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Enzymes, metabolism and cellular respiration BTEC National Level 3 Unit 9: Applied Science for Health and Social Care Syllabus content: 3. Understand the principles of metabolism Metabolism: anabolic and catabolic change Enzymic reactions: lock-and-key principle, co-enzymes, effects of substrate and enzyme concentrations, temperature and pH on rate of reaction Cell respiration: chemical changes associated with: glycolysis, Krebs cycle, generation of ATP, anaerobic respiration, lactic acid, oxygen debt and recovery. Metabolism The metabolism of a cell is the sum of all biochemical reactions occurring within it. The metabolism of the human body is the sum of all biochemical reactions occurring within all the body’s cells. These biochemical reactions can be divided into two main classes: 1. Anabolic reactions: require energy and build more complex molecules from simpler molecules and are biosynthetic, e.g. the formation of polypeptides and proteins from amino acids. Anabolism is the sum of all anabolic reactions. 2. Catabolic reactions: biochemical reactions in which complex molecules are broken down or degraded into simpler molecules, e.g. the respiration of glucose into carbon dioxide and water. Catabolic reactions typically release energy which may be usable by the cell. Catabolism is the sum of all the catabolic reactions. Metabolism = anabolism + catabolism Metabolic pathway: A series of biochemical reactions linked together in a straight chain, a branched chain or a cycle. One or more of the products of a preceding reaction act as reactant(s) in the subsequent reaction. Cellular respiration (internal respiration) is an example of a metabolic pathway!

Enzymes 1 There are six classes of enzyme: Catalyst: A substance that increases the rate of a chemical reaction without being consumed in the reaction; a substance that lowers the activation energy for a chemical reaction. Enzyme: An enzyme is a globular protein that functions as a biological catalyst. Names usually end in –ase. There are six classes of enzyme: 1. Hydrolases: hydrolyse molecules, i.e. they add water to a molecule in order to split it, e.g. pepsin hydrolyses proteins into smaller peptides, amylase hydrolyses starch into maltose, maltase hydrolyses maltose into glucose. 2. Transferases: transfer a chemical group (group of atoms) from one molecule to another, e.g. glucokinase transfers a phosphate group from ATP to glucose, to form glucose-phosphate. Kinases are transferases that transfer phosphate groups (phosphotransferases). 3. Lyases: make or break double bonds, e.g. C=C bonds. Make or break chemical bonds by means other than hydrolysis and oxidoreduction. 4. Ligases: enzymes that link together two molecules, e.g. DNA ligase links fragments of DNA together into a single larger DNA molecule. 5. Isomerases turn a molecule into one of its isomers, e.g. Phosphohexose isomerase converts glucose-6-phosphate into fructose-6-phosphate (glucose and fructose are isomers). 6. Oxidoreductases: these enzymes catalyses oxidoreductase (redox) reactions, e.g. many respiratory enzymes! Oxidation: Oxidation is the combination of a substance with oxygen. Oxidation can also describe a type of reaction in which the atoms lose electrons. Oxidation is also a type of reaction in which the molecule loses hydrogen. Reduction: Reduction is the combination of a substance with hydrogen. Reduction can also describe a type of reaction in which the atoms gain electrons. Reduction is also a type of reaction in which the molecule loses oxygen. OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons). Oxidoreduction (redox) reactions are central to cellular respiration.

Enzymes 2 Enzymes are biological catalysts that increase the rate of reaction without taking part in the reaction itself. Small amounts of enzyme are required as the enzyme can be used repeatedly. Enzymes reduce the activation energy of a reaction and so speed up a reaction as much as one hundred million million times ( = one hundred thousand billion times = 1014 times). A typical enzyme catalyses 100 reactions each second. Enzymes are globular proteins with tertiary structure. Enzymes are specific, that means that each enzyme can only catalyse one type of reaction. The lock and key theory suggests that enzymes have an active site with a specific 3D shape into which only one substrate can fit. The substrate fits the active site to form an enzyme-substrate complex. The concentration of the substrate and the enzyme affect the rate of reaction. As do temperature and pH!! Many enzymes require cofactors to work properly. Enzymes are affected by inhibitors which can be reversible or non-reversible, competitive (site-directed) or non-competitive (non-site directed). By controlling enzymes cells can control metabolism. Cofactor: A small non-protein compound or ion needed by the enzyme to function properly. E.g. chloride ions (Cl-) and salivary amylase. Cofactors may be: 1) tightly bound non-protein organic compounds (so-called prosthetic groups); 2) less tightly bound non-protein organic compounds called coenzymes, or 3) metal ion activators. Coenzyme: A small molecule associated with an enzyme that participates in enzymatic catalysis. E.g. electron/hydrogen carriers (NAD, FAD) are a type of coenzyme, CoA. Lock and Key Hypothesis: Substrate (‘key’) Product(s) (what the substrate has become!) Enzyme (‘lock’) Enzyme-substrate complex

Understanding Metabolic Pathways This question is about a metabolic pathway in the bacterium Corynebacterium glutamicum. This bacterium uses the pathway to produce the amino acid lysine. Commercially this bacterium is cultured and the lysine is used to supplement cereal protein. Do not learn this pathway!! You do not need to know the pathway to answer the questions! aspartate Enzyme A aspartyl phosphate Enzyme B Enzyme D aspartic semialdehyde homoserine Enzyme C lysine Explain why although mutants lacking enzyme B die, they will grow normally if aspartic semialdehyde is added to their diet. Explain why mutants lacking enzyme C and fed lysine are able to grow, but produce more homoserine than normal wild type cells.

Factors affecting the rate of enzyme activity Complete the following sketch graphs with typical examples of enzyme behaviour: Rate of reaction Rate of reaction Temperature pH Rate of reaction Rate of reaction Enzyme concentration Substrate concentration

Assignment: Cell metabolism and cell respiration Grading Criteria: P5: explain the chemical processes involved in cell respiration in animal cells M4: explain the links between cell metabolism and body activity. D1: analyse how cell organelles may contribute to the metabolic processes of the human body. This assignment covers P5 and M4 and provides some of the background needed for D1. Approach used: the teacher will introduce key concepts, then students will expand these concepts by researching the topics required by the syllabus and producing a written assignment. A set of questions will serve as pointers to guide the students.

Glucose Pyruvate Pyruvate Glycolysis ATP NAD+ NADH ATP ATP ATP ADP + Pi Fructose-1,6-bisphosphate NAD+ ADP + Pi NADH ATP Phosphoenol pyruvate (PEP) Phosphoenol pyruvate (PEP) ADP + Pi ADP + Pi ATP ATP Pyruvate Pyruvate

Glycolysis

Glucose Pyruvate Pyruvate Glycolysis ATP H2O H2O NAD+ NADH ATP ATP ATP ADP + Pi Fructose-1,6-bisphosphate H2O H2O NAD+ ADP + Pi NADH ATP Phosphoenol pyruvate (PEP) Phosphoenol pyruvate (PEP) ADP + Pi ADP + Pi ATP ATP Pyruvate Pyruvate

Glycolysis