Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis Maintaining a Balance Topic 1: Enzymes and Metabolism

DOT POINT Identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substances Identify the pH as a way of describing the acidity of a substance

Introduction Most organisms are active within a limited temperature range, despite the large fluctuations in temperatures that occur in the outside environment. Organisms that live in environments where they may be subjected to extremes of temperature have adaptations that enable them to keep their internal temperature within a relatively narrow range. world.edu

Introduction Organisms must also maintain a relatively constant balance of chemicals within their bodies if they are to remain functionally active. One of the main reasons why the maintenance of a constant temperature and chemical balance is important is to ensure efficient metabolism. Metabolism is the sum total of all chemical reactions occurring within a living organism. whatdoino-steve.blogspot.com

Introduction All metabolic reactions in living cells are controlled by enzymes. Enzymes are protein molecules, present in cells, which act as catalysts, controlling the rate of each part of the complex chemical reactions that take place in cells. weartfestival.com

Introduction Catalysts are chemical substances that can accelerate chemical reactions, but they remain unchanged at the end of the reaction and can be reused. They function very rapidly at low temperatures, making them ideal for cell functioning. scienceclarified.com

Introduction Metabolism is divided into two: Anabolic: Reactions that involve building up large organic compounds from simpler molecules Catabolic: Reactions that involve breaking down complex organic compounds to simpler ones. en.wikipedia.org

Introduction An example of anabolic metabolism is the breakdown of starch. Starch is a large polysaccharide molecule made from small monosaccharide units such as glucose, a product of photosynthesis in plants. Anabolic steroids increase protein synthesis within cells, which results in the buildup of cellular tissue (anabolism), especially in muscles. ayushveda.com

Introduction An example of catabolic metabolism is the digestion of food. Large food molecules such as protein are broken down into small units called amino acids, which can then be easily absorbed from the gut into the bloodstream. old.maxfitmag.com

Introduction By understanding the chemical composition, functions and characteristics of enzymes, we can better understand their role in controlling chemical reactions in cells and therefore metabolism in living organisms. simple.wikipedia.org

The Chemical Composition of Enzymes Enzymes are protein molecules and are made by living cells. They are globular proteins, meaning that they have long chains or sequences of amino acids that have been folded into a specific shape. Their effective functioning relies on their shape. en.wikipedia.org

The Chemical Composition of Enzymes The molecule on which an enzyme acts is called a substrate. An enzyme fits together with its substrate molecule at a precise place on the surface of the much larger enzyme molecule, called the active site. The shape of this active site must not be altered if the enzyme is to function. (This is much like a key fitting a particular lock) students.cis.uab.edu Sketch diagram

The Chemical Composition of Enzymes Some enzymes have a non-protein group such as a vitamin or metal ion (zinc, copper or iron) that binds with the protein part and helps to form the active site. This is termed a co-enzyme or cofactor. It can easily be separated from the protein part of the enzyme, but its presence is essential for the enzyme reaction to occur. immunesystemimmunity.blogspot.com

The Chemical Composition of Enzymes A functional enzyme may therefore consist of protein only, or it may be in the form of an enzyme-cofactor complex, where the enzyme part of the complex is a protein. sciencedirect.com

The Chemical Composition of Enzymes Poisons are substances that have harmful effects on living organisms. Some poisons exert their toxic effect by disabling cofactors and thereby inhibiting enzyme functioning. The heavy metal mercury and cadmium replace zinc cofactors in some enzymes and inhibit their functioning. biologycorner.com

The Role of Enzymes in Metabolism Enzyme catalysts are able to speed up or slow down reactions without a change in temperature. This is extremely important in cells, since heat damages living tissue. For a chemical reaction to begin, activation energy is necessary. The role of the enzyme is to lower the activation energy needed to start a reaction, so that the reaction can proceed quickly, without a change in temperature. rtmsd.org

The Role of Enzymes in Metabolism In chemical reactions that occur in the non-living world, heat could provide the necessary activation energy for a chemical reaction. It is important to remember that an enzyme does not provide activation energy, it reduces the amount of activation energy needed by bringing specific molecules together, rather than relying on them colliding randomly. sciencephoto.com

The Role of Enzymes in Metabolism For example, oxygen and glucose may be chemically combined to release energy. In the lab, we can activate this by adding heat. We can burn the glucose, cause it to react with oxygen in the air and cause it to release energy as heat and light. In the human body, an enzyme is necessary to lower the required activation energy so that glucose can react with oxygen to release energy. sciencephoto.com

The Role of Enzymes in Metabolism Enzymes are substrate specific, meaning that one particular enzyme can work on only one particular substrate molecule. This is because the active site is reciprocally shaped to bind with that molecule. students.cis.uab.edu

The Role of Enzymes in Metabolism The enzyme itself is not chemically changed in the reaction so it can be reused in subsequent reactions. Enzyme controlled reactions are always reversible. students.cis.uab.edu

How Enzymes Work Enzymes are large, globular protein molecules with one or more indentations on their surface called active sites. For an enzyme to catalyse a reaction, the small substrate molecules must temporarily bind to these active sites. alevelnotes.com

How Enzymes Work At first a lock-and-key model was proposed. It was thought that the active site is rigid and the small substrate molecule is reciprocally shaped and fits into the active site, like a lock fits a key. Once this enzyme-substrate complex has formed, the close proximity of the molecules allows the reaction to be rapidly catalysed and the products of the reaction are released. acrazychicken.blogspot.com

How Enzymes Work To validate this model, predictions were made and tested. The results led to the proposal of the currently accepted amended version of the model, known as the induced-fit model. This model is based on the realisation that proteins are not rigid. Evidence suggests that the binding of a substrate to the active site of an enzyme induces the enzyme to alter its shape slightly, to fit more tightly around the substrate. intranet.canacad.ac.jp

How Enzymes Work Enzymes are highly efficient. They work rapidly, having a high rate of reaction or turnover number (the number of substrate molecules that one enzyme can act on in 1 minute). Catalase is the fastest acting of all enzymes, having a turnover number of 5 million substrate molecules per minute. Enzymes are also highly effective. Only minute traces are needed to bring about reactions and they can be reused. bioweb.wku.edu

How Enzymes Work The rate of an enzyme controlled reaction is affected by the concentration of the substrate. If an enzyme and substrate have a high affinity for each other, the reaction will proceed rapidly. The higher the substrate concentration, the greater the rate of enzyme reaction, until all available enzymes are being used to catalyse reactions. This is known as the saturation point. schools-wikipedia.org

How Enzymes Work Increasing the substrate concentration beyond the saturation point will not increase the rate of reaction, since all of the enzymes are working at their maximum turnover rate and will have to be reused to act on the additional substrate. The only way to increase the reaction rate would be to increase the enzyme concentration. schools-wikipedia.org

Characteristics of Enzymes Enzymes, due to their protein nature, are sensitive to temperature and to pH. Enzymes within cells function best at the body temperature of the living organism. In most living things, they function normally at temperatures up to 40  C. Above this, their efficiency (rate of reaction) decreases. smh.com.au

Characteristics of Enzymes At temperatures above 60  C, most enzymes stop functioning altogether. This is because heat causes the hydrogen bonds that maintain the form of the enzyme to break. This in turn changes the shape and structure of the molecule which is said to denature. chemguide.co.uk

Characteristics of Enzymes Any change in shape that affects the active site will alter the functioning of the enzyme because the active site is no longer reciprocally shaped to the substrate molecule. livingscience.co.uk

Characteristics of Enzymes Excessive cold also causes the enzyme to change shape and its functioning to slow down or stop. However, the change in shape due to extreme cold is often reversible. students.cis.uab.edu

Characteristics of Enzymes Each enzyme also has its own narrow range of pH within which it functions most efficiently. Levels of alkalinity or acidity outside of the optimum pH have a similar effect to that of temperature changes. They alter the shape of the enzyme and slow down or stop its functioning. Extremes of pH, like temperature, cause the enzymes to denature. chemistryinyourcupboard.org

Characteristics of Enzymes Within cells, most enzymes function at or near neutral, but enzymes in the digestive tract function in an acidic or alkaline medium. For example, the protein-digesting enzymes pepsin and rennin, found in gastric juice in the stomach, function best in strong acid. paraibaparadise.com

What is pH abundanthealthcenter.com

What is pH The pH scale runs from 0 to 14, where 7 is neutral. The presence of hydrogen ions in a solution makes it more acidic and so solutions with a pH below 7 are acidic and those with a pH above 7 are alkaline. The further away from the neutral value of 7, the stronger the respective acid or base. adrianasassoon.wordpress.com

Activity -Students to complete DOT Point Question 1.1 (see HSC DOT Point book)