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October, 2006
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Coenzyme A:

Pyruvate Oxidation

JoVE 10740

After glycolysis, the charged pyruvate molecules enter the mitochondria via active transport and undergo three enzymatic reactions. These reactions ensure that pyruvate can enter the next metabolic pathway so that energy stored in the pyruvate molecules can be harnessed by the cells.

First, the enzyme pyruvate dehydrogenase removes the carboxyl group from pyruvate and releases it as carbon dioxide. The stripped molecule is then oxidized and releases electrons, which are then picked up by NAD+ to produce NADH, forming acetate. Finally, coenzyme A—a sulfur-containing compound derived from a B vitamin—attaches to the acetate via its sulfur atom to create acetyl coenzyme A, or acetyl CoA. Acetyl CoA then moves into the citric acid cycle where it will be further oxidized.

 Core: Cellular Respiration

Enzyme Activity- Concept

JoVE 10585

Biological Catalysts

All living organisms continuously perform numerous biochemical reactions to sustain their presence. Most of these reactions require an input of energy to start, which is called the activation energy. Catalysts are chemicals that lower the activation energy. Even though catalysts facilitate a chemical reaction, they are not consumed by it. This means a catalyst …

 Lab Bio

Enzyme Inhibition

JoVE 11004

Inhibitors are molecules that reduce enzyme activity by binding to the enzyme. In a normally functioning cell, enzymes are regulated by a variety of inhibitors. Drugs and other toxins can also inhibit enzymes. Some inhibitors bind to the enzyme’s active site, while others inhibit enzymatic activity by binding to other sites on the protein structure.

Competitive inhibitors occupy the active site of enzymes, making them unable to accommodate the substrate. However, sufficiently high concentrations of the substrate can outcompete the inhibitor; as a result, competitive inhibitors slow an enzymes initial reaction rate but do not impact the enzyme’s maximum rate. One example of a competitive inhibitor is the drug disulfiram, used to treat chronic alcoholism. When alcohol is ingested, it is normally converted to acetaldehyde, which is then converted to acetyl coenzyme A by acetaldehyde dehydrogenase. Disulfiram binds to and occupies the active site of acetaldehyde dehydrogenase, making the enzyme unable to perform this conversion. As a result, a patient taking disulfiram immediately begins to experience hangover-like symptoms, such as headache, thereby decreasing alcohol consumption. Noncompetitive inhibitors bind to distinct sites on the enzyme, away from the active site. These are called allosteric sites and when molecules bind to them, the shape of

 Core: Metabolism

The Citric Acid Cycle

JoVE 10741

The citric acid cycle, also known as the Krebs cycle or TCA cycle, consists of several energy-generating reactions that yield one ATP molecule, three NADH molecules, one FADH2 molecule, and two CO2 molecules.

Acetyl CoA is the point-of-entry into the citric acid cycle, which occurs in the inner membrane (i.e., matrix) of mitochondria in eukaryotic cells or the cytoplasm of prokaryotic cells. Prior to the citric acid cycle, pyruvate oxidation produced two acetyl CoA molecules per glucose molecule. Hence, the citric acid cycle runs twice per glucose molecule. The citric acid cycle can be partitioned into eight steps, each yielding different molecules (italicized below). With the help of catalyzing enzymes, one acetyl CoA (2-carbon) reacts with oxaloacetic acid (4-carbon), forming the 6-carbon molecule citrate. Next, citrate is converted into one of its isomers, isocitrate, through a two-part process in which water is removed and added. The third step yields α-ketoglutarate (5-carbon) from oxidized isocitrate. This process releases CO2 and reduces NAD+ to NADH. The fourth step forms the unstable compound succinyl CoA from α-ketoglutarate, a process that also releases CO2 and reduces NAD+ to NADH. The fifth

 Core: Cellular Respiration

The ATP Bioluminescence Assay

JoVE 5653

In fireflies, the luciferase enzyme converts a compound called luciferin into oxyluciferin, and produces light or “luminescence” as a result. This reaction requires energy derived from ATP in order to proceed, so researchers have exploited the luciferase-luciferin interaction to gauge ATP levels in cells. Given ATP’s role as the cell’s currency of…

 Cell Biology

An Introduction to Cell Metabolism

JoVE 5652

In cells, critical molecules are either built by joining together individual units like amino acids or nucleotides, or broken down into smaller components. Respectively, the reactions responsible for this are referred to as anabolic and catabolic. These reactions require or produce energy typically in the form of a “high-energy” molecule called ATP. Together,…

 Cell Biology

Dietary Connections

JoVE 10746

Metabolic pathways are interconnected. The cellular respiration processes that convert glucose to ATP—such as glycolysis, pyruvate oxidation, and the citric acid cycle—tie into those that break down other organic compounds. As a result, various foods—from apples to cheese to guacamole—end up as ATP. In addition to carbohydrates, food also contains proteins and lipids—such as cholesterol and of these organic compounds are used as energy sources (i.e., to produce ATP). The human body possesses several enzymes that break down carbohydrates into simple sugars. While glucose can enter glycolysis directly, some simple sugars, such as fructose and galactose, are first converted into sugars that are intermediates of the glycolytic pathway. Proteins are broken down by enzymes into their constituent amino acids, which are usually recycled to create new proteins. However, if the body is starving or there is a surplus of amino acids, some amino acids can lose their amino groups and subsequently enter cellular respiration. The lost amino groups are converted into ammonia and incorporated into waste products. Different amino acids enter cellular respiration at different stages, including glycolysis, pyruvate oxidation, and the citric acid cycle. Amino acids can also be produced from intermediates in cellular respiration processes. Lipids, such as choleste

 Core: Cellular Respiration

Biosynthesis of a Flavonol from a Flavanone by Establishing a One-pot Bienzymatic Cascade

1College of Bioscience and Biotechnology, Yangzhou University, 2Key Laboratory of Prevention and Control of Biological Hazard Factors (Animal Origin) for Agrifood Safety and Quality, Ministry of Agriculture of China, Yangzhou University, 3Joint International Research Laboratory of Agriculture & Agri-Product Safety, Yangzhou University, 4Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, 5The Testing Center, Yangzhou University

JoVE 59336


A Familial Hypercholesterolemia Human Liver Chimeric Mouse Model Using Induced Pluripotent Stem Cell-derived Hepatocytes

1Department of Medicine, University of Hong Kong-Shenzhen Hospital, 2The Cardiology Division, Department of Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, 3School of Biomedical Sciences, Institute of Vascular Medicine, Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, 4Key Laboratory of Regenerative Biology of the Chinese Academy of Sciences, Joint School of Life Sciences, Guangzhou Institutes of Biomedicine and Health and Guangzhou Medical University, 5Laboratory of RNA, Chromatin, and Human Disease, CAS Key Laboratory of Regenerative Biology and Guangdong Provincial Key Laboratory of Stem Cells and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, 6Research Centre of Heart, Brain, Hormone, and Healthy Ageing, Li Ka Shing Faculty of Medicine, University of Hong Kong, 7Hong Kong-Guangdong Stem Cell and Regenerative Medicine Research Centre, University of Hong Kong and Guangzhou Institutes of Biomedicine and Health

JoVE 57556

 Developmental Biology

An Optimized Protocol to Analyze Glycolysis and Mitochondrial Respiration in Lymphocytes

1Laboratory of Mitochondrial Biology and Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, 2Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 3Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health

JoVE 54918

 Immunology and Infection

Purification of Extracellular Trypanosomes, Including African, from Blood by Anion-Exchangers (Diethylaminoethyl-cellulose Columns)

1Univ. Bordeaux UMR INTERTRYP 177 IRD CIRAD, 2IRD UMR 177 INTERTRYP CIRAD, 3CNRS, UMR 5234, Microbiologie Fondamentale et Pathogénicité, Univ. Bordeaux, 4Centre Hospitalier Université Bordeaux

JoVE 58415

 Immunology and Infection

Processing of Human Cardiac Tissue Toward Extracellular Matrix Self-assembling Hydrogel for In Vitro and In Vivo Applications

1Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 2Berlin-Brandenburg Center for Regenerative Therapies (BCRT), 3German Center for Cardiovascular Research (DZHK), 4Deutsches Herzzentrum Berlin (DHZB), 5Department of Cardiovascular Surgery, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health

JoVE 56419

 Developmental Biology

Methods to Study Lipid Alterations in Neutrophils and the Subsequent Formation of Neutrophil Extracellular Traps

1Department of Physiological Chemistry, University of Veterinary Medicine Hannover, 2Fish Disease Research Unit, University of Veterinary Medicine, 3Department of Clinical Sciences, Biomedical Center, Lund University, 4Research Center for Emerging Infections and Zoonoses (RIZ), University of Veterinary Medicine Hannover

JoVE 54667

 Immunology and Infection

LC-MS Analysis of Human Platelets as a Platform for Studying Mitochondrial Metabolism

1Center for Cancer Pharmacology, University of Pennsylvania, 2Center for Excellence in Environmental Toxicology, University of Pennsylvania, 3Penn SRP and Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, 4Division of Traumatology, Department of Surgery, Critical Care and Acute Care Surgery, University of Pennsylvania, 5A.J. Drexel Autism Institute, Drexel University

JoVE 53941


Lignin Down-regulation of Zea mays via dsRNAi and Klason Lignin Analysis

1The School of Plant Sciences, University of Arizona, 2Department of Chemical Engineering and Materials Science, DOE Great Lakes Bioenergy Research Center, Michigan State University, 3The Institute for Sustainable and Renewable Resources, The Institute for Advanced Learning and Research, 4Department of Plant, Soil and Microbial Sciences, Michigan State University

JoVE 51340

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