Molecules: Enzymes and Metabolism, Intracellular and Extracellular Reactions

Enzyme Interactions with Molecules

Guiding Questions

"In what ways do enzymes interact with other molecules? "What are the interdependent components of metabolism?"

Syllabus Objectives

C1.1.11 AHL Intracellular and extracellular enzyme-catalysed reactions Include glycolysis and the Krebs cycle as intracellular examples and chemical digestion in the gut as an extracellular example.

C1.1.12 AHL Generation of heat energy by the reactions of metabolism Include the idea that heat generation is inevitable because metabolic reactions are not 100% efficient in energy transfer. Mammals, birds and some other animals depend on this heat production for maintenance of constant body temperature.

C1.1.13 AHL Cyclical and linear pathways in metabolism Use glycolysis, the Krebs cycle and the Calvin cycle as examples.

C1.1.14 AHL Allosteric sites and non- competitive inhibition Students should appreciate that only specific substances can bind to an allosteric site. Binding causes interactions within an enzyme that lead to conformational changes, which alter the active site enough to prevent catalysis. Binding is reversible.

C1.1.15 AHL Competitive inhibition as a consequence of an inhibitor binding reversibly to an active site Use statins as an example of competitive inhibitors. Include the difference between competitive and noncompetitive inhibition in the interactions between substrate and inhibitor and therefore in the effect of substrate concentration.

C1.1.16 AHL Regulation of metabolic pathways by feedback inhibition Use the pathway that produces isoleucine as an example of an end product acting as an inhibitor.

C1.1.17 AHL Mechanism-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor Use penicillin as an example. Include the change to transpeptidases that confers resistance to penicillin.

Intracellular and Extracellular Enzyme-Catalysed Reactions

1 | PageIntracellular and extracellular enzyme-catalysed reactions Enzyme catalysed reactions can take place inside or outside of cells

Intracellular Enzyme Reactions

Krebs cycle inside mitochondria HO ATP Electron Transport Chain + O. Example Glucose Electron Carriers Glycolysis Acetyl CoA Krebs Cycle mitochondrion ATP ATP CO2 CO. cytoplasm

Extracellular Enzyme Reactions

Digestion of food in the small intestine Stomach Duodenum Jejunum Small intestine Ileum

Features of Enzyme-Catalysed Reactions

Features Often inside organelles (e.g. mitochondria, nucleus) cytoplasm or bound to membranes where reactions are catalyzed by enzymes produced by free ribosomes in the cell.

Exoenzymes synthesized by the rER which are released from glands or specialized cells into the interior of an organ catalyzing the breakdown of larger macromolecules into monomers.

Examples of Enzyme Reactions

Can you think of other examples? DNA polymerase, helicase during DNA replication; Lysozymes in lysosomes to break down waste products.

Digestive eynzymes (lactase, pepsin, amylase, lipase); Acetylcholinesterase breaks down a neurotransmitter; Enzymes released by fungi or bacteria

Questions on Enzyme Secretion

Questions 1. Suggest what the dark blue organelles are in the image. 2. Suggest a reason for storing digestive enzymes in vesicles, instead of secreting them immediately after they are produced. 3. Suggest reasons for the variation in size of the vesicles in these cells.

Figure 24 False-colour scanning electron micrograph of enzyme-secreting cells in the pancreas, with the cytoplasm coloured pale blue. Before secretion, the enzymes are stored inside membrane-bound sacs called vesicles (coloured yellow). The enzymes are secreted into the small intestine via the pancreatic duct and after activation they help the digestion of carbohydrates, fats and proteins

Generation of Heat Energy by Metabolic Reactions

2 | PageGeneration of heat energy by the reactions of metabolism 33.4℃ 25.4℃ 34.5°C 27.0℃ 30.7ºC Metabolic reactions often result in the release of heat energy. This is because the products of a reaction usually have less energy than the reactions. The additional energy is converted to heat.

Heat Use by Birds and Mammals

How is the heat, generated by reactions of metabolism, used by birds and mammals? Birds and mammals use this energy to maintain a body temperature greater than their environment.

Mechanisms of Heat Regulation

Perspiration and evaporation Exhalation of warm air Forced and natural convection Shivering Metabolism Thermal conduction Infrared radiation

Behavioral Adaptations for Heat

In very cold conditions, emperor penguins huddle together in groups to take advantage of the metabolic heat released by neighbours. -4.5°C -5 -10 .15 -20

Physiological Adaptations for Heat

White fat cells Brown fat cells 30℃ In addition to behavioural adaptations, birds and mammals also show other adaptations to raise their metabolic rate above the external temperature.

Brown Fat in Adipose Tissue

Brown fat in adipose tissue: Brown fat cells in adipose tissue contains more mitochondria than white fat cells or any other body tissue. 32℃ More energy can be generated through uncoupled respiration (without the production of ATP) uncoupled respiration - all of the energy released from metabolism is released as heat, and ATP is not produced

Involuntary Muscle Contractions

Involuntary muscle contractions: Involuntary muscle contractions which result in shivering also generate more heat and raise the body temperature.

Metabolic Heat Generation in Compost

Decomposing manure or compost can become very hot, as can be seen by this steaming heap. What organisms are responsible for this metabolic heat generation? Activity of aerobic bacteria, such as thermophilic bacteria that thrive in high-temperature conditions, between 46-71 0C. They rapidly break down organic materials: proteins, fats and complex carbohydrates.

Metabolic Pathways

3 | PageMetabolic pathways: metabolites - substances involved in metabolism (chemical processes in living organisms) In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function properly. Because of the many chemicals (a.k.a. "metabolites") that may be involved, metabolic pathways can be quite elaborate. In addition, numerous distinct pathways co-exist within a cell.

enzyme enzyme enzyme A B C substrates product The synthesis of biological molecules often requires many enzyme-catalyzed steps. The entire set of steps is a metabolic pathway.

Challenge: Word Transformation

Challenge: by changing just one letter at a time, get from 'Tread' to 'Blink'. All intermediates must be real (English) words. TREAD BLINK

Features of Metabolic Pathways

What are the three features of a metabolic pathway? 1. Most chemical changes happen not in one large jump, but in a sequence of small steps (called a metabolic pathway.) 2. Most metabolic pathways involve a linear chain of reactions. 3. Some metabolic pathways form a cycle. (The end product of one reaction that starts the rest of the pathway)

Examples of Metabolic Pathways

A large number of different processes in the body are metabolic pathways - blood clotting, cell respiration, amino acid synthesis are only a few events that include enzyme-catalyzed steps.

The Krebs cycle (cell respiration) and the Calvin cycle (photosynthesis) are examples of enzyme catalyzed, cyclical metabolic pathways.

Krebs Cycle (Cell Respiration)

cell respiration in mitochondria Krebs (citric acid cycle) Pyruvate (from glycolysis, 2 molecules per glucose) NADH CO2 NADH CoA + H* Acetyl COA CoA CoA FADH KREBS CYCLE FAD 3NAD+ CO2 ADP + P. 3 NADH + 3 H+ ATP http://www.sparknotes.com/health/carbohydrates/section3.rhtml

Calvin Cycle (Photosynthesis)

(light-independent reactions) photosynthesis in chloroplasts Calvin three molecules Co 1C three molecules six esolecules 3-phosphoglycerate 3C 3 ATP ATP three molecules 6 ADP Titulose 6- phosphate SC sis molecules 1.3-diphosphoglycerate 3C NADPH 6 NADP five molecules glyceraldehyde 3-phosphate 30 glyceraldehyde 3 phosphate 3C three molecules of CO2 fixed give a net vield of one molecule one molecule of glyceraldehyde 3-phosphate at a net cost of nine molecules of ATP and six molecules of NADPH glyceraldehyde 3-phosphate 3C H-C-O H-C-OH CHOC SUGARS, FATTY ACIDS, AMINO ACIDS http://library.thinkquest.org/C004535/calvin_cycle.html 4 | Page

Bis molecules tibulose 1. 5-bitphosphate

Enzyme Inhibition

Enzyme inhibition: Some chemical substances reduce or even prevent enzymatic reactions to happen by blocking the enzyme. These chemical substances are called inhibitors or enzyme inhibitors. Enzyme inhibition can be competitive or noncompetitive. Using the information from the book, teacher input and research, compare the two types.

(a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition Substrate Active site Competitive inhibitor Enzyme · 2011 Pearson Education, Inc http://images.slideplayer.com/1/277615/slides/slide_53.jpg

Comparing Competitive and Non-Competitive Inhibition

Comparing competitive (mechanism based) and non-competitive inhibition: (allosteric)

Competitive (Mechanism Based) Inhibition

Competitive (mechanism based) inhibition Substrate Competitive inhibitor Substrate Active site Enzyme Distorted active site (a) Enzyme Substrate Reversible competitive inhibitor Allosteric site (a) Allosteric inhibition Allosteric- inhibitor Increase in substrate concentration (b) Enzyme Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings.

Differences in Inhibition

Differences Inhibitors bind directly to the active site of the enzyme, competing with the substrate for access. Inhibitors are structurally similar to the substrate. Increasing substrate concentration can overcome inhibition by displacing the inhibitor.

Increasing substrate concentration does not overcome inhibition.

Inhibitors bind to allosteric sites (separate from active site), causing a conformational change that affect the binding activity of the enzyme. Inhibitors do not resemble the substrate and bind to different sites on the enzyme.

Similarities in Inhibition

Similarities Both reduces enzyme activity. Both processes can be reversible, depending on the nature of the inhibitor and the interactions with the enzyme. They are important in maintaining homeostasis and adapt to environmental changes.

Examples of Enzyme Inhibitors

ACE inhibitors, Statins ACE Normal artery Dilated Contracted Dilated artery= lower blood pressure 호 Opens coronary arteries ACE Angiotensin production a receptor receptor Heavy metals (Lead, Mercury), ATP Hg2+ SH Hg S + 2H+ SH Covalent bond formation S Active enzyme Inactive enzyme Active site Changed active site Normally, angiotensin is a substance produced by an enzyme (ACE) which binds to receptors in the wall of arteries, inducing a constriction (narrowing) of blood vessels and an increase in blood pressure. ACE inhibitors inhibit the action of this enzyme helping to control high blood pressure by preventing the binding of ACE.

Heavy metals (e.g. mercury, lead or copper) inhibit the activity of a wide range of enzymes, such as dehydrogenases (lactate and malate dehydrogenases), and digestive enzyme ({alpha}-amylase) by irreversibly binding to the allosteric site and preventing binding of the substrate. This is the case in all kinds of heavy metal poisoning, resulting in a wide range of symptoms. 5 | Page

Examples Smooth muscle cell a ACE Inhibitors stop angiotensin production receptor ACE Inhibitors Lower blood pressure and increase blood to heart

Non-Competitive Inhibition

Non-competitive competition Noncompetitive inhibitor