This page is going through major updates. If you see errors, misspellings, incorrect links, please let the instructor know in the HELP DESK. Back... Learning Resource 03. The Learning Resource goal is to use the Internet and become independent of the textbook. It is a project in progress... Ch. x Ch. x Ch. x Energy and Enzymes ENERGY In order to maintain their organization and carry out metabolic activities, cells/organisms need a constant supply of energy. Energy is defined as the ability to do work. Organic nutrients, produced by photosynthesizers (green) plants, photosynthetic (green) bacteria, and photosynthetic (green) protistans, directly provide organisms with energy. Photosynthesizers use solar energy, therefore, life on Earth is ultimately dependent on solar energy. --- Energy, flow of energy, energy transformations (physics) --- Energy occurs in two forms: kinetic energy and potential energy. Kinetic energy is energy of motion -- as when a moose (see picture above) walk through grass. Potential energy is stored energy, such as the energy stored in food we eat, and can be converted to various types of kinetic energy. Food is called chemical energy because it is composed of organic molecules such as carbohydrates, proteins and lipids. Two physical laws regulate energy relationships and how it flows through ecosystems and cells. The First Law of Thermodynamics states that "energy can be neither created nor destroyed" (Law of Conservation of Energy) (Source: https://chemistry.osu.edu/~woodward/ch121/ch5_law.htm). However, energy can be changed (transformed) from one form to another. When leaf cells photosynthesize, they use solar energy to form carbohydrate molecules -- chemical energy. But not all the captured solar energy becomes carbohydrates, some becomes heat, which dissipates into the environments -- no longer usable. Ultimately all energy will one day be transformed to heat, as explained by the second law of thermodynamics... The Second Law of Thermodynamics states that "every system left to its own devices always tends to move from order to disorder, its energy tending to be transformed into lower levels of availability, finally reaching the state of complete randomness and unavailability for further work" (Law of Energy Decay) (Source: http://www.talkorigins.org/faqs/thermo/probability.html). Often expresse as increase of entropy (disorder), or "crumbling of the house". Ultimately all energy will one day be transformed to heat... As a result of the second law of thermodynamics, no process requiring a conversion of energy is ever 100 percent efficient. Much of the energy is lost as heat. In gas engines the efficiency is between 20 - 30 percent, while the efficiency of cells is about 40 percent. --- ATP and the ATP Cycle --- ATP, adenosine triphosphate, is the common energy currency of cells. ATP is a carrier of energy between exergonic and endergonic reactions in the ATP Cycle. It is called a "high-energy" compound because a phosphate group can easily be removed (see the figure of the ATP cycle). --- Enzymes --- > An enzyme is a protein that functions as an organic catalyst to speed a chemical reaction without itself being affected by the reaction. Reactions in cells do not occur haphazardly in cells. Instead they are part of metabolic pathways, a series of linked reactions that requires enzymes. The photosynthesis discussed in chapter 7 and the cellular respiration discussed in chapter 8 are metabolic pathways. Enzymes can be inhibited -- Feedback inhibition. (Fair use for educational purposes. Source on the figure. There are two kinds of inhibitions -- competitive inhibition and allosteric inhibition.) Molecules often do not react with one another unless they are activated some way. The energy that must be added to cause molecules to react with one another is called energy of activation. The figure below compares when an enzyme is not present to when an enzyme is present, illustrating that enzymes lower the amount of energy required for activation to occur. In our cells, enzymes allow reactions to take place under mild conditions (that otherwise would require heat -- which would destroy the cell), by bringing the reactants into contact with one another in an "enzyme-substrate complex". The enzyme has an active site where the substrate fits in a "lock-and-key" fit. Several factors, e.g., temperature and pH, can affect and even destroy an enzyme. TEMPERATURE. Enzymes usually have an optimum where they work best, which is within the normal conditions of an organisms, e.g., in humans most enzymes work best at a temperature close to normal human body temperature, or slightly above (some enzymes function a little better under slight fever conditions). pH. Many enzymes work best when pH is close to neutral, or in the case of digestive enzymes close to the pH where they are active, e.g., the enzyme pepsin active in the digestive process in the stomach, functions best around pH 2 -- the pH in our stomach, while the enzyme trypsin works best around pH 9, the pH in the small intestine. --- Organelles and the Flow of Energy --- Two organelles are particularly involved in the flow of energy from the sun through all living things. Photosynthesis, a process that captures solar energy to produce carbohydrates, takes place in the chloroplasts. Cellular respiration, which breaks down carbohydrates, takes place in the mitochondria. The overall reaction of the photosynthesis can be written: Light energy + 6CO2 + 6H2O -----> C6H12O6 + 6O2 The overall reaction of the cellular respiration can be written: C6H12O6 + 6O2 -----> 6H2O + 6CO2 + 36ATP VIRTUAL EXERCISE **. The virtual lab as it looks when you log in to the site... Welcome to the Rate of enzyme-controlled reactions Virtual Lab. To proceed, read and follow the instructions below. Rate of enzyme-controlled reactions (Session 1) The following text is from the present lab manual used for General Biology F2F majors at STC. Read the text if you have not done so already. (If you are in a F2F class, this is the same text you submitted one of the fill-in-the-blank-quizzes for.) This is an activity for the web-enhanced Face-to-Face class, online students, unless interested, are not required to do this activity. Enzymes: Factors Affecting Rate of Activity (Vodopich, and Moore. Biology Lab Manual. Pages 147 - 148.) Fortunately, not all chemical reactions within our cells occur spontaneously. If they die, our metabolism would be chaotic. Instead, most reactions in cells are controlled by proteins called enzymes. Enzymes are biocatalysts, meaning that they accelerate metabolic reactions to biologically useful rates. Specifically, enzymes catalyze (accelerates) reactions by lowering the activation energy needed for the reaction to occur. Enzymes act by binding to reacting molecules, called the substrate, to form an enzyme-substrate complex. This complex stresses or distort chemical bonds to form a transition state in which the substrate becomes more reactive and the metabolic rate accelerates. The energy needed to form the transition state is called energy of activation and is lowered by the enzyme. The site of attachment and the surrounding parts of the enzyme that stress the substrate's bonds constitute the enzyme's active site. The reaction is complete when the product forms and the enzyme is releases in its original condition. The enzyme then repeats the process with other molecules of substrate. Enzymes are proteins made of long chains of amino acids that form complex shapes. Although cells contain many enzymes, each type of enzyme has a precise structure and function, and each enzyme catalyzes a specific reaction. The specificity results from an enzyme's unique structure and shape. For example, the complex shape of the active site on the enzyme's surface usually couples with only one type of substrate. Any structural change in an enzyme may denature or destroy its effectiveness by altering the active site and slowing down the reaction. Denaturing enzymes may result from extreme temperature, extreme pH, or any environmental condition that fundamentally alters a protein's structure. Therefore, the rate of an enzymatic reaction depends ob conditions in the immediate environment. These conditions affect the shape of the enzyme and modify the active site and precise fit of an enzyme and its substrate. The range of values for the environmental factors such as temperature and pH within which an enzyme functions best represents that enzyme's optimal conditions. the optimal conditions for the enzymes of an organism are usually adaptive for the environment of the organisms. Other factors such as the amount of substrate or concentration of enzyme also affect the reaction rate. The text above is not very specific about the chemicals involved. Here is first the general chemical reaction formula, followed by the more specific reaction, where the disaccharide Lactose (milk sugar) is split into the two monosaccharide building blocks glucose and galactose: Enzyme + substrate ---> enzyme substrate ---> enzyme + product (The enzyme is reused again in the next reaction.) Lactase + Lactose ---> Lactase-Lactose complex ---> Lactase + Glucose + Galactose (The enzyme Lactase is reused again in the next reaction.) (Souce: Paraphrased from McGrawHill) Short instructions To do the lab as smoothly as possible, pay attention to the online instructions. You will work with your team. When you have navigated to the lab and you are ready to start, follow the instructions in the text frame to the left of the lab. (If you are in a F2F class, that is the same text you submitted one of the fill-in-the-blank-quizzes for.) The video on the TV will be shown by your instructor already in the regular lab before moving to the computer lab, since there are no speakers on the computer units in the lab. (When you start doing the experiment you may notice there are actually two ways to conduct the experient to obtain the same results -- by using different amount of lactose at constant pH, or to use the same amount of lactose at different pH levels.) We all work at different speeds. You will record the data both in the table on the computer screen (to obtain the resulting graph to show the instructor), AND also on the paper copy of the table provided by the instructor (to submit for a grade). When you have filled in the data table on the screen, click on the Graph button to see the results. The printer (usually) doesn't work in the Biology Computer Lab. When ALL members of the team have finished and have the Graph on the screen -- with ALL five pH level curves, call the instructor over. When ALL team members are finished ALL team members must show the instructor the graph on THEIR OWN COMPUTER SCREEN --- If you have not paid attention to the instructions and deleted the data on your own screen before the instructor can look at it, you must repeat the lab in order fot the TEAM to EARN a grade. Cooperation between team members is important, because no team member can leave the lab until ALL team members of the team have showed the graph with ALL 5 curves to the instructor --- Here is the link -- start doing the lab: http://www.mhhe.com/biosci/genbio/virtual_labs_2K8/labs/BL_02/index.html When finished in the face-to-face class, sign the participation roster (provided by the instructor) to end your participation in class. All team members submit the paper copy of data table -- AT THE SAME TIME. Sign the roster. You have finished the first session of the lab. The results will be discussed during second session of the lab. You will then also complet the assignment called a "Journal". Whether you are in an online class, or if you did this in the classroom: Work well done! Addendum: At some point during the lab you will see a table and a graph. A short explanation of these will be given in the face-to-face class. They are also explained in the online instructions in the virtual lab. Table after conducting the experiment at pH 7... Graph after conducting the experiment at pH 7... - - - Connecting the Concepts - - - All cells use energy. Energy is the ability to do work. The cells use ATP for cellular work through metabolic pathways. A metabolic pathway consists of a series of chemical reactions, each with its own enzyme. The ultimate source of energy is from the sun. In the next chapter we will learn how photosynthesis inside chloroplasts transforms solar energy into chemical energy and carbohydrates. (Source: Mader, S.S. 2010. Biology. Ed. 10. Used for educational purpose.) (Source: Dr. Nilsson's old lecture notes, and Mader, S.S. 2010. Biology. Ed. 10. Used for educational purpose.Permission given in 2001 by McGraw-Hills then sales representative, Don Grainger, to use the picture online on lecture notes.)