Cellular Metabolism Quiz

Overview of the Living Cell (I)

• Bioenergetics is the quantitative study of energy transformation in living cells. This includes changes in energy form, such as from light energy to chemical energy.
• Cellular energy exists in two forms: potential energy (e.g., chemical bonds, concentration gradients, electrical charges) and kinetic energy (e.g., heat).
• Metabolism is a series of chemical reactions within a living organism that sustain life. Metabolism involves energy flow during chemical processes.

Learning Objectives

• Understand the principles of catabolism and anabolism.
• Overview of the metabolisms of carbohydrates, proteins and lipids.
• Recognize the role of ATP and mitochondria in the energy production processes in the human body.
• Discuss the role of the liver in different metabolic processes.

Key Concepts on Metabolism

• Metabolic pathways can be broadly divided into catabolism and anabolism.
• Catabolism breaks down complex molecules into simpler ones, releasing energy (e.g., glycolysis, β-oxidation).
• Anabolism builds complex molecules from simpler ones, storing energy (e.g., glycogenesis, protein synthesis).
• Metabolic intermediates are the chemical species formed within metabolic pathways.
• These reactions are catalyzed by metabolic enzymes.
• Enzyme activity is regulated by physiological needs and changes.
• Some metabolic enzymes require co-enzymes.

Glucose Metabolism

• Glucose is the primary carbohydrate used to produce ATP (adenosine triphosphate).
• Glucose oxidation happens in three stages: glycolysis, citric acid cycle, and oxidative phosphorylation.

Glycolysis

• Glycolysis is the breakdown of glucose into pyruvate.
• It takes place in the cytosol.
• The starting molecule is glucose (1X), and the end product is pyruvate (2X).
• It releases 2 ATP.
• It also produces NADH (2X).

Glycolysis (complete steps)

• Details about the steps of glycolysis, including enzymes involved (Hexokinase, phosphofructokinase, pyruvate kinase).
• Explanation of the regulation of glycolysis, including how enzymes like hexokinase and phosphofructokinase are regulated.

Import notes of glycolysis

• Glycolysis is a metabolic pathway that breaks down glucose into pyruvate, producing ATP and NADH.
• Its primary function is generating energy (ATP) for other metabolic processes and the production of intermediates in cells.
• It's the only metabolic pathway that happens in all body cells.
• Critically important for cells without mitochondria, such as brain cells and red blood cells.
• Glycolysis works under both aerobic and anaerobic conditions.

Glycolysis in anaerobic environment

• Muscle cells convert pyruvate to lactic acid, regenerating NAD+.
• Fermentation is a process that converts pyruvate into CO2 and ethanol in some cells, such as yeast.

Cori cycle

• Lactate produced in muscles is transported to the liver.
• Lactate is converted back to pyruvate and then to glucose in the liver.
• The Cori cycle prevents lactate acidosis in muscles during anaerobic conditions.

Glycolysis in aerobic environment

• Aerobic respiration is the breakdown of glucose to produce much more ATP, using oxygen.

Tricarboxylic acid (TCA) cycle

• Pyruvate is converted to Acetyl-CoA inside mitochondria, acting as the entry point of the TCA cycle.
• Acetyl-CoA undergoes an 8-step process, generating 3 NADH, 1 FADH2, 1 GTP and released CO2.

Oxidative phosphorylation (electron transport system)

• Electrons from NADH and FADH2 are passed to an electron transport chain.
• This generates a proton gradient across the mitochondrial inner membrane.
• The proton gradient drives ATP synthesis.

Synthesis of ATP by ATP Synthase

• Chemiosmosis is the movement of ions across a membrane.
• The proton gradient formed by the electron transport chain drives ATP synthase to make ATP.

Comparison of energy released from glucose

• Aerobic respiration yields 38 ATP per glucose molecule.
• Anaerobic respiration (glycolysis) yields 8 ATP per glucose molecule.

ATP and GTP

• ATP (adenosine triphosphate) and GTP (guanosine triphosphate) are energy-carrying molecules.
• Hydrolysis of ATP (breaking the phosphate bonds) releases energy to drive endergonic processes.

Summary of glucose metabolism

• Glucose can undergo glycolysis (anaerobic) or the aerobic pathways that include TCA cycle and oxidative phosphorylation to generate energy.

Gluconeogenesis

• Gluconeogenesis is a metabolic pathway that synthesizes glucose from non-carbohydrate sources.
• Important for maintaining blood glucose during fasting and exercise.
• Key organs are the liver and kidneys.

Glycogenolysis

• Glycogenolysis is the breakdown of glycogen into glucose.
• Important for providing glucose during periods of fasting and exercise.

Glycogenesis

• Glycogenesis is the synthesis of glycogen from glucose.
• Important for storing glucose for later use.

Blood glucose homeostasis

• Blood glucose levels are maintained at ~5 mM (3.9-7.1 mM) through the actions of insulin and glucagon.
• Insulin stimulates glucose uptake, glycolysis, and glycogenesis, lowering blood glucose.
• Glucagon stimulates glucose release, gluconeogenesis, and glycogenolysis - raising blood glucose.

Signaling pathways in response to insulin and glucagon

• Describes how insulin and glucagon influence different metabolic processes in cells, influencing enzymes involved in glycolysis, glycogenesis and gluconeogenesis via hormones and signal pathways

Insulin actions in liver, muscle and adipose tissue

• Insulin promotes glucose uptake and storage in muscles, liver and adipose tissue. It also promotes the synthesis of glycogen, proteins, lipids and inhibits gluconeogenesis.
• These actions maintain blood glucose levels.

Physiological responses to energy supply (1 & 2 & 3)

• Describes the body's response to different energy states.

Lipid metabolism – structure of fat

• Fats are composed of glycerol and fatty acids. Triglycerides are the major storage and transport form.

Lipid metabolism

• Triglycerides are broken down to glycerol and fatty acids.
• Glycerol can enter glycolysis or gluconeogenesis.
• Fatty acids undergo beta-oxidation in mitochondria producing Acetyl-CoA for energy.

B-oxidation of fatty acids

• Describes the steps of beta-oxidation in fats to liberate energy in the form of Acetyl-CoA.

Nitrogen metabolism

• Nitrogen is removed from amino acids to produce urea, an excreted product.
• Amino acids contribute carbon skeletons for other metabolic pathways, such as TCA cycle
• Describes the overall metabolic processes of protein catabolism to liberate energy

Example of amino acid metabolism

• Shows specific pathways for the breakdown of isoleucine