Metabolism and Energy Production Quiz

Metabolic Pathways

• Metabolism is the process of converting nutrients into energy in the body.
• In the fed state, nutrients are stored, and in the fasting state, they are oxidized for energy production.
• Nutrients are digested and broken down into carbohydrates (glucose), fats (fatty acids and glycerol), and proteins (amino acids).

Carbohydrate Metabolism

• Glycolysis is the metabolic pathway for glucose.
• Glucose is stored as glycogen or fat.
• Glycogen and fat are oxidized for energy.
• Glycolysis produces ATP.
• In a starvation state, fatty acids are used to produce ketone bodies, which can be used as fuel.

Fat Metabolism

• Fatty acids undergo beta-oxidation, producing acetyl CoA.
• Acetyl CoA enters the Krebs' cycle.
• Glycerol is used to create glucose for brain and blood cells.

Protein Metabolism

• Amino acids undergo transamination.
• Amino acids are synthesized into new proteins.
• Amino acids are oxidized for energy.
• Keto acids are produced and can enter the citric acid cycle.

Cellular Respiration

• Glycolysis, Link Reaction, Krebs cycle, and Chemiosmosis are the four stages of aerobic respiration.
• Glucose starts the process in the cytosol.
• Pyruvate is transported into the mitochondria
• Acetyl CoA is produced into the mitochondria.
• The Krebs Cycle takes place in the mitochondrial matrix, producing ATP, NADH, and FADH₂.
• Electrons are passed along the electron transport chain (ETC), causing protons to be pumped into the intermembrane space.
• ATP is synthesized by ATP synthase when protons flow back into the mitochondrial matrix.
• Anaerobic respiration takes place when oxygen is not available.
• Lactate or ethanol are produced as byproducts of anaerobic respiration.

Glycolysis

• Glycolysis breaks down glucose into pyruvate.
• 2 ATP molecules are produced in the process.
• It occurs in the cytoplasm.
• Important enzymes: Hexokinase, Phosphofructokinase, Aldolase, Glyceraldehyde 3-phosphate dehydrogenase, Phosphoglycerate kinase, Pyruvate kinase.

Gluconeogenesis

• Gluconeogenesis is the process of producing glucose from non-carbohydrate sources.
• This pathway is not completely reversible to glycolysis.
• Precursors include lactate, glycerol (from triglycerides), alanine, and glutamine.
• Important enzymes: pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, glucose-6-phosphatase.
• It takes place in the cytosol and mitochondria.

Citric Acid Cycle

• The Citric Acid Cycle (Krebs Cycle) is a central metabolic pathway.
• Eight enzymatic reactions.
• It takes place in the mitochondrial matrix.
• Acetyl CoA is a key input.
• 6 NADH and 2 FADH₂ are produced along with 2 GTP (equivalent to 2 ATP).
• ATP is regulated by isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase.

Electron Transport Chain

• The Electron Transport Chain (ETC) is a series of protein complexes in the inner mitochondrial membrane.
• It utilizes electrons from NADH and FADH₂ to pump protons (H⁺) across the membrane.
• Chemiosmosis is the process of ATP production driven by the proton gradient generated by the ETC.
• ATP synthase utilizes the proton gradient to produce ATP.

Fatty Acid Activation

• Free fatty acids need to be activated before entering beta-oxidation.
• This is done through addition of Coenzyme A (CoA) via Acyl-CoA Synthase.
• This process consumes energy (ATP) to AMP+PPi.

Fatty Acid Transport

• To be further oxidized, fatty acids are transported to the mitochondria via the carnitine shuttle.
• Acyl CoA interacts with carnitine and enters mitochondria via acylcarnitine/carnitine translocase.

Beta-Oxidation

• A series of four enzyme-catalyzed reactions that break down fatty acyl-CoA.
• Each cycle produces Acetyl-CoA, NADH, and FADH₂.
• Products from beta-oxidation move to the Citric Acid cycle for further ATP production.

ATP Production

• Each acetyl CoA produced in beta-oxidation leads to 10 ATP if entering the Citric Acid cycle.
• Each NADH results in about 2.5 ATP in the electron transport chain.
• Each FADHz results in about 1.5 ATP in the electron transport chain.

Amino Acid Metabolism

• Proteins are broken down into amino acids.
• Amino groups are removed via transamination or deamination.
• The remaining carbon skeletons enter metabolic pathways.
• Some amino acids are glucogenic (produce glucose), while others are ketogenic (produce ketone bodies).

Carbohydrates vs. Lipids

• Carbohydrates are a ready energy source.
• Lipids (fats) provide more energy per gram but are less easily digested.
• They are less immediately available for energy and are oxidized differently.