Cellular Metabolism • Metabolism = Sum of all reactions in the body
Metabolic reactions are of two types Anabolism • Synthesizes smaller molecules into larger molecules • Provides materials for growth and repair • Consumes energy
Catabolism • Large molecules decompose into smaller molecules • Releases energy for cellular use ATP = energy
Dehydration Synthesis • Type of anabolic reaction • Joins triglycerides, polysaccharides, and proteins • Water is formed from dehydration synthesis
Dehydration synthesis joining amino acids together
Dehydration Synthesis • Synthesizes polysaccharides from monosaccharides
• Synthesizes proteins from amino acids • Joins fatty acids to glycerol, forming form fats • Synthesizes nucleic acids from nucleotides
Catabolism • Reverse of Anabolism • Breaks down molecules • Releases energy from chemical bonds • Example: Hydrolysis
Hydrolysis • Type of Catabolic reaction • Reverse of dehydration synthesis • Requires water to break bonds
Hydrolysis • Decomposes Polysaccharides into monosaccharides & disaccharides • Decomposes proteins into amino acids • Decomposes Fats into fatty acids & glycerol • Decomposes Nucleic Acids into nucleotides
Anabolism & Catabolism are reversible reactions Enzymes control direction & rate of reactions
Enzyme Actions Enzymes • Are biological catalyst • They greatly reduce the activation energy required to start a reaction.
Substrate • Target molecule of an enzyme • Each enzyme acts on a specific substrate
Enzyme Characteristics • Most all are Proteins • Catalyze reactions - Increases the rate of reactions • Reusable - Not consumed by reaction • Specificity – Able to “recognize” a specific substrate
Enzyme Names • Named for substrate they act upon • Usually end with ____ ase. • Examples: • Lipase: decomposes lipids • Protease: decomposes proteins • Nuclease: decomposes nucleic acids • ATP Synthase: synthesizes ATP molecules
a. Active site • Region of enzyme that binds to substrate
b. EnzymeSubstrate Complex • Enzyme temporarily binds to substrate
Enzyme releases product • Enzyme is reused to join new substrates
Rates of reactions are limited by:
• The concentration of substrate • The concentration of enzyme • The efficiency of enzymes • Some enzymes handle 2-3 molecules per second • Other enzymes handle thousands per second
Metabolic Pathways • Complex series of reactions leading to a product • Pathways are controlled by several enzymes
Example: Catabolic pathway for the breakdown of glucose
Metabolic Pathways • The product of each reaction becomes the substrate of next reaction. • Each step requires its own enzyme • “Rate-Limiting Enzyme” • Least efficient enzyme in group • Rate-limiting enzyme is usually first in sequence
• Enzyme A = Rate-limiting Enzyme
Negative Feedback in Metabolic Pathway • Product of reaction often inhibits the rate-limiting enzyme. • Negative feedback prevents the overproduction of a product.
Cofactor • Combines with and activates some enzymes • Exposes the active site of enzyme to substrate • Cofactors are non-proteins • Include ions (zinc, iron, copper) and coenzymes
Coenzymes = organic cofactors • Coenzymes include Vitamins (Vitamin A, B, D) • Reusable – required in small amounts
Vitamins • Essential organic molecules that humans cannot synthesize - must come from diet • Many vitamins are coenzymes • Vitamins can function repeatedly, so can be used in small amounts. • Example: Coenzyme A
Energy for Metabolic Reactions Energy: is the capacity to change something, or ability to do work.
Common forms of energy: Heat Light Sound Chemical energy Mechanical energy Electrical energy
Energy cannot be created or destroyed. Only transferred from one form to another Think of a combustion engine
Fuel (chemical energy) + Oxygen
= Kinetic Energy + CO2 + H2O
Cellular Respiration • Cell Respiration: is the transfer of energy from food to make available for cellular use • Energy is stored in the electrons of food molecules • Oxidation: “controlled burning” of food molecules to release their energy • Cellular respiration requires enzymes
Cellular Respiration Glucose (C6H12O6) + 6O2 → Energy for ATP + H2O + CO2
ATP
Energy from foods such as glucose is used to make ATP
End of Section 1, Chapter 4