzyme is responsible for the conversion of hydrogen peroxide in the presence of glutathione?

Glutathione peroxidase Signup and view all the answers

In red blood cells (RBCs), what is the primary source of NADPH?

HMP pathway Signup and view all the answers

What happens to the HMP when NADPH levels are low?

It is activated Signup and view all the answers

What is the role of glutathione reductase in the context of oxidative stress?

To reduce glutathione disulfide to reduced glutathione Signup and view all the answers

Which of the following is NOT a component of the glutathione mechanism?

Cytochrome c Signup and view all the answers

In the context of the HMP, what is the fate of NADPH?

It is used as a reducing agent in biosynthetic reactions Signup and view all the answers

What is the primary reason G6PD cannot be continually synthesized?

There is no nucleus. Signup and view all the answers

Which pathway is associated with the production of NADPH?

Pentose pathway Signup and view all the answers

What role does glutathione play in the metabolic process described?

It provides electrons for glutathione peroxidase. Signup and view all the answers

What happens to NADPH during the interaction with Pamaquin in red blood cells?

It get reduced spontaneously. Signup and view all the answers

What compound is involved in the nonenzymatic reduction alongside NADPH?

Hydrogen peroxide Signup and view all the answers

Why is the reduction of oxidized pamaquin significant in red blood cells?

It helps mitigate oxidative stress. Signup and view all the answers

What is the relationship between NADPH and glutathione in the described metabolic pathway?

NADPH reduces oxidized glutathione. Signup and view all the answers

What role does glutathione peroxidase play in the metabolic process?

It catalyzes the reduction of hydrogen peroxide. Signup and view all the answers

What is the overall equation of glycolysis?

Glucose + 2NAD+ + 2ADP + 2Pi → 2 Pyruvate + 2NADH + 2H+ + 2ATP + 2H2O Signup and view all the answers

Which of the following phases of glycolysis involves energy consumption?

Preparatory phase Signup and view all the answers

In glycolysis, how many molecules of ATP are generated?

2 ATP Signup and view all the answers

How much of the total energy in glucose is harvested during glycolysis?

5.14% Signup and view all the answers

What is the primary role of hexokinase in glycolysis?

To phosphorylate glucose, making it irreversible Signup and view all the answers

Which step in glycolysis represents the first committed step?

Conversion of fructose 6-phosphate to fructose 1,6-bisphosphate Signup and view all the answers

Which of the following statements about RBCs and glycolysis is true?

RBCs bypass step 7, yielding no net ATP synthesis. Signup and view all the answers

What is the change in free energy ($ riangle G$) for the overall glycolysis reaction?

$-85 kJ/mol$ Signup and view all the answers

At which stage of glycolysis is NADH produced?

Step 6 Signup and view all the answers

Which enzyme is specifically highlighted as playing a key role in regulating glycolysis?

PFK-1 Signup and view all the answers

Study Notes

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

Glucose is a central molecule in metabolism, acting as both an energy source and a precursor for other molecules
Glucose is an energy-rich fuel, with the overall reaction of glycolysis producing energy in the form of ATP and NADH:
- C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O ΔG = -2840 kJ/mol
Glycolysis (Embden-Meyerhof Pathway) is a multi-step process breaking down glucose into pyruvate
Two main phases of glycolysis:
- Preparatory phase (energy investment): glucose is activated with energy consumption
- Payoff phase (energy liberation): glucose breaks down with the release of ATP and NADH
Glycolysis is a key process for energy generation
Glucose is stored in the form of polymers (starch, glycogen)
Glycogenolysis breaks down glycogen into glucose
Glycogenesis converts glucose into glycogen
Glycolysis and gluconeogenesis share some steps but use different enzymes in certain irreversible steps to allow for controlled directionality
Gluconeogenesis builds glucose from simpler precursors.
Pentose Phosphate Pathway (HMP) converts glucose 6-phosphate into ribose 5-phosphate and NADPH.
- Non-oxidative phase recycles pentose phosphates to glucose 6-phosphate
- NADPH is important for reducing reactive oxygen species and for biosynthesis of fatty acids, sterols, etc.
- Ribose 5-phosphate is a precursor for nucleotides, DNA, RNA.
Glucose dynamics in living organisms is tightly regulated
Different energy storage systems in organisms - triglycerides (long-term). Glucose and its polymers are enough for 1 or 2 days. ATP, phosphocreatine, and other phosphorylated esters (e.g., acetyl-coA) are dynamic energy-rich forms.

Glucose Dynamics

Note different energy storage systems in organisms:
- Triglycerides (long-term energy reserves).
- Glucose and starch/glycogen (short-term).
Glucose is tightly regulated.

Glycolysis (Embden-Meyerhof Pathway)

Biochemical process breaking down glucose to pyruvate
- 10 distinct steps, with energy release in form of ATP (2 from one glucose molecule; 4 created then 2 needed to start) and NADH
Preparatory and Payoff phases
- Preparatory phase involves energy input to activate glucose & cleave it.
- Payoff phase releases energy through cleaving glucose and generating ATP and NADH.
Overall, glycolysis is an essential process.
Glycolysis is not super efficient in terms of energy generation
- Only 5-6% of total energy is released as ATP from glucose oxidation to CO₂ and H₂O

Glycolysis Steps (Details)

Glucose enters cells via glucose transporters (GLUT)
Glucose is marked for degradation by phosphorylation.
Each step of glycolysis is catalyzed by a specific enzyme. (e.g., hexokinase/ glucokinase, phosphofructokinase, aldolase, etc.)

Glycolysis: Energetics

Overall equation of glycolysis: Glucose + 2NAD⁺ + 2ADP + 2Pᵢ → 2Pyruvate + 2NADH + 2H⁺ + 2ATP + 2H₂O.
Glycolysis is essential and irreversible due to a net decrease in free energy.
Glycolysis is relatively inefficient.

Gluconeogenesis (Carbohydrate Synthesis from Simple Precursors)

Biosynthesis of glucose from non-carbohydrate precursors (e.g., pyruvate, lactate, amino acids, glycerol).
Reversal of some steps; others must be bypassed due to the highly exergonic nature of glycolysis
Important in maintaining blood glucose levels, especially during fasting.

Gluconeogenesis: Enzymatic Steps

Reverses some enzymatic steps in glycolysis that are highly irreversible.
Steps 10, 6, 3 are bypassed

Gluconeogenesis: Energetics

Requires energy input in the form of ATP and GTP.
Gluconeogenesis is energetically costly in terms of ATP and GTP usage.

Gluconeogenesis: Pathway

Breakdown of simple precursors, such as lactate for example.
Important that glucose is generated inside of the cell, then released from the cell.

Pentose Phosphate Pathway (HMP)

Generates NADPH and ribose-5-phosphate
Important for biosynthesis of fatty acids, sterols, & nucleotides.
The pathway is flexible in generating important forms of glucose

Oxidative "Stress" and the Role of Glutathione

Reactive Oxygen Species (ROS).
Important role of the pentose phosphate pathway (HMP) in maintaining the balance between oxidizing and reducing compounds.
Anti-oxidant properties of glutathione
- Necessary for reducing reactive oxygen species (ROS).
The HMP produces NADPH and is necessary for reducing glutathione.

Polyol Pathway

Alternative pathway to glycolysis utilizing cells lacking sorbitol dehydrogenases.
Excess glucose accumulation and buildup of sorbitol leads to osmotic damage

Drugs and Diseases

Diseases related to the malfunction of pathways (i.e., galactosemia, cancer, beri-beri, malaria, diabetes).
Drugs impacting pathways (i.e., FdG imaging agents, thiamine, pamaquin)

Metabolic Characteristics of Glycolysis

Regulation of glycolysis (well-fed state vs fasting)
- Involves various enzymes, regulatory molecules, and hormones.

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Description

This quiz explores the essential biochemical processes of glycolysis, gluconeogenesis, and the pentose phosphate pathway. It focuses on the breakdown and synthesis of glucose, energy production, and the regulation of these metabolic pathways. Test your knowledge of how glucose serves as a crucial energy source in cell metabolism.