Metabolism and Bioenergetics Quiz

Introduction to Metabolism

• Metabolism is the sum of all chemical reactions in cells.
• It's a highly coordinated cellular activity with directionality and matter/energy exchange with the environment.
• Specific functions include: obtaining energy from light or food, converting nutrients into cell components, assembling components into macromolecules, and forming/degrading specialized cellular molecules.

Digestion

• Breaks down carbohydrates, lipids, and proteins into absorbable forms (glucose, fatty acids, amino acids).

Absorption

• The absorption process moves digested products, along with vitamins, minerals, water, etc., from the digestive system into the body.

Metabolic Phases

• Absorption: Substances and energy enter the cell protoplasm from the environment.
• Transformation: The cell processes absorbed substances and energy, including secretion, digestion, assimilation, and dissimilation processes.
• Excretion: Removal of substances not incorporated into the cell protoplasm.

Metabolic Stages

• Stage 1: Large molecules are broken down into monomers (e.g., polysaccharides into glucose, lipids into glycerol and fatty acids, proteins into amino acids). This stage does not produce usable energy.
• Stage 2: Monomers are further broken down into simpler molecules, a key one being acetyl CoA. A small amount of ATP (energy) is created during this stage.
• Stage 3: Acetyl CoA is oxidized to water and carbon dioxide, resulting in the majority of ATP production from the food molecules.

Metabolism Divisions: Anabolism and Catabolism

• Anabolism: Constructive, building large molecules from smaller ones, using energy (ATP). Used to make proteins from amino acids.
• Catabolism: Degradative, breaking down large molecules from food or body stores into smaller ones, releasing energy. Energy is stored in special molecules for later use.
• Amphibolic Pathways: Mixed pathways that interconvert intermediates between the start of anabolic pathways and the end of catabolic ones.

Energy

• Energy is the capacity to do work. It exists as heat, light, electricity, and movement.

Metabolic Pathways

• A sequence of linked chemical reactions, where the product of one reaction is the substrate for the next (e.g., glycolysis). Includes a series of reactions that convert an initial substrate to final products through a series of intermediate metabolites.

Types of Metabolic Pathways

• Catabolic pathways: Oxidative pathways that release energy and reducing power, and create ATP (e.g., glycolysis, beta-oxidation).
• Anabolic pathways: Reductive pathways that consume energy (ATP), and reducing power to build molecules (e.g., gluconeogenesis, Calvin cycle).
• Amphibolic pathways: Mixed catabolic and anabolic pathways (e.g., Krebs cycle).

Glycolysis (Glycolysis)

• The process to break down glucose for energy in cells.
• 10 enzymatic reactions turn glucose into two pyruvate molecules for further energy delivery or other metabolic pathways.
• Produces ATP and NADH, and is involved in aerobic respiration (with oxygen) and fermentation (without oxygen).
• Occurs in the cytoplasm.
• Doesn't require oxygen.
• Involves a 6-carbon glucose turning into two 3-carbon pyruvate molecules.

Pentose Phosphate Pathway

• An alternative pathway for glucose catabolism (alternative to glycolysis).
• Occurs in the cytoplasm.
• Oxidizes glucose to provide reducing power (NADPH+H+) needed for anabolic processes and to act as an antioxidant in cells, primarily in red blood cells.
• Also produces pentoses (ribose) needed for building nucleic acids and other important coenzymes.
• Has two phases: oxidative and non-oxidative.

Krebs Cycle (Citric Acid Cycle)

• A key part of cell respiration.
• Occurs in the mitochondria (in cells).
• Converts intermediate molecules in earlier steps into carbon dioxide and water.
• Generates energy in the form of ATP and reducing power (molecules that can donate electrons). A complex route with multiple steps.

Cori Cycle

• A metabolic cycle happening between muscle and liver.
• During intense muscle activity, lactic acid forms from glucose, moving to the liver.
• The liver converts the lactate (lactic acid) back to glucose, which returns to the muscle for energy.
• Important for providing energy quickly during intense activities or low oxygen conditions.
• Glucose-muscle-lactate-liver-glucose-muscle

Transamination

• Transferring an amino group from an amino acid to a keto acid.
• Amino acid becomes a keto acid; keto acid becomes the new amino acid.
• Crucial for amino acid metabolism.
• Uses a coenzyme, pyridoxal phosphate (vitamin B6).
• Key amino acid donors: Glutamate, alanine, and aspartate.
• Key keto acid acceptors: α-ketoglutarate, pyruvate, and oxaloacetate.

Oxidative Deamination

• Removing an amino group from an amino acid, producing ammonia.
• Carried out by glutamate dehydrogenase.
• Part of amino acid catabolism.
• The major source of ammonia in our bodies comes from this reaction.
• Results in the production of ammonia and α-ketoglutarate.

Urea Cycle

• Metabolic process for removing excess nitrogen from the body.
• The breakdown of proteins produces ammonia; this cycle converts ammonia to urea.
• Happens primarily in the liver.
• Several enzymatic reactions are needed to produce urea from ammonia and other compounds.

Gluconeogenesis

• The synthesis of glucose from non-carbohydrate sources (e.g. amino acids, lactate).
• Crucial for maintaining blood glucose levels, especially between meals or during fasting.
• Happens primarily in the liver, and partially in the kidneys.
• Opposite of glycolysis (where glucose is broken down).
• Involves eleven enzymatic reactions; seven are the reverse of the glycolytic pathway; four reactions are unique to gluconeogenesis.

Glycogenolysis

• Breakdown of glycogen (stored glucose) to release glucose.
• Important for maintaining blood glucose levels between meals.
• Primarily uses the enzyme glycogen phosphorylase.

Glycogenesis

• Production of glycogen from glucose.
• Primarily in liver and muscles.
• Key enzymes include UDP-glucose pyrophosphorylase, glycogen synthase, and glycogen branching enzymes.

Amino Acid Classification

• Glucogenic amino acids: Produce intermediates used in gluconeogenesis.
• Ketogenic amino acids: Produce ketone bodies.
• Some amino acids can be both.
• Important in metabolism due to variety of processes they enter.