Metabolism And a little on enzymes too!

Enzyme Summary –Most enzymes are proteins. –Speed up reactions by lowering the E A –Enzymes are substrate specific –Enzymes are not permanently changed in the reaction. Enzymes can be used over and over again. –A single enzyme may act on thousands or millions of substrate molecules per second!

Enzyme available with empty active site Active site Glucose Fructose Products are released Enzyme (sucrase) Substrate (sucrose) H2OH2O Substrate is converted to products Substrate binds to enzyme with induced fit

Enzyme Terms Simple enzyme – protein only Conjugated enzyme – protein and nonprotein components –Protein = apoenzyme –Nonprotein = cofactor Add additional functional groups to those of the amino acids –Holoenzyme = protein and cofactor together Biologically active

Cofactors Organic cofactors are called coenzymes –Many vitamins serve as coenzymes Minerals often serve as inorganic co- factors –Typically have 2+ charge –Ca +2 Mg +2 Fe +2 Zn +2

Enzyme Inhibitors Inhibitors are substances that interfere with an enzyme’s ability to function –Many toxins/poisons are enzyme inhibitors For example: Mercury binds to sulfur groups on enzymes and cause the enzyme to change shape and lose function

Enzyme Inhibitors Inhibitors may bind to the enzyme with covalent bonds or H bonds –Covalent bonding inhibitors  irreversible inhibition –H bonding inhibitors  reversible inhibition

More on Enzyme Inhibitors Irreversible enzyme inhibitors have many uses. –Some inhibitors are deadly Cyanide – inhibits an enzyme needed to make ATP Sarin – inhibits an enzyme needed for nerve transmission Pesticides and herbicides – bind to key enzymes in insects and plants

Types of Inhibitors Competitive inhibitors – compete with the substrate for binding at the active site –Competitive inhibitors are similar in structure to the “real” substrate

Types of Inhibitors Noncompetitive inhibitors – bind to the enzyme at a location other than the active site –Binding changes the shape of the active site so that the substrate cannot bind Called allosteric control –Release of the inhibitor returns the active site to its proper shape

Substrate Enzyme Active site Normal binding of substrate Competitive inhibitor Noncompetitive Inhibitor -- also called an allosteric inhibitor Enzyme inhibition

Key Players in Metabolism

ATP – cell’s primary energy carrier

FAD and NAD +

Synthesis of FADH 2 and NADH Oxidation – loss of electrons Reduction – gain of electrons o Reduction often involves adding H + to a substance. o The reactions shown are ______ reactions. FAD+ 2 H + + 2e  FADH 2 NAD + + 2H + + 2e  NADH + H + o These reactions are coupled with _________ reactions

Co-Enzyme A Co-Enzyme A binds an acetyl group at the –SH group, an acetyl replaces the H and a thioester forms

Common Metabolic Pathways Citric Acid Cycle –Also called the Krebs Cycle Electron Transport Chain Oxidative Phosphorylation All occur in the mitochondria

Fats, Carbohydrates, Proteins See board for an overview of how the 3 energy-yielding nutrients enter the common metabolic pathways.

Carbohydrate Metabolism Our focus will be on the metabolism of carbohydrates. –Metabolic pathway called glycolysis prepares carbohydrates for entry into the common metabolic pathways

Mitochondrion CO 2 NADH ATP High-energy electrons carried by NADH NADH C ITRIC A CID C YCLE G LYCOLYSIS Pyruvate Glucose and FADH 2 Substrate-level phosphorylation Substrate-level phosphorylation O XIDATIVE P HOSPHORYLATION (Electron Transport and Chemiosmosis) Oxidative phosphorylation ATP Cytoplasm Inner mitochondrial membrane

Carbohydrate Metabolism Glucose is the cell’s primary source of energy. Glucose needs to be converted to acetyl groups to enter the citric acid cycle. This requires 2 pathways: 1.Glycolysis – does not require oxygen. 2.Preparatory step (your text doesn’t name this step). –This step requires aerobic conditions

Glycolysis In a series of biochemical reactions glucose is converted into: 2 pyruvate –3 C carboxylic acids In the process: –2 NADH are made –2 ATP are converted to ADP –4 ATP are made Net gain of _____ 2 ATP

Glucose NAD ADP NADH2 P2 2 ATP 2 + H+H+ 2 Pyruvate Glycolysis simple form (Net)

Steps – ATP and pyruvate are produced. Step A redox reaction generates NADH. Step A six-carbon intermediate splits Into two three-carbon intermediates. Steps – A fuel molecule is energized, using ATP. ENERGY INVESTMENT PHASE Glucose Glucose-6-phosphate 1 Fructose-6-phosphate Step ADP ATP P 3 ADP ATP P 2 P 4 P Fructose-1,6-bisphosphate 5 5 PP P P P P NAD + P P ENERGY PAYOFF PHASE Glyceraldehyde-3-phosphate (G3P) 1,3-Bisphosphoglycerate NADH NAD + NADH + H + ADP ATP Phosphoglycerate 2-Phosphoglycerate PP PP P P H2OH2OH2OH2O ADP ATP 9 9 Phosphoenolpyruvate (PEP) Pyruvate Glycolysis Not so simple form!

Glycolysis

Glycolysis, cont’d

Fates of Pyruvate What happens to the pyruvates made during glycolysis depends upon: –Cell conditions. Is O 2 present or not? –Type of organism

Anaerobic Conditions - Fermentation Under anaerobic conditions the pyruvate remain in the cytoplasm and are converted to either lactate or ethanol –Which depends on the organism –Called fermentation NADH are converted back to NAD + during the fermentation reaction(s) –NAD+ is used to keep glycolysis going

Alcoholic Fermentation Alcoholic fermentation occurs in yeast and other organisms.

32 Lactate Fermentation Lactate fermentation occurs in animals and other organisms.

Cori Cycle - Glucogenesis

Gert and Carl Cori

Aerobic Conditions Under aerobic conditions the pyruvate are converted into acetyl Co-A as they enter the matrix of the mitochondria. –The acetyl Co-A then enter into the Citric Acid Cycle –The NADH made in glycolysis deliver their electrons and hydrogen ions to the ETC

36 Aerobic Conditions Pyruvate is converted to acetyl CoA and enters the citric acid cycle O || CH 3 –C –COO - + NAD + + CoA pyruvate O || CH 3 –C –CoA + CO 2 + NADH + H + acetyl CoA

Citric Acid Cycle Citric acid cycle is a series of reactions in which acetyl (2C) groups are oxidized to form: –2 CO 2 –3 NADH –1 FADH 2 –1 GTP which is used to make ATP many texts show as ATP

Citric Acid Cycle Reaction Types Isomerization – rearranges atoms in molecule Hydration – adds water Decarboxylation reaction  CO 2 Oxidation/reduction reactions  NADH and FADH 2 Phosphorylation reaction  GTP (ATP) –Called substrate-level phosphorylation

Citric Acid Cycle Citric acid cycle is a series of reactions in which acetyl (2C) groups are oxidized to form: –2 CO 2 –3 NADH –1 FADH 2 –1 GTP which is used to make ATP many texts show as ATP

NADH and FADH 2 NADH and FADH 2 deliver H + and electrons to the Electron Transport Chain (ETC). The ETC is a series of electron carriers and enzymes located on the inner membrane of the mitochondria.

Electron Transport Chain

ETC – Proton Pumps

ETC The pumping of protons (H+) into the intermembrane space creates a chemical gradient. This gradient is a form of potential energy. The more protons pumped into the space, the more potential energy. –Therefore ______ creates more potential energy than _______.

ATP Synthesis at ATP Synthase 1 ATP is made for every 4 H+ that pass through ATP synthase –Each NADH results in 10 H+ being pumped out of the matrix  2.5 ATP/NADH –Each FADH2 results in 6 H+ being pumped out of the matrix  1.5 ATP/NADH

Copyright © Cengage Learning. All rights reserved 48 Ten molecules of ATP are produced for each acetyl CoA catabolized –3 NADH  7.5 ATP –1 FADH2  1.5 ATP –1 GTP  1 ATP Total 10 ATP per Acetyl CoA

ATP Summary/Glucose Glycolysis –2 ATP net –2 NADH  3 or 5 ATP depending on cell type Pyruvate  Acetyl Co-A –2 NADH  5 ATP Citric Acid Cycle –2 GTP  2 ATP –6 NADH  15 ATP –2 FADH 2  3 ATPTOTAL: 30 (32) ATP