Metabolism Chapter 7
Metabolism • Metabolism: All chemical reactions within organisms that enable them to sustain life. The two main categories are catabolism and anabolism.
Metabolism • Catabolism: Any metabolic process whereby cells break down complex substances into simpler, smaller ones. • Anabolism: Any metabolic process whereby cells convert simple substances into more complex ones.
Metabolism • Thousands of chemical reactions occur every moment in cells throughout the body. • The most active metabolic sites are the liver, muscle, and brain cells.
Energy: Fuel for Work • Energy source • Chemical energy (stored in molecular bonds) in carbohydrates, fat, protein • Food energy to cellular energy • Stage 1: digestion, absorption, transport • Stage 2: breakdown of molecules to a few key metabolites • Stage 3: transfer of energy to a form cells can use
What Is Metabolism? • Catabolism • Reactions that breakdown compounds into small units • Anabolism • Reactions that build complex molecules from smaller ones
What Is Metabolism? • Cell is the metabolic processing center • Nucleus • Cytoplasm • Cytosol + organelles • ATP is the body’s energy currency • ATP = adenosine triphosphate • Form of energy cells use • NAD and FAD: transport shuttles • Accept high-energy electrons for use in ATP production
Breakdown and Release of Energy • Extracting energy from carbohydrate • Glycolysis • Pathway splits glucose into 2 pyruvates • Transfers electrons to NAD • Produces 2 ATP • anaerobic • Pyruvate to acetyl CoA • Releases CO2 • Transfers electrons to NAD
Breakdown and Release of Energy • Extracting energy from carbohydrate • Citric acid cycle • Releases CO2 • Produces GTP (like ATP) • Transfers electrons to NAD and FAD • Electron transport chain • Accepts electrons from NAD and FAD • Produces large amounts of ATP • Produces water • End products of glucose breakdown • ATP, H2O, CO2
Breakdown and Release of Energy • Extracting energy from fat • Split triglycerides into glycerol and fatty acids • Beta-oxidation • Breaks apart fatty acids into acetyl CoA • Transfers electrons to NAD and FAD • Citric acid cycle • Acetyl CoA from beta-oxidation enters cycle • Electron transport chain • End products of fat breakdown • ATP, H2O, CO2
Breakdown and Release of Energy • Extracting energy from protein • Split protein into amino acids • Split off amino group • Converted to urea for excretion • Carbon skeleton enters breakdown pathways • End products • ATP, H2O, CO2, urea
Cellular Respiration • Cellular respiration is the controlled release of chemical-bond energy from large, organic molecules. • This energy is utilized for many activities to sustain life. • Both autotrophs and heterotrophs carry out cellular respiration.
Aerobic Vs. Anaerobic • Aerobic respiration requires oxygen. • Anaerobic respiration does not require oxygen.
Aerobic Respiration • Aerobic cellular respiration is a specific series of enzyme controlled chemical reactions in which oxygen is involved in the breakdown of glucose into carbon-dioxide and water. • The chemical-bond energy is released in the form of ATP. • Sugar + Oxygen carbon dioxide + water + energy (ATP)
Aerobic Respiration • Simplified Reaction: • C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) ΔHc -2880 kJ • Covalent bonds in glucose contain large amounts of chemical potential energy. • The potential energy is released and utilized to create ATP.
Glycolysis • Glycolysis is a series of enzyme controlled anaerobic reactions that result in the breakdown of glucose and the formation of ATP. • A 6-carbon sugar glucose molecule is split into two smaller 3-carbon molecules which are further broken down into pyruvic acid or pyruvate.
Glycolysis • 2 ATP molecules are created during glycolysis and electrons are released during the process.
Krebs Cycle • The Krebs cycle is a series of enzyme-controlled reactions that take place inside the mitochondrion. • Pyruvic acid formed during glycolysis is broken down further. • Carbon dioxide, electrons, and 2 molecules of ATP are produced in this reaction.
Electron Transport System • The electrons released from glycolysis and the Krebs cycle are carried to the electron-transport system (ETS) by NADH and FADH2. • The electrons are transferred through a series of oxidation-reduction reactions until they are ultimately accepted by oxygen atoms forming oxygen ions. • 32 molecules of ATP are produced.
Aerobic Respiration Summary • Glucose enters glycolysis. • Broken down into pyruvic acid. • Pyruvic acid enters the Krebs cycle. • Pyruvic acid is further broken down and carbon-dioxide is released. • Electrons and hydrogen ions from glycolysis and the Krebs cycle are transferred by NADH and FADH2 to the ETS. • Electrons are transferred to oxygen to form oxygen ions. • Hydrogen ions and oxygen ions combine to form water.
Anaerobic Cellular Respiration • Anaerobic respiration does not require oxygen as the final electron acceptor. • Some organisms do not have the necessary enzymes to carry out the Krebs cycle and ETS. • Many prokaryotic organisms fall into this category. • Yeast is a eukaryotic organism that performs anaerobic respiration.
Fat Respiration • A triglyceride (neutral fat) consists of a glycerol molecule with 3 fatty acids attached to it. • A molecule of fat stores several times the amount of energy as a molecule of glucose. • Fat is an excellent long-term energy storage material. • Other molecules such as glucose can be converted to fat for storage.
Protein Respiration • Protein molecules must first be broken down into amino acids. • The amino acids must then have their amino group (-NH2) removed (deamination). • The amino group is then converted to ammonia. In the human body ammonia is converted to urea or uric acid which can then be excreted.
Biosynthesis and Storage • Making carbohydrate (glucose) • Gluconeogenesis • Uses pyruvate, lactate, glycerol, certain amino acids • Storing carbohydrate (glycogen) • Liver, muscle make glycogen from glucose • Making fat (fatty acids) • Lipogenesis • Uses acetyl CoA from fat, amino acids, glucose • Storing fat (triglyceride) • Stored in adipose tissue
Biosynthesis and Storage • Making ketone bodies (ketogenesis) • Made from acetyl CoA • Inadequate glucose in cells • Making protein (amino acids) • Amino acid pool supplied from • Diet, protein breakdown, cell synthesis
Regulation of Metabolism • May favor either anabolic or catabolic functions • Regulating hormones • Insulin • Glucagon • Cortisol • Epinephrine
Special States • Feasting • Excess energy intake from carbohydrate, fat, protein • Promotes storage
Special States • Fasting • Inadequate energy intake • Promotes breakdown • Prolonged fasting • Protects body protein as long as possible
The ADP–ATP Cycle • When extracting energy from nutrients, the formation of ATP from ADP + P captures energy. • Breaking a phosphate bond in ATP to ADP + P, releases energy for biosynthesis and work.
When Glycolysis Goes Awry • Red blood cells do not have mitochondria, so they rely on glycolysis as their only source of ATP. • They use ATP to maintain the integrity and shape of their cell membranes. • A defect in red blood cell glycolysis can cause a shortage of ATP, which leads to deformed red blood cells. • Destruction of these cells by the spleen leads to a type of anemia called hemolytic anemia.
Electron Transport Chain • This pathway produces most of the ATP available from glucose. NADH molecules deliver pairs of high-energy electrons to the beginning of the chain. • The pairs of high-energy electrons carried by FADH2 enter this pathway farther along and produce fewer ATP than electron pairs carried by NADH. • Water is the final product of the electron transport chain.
Carnitine • Without assistance, activated fatty acid cannot get inside the mitochondria where fatty acid oxidation and the citric acid cycle operate. • This entry problem is solved by carnitine, a compound formed from the amino acid lysine. • Carnitine has the unique task of ferrying activated fatty acids across the mitochondrial membrane, from the cytosol to the interior of the mitochondrion.
Deamination • A deamination reaction strips the amino group from an amino acid.
Fuel for Distance Walking • A recent study sought to explore whether or not humans naturally select a preferred walking speed (PWS), and that the body’s fuel selection can be critical to the total distance traveled. The hypothesis maintained that humans select a preferred walking speed that primarily uses fat as fuel and does not deplete carbohydrate (CHO) stores. • The major finding of this study was that able-bodied subjects naturally selected a walking speed just below the speed preceding an abrupt rise in CHO oxidation that would deplete the body’s small stores of CHO quickly.
Ketones • Organic compounds that contain a chemical group consisting of C=O (a carbon–oxygen double bond) bound to two hydrocarbons. • Pyruvate and fructose are two examples of ketones. • Acetone and acetoacetate are both ketones and tetone bodies. • While betahydroxybutyrate is not a ketone, it is a ketone body.
Cholesterol • Your body can make cholesterol from acetyl CoA by way of ketones. In fact, all 27 carbons in synthesized cholesterol come from acetyl CoA. • The rate of cholesterol formation is highly responsive to cholesterol levels in cells. If levels are low, the liver makes more. If levels are high, synthesis decreases. • That is why dietary cholesterol in the absence of dietary fat often has little effect on blood cholesterol levels.
Transamination • A transamination reaction transfers the amino group from one amino acid to form a different amino acid.
Indispensable and Dispensable Amino Acids • Proteins are made from combinations of indispensable and dispensable amino acids. • The body synthesizes dispensable amino acids from pyruvate, other glycolytic intermediates, and compounds from the citric acid cycle. • To form amino acids, transamination reactions transfer amino groups to carbon skeletons.