Biology 189 Chapter 4

Chapter 4 How Cells Obtain Energy: Cellular Respiration  Chapter 4 Outline  Defining metabolism and the role of energy in living systems  Enzymes: structure and function  The process of cellular respiration ◦ Three steps: Where and how much energy?  Glycol...

Chapter 4 How Cells Obtain Energy: Cellular Respiration  Chapter 4 Outline  Defining metabolism and the role of energy in living systems  Enzymes: structure and function  The process of cellular respiration ◦ Three steps: Where and how much energy?  Glycolysis  Citric Acid Cycle  Oxidative Phosphorylation ◦ Fermentation – a special type of respiration  Energy in Living Systems  Metabolism is the sum of all chemical reactions in the body  Most reactions require the assistance of enzymes to catalyze from reactants  products  Two types of metabolic pathways:  Catabolism  Anabolism  What is Metabolism?  Catabolism: ◦ Breaks down complex molecules ◦ Releases energy (ATP)  Anabolism: ◦ Builds/creates complex molecules out of smaller compounds ◦ Requires energy (ATP) Which of these is Which of these is cellular respiration? photosynthesis?  Energy in Living Systems  Energy: the ability to do work or create some type of change  Types of energy include: ◦ electrical, light, radiant, heat  Kinetic energy – the energy of objects in motion  Potential energy – stored energy, based on location and structure of matter Potential vs. kinetic energy Potential vs. kinetic energy  Energy in Living Systems  Metabolism transfers energy and follows the Laws of Thermodynamics ◦ Open system – energy can be exchanged with its surroundings (*biological systems) ◦ Closed system – can’t exchange energy with its surroundings  There are 4 laws – biology focuses First and Second  Laws of Thermodynamics 1st Law: Conservation of 2nd Law: When reactions Energy - Energy cannot occur, they become be either created or more disordered = destroyed, it changes entropy (this can be forms measured as heat)  Energy is transferred and transformed, but it is not created or destroyed  Energy in Living Systems  Chemical reactions proceed as reactants  products ◦ If catabolic:  Products are smaller molecules  Energy is released  Can happen spontaneously, but may be slow – enzymes assist ◦ If anabolic:  Products are larger molecules  Requires energy - reactions are not spontaneous – enzymes needed  Energy in Living Systems  Enzymes are biological catalysts ◦ Most critical reactions occur on their own, but slowly ◦ Enzymes increase the speed of reaction by lowering the activation energy  This is the energy needed to “jump start” a reaction  Energy in Living Systems: Enzymes  Each enzyme has a specific function in a reaction  3-dimensional shape determines the function  Enzyme binds a substrate (=reactant) to its active site ◦ Induced fit: active site molds around the substrate  Products are made from the reaction Starch Glucose Protease – proteins Salivary Lipase – amylase lipids/fats  Special Features of Enzymes  Each enzyme is very selective ◦ It catalyzes specific reactions ◦ It recognizes a specific substrate An enzyme active site interacts with the substrate The active site fits to the substrate, and the enzyme changes shape slightly to make snug fit in induced fit The interaction results in products Enzymes can be used over and over again They do not change or get consumed in the process Enzymes names often end in –ase They are typically named for what they do Learn more about enzyme differences between mammals ARTICLE  An Enzyme of Respiration: Carbonic Anhydrase  Helps body get rid of carbon dioxide from respiration ◦ CO2 can be deadly in high concentrations  This enzyme speeds up reaction of CO2 with H2O ◦ Makes an ion (bicarbonate) that dissolves in blood  Bicarbonate is then converted back to CO2 in the lungs and respired out  Special Features of Enzymes  Enzyme needs change depending on where in the body, demand for use, conditions for use ◦ Enzymes determine which reactions proceed and at what rates ◦ Activity of any given enzyme is controlled by environmental factors – pH, temperature, salt conc., cofactors (inorganic ions) or coenzymes (organic molecules; vitamins are these) Vitamin C is needed for collagen formation Click on the image to learn more about enzymes and how they work!  Energy Carrier Molecules  Living cells can’t store significant free energy, must be stored safely  ATP is the universal energy “currency” of all cells ◦ Stores energy in phosphate bonds ◦ Releases energy when these bonds are broken  In addition to ATP, other molecules also function to carry energy in the form of electrons: ◦ NADH, FADH2 – used in cellular respiration ATP (adenosine triphosphate) ◦ NADPH – used in photosynthesis  Electrons in Biological Systems  Remember that: Electrons in motion = Energy  But, electrons can’t move alone in cells – they can only move when attached to hydrogen (H) atoms ◦ When e- move around from one molecule to the next, the H are moving too  And if e- (with the H) leave/are lost from one molecule, then they are gained by another molecule  This is called a redox reaction reduction oxidation  Transfer of Electrons: Coupled Reactions - Redox  Oxidation and reduction reactions move electrons, and are coupled in biological reactions as redox reactions ◦ Reduction – gain e- ◦ Oxidation – lose e- LEO  Let’s return to a high-energy carriers the GERman ◦ NADH – used in cellular respiration ◦ This high-energy molecule becomes reduced when carrying e- (and H+) and oxidized when it loses e- OIL RIG NAD+  NADH This form is This form is oxidized reduced  Energy: Living on Earth  Living organisms all require energy to survive  The sun is source of most energy on Earth ◦ Light energy is used by producers (=plants) to make sugars (such as glucose) by photosynthesis (see more in Ch. 5!) ◦ Consumers (including us) acquire energy from food molecules (either directly from plants or indirectly from things that eat plants)  All life depends on the process of cellular respiration to acquire this needed energy What is Cellular Respiration?  Cellular respiration is a series of catabolic reactions that break down molecules to produce ATP  ATP is then used by the cell to do work, such as:  moving molecules across membranes  making muscles move  along with enzymes, making molecules bind together *Remember that anabolic reactions use energy to make molecules Cellular Respiration: Overall Process  Glucose/food is used as “fuel” to get ATP energy Reactants Products + Heat Glucose contains more energy than CO2 and water (or CO2 and water contain less energy than glucose) ◦ Glucose – lots of energy to get from a molecule! ◦ CO2 – lousy source of energy – went to ATP (and lost to heat)  Cellular Respiration: Aerobic Harvest of Food Energy  The overall process of our cellular respiration is aerobic - requires O2 ◦ Gasoline combustion also requires O2! Your food is also burned!  Q: Who Undergoes Cellular Respiration? - A: Every living thing undergoes some form of cellular respiration - The steps occur in the cytoplasm and mitochondria - All eukaryotes have mitochondria – including plants! - Prokaryotes (bacteria), with no mitochondria, still have cytoplasm & a cell membrane for this function  Click on image for an overview of the processes of cellular respiration  Cellular Respiration  The process of cellular respiration takes place in three steps: (1) Glycolysis (2) Citric acid cycle – aka the Krebs cycle (3) Oxidative phosphorylation – aka electron transport chain CH2O Goal: To “squeeze” as many e- out of a molecule of glucose as possible, in order to maximize synthesis of ATP ATP  Steps of Cellular Respiration  Glycolysis  Occurs in the cytoplasm of the cell  Goal: To break down glucose into pyruvate (=pyruvic acid) molecules Steps:  Glucose has to be “activated” using 2 ATP  It takes energy to start making energy!  Steps of Cellular Respiration  Glycolysis Steps:  That activated glucose is split apart into two molecules  As that occurs, electrons are moved to NAD+ to make NADH and P bonds to ADP to make ATP  Produces a net of 2 ATP, and also 2 NADH molecules (reduced from NAD+)  This process is anaerobic (doesn’t need oxygen)  This process is open (to the next step)  Steps of Cellular Respiration  Citric Acid Cycle  Occurs in the matrix of mitochondria  Goal: To use the pyruvate molecules from glycolysis to generate energy carriers & ATP CAC  Goal: To “use up” the C by transferring all electrons to energy carriers  The process is aerobic (requires oxygen)  Steps of Cellular Respiration  Citric Acid Cycle Steps:  Pyruvate is transformed into a 2-carbon molecule  Coenzyme A catalyzes the reaction to form acetyl CoA, and a carbon is lost as CO2  This 2-carbon acetyl CoA molecule then enters the cycle  This molecule loses electrons to form energy carriers NADH and FADH2  This molecule also loses C to form CO2 Coenzyme A is made from vitamin B5  Steps of Cellular Respiration  Citric Acid Cycle, continued -  For one molecule of pyruvate, the eight steps of the cycle produce:  3 CO2 molecules  1 ATP  4 NADH and 1 FADH2 (these are energy carriers) *Remember* that a molecule of glucose makes two molecules of pyruvate, so the citric acid cycle turns two times for each molecule of glucose Need to double the products above to account for a single glucose molecule  Steps of Cellular Respiration  Citric Acid Cycle: End of the process  By the end of the cycle:  The entire glucose molecule has been converted to CO2 (all 6 carbons of a glucose molecule are oxidized to CO2)  Only the energy carriers (NADH and FADH2) go on to the next step  This is a closed process (=a cycle):  The molecule made at the end of the loop is recycled and used to fuel the beginning of the loop  Steps of Cellular Respiration  Oxidative phosphorylation ◦ Occurs in the inner membrane folds of mitochondria CAC ◦ Here, an electron transport chain (ETC – chain of proteins) is used to pass along electrons to make ATP ◦ Goal: To produce the most ATP (~34) of all respiration processes ◦ Is aerobic – here, O2 functions as the final electron acceptor and water is produced Overview of Oxidative Phosphorylation Step 1: 1  NADH donates toe- membrane proteins across the inner membrane – this creates energy Step 2:  This energy is used to 2 pump protons (H+) from mitochondrial matrix to the intermembrane space – this process creates an H+ gradient Overview of Oxidative Phosphorylation Step 3:  These H+ are driven through the last protein, ATP synthase, which acts as a tiny generator to provide energy to regenerate ADP ATP ATP Synthase in action  The e- are passed along the ETC where O2 is 3 waiting as the (final) terminal electron acceptor  O2 picks up e-, then attracts 2H+ to form H2O  Q: Why is Oxygen Important to Respiration?  O2 functions as the final (terminal) electron acceptor, H2O is made as a result ◦ If not present, electrons would pile up and H+ pumping would grind to a halt – no more ATP ◦ No more ATP produced  cells stop working  organism dies Many deadly cellular poisons (carbon monoxide, cyanide) block the transfer of electrons from electron transport chains to O2  The human survival “rule of threes” Oxygen, water and glucose are essential for life!  Cellular Respiration & Metabolic Pathways  Most common fuel source is glucose, but other macromolecules can be used in catabolic pathways ◦ Glycolysis: metabolism of glucose begins here ◦ Other macromolecules enter at different stages (fatty acids and some amino acids at the Citric Acid Cycle, etc.)  Some macromolecules are broken down and monomer units are used for anabolic pathways ◦ Nucleic acids (=nucleotides) and proteins (=amino acids) from food you eat are used to build new DNA and new proteins You truly are what you eat!  Variations on Cellular Respiration: Anaerobic Respiration  Anaerobic Respiration ◦ Is an alternative process of cellular respiration, performed by microbes (Bacteria and Archaea) that do not use O2 as a terminal electron acceptor  These organisms also create a proton gradient/respiratory chain across a membrane (similar to that on ETS)  But, instead of O2 waiting, other chemicals serve this role: nitrate (NO3-), sulfate (SO42-), iron  These are poorer electron acceptors than O2 so anaerobic respiration is less efficient than aerobic  Example: methanogens (create methane from CO2)  A Special Type of Respiration: Fermentation  Fermentation: ◦ Is a specialized type of respiration that doesn’t require oxygen to occur - is an anaerobic process ◦ But, unlike cellular respiration, no respiratory chain (ETC) is involved ◦ This process produces very little ATP, but it is enough to keep cells alive So, what’s the advantage? A Special Type of Respiration: Fermentation  If cells are capable of using glucose and undergoing fermentation, they can grow under conditions of low to eventually no oxygen  It is really just a way to regenerate electron carriers (NAD+) to be used (=reduced) again in glycolysis and to keep that pathway going  So, fermentation is really only glycolysis  Fermentation Pathway: Lactic Acid Fermentation  This fermentation In this pathway, lactic acid is produced directly from pyruvate by accepting e- pathway occurs in mammalian RBCs and skeletal muscles when insufficient O2 is present for intense aerobic work  Provides a way to get ATP and energy carriers when limited O2 conditions would prevent it  Produces lactic acid stiffness/fatigue/pain Fermentation in Microorganisms  Alcoholic fermentation ◦ Occurs in yeast and some bacteria ◦ Produces CO2 and ethanol (EtOH) from glucose by using NADH as a way to recycle e- and keep glycolysis going ◦ Yeast fermentation also happens in bread!  Lactic acid fermentation ◦ Occurs in some bacteria, like those in ◦ Also used to make: yogurt -Bifidobacteria, Lactobacillus = pickles kefir “live cultures” kimchi kombucha soy sauce sour cream sauerkraut cheese  ENZYME FUN FACTS! Fermented foods have an entire branch of biology in their honor: Zymology The term enzyme comes from zymosis, the Greek word for fermentation The first enzyme discovered was diastase - Breaks down starch glucose - Was first isolated in malt (grains used in brewing) Diastase is now known as amylase (enzyme in saliva, breaks down starch)  Complete this table of steps and processes in cellular respiration 1 molecule Where Is O2 Is CO2 Notable # ATP CH2O in occurs needed? produced? products (in cell) Glycolysis Citric Acid Cycle Oxidative phosphorylation Total ATP for all steps = ~38 Chapter 4 Review Questions  Self-Check Concept Quiz Which of the following statements about enzymes is not correct? A. They are consumed by the reactions they catalyze. B. They are usually made of amino acids C. They lower the activation energy of chemical reactions. D. Each one is specific to the substrate(s) to which it binds. A  Self-Check Concept Quiz Consider enzymes and homeostasis. Why would you suspect that high fevers can be dangerous and sometimes life-threatening? A. Molecules move faster at higher temperatures. B. Enzymes may change shape at high temperatures. C. Invading microbes survive better and reproduce faster at high temperatures. B  Self-Check Concept Quiz Most of the ATP produced by aerobic respiration comes from: A. Glycolysis B. The citric acid cycle C. Oxidative phosphorylation D. Fermentation C  Self-Check Concept Quiz Which of the following organisms undergo cellular respiration? Choose all that apply. A. plants B. animals C. bacteria D. humans A, B, C, D  Self-Check Concept Quiz Which of the following statements best describes the type of the cellular respiratory pathway known as fermentation? A. May result in the production of CO2 and alcohol B. Occurs under conditions of high oxygen C. Occurs in the chloroplasts of green plants D. Results in the production of O2 and H2O A  Short Answer Review Questions 1.) What are the features of enzymes? What is the difference between catabolic and anabolic reactions, and what is the role of enzymes in these reactions? Give an example of each type of reaction. 2.) Complete the table in this presentation for each of the steps in cellular respiration – We will complete the table together in class, but also be able to do it on your own