L7 BIO 101 Energy & Metabolism PDF

Chapter 7 Energy & Metabolism Course: BIO 101, Introduction to Biology 1 What is Energy Energy is the ‘capacity to do work’. Anything our body does, it needs a certain level of energy to function. Examples of activities that require energy include: ✔walking ✔r...

Chapter 7 Energy & Metabolism Course: BIO 101, Introduction to Biology 1 What is Energy Energy is the ‘capacity to do work’. Anything our body does, it needs a certain level of energy to function. Examples of activities that require energy include: ✔walking ✔running ✔exercising ✔doing homework ✔eating ✔sleeping ✔breathing 2 Energy exists in different forms! Potential energy: energy that is stored in an object at rest, based on the position it is in. ✔ E.g. A bike resting on top of a hill Kinetic energy: Energy used by a moving object ✔ E.g. A bike moving up and down a hill. 3  Thermodynamics Heat is a form of energy, called thermal energy. The study of the conversion of thermal energy to and from other types of energy is called thermodynamics. All metabolic reactions release some amount of heat. First Law of Thermodynamics Energy cannot be created or destroyed, can be converted from one form to another. Second Law of Thermodynamics Energy tends to spread out or disperse spontaneously from high energy forms to forms lower in energy. The tendency of entropy to increase is the second law of thermodynamics. Entropy Measure of how much the energy of a particular system has become dispersed. 4  Metabolism Metabolism is collectively all the chemical reactions that take place within each cell of a living organism for, providing energy to vital processes for synthesizing new organic material. Cells store energy by building organic molecules and retrieve energy by breaking them down. Fig: A simple Metabolic pathway 5  Participants in metabolic pathways A reaction occurs when components undergo the following changes: Several biological molecules assist in completion of a reaction, which are: Energy Carriers: ATP Enzymes: Biological molecules that speed up a reaction Cofactors: Non-protein chemical compounds that aid in an enzyme’s activity 6  Types of Metabolic pathways Anabolic Pathway Catabolic Pathway 7  Energy in the Molecules of Life Chemical Energy: Every chemical bond holds a certain amount of energy. This is the amount of energy required to break the bond, and it is also the amount of energy released when the bond forms. The particular amount of energy held by a bond depends on which elements are taking part in it. For example, two covalent bonds—one between an oxygen and a hydrogen atom in a water molecule, the other between two oxygen atoms in molecular oxygen (O2)—both hold energy, but different amounts. Energy changes in living body/cells occurs mostly via two types reactions: 1. Endergonic Reactions 2. Exergonic Reactions Energy input required. Energy is released. Product has more energy than Products have less energy than starting substance. starting substances. Catabolic reactions are exergonic. Anabolic reactions are endergonic. Energy “out” Energy “in” 8 9  What is (ATP)? Adenosine triphosphate ATP is the energy-carrying molecule found in cells of living organisms. It is composed of : One adenosine (adenine + ribose sugar) & three phosphate groups One adenosine + two phosphate=ADP (Adenosine diphosphate) 10  The Role of ATP? Cells “earn” energy (ATP) in exergonic reactions Cells “spend” energy (ATP) in endergonic reactions  Activation Energy For a reaction to occur, an energy barrier must be overcome. Activation energy is the minimum amount of energy needed for a chemical reaction to occur Its like a hill that reactants must climb before they can coast down the other side to become products Enzymes make the energy barrier (activation energy) smaller, hence the reaction runs faster. Both endergonic and exergonic reactions have activation energy, but the amount varies with the reaction. 12  Membrane Transport Mechanism Nutrients and other compounds are required for energy production, for cell growth and normal activities. To utilize the compounds, cell must uptake nutrients from the environment. Uptake mechanisms must be specific- that is the necessary substances, not others, must be acquired. So, special transport systems are required for nutrient uptake. Transport systems are located in the cytoplasmic membrane, a selectively permeable membrane, to enter into the cell, nutrients must cross the other layer of cell. Types of transport system Diffusion across lipid bilayer Passive transport Active transport 13 Passive Transport Flow of solutes through the interior of passive transport proteins down their concentration gradients (From high to low concentration). Passive transport proteins allow solutes to move both ways. Does not require any energy input. 14 Active Transport Movement of molecules from an area of lower concentration to the area of higher concentration (against concentration gradient). Transport protein must be activated. ATP gives up phosphate to activate transport protein. Binding of phosphate changes transport protein shape and affinity for solute. The other side opens, solute is released Removal of phosphate Requires energy Protein goes back to its original state 15 How Cells Release Stored Energy 16  Cellular Respiration Pathway that breaks down an organic molecule to form ATP. In this process, organisms take molecules broken down from food and release the chemical energy stored in the chemical bonds of those molecules. Example: Cells convert sugar into energy Aim: To create ATP to power cellular reactions, cells require fuel and an electron acceptor which drives the chemical process of turning energy into a usable form. The energy that is released from chemical bonds during cellular respiration is stored in molecules of ATP ATP is called the energy currency of all biochemical processes! 17 What types of organisms undergo cellular respiration? Animals, plants, fungi, algae and other protists (also in prokaryotes in cytoplasm) What types of molecules are broken down? Any food (organic) molecule, or nutrient, including carbohydrates, fats/lipids and proteins can be processed and broken down to produce ATP 18 Stages of Cellular Respiration/ Aerobic Respiration 1. Glycolysis 2. Pre-Krebs Cycle (Pyruvate to Acetyl Co-A ) 3. Citric Acid Cycle/TCA cycle/Krebs Cycle 4. Electron Transport Chain Simple equation of cellular respiration 19 Cellular Respiration/ Aerobic Respiration Overall, cellular respiration is a process that is aerobic. Aerobic means that it requires the presence of oxygen. One step: Glycolysis, of cellular respiration do not require the presence of oxygen and is therefore an anaerobic step. This is the only stage that is completed in cytoplasm. Rest of the stages are completed in mitochondria (powerhouse: produces majority of cell’s ATP). Energy carriers found within this process: ATP Electron carriers found within the process: NADH, FADH2  Mitochondria Cytoplasm 21  Glycolysis First stage of aerobic respiration. Set of reactions that produce ATP by converting one glucose to two pyruvates. All reactions are mediated by enzymes. Anaerobic step in the cellular respiration pathway therefore it DOES NOT require oxygen Location: Cytoplasm (For both prokaryotes & eukaryotes) Product: 2 Pyruvate, net yield of two ATP and two NADH. Pyruvate moves to mitochondria 22  Pre-Krebs Cycle (Pyruvate to Acetyl-CoA) Before a pyruvate enters the Kreb’s Cycle, it combines with an enzyme called Coenzyme A (CoA). This reaction produces one molecule of Acetyl CoA from one pyruvate. Acetyl CoA is a molecule produced by almost all nutrients (carbohydrate, protein, lipid) before entering the Kreb’s cycle. Location: mitochondrial matrix (eukaryotes), cytoplasm (prokaryotes) Fig: Pathway to Citric Acid Cycle Product: Acetyl CoA; CO2 released, NADH produced. 23  Krebs Cycle Named after Hans Krebs. Requires oxygen (aerobic). An Acetyl CoA (formed from Pyruvate) combines with a four-carbon molecule to make one molecule of citric acid: starting molecule of Kreb’s cycle. Citric acid is broken down in several steps providing the energy to make NADH, FADH2 , ATP. Hans Adolf Krebs (1900-1981) Cyclical series of oxidation reactions that give off CO2 and produce one ATP per cycle. Turns twice per glucose molecule (produces 1 ATP per turn). Produces (2 X 1 ATP) = 2 ATP molecules from 1 glucose molecule. Location: Mitochondrial matrix (eukaryotes), Cytoplasm (prokaryotes) Product: NADH, FADH2 , ATP; CO2 released. 24 Product summary/ glucose molecule 25 Electron Transport Chain The ETC is a series of proteins located in the inner mitochondrial membrane. It accepts high energy electrons from the NADH and FADH2 provided by the previous steps As the electrons move down the chain, energy is released. This energy is used to move H+ (proton) out of matrix which creates a concentration gradient. These H+ flows down the concentration gradient, into matrix through ATP synthase to form ATP. Oxygen is used as the final electron acceptor at the end of the ETC. Oxygen receives electrons and hydrogen ions (H+) and produces H2O. Location: Inner mitochondrial membrane (Eukaryotes) Cytoplasmic membrane (Prokaryotes) The mitochondria is considered to be the “powerhouse” of the cell because it produces the majority of a cell’s ATP 26  Electron Transport Chain ETC Product Summary 34 ATP Usable energy H 2O By product Courtesy of: Khan Academy 27  Cellular Respiration ATP Tally (for 1 glucose mol.) 1. Glycolysis = 2 ATP 2. Krebs Cycle = 2 ATP 3. ETC = 32 to 34 ATP Grand Total = 36 – 38 ATP Courtesy of: Khan Academy 28 What happens after glycolysis if oxygen is not present? 29 Fermentation Glucose-breakdown pathways, that make ATP without the use of oxygen or electron transfer chains. If oxygen is not present, the products of glycolysis (pyruvate and NADH) will enter an alternative process called fermentation. Like aerobic respiration, fermentation begins with the glycolysis pathway (anaerobic step). Uses pyruvate/ other molecules, as a final electron acceptor (instead of O2) Location: Cytoplasm Two types of fermentation: Lactic Acid Fermentation = Humans (muscle cells) Alcoholic Fermentation = Yeasts (bread making) 30 Examples of Fermentation Lactic Acid fermentation After doing heavy exercise, the body cannot supply oxygen into the cells in the appropriate amount, then muscles switch to fermentation (anaerobic process) to produce energy by producing lactic acid. The result of lactic acid fermentation in muscles and body parts leads to stiffness or cramps. Electron acceptor: Pyruvate Location: Cytoplasm Product: Lactic acid, ATP (generated only in glycolysis) 31 Examples of Fermentation Alcoholic Fermentation Saccharomyces cerevisiae, also known as brewer's or baker's yeast, converts sugars and starches into alcohol and carbon dioxide during the fermentation process. Electron acceptor: Acetaldehyde Location: Cytoplasm Product: Ethanol, ATP (generated only in glycolysis) 32  Aerobic Respiration Fermentation Oxygen is required to derive Oxygen is not required in this energy. process. Site of occurrence : Cytoplasm & Site of occurrence: Cytoplasm. Mitochondria. End products are CO2 & water. End products are lactic acid; ethanol, CO2. Involvement of electron transport No electron transport chain & chain & kreb’s cycle. kreb’s cycle. Final electron acceptor: Molecular Final electron acceptor: Organic oxygen. molecule (e.g Pyruvate). About 36 molecules of ATP are Only 2 molecules of ATP are produced. generated. Mainly occurs in higher organisms. Mainly occurs in microorganisms. 33 Advantages of Fermentation Increases habitat: It lets organisms live in places where there is little or no oxygen. Such places include deep water, soil, and the digestive tracts of animals such as humans, some bacteria live in the human digestive tract. Speed: It produces ATP very quickly. For example, it lets muscle cells get the energy they need for short bursts of intense activity. Aerobic respiration, on the other hand, produces ATP more slowly. Aerobic Respiration vs Fermentation Aerobic respiration produces much more ATP than fermentation. Fermentation occurs more quickly than aerobic respiration. 34 Overview of the Process 35  Thank You! In photosynthetic plants too! 36 Courtesy of LibreTexts Biology