Lesson 9. Introduction to Metabolism PDF

Biochemistry Cellular Metabolism. Introduction CHAPTER OUTLINE 1. Cellular metabolism: Obtaining matter and energy Autotrophs (Chemical synthesizers, Photosynthesizers) and Heterotrophs 2. Metabolic processes: nutrition, respiration and biosynthesis 3. Concept of metabolism: Metabolic pathways Che...

Biochemistry Cellular Metabolism. Introduction CHAPTER OUTLINE 1. Cellular metabolism: Obtaining matter and energy Autotrophs (Chemical synthesizers, Photosynthesizers) and Heterotrophs 2. Metabolic processes: nutrition, respiration and biosynthesis 3. Concept of metabolism: Metabolic pathways Chemical energy: ATP and reducing power Endergonic and exergonic reactions 4. Catabolism and Anabolism CELLULAR METABOLISM CELL ACTIVITY IN WHICH MANY multienzyme systems cooperate to reach four functions: 1 –CHEMICAL ENERGY PRODUCTION (example: ATP) 2 - CONVERT NUTRIENT MOLECULES INTO MOLECULES OF THE CELL 3 - POLYMERIZE MONOMER PRECURSORS INTO POLYMERS 4 - SYNTHESIS AND DEGRADATION of required BIOMOLECULES based on specialized cellular functions (pigments, membrane lipids, etc.) HOW ORGANISMS OBTAIN MATTER AND ENERGY? Living organisms need matter (carbon) and energy to build organic molecules.  According to the carbon source, they are classified as: AUTOTROPHS: they synthesize glucose and other organic compounds from atmospheric CO2 (ex. Plants) HETEROTROPHS: they use organic molecules (ex. Animals)  According to the source of energy, they are classified as: PHOTOTROPHS: they obtain it from the sun CHEMIOTROPHS: they obtain it from chemical reactions The type of metabolism that takes place in a cell of a particular organism depends on the enzymes it has (genetic) METABOLIC CLASSIFICATION OF ORGANISMS Metabolic Classification of Organisms According to Their Carbon and Energy Requirements Classification Carbon Source Energy Source Electron Donors Examples Photoautotrophs CO2 Light H2O, H2S, S, other inorganic compounds Green plants, algae, cyanobacteria , photosynthetic bacteria Photoheterotrophs Organic compounds Light Organic compounds Nonsulfur purple bacteria Chemoautotrophs CO2 Oxidationreduction reactions Inorganic Nitrifying bacteria; hydrogen, sulfur compounds: H2, H2S, and iron bacteria + 2+ NH4 , NO2 , Fe , Mn2+ Chemoheterotrophs Organic compounds Oxidationreduction reactions Organic compounds, All animals, most microorganisms, nonphotosynthetic plant tissue such as e.g., glucose roots, photosynthetic cells in the dark A third criteria can also be used: the presence or absence of molecular oxygen Aerobes or stric aerobes Anaerobes facultative anaerobes DEFINING METABOLISM AND CHEMICAL ENERGY The cells require a constant supply of energy to generate and maintain the biological order that keeps them alive. This energy is derived from the chemical bond energy in food molecules, which thereby serve as fuel for cells. METABOLISM Ordered set of chemical reactions taking place in the cell, catalyzed by enzymes and whose objective is to obtain materials and energy to support the different vital functions ATP It is the Universal molecule carrying chemical energy in living organisms METABOLIC PROCESSES Nutrition, Respiration and Biosynthesis As raw MATERIAL SYNTHESIS Production of structures and material needed NUTRITION NUTRIENTS As a source of ENERGY CELLULAR RESPIRATION Biological processes to dissociate molecules ENERGY Muscle contraction Nervous impulse conduction Movement of matter inside and outside of the cell Other forms of cellular activity METABOLISM ELEMENTS:  Arranged and interconnected reactions: metabolic pathways or routes.  Catalyzed by specific enzymes with the possibility of regulation. Metabolic pathway  Intermediaries: metabolites Initial substrate Enz-1 Cells obtain MATTER AND ENERGY Metabolite-1 CHEMICAL REACTIONS ARE CLASSIFIED AS: • • exergonic (energy-releasing) or endergonic (with use of energy) Enz-2 Metabolite-2 Metabolism requires of exergonic and endergonic reactions Enz-3 Final product CELLULAR METABOLISM Metabolism have two fundamentally different purposes: the generation of energy to drive vital functions and the synthesis of biological molecules. To achieve these ends, metabolism consists largely of two contrasting and complementary processes, catabolism and anabolism.  CATABOLISM: Catabolic pathways are characteristically energyyielding. Catabolism involves the oxidative degradation of complex nutrient molecules (carbohydrates, lipids, and proteins) obtained either from the environment or from cellular reserves  ANABOLISM: anabolic pathways are energy-requiring. Anabolism is a synthetic process in which the varied and complex biomolecules (proteins, nucleic acids, polysaccharides, and lipids) are assembled from simpler precursors. Such biosynthesis involves the formation of new covalent bonds, and an input of chemical energy is necessary to drive such endergonic processes. The ATP generated by catabolism provides this energy. CATABOLISM versus ANABOLISM CATABOLISM POLYMERS: proteins nucleic acids, polysaccharides, lipids ANABOLISM MONOMERS: Amino acids, nucleotides, sugars, fatty acids, glycerol METABOLIC INTERMEDIARIES Pyruvate, acetyl-CoA, Krebs cycle intermediaries ENERGY NET PRODUCTION ENERGY Simple small molecules H2O, CO2, NH3 NET INTAKE CELLULAR METABOLISM METABOLITES: GLUCOSE, CITRIC ACID………… CHEMICAL ENERGY ADP/ATP CARRIERS OF ELECTRONS: reducing power NADP+/NADPH NAD+/NADH FAD+/FADH2 CELLULAR METABOLISM CELLS REQUIERE SOURCES OF FREE ENERGY The energy that cells can and must use is free energy, described by the Gibbs free-energy function G: • prediction of the direction of chemical reactions, • their exact equilibrium position, • and the amount of work they can (in theory) perform at constant temperature and pressure. Heterotrophic cells acquire free energy from nutrient Molecules. Photosynthetic cells acquire it from absorbed solar radiation. Both kinds of cells transform this free energy into ATP and other energy-rich compounds. The free energy change for ATP hydrolysis is large and negative. In standard conditions is -30.5 KJ/mol EXERGONIC AND ENDERGONIC CHEMICAL REACTIONS EXERGONIC REACTION: When a reaction proceeds with the release of free energy (that is, when the system changes so as to possess less Free energy), the free-energy change, ∆G, has a negative value. In this case, the products contain Iess free energy than the reactants and the reaction will proceed spontaneously under standard conditions. ENDERGONIC REACTION: When a reaction proceeds with the gain of free energy, the freeenergy change, ∆G, has a positive value. In this case, the products of the reaction contain more free energy than the reactants and this reaction will tend to go in the reverse. When ∆G is large and negative, the reaction tends to go in the forward direction. when ∆G is large and positive, the reaction tends to go in the reverse direction; when ∆G is 0, the system is at equilibrium. Free-energy changes are additive; the net chemical reaction that results from successive reactions sharing a common intermediate has an overall free-energy change that is the sum of the ∆G values for the individual reactions. EXERGONIC EXERGONIC EXERGONIC AND ENDERGONIC CHEMICAL REACTIONS ENDERGONIC EXERGONIC EXERGONIC AND ENDERGONIC CHEMICAL REACTIONS CATABOLISM From the Greek kata, which means “down” The part of metabolism that consists in the transformation of complex organic molecules or biomolecules in simple molecules and, if the degradation is complete, in inorganic molecules. ENERGY is obtained: in the form of ATP and reducing power and waste products. OXIDATION C6H12O6 + 6O2 6CO2 + 6H2O + Energy REDUCTION ATP MOLECULES WITH HIGH CHEMICAL ENERGY CONTENT ATP have phosphoanhydride bonds containing high chemical energy ATP: biological energy, useful for cellular functions ATP HYDROLYSIS: breaking of high energy bonds P P P Adenosine triphosphate (ATP) The bonds between the phosphate groups of the tail of ATP may rupture by hydrolysis, releasing energy Pi + Inorganic phosphate P H2O P + The released energy comes from the change from a higher free energy state to another of lower free energy , not from the phosphate bond itself. Energy Adenosine diphosphate (ADP) ATP hydrolysis is an EXERGONIC reaction (RELEASES ENERGY) ATP IS SYNTHETISED IN A CYCLIC REACTION: ATP-ADP cycle The ATP-ADP cycle is basic for the exchange of energy in biological systems RELEASE OF ENERGY P MOVEMENT ACTIVE TRANSPORT BIOSYNTHESIS ATP 1. PHOTOSYNTHESIS 2. OXIDATION of FUEL MOLECULES ADP P SIGNAL AMPLIFICATION ENERGY IS CONSUME SYNTHESIS OF ENERGY in the form of ATP Heterotrophic organisms get their free energy from OXIDATION of nutrient molecules IN TWO WAYS: 1) DIRECT PATHWAY: forming ATP directly Phosphorylation at the level of substrate 2) INDIRECT PATHWAY: Forming ATP indirectly through intermediaries: Carrier of electrons: reduced coenzyme NADH/FADH (energy in the form of reducing power) Oxidative phosphorylation OXIDATION NUTRIENTS NADH FADH DIRECT ATP OXIDATIVE PHOSPHORYLATION DIRECT PATHWAY: PHOSPHORYLATION at the level of SUBSTRATE Enzyme Enzyme ADP P Substrate + ATP Product During the generation of energy, the compounds containing high-energy phosphate bonds transfer them to ADP, giving ATP. A high-energy phosphate bond is formed, driven by the degradation of a substrate with a higher energy. phosphoenolpyruvate ADP + Pi + H2O ATP + H2O pyruvate EXERGONIC + Pi ΔGº’ = -61,9 kcal/mol ΔGº’ = +30,5 kcal/mol ΔGº’ = -31,4 kcal/mol INDIRECT PATHWAY: ENERGY in the form of REDUCING POWER 2.Forming ATP indirectly through intermediaries Redox: Oxidation and Reduction reactions The chemical reactions that transfer electrons between reactants are called oxidation-reduction or redox reactions OXIDATION: a substance loses electrons or is oxidized REDUCTION: a substance gains electrons or is reduced OXIDATION (lose electron) Xe- + Y X + REDUCTION (gains electron) Ye- A donor of electrons is called reducing agent An acceptor of electrons is called oxidizing agent Review…..OXIDATION-REDUCTION Reducing power as NADH + H + generated through the catabolic pathways and consumed in biosynthetic processes Macromolecules (initially reduced) H+ Oxidized waste products CATABOLISM OXIDATION NADH + H+ reduction NAD+ Oxidative phosphorylation NADH oxidation Own biomolecules (reduced) BIOSYHTESIS REDUCTION NAD+ + 2H+ + 2e- → NADH + H+ ATP CATABOLISM Main catabolic pathways: Aerobic and anaerobic processes Aerobic: requieres oxygen and can use lipids, proteins and carbohydrates. It is more efficient. Anaerobic: not oxygen and only can use carbohydrates. Less efficient. The initial phase of catabolism of carbohydrates. Glucose pyruvate GLYCOLYSIS ANAEROBIC Glycolysis With oxygen Cellular respiration FERMENTATION Without oxygen ANAEROBIC Fermentation Pyruvate is reduced to lactate when tissues have insufficient aerobic conditions to oxidize NADH formed in glycolysis Pyruvate oxydation Cytric acid cycle Respiratory chain Oxidative metabolism Cellular Respiration AEROBIC Includes oxidation of pyruvate, the citric acid cycle, electron transport and oxidative phosphorylation RED AND WHITE MUSCLE FIBERS OBTAIN ATP THROUGH AEROBIC AND ANAEROBIC METABOLISM Fatigue occurs due to depletion of glycogen, oxygen, ATP and accumulation of lactic acid. The accumulation of lactic acid in the muscles causes a burning sensation, pain and fatigue Type I: large amounts of ATP through an aerobic metabolism. Type IIA. ATP is used at a fast rate through aerobic and anaerobic metabolism Type IIB. ATP is used at a low rate through anaerobic metabolism. are capable of producing repeated low-level contractions and so produce fast, strong muscle contractions so produce short, and fast burst of power and quick fatigue. Stages of catabolism Aerobic catabolism consists of three distinct stages. In stage 1, the nutrient macromolecules are broken down into their respective building blocks In stage 2, the collection of product building blocks generated in stage 1 is further degraded to yield an even more limited set of simpler metabolic intermediates. The combustion of the acetyl groups of acetyl-CoA by the citric acid cycle and oxidative phosphorylation to produce CO2 and H2O represents stage 3 of catabolism ANABOLISM From the Greek Ana, which means “up” The part of metabolism responsible for the synthesis of:  Complex organic molecules (biomolecules) from simple molecules or nutrients.  Or simple organic molecules from inorganic molecules (photo and chemosynthesis). - with energy requirement, different from catabolism. - Reduction reactions predominate (use of reducing power) and endergonic reactions (use of ATP). RESPONSIBLE for: - the formation of cellular components and body tissues. - the storage of energy by chemical bonds in organic molecules. INVOLVED in: - DNA replication - RNA synthesis (transcription) - Protein synthesis - Carbohydrates synthesis - Lipid synthesis Stage 3 proteins Amino acids Stages of anabolism Nucleic Acid Nucleotide Polysaccharides lipids Monosaccharides Glycerol lipids Fatty acids glucose Stage 1. synthesis of intermediate Compounds. Stage 2 Stage 2: synthesis of monomeric units Glyceraldheide-3-phosphate Pyruvate Stage 3. Synthesis of polymers Stage 1 Cytoplasm Mitochondria Krebs cycle photosynthesis Cloroplast BASIC CONCEPTS • Cellular metabolism • Metabolic classification of organisms • Metabolic processes and metabolic pathways • Molecules storaging energy: ATP and reducing power • Synthesis of ATP: Direct and indirect pathway • Endergonic and exergonic reactions • Definition and stages of Catabolism and anabolism • Main catabolic pathways: aerobic and anaerobic processes