Glycolysis and Gluconeogenesis Quiz

Carbohydrate Metabolism

• Carbohydrates are a major fuel source for organisms.
• Complete oxidation of glucose releases ~2,840 kJ/mol of energy.
• Glucose can be used to synthesize the carbon skeletons of many other molecules.
• In plants and animals, glucose can be stored as polysaccharides (e.g., glycogen, starch) or sucrose.
• Glucose can be oxidized to a 3-carbon compound (pyruvate) via glycolysis.
• Glucose can be oxidized to pentoses (used in nucleic acid synthesis).

Outline of the Section

• Carbohydrates: nutritional perspective
• Metabolism of carbohydrates
• Metabolism of carbohydrates: nutritional perspective

Glucose

• Major fuel source for most organisms.
• Oxidation yields approximately -2,840 kJ/mol of energy
• Precursor for many molecules
• Stored in higher plants and animals as polysaccharides like sucrose.
• Oxidized to pyruvate via glycolysis.
• Oxidized to pentoses for nucleic acid synthesis

Fates of Glucose

• Synthesis of structural polysaccharides for cell walls of bacteria and plants and extracellular matrix components.
• Synthesis of structural polymers (e.g., cell wall polysaccharides)
• Oxidation via pentose phosphate pathway (generates NADPH, used in biosynthesis of lipids & nucleotides)
• Oxidation via Glycolysis (production of ATP and pyruvate)
• Storage (glycogen, starch) for later energy needs

Glycolysis

• Almost universal pathway for carbohydrate catabolism.
• Stores energy in ATP and NADH.
• Anaerobic or aerobic catabolism of glucose.
• Two-phase process: investment and payoff phases.
• Net gain of 2 ATP per glucose molecule.

Fates of Pyruvate

• Aerobic conditions: Pyruvate is oxidized to acetyl-CoA, which enters the citric acid cycle.
• Anaerobic conditions (e.g., animals, microbes): Pyruvate converted to lactate to regenerate NAD+ which is needed to continue glycolysis (lactic acid fermentation)

Summary of Glycolysis and Energetics

• 5.2% of glucose energy is removed in glycolysis (oxidation-reduction only).
• Much energy remains in pyruvate for further oxidation.
• Glycolysis: Glucose + 2ADP + 2NAD+ → 2Pyruvate + 2ATP + 2NADH + 2H+ + 2H₂O
• Net reaction: Glucose + 2NAD+ +2ADP + 2Pi → 2 Pyruvate + 2NADH + 2H+ + 2ATP + 2H₂O

Glycolysis: Steps 1-10 (Detailed)

• Each section (1-10) outlines individual enzymatic steps during glycolysis, highlighting the inputs, outputs, reaction types (exergonic or endergonic), involved enzymes, thermodynamic parameters, and regulation details.

Other Pathways Can Lead to the Glycolysis Pathway

• Multiple pathways feed into glycolysis, including those involving disaccharides (e.g., sucrose, lactose) and polysaccharides (e.g., starch, glycogen).
• These pathways break down complex carbohydrates into single sugars that can enter glycolysis.

Monosaccharide Feed-in to Glycolysis

• Many monosaccharides like fructose, mannose, and galactose can be converted into glucose or glycolysis intermediates.

Anaerobic Metabolism (Pyruvate to Lactate)

• During vigorous exercise when oxygen supply is limited, lactate is formed from pyruvate.
• This regenerates NAD+ needed for glycolysis
• The accumulation of lactate leads to muscle pain.

Anaerobic Metabolism (Pyruvate to Ethanol)

• In some microorganisms (yeast), pyruvate is decarboxylated to acetaldehyde, then to ethanol.
• This regenerates NAD+ needed for glycolysis.

From Catabolism to Anabolism

• Convergent catabolic pathways and divergent anabolic pathways often share related intermediates.
• ATP, NADH/NADPH are common precursors.

Carbohydrate Biosynthesis

• Focuses on how human (animal) cells synthesize carbohydrates, including glucose formation from various precursors.
• Pathways like gluconeogenesis convert lactate, amino acids, and other compounds into glucose

Gluconeogenesis

• Synthesis of glucose from non-carbohydrate precursors (e.g., lactate, amino acids, oxaloacetate).
• Bypass steps in the glycolysis reaction are used.
• The process consumes energy.

Glycolysis and Gluconeogenesis

• Seven reactions are common to both glycolysis and gluconeogenesis.
• Specific reactions bypass the three irreversible steps in glycolysis.

Pentose Phosphate Pathway

• An alongside glycolysis pathway that generates NADPH.
• The pathway offers alternative reactions to generate intermediates for nucleotide synthesis and reducing power.
• NADPH is critical for reductive biosynthesis in the body.

PPP, NADPH and Anti-oxidation

• NADPH is an essential reducing agent needed to protect cells from oxidative damage.
• NADPH levels can be used to determine the use of glucose in glycolysis or Pentose phosphate pathways

Additional Details (Steps, Enzymes, Mechanisms):

• Each step of glycolysis, gluconeogenesis, and the pentose phosphate pathways details are available in the provided documents. This is crucial for understanding their functions. (The specific mechanisms and functions of each enzyme involved in these processes are thoroughly covered in the detailed steps)