The Energy of Life (Lecture 1) PDF

THE ENERGY OF LIFE CHAPTER 4: LECTURE 1 LECTURER: Ms. Thabisa Mdlangu [email protected] Department of Biodiversity & Conservation Biology Life Sciences Building, Core 2: 5th Floor All living things require energy to do work necessary for survival and reproduction This is true for all organisms from...

THE ENERGY OF LIFE CHAPTER 4: LECTURE 1 LECTURER: Ms. Thabisa Mdlangu [email protected] Department of Biodiversity & Conservation Biology Life Sciences Building, Core 2: 5th Floor All living things require energy to do work necessary for survival and reproduction This is true for all organisms from bacteria, plants, and animals Energy as the ability to do work Work is done when a force moves an object, e.g. : o You need energy to get out of bed in the morning o You need energy to come to class, sit down, and be able to process this lecture o You need energy to perform any task and even reproduce Where does energy come from? From the sun Plants use energy to make Sugar and Oxygen from Carbon dioxide and Water, this is known as photosynthesis Organisms in turn eat the plants to obtain this energy…. They use this sugar as a source of energy to do work All Cells Capture And Use Energy Physicists define Energy as the ability to do work Fundamental to life as many cellular processes require energy Total amount of energy in any object is the sum of energy’s two forms: Kinetic energy and Potential energy Potential Energy, which is stored energy available to do work (covalent bonds of molecules, such as ingredients of your energy bar contain a form a potential energy known as chemical energy) Kinetic Energy, which is energy being used to do work, any moving object possesses kinetic energy Calories are units used to measure energy One calorie (cal) is the amount of energy required to raise the temperature of 1 gram of water by 1 C The most common unit for measuring the energy content of food is kilocalories (kcal) which equals 1000 calories Energy conversions: In photosynthesis, plants transform kinetic energy in sunlight into potential energy stored in the chemical bonds of sugars and other molecules Respiration on the other hand releases this potential energy, and heat is lost to the environment in each and every step of the way The laws of Thermodynamics describe energy transfer Thermodynamics: The study of energy transformations 1st and 2nd laws describe the energy conversions that are vital for life, as well as those that occur in the non-living world 1st Law of Thermodynamics: The law of energy conservation - It states that energy cannot be created or destroyed, although energy can be converted to other forms. This means that the total amount of energy in the universe does not change Living organisms constantly convert energy from one form to another The most important energy transformations are Photosynthesis and Respiration Photosynthesis: Plants and some microbes use CO2, water, and kinetic energy in the sun to produce sugars that are assembled into glucose and other carbohydrates During cellular respiration, the energy-rich glucose molecule changes back to Carbon dioxide and water – liberating the energy necessary to power life 2nd Law of Thermodynamics: states that all energy transformations are inefficient because every reaction loses some energy to the surroundings as heat With every chemical reaction, you will lose some energy as heat.. The process is irreversible, cells cannot use the energy that has been converted to heat Heat energy is disordered because it results from random molecular movements Because heat is disordered and all energy transformations become heat, it follows that all energy transformations must head towards increasing disorder Entropy: is the measure of this randomness The more disordered a system is, the higher the entropy Because organisms are highly organized, they may seem to defy the 2nd law of Thermodynamics, but organisms are not isolated from their surroundings Instead a constant stream of incoming energy and matter allow organisms to maintain their organization and stay alive – using the information in DNA Ultimately, life remains ordered and complex because the sun is constantly supplying energy to the earth Networks of chemicals sustain life The number of chemical reactions occurring in even the simplest cell is astonishing Metabolism: Encompasses all of these chemical reactions in cells, including those that build new molecules and those that break down the existing Each reaction rearranges atoms into new compounds and each reaction either absorbs or releases energy Digesting your energy bar and using its carbohydrates to fuel muscle movement are part of your metabolism Photosynthesis and respiration are part of metabolism of the grass under your feet Metabolism is the sum of all the chemical reactions within the human body This includes any chemical process by which a substance is broken down, produced or chemically modified Catabolism: The process of breaking down materials within the body Anabolism: The process of making larger substances from smaller substances Factors affecting metabolism The amount and type of food consumed Age and gender can affect the speed of metabolism within the body Temperature or disease can also increase or decrease the speed of metabolism in the body Chemical reactions require energy input or release energy Biologists group metabolic reactions into two categories based on energy requirement: - Endergonic and exergonic reactions Endergonic reaction: requires an input of energy to proceed The products contain more energy than the reactants These reactions build complex molecules from simpler components E.g. Photosynthesis: Glucose product of photosynthesis contain more potential energy than do the CO2 and H2O reactants The energy source that powers this reaction is the sunlight Exergonic reaction: Releases energy Products contain less energy than the reactants Breaks large, complex molecules into their smaller, simpler components E.g. Cellular respiration: Breaking down of Glucose to CO2 and H2O These products contain less energy than glucose Linked Oxidation and Reduction Reactions Form Electron Transport Chains Electrons can carry energy Most energy transformations in organisms occur in Oxidation-Reduction (Redox) reactions, which transfer energized electrons from one molecule to another. Oxidation means the loss of electrons from a molecule, atom, or ion. Oxidation reactions are exergonic and they release energy as they degrade complex molecules into simpler products. Reduction means a gain of electrons (plus any energy contained in the electrons). Reduction reactions are therefore endergonic and they require a net input of energy. Oxidation and reduction occur simultaneously because electrons removed from one molecule during oxidation must join another molecule and reduce it, i.e. if one molecule is reduced (gains electrons), then another must be oxidized (loses electrons). The electron donor has more potential before it is oxidized than it does after the reaction is complete Reduction half is endergonic: The acceptor molecule has gained the energy-rich electrons so it ends up with more potential energy than it had before the reaction started Some proteins are electron-shuttling specialists. Groups of electron carriers often align in membranes … In an Electron Transport Chain, each protein accepts an electron from the molecule before it and passes it to the next Small amounts of energy are released at each step of an electron transport chain and the cell uses this energy in other reactions Each protein is first reduced and then oxidized Both photosynthesis and respiration depend on this electron transport chain to harvest energy ATP is Cellular Energy Currency Covalent bonds of Adenosine Triphosphate or ATP temporarily store energy … Released during exergonic reactions in the cells. A nucleotide with an adenine base, a five-carbon sugar, three phosphate groups Phosphate groups place three negative charges very close to one another In eukaryotic cells mitochondria produce most of the cell’s ATP during cellular respiration Energy released from ATP in exergonic reaction where the endmost phosphate group is removed through hydrolysis to yield Adenosine diphosphate, a free phosphate group, and a burst of energy. A nucleotide with an adenine base, a five-carbon sugar, three phosphate groups ATP represents short-term energy storage Organisms require large amounts of ATP and organisms recycle ATP at a furious pace Even though ATP is essential to life, organisms do not stockpile it in large quantities Instead, cells store energy-rich molecules such as fats starch and glycogen When ATP supplies run low, cells divert some of their lipid and carbohydrate reserves to the pathways of cellular respiration The process soon produces additional ATP For animals that hibernate, stored fat and glycogen are critical for winter survival Hibernation: Hibernation Definition, Process & Purpose - Lesson | Study.com Enzymes Speed Biochemical Reactions Enzymes are organic molecules that Catalyse (speed up) chemical reactions without being consumed. Among the most important of all biological molecules. Most enzymes are proteins but some may be made up of RNA. Functions are varied and many organelles such as the mitochondria, chloroplasts, lysosomes etc. are specialized sacs of enzymes. Speed up reactions by lowering the Activation Energy, the amount of energy required to start a reaction. Bring reactants (or Substrates) into contact with one another so that less energy is required for the reaction to proceed. Most enzymes can only catalyse one or a few reactions. Key to this specificity lies in the shape of the enzyme’s Active Site, the region to which the substrates bind. Substrates fit like puzzle pieces into the active site (lock-and-key model). Once the reaction occurs the enzyme releases the products. Its active site is then empty and ready to pick up more substrate. Enzyme-substrate complex (ES) is a temporary molecule formed when an enzyme comes into perfect contact with its substrate Enzymes are very sensitive to conditions in the cell: pH Changes (Mostly between 6 and 8) - Pepsin in the stomach (between 2 & 4) Salt concentrations become too high or too low Temperature: Each enzyme has an optimum temperature at which it functions best. Can denature if the temp is too high Pharmaceutical Drugs can also inhibit enzyme function. One faulty or missing enzyme can have dramatic effects: e.g. Lactose intolerance: People who can’t secrete the enzyme lactase cannot digest lactose-containing foods Non-Protein helpers called Cofactors These are substances that must be present for an enzyme to catalyse a chemical reaction Cofactors are often oxidized or reduced during the reaction but they are also not consumed Instead they return to their original state once the reaction is complete. Some Cofactors are metals such as zinc, iron, and copper. Other Cofactors are organic molecules and are called Coenzymes. The cell uses many water soluble vitamins produce coenzymes A diet that lacks in vitamins can lead to reduced enzyme function and eventually serious illness or even death Enzymes - Catalysts - YouTube Cells control reaction rates Cells precisely control the rates of their chemical reactions If they did not, some important compounds would be in short supply and some would be wasteful They do this through Negative and Positive feedback Negative feedback: Slows down the synthesis of a chemical product It inhibits the enzyme that catalyzes the initial reaction, and the entire pathway slows down Negative feedback works in two ways:  Competitive inhibition: The inhibitor attaches to the active site, preventing it from binding to the substrate -The inhibitor competes with the substrate to occupy the active site  Non-competitive inhibitor: The inhibitor binds to the enzyme at a location other than the active site (Allosteric site). This changes the shape of the enzyme such that it cannot fit with the substrate Positive feedback A process that reinforces an existing condition E.g. blood clotting: Once the clot starts to form, the reaction accelerates which further stimulates clotting: speeding up the reaction even more Some examples of enzyme names:  Protease: Protein and polypeptide breakdown  Lipase: Lipids and fats breaking down  Transferase: Transfer functional groups from one molecule to the other  Dehydrogenase: Removes hydrogen atoms from a molecule  Amylase: Break down starch into simple sugars  Oxidoreductase: Catalyzes oxidation-reduction reactions Next week’s Prac Cell Membrane Transport - Transport Across A Membrane - How Do Things Move Across A Cell Membrane (youtube.com)