Chapter 9 Cellular Respiration and Fermentation

Chapter 9: Cellular Respiration and Fermentation - Why do cells need energy? They need energy to fuel their activities What activities do cells need to carry out? Synthesizing macromolecules, creating concentration gradients by pumping substances across membranes, moving themselves or materials, and carrying out cell division Organic molecules always come from the sun, energy flows through the ecosystem as sunlight Catabolic Pathways - Reactions that breakdown polymer reactants into monomer products Used for recycling building blocks that can later be used in other metabolic reactions to make new molecules Main molecule that moves energy throughout the cell; ATP Metabolic Pathways that Produce ATP - Fermentation: without oxygen, breaking down glucose and gain a tiny usable amount of ATP Aerobic Respiration: with the use of oxygen, more energy comes from it Anaerobic respiration: oxidizing things Cellular Respiration: used with both aerobic and anaerobic Combustion is exergonic, releases energy, ATP from this can help anabolic reactions to help build other things up Goal of Aerobic cellular respiration: produce ATP ATP/ADP cycle is an example of oxidation and reduction reactions Oxidation: removal of electrons Reduction: addition of electrons In each redox reaction, one molecule is reduced while another is oxidized OILRIG: Oxidation Is Lost, Reduction Is Gained NAD+ is used as an electron carrier, NADH is when it already has electrons and is a coenzyme Cellular Respiration: process by which living cells obtain energy from organic molecules, primary aim is to make ATP and NADH, primarily uses glucose Aerobic respiration uses oxygen Aerobic Cellular Respiration Harvesting energy from glucose by cellular respiration occurs in 3 stages 1. Glycolysis: breaks down glucose into two molecules of pyruvate 2. Pyruvate oxidation and the citric acid cycle complete the breakdown of glucose to CO2 3. During oxidative phosphorylation 2 ways to make ATP in the cell - Oxidative phosphorylation Substrate-level phosphorylation Steps of Aerobic Cellular Respiration 1. Glycolysis - Stage 1 of cellular respiration, takes place in the cytoplasm, can be ran without oxygen, happens in aerobic and anaerobic, glucose (6-carbon carbohydrate) gets split into two pyruvate molecules (3-carbon molecules), steps are nearly identical in all species 1. energy investment 2. energy payoff 2. Pyruvate Oxidation and the citric acid cycle complete the breakdown of glucose of CO2 3. During oxidative phosphorylation the electron transfer chain and chemiosmosis facilitate synthesis of most of the cell’s ATP - Mitochondrial matrix: core of mitochondria Pyruvate is broken down by pyruvate dehydrogenase; facilitates reaction sequence; take off carboxyl group (COO) 3 reactions o The carboxyl group is oxidized and released as a molecule of CO2 o Remaining 2 carbon compound is oxidized and reduces NAD+ to NADH o Resulting acetyl group is attached to CoA to make acetyl CoA Citric Acid Cycle - Stage 2 of cellular respiration, metabolic cycle, occurs in series of 8 steps each catalyzed by its own enzyme In the first step, the acetyl group is removed from Acetyl CoA and attach it to oxaloacetate to form citrate (citric acid) Remaining steps releases 2 CO2, 1 ATP, 3 NADH. And FADH2 Oxaloacetate is regenerated so the cycle can start again Aka Kreb’s Cycle or Tricarboxylic Acid Cycle (TCA) Oxidative Phosphorylation - Stage 3 of cellular respiration High energy electrons removed from NADH and FADH2 to make ATP Requires oxygen and involves electron transport chain (ETC) - o Protein complexes and small organic molecules embedded in the inner mitochondrial membrane, this provides energy for the next step of synthesizing ATP Phosphorylation of ADP occurs by ATP synthase Electron Transport Chain - Collection of molecules in the inner mitochondrial membrane Thousands of copies doing the same process, pumping protons Each complex consists of multiple proteins with electron carriers and each complex likes electrons more than the last one, the complexes are slowly removing energy from the electrons as they move through Drain in the air is oxygen, used to pick up electrons to turn into water Chemiosmosis - Electron transport chain is an energy converter, it uses the exergonic flow of electrons from NADH and FADH2 to pump H+ across inner mitochondrial membrane Creates a large concentration gradient for H+ o High concentration in the intermembrane space and low concentration in the matrix, called the proton-motive force ATP synthase is a “reverse” H+ pump o The only site that provides a route for the H+ to flow from the area of high concentration to low concentration o Energy released from the movement of H+ is used by ATP synthase to add Pi to ADP to generate ATP, this is called chemiosmosis and is a form of oxidative phosphorylation ATP Yield Isn’t Exact - Energy flows from glucose to NADH to ETC to proton motive force to ATP Each glucose molecule is oxidized to approximately 30-32 molecules of ATP Exact number can’t be determined because redox reactions are not directly coupled to each other 1 NADH results in H+ being pumped into intermembrane space Entire process is still 34% efficient at converting energy in glucose to the energy in ATP Anaerobic Respiration and Fermentation - These can occur in environments that lack oxygen or during oxygen-deficient times Aerobic respiration uses O2 as the final electron acceptor o If O2 isn’t available then other pathways can be used to generate ATP o Anaerobic respiration uses and ETC but fermentation does not - Two different strategies o Anaerobic respiration- use substance other than O2 as final electron acceptor in electron transport chain o Fermentation- produces ATP only via substrate-level phosphorylation Fermentation - - An extension of glycolysis o Additional steps oxidize NADH by transferring electrons to pyruvate ▪ This regenerates NAD+ so that glycolysis can continue Two common types o Alcohol fermentation: pyruvate is converted into ethanol and releases CO2 o Lactic acid fermentation: pyruvate is converted into lactate and does not release CO2 o Produces far less ATP than oxidative phosphorylation