Cell Respiration Anaerobic & Aerobic Respiration
Understandings/Objectives 2.8.U1: Cell respiration is the controlled release of energy from organic compounds to produce ATP. Define cell respiration State the reaction for cellular respiration State the types of organic compounds used in cellular respiration by animals and plants 2.8.U2: ATP from cell respiration is immediately available as a source of energy in the cell. State 3 example uses of cellular energy. Outline energy transfer in the formation and use of ATP. State 3 reasons why cellular respiration must be continuously performed by all cells.
The Big Picture: Cell respiration supplies energy for the functions of life. Where do you get the energy you need to live? Nutrients, such as carbohydrates, are broken down into glucose. It is absorbed by the blood and is taken up by cells. Body prepares for cellular respiration.
ATP What does ATP stand for? Adenosine triphosphate Made in the mitochondria Energy is produced when ATP is hydrolysed. This energy was generated during respiration and stored in the energy-rich phosphate bond of ATP. Cellular Respiration is the gradual and controlled release of energy by breaking down organic compounds to produce ATP.
Cell Respiration and ATP Glucose is the most widely used source of energy in living organisms. The use of enzymes that control the process to make sure energy is being made when it is needed. 3 main processes of cellular respiration: 1. 2. 3. Glycolysis The Krebs Cycle Electron Transport Chain
4 steps that will be discussed later... 1. 2. 3. 4. In glycolysis, glucose is broken down to pyruvate in the cytoplasm. In the link reaction, pyruvate is converted into acetyl-coa and enters the mitochondrion. Acetyl-CoA enters the Krebs cycle, generating FADH2 and NADH + H+. The FADH2 and NADH + H+ is oxidised in the electron transport chain and ATP is produced.
Be Aware Do NOT confuse respiration with breathing. In some languages, e.g. French, 'respire' means breathing. In biology, respiration always refers to the breakdown of organic compounds and the production of ATP in the cell.
STOP! Checkpoint time! 1. Where does glycolysis take place in eukaryotic cells? In the cytoplasm 2. What happens during glycolysis? Glucose is broken down into pyruvate 3. Where is the electron transport chain located in the diagram of a mitochondrion? C. A = the outer mitochondrial membrane B = intermembrane space C = the inner mitochondrial membrane (folded into cristae) where the ETC takes place D = the mitochondrial matrix
Anaerobic Respiration Cell respiration can take place with or without oxygen. Without oxygen = anaerobic respiration Occurs only in the cytoplasm as it involves only glycolysis. Anaerobic respiration generates far LESS ATP (you will soon see why). Lactic acid formation in humans (causes soreness).
Main Points of Anaerobic Respiration 1. 2. 3. 4. 5. Takes place in the cytoplasm Takes place without the presence of oxygen Generates a smaller amount of ATP (only 2 ATP) than aerobic respiration In yeast, it produces alcohol and CO2 In animal muscle cells, it produces lactate
STOP! Checkpoint time! 1. Which of the following occurs in the cytoplasm of a human muscle cell? a. b. c. d. Glycolysis and lactate production Ethanol production Fermentation Krebs cycle 2. What is produced by yeast during fermentation? Ethanol and carbon dioxide
Glycolysis
Glycolysis 8.2.U3: In glycolysis, glucose is converted to pyruvate in the cytoplasm. Outline the glycolysis reaction, including phosphorylation, lysis, and energy harvest. 8.2.U2: Phosphorylation of molecules makes them less stable. Define phosphorylation. State the consequence of a molecule being phosphorylated. 8.2.U4: Glycolysis gives a small net gain of ATP without the use of oxygen. State the formula for the glycolysis reaction. State that glycolysis occurs in both anaerobic and aerobic respiration. State that glycolysis is an example of a metabolic pathway. 8.2.U1: Cell respiration involves the oxidation and reduction of electron carriers. Outline oxidation and reduction reactions in terms of movement of electrons, hydrogen or oxygen atoms. Define electron carrier. State the name of the electron carrier molecule used in cellular respiration.
Glycolysis: Glucose is converted to pyruvate in the cytoplasm Glucose Pyruvate in a series of steps (Glycolysis). Pyruvate then gets converted to acetyl CoA (then into the mitochondria) [This is the link reaction because it links glycolysis and the Krebs cycle]. Glycolysis is a metabolic pathway which gives a small yield of 2 ATP and 2 reduced NADH + H+. This is shown in Figure 1. (The names of the intermediate compounds in the glycolysis cycle are not required.) YOU CRAVE IT ALL THE TIME!
Glycolysis
Decarboxylation and Oxidation At the end of the glycolytic pathway, two molecules of pyruvate are formed, which are linked to CoA in the link reaction if oxygen is available. This is an example of a decarboxylation reaction as carbon is lost as carbon dioxide. Since pyruvate also loses hydrogen, it is oxidised to acetyl CoA. Overall, the conversion of pyruvate to acetyl CoA involves both decarboxylation and oxidation reactions.
The Link Reaction Some of the CO2 you breathe out originates from the sugar you eat. NADH + H+ is referred to as NADH for simplicity. The link reaction (and all other proceeding reactions) only occurs if oxygen is available (aerobic).
STOP! Checkpoint Time! 1. When a glucose molecule loses a hydrogen atom as a result of an oxidation-reduction reaction, the molecule becomes: a. b. c. d. Hydrolysed Hydrogenated Oxidised Reduced 2. During glycolysis, when each glucose molecule is catalytically broken down to 2 molecules of pyruvate, most of the potential energy contained in glucose is: a. b. c. d. Transferred to ADP, forming ATP Transferred directly to ATP Retained in the two pyruvates Stored in the NADH produced Options #1, #2 and #4 are all true except the gain in energy is small compared to the rest of the energy that is still available in pyruvate. When pyruvate enters the Krebs cycle via the link reaction, much more energy is released, so option #3 is the correct answer.
Redox Reactions and Phosphorylation Redox Reactions: Involve one compound being oxidised, while another compound is reduced. Involve the gain or loss of electrons, as charged subatomic particles carrying energy. Usually coupled to an electron carrier, like NAD (Nicotinamide Adenine Dinucleotide). The reactions often transfer two hydrogen atoms (NOT hydrogen ions, H+) to the carrier.
Ways that substances can be oxidised or reduced Component involved Oxidation Reduction Make sure you remember these: TAKE YOUR PICK! Oxygen Gained Lost 1. LEO the lion goes GER: Loss of Electrons: Oxidized, Gain of Electrons: Reduced. Hydrogen Lost Gained 2. OIL RIG: Oxidation Is Loss (of electrons) and Reduction Is Gain (of electrons). Electron Lost Gained
Phosphorylation Adding a phosphate group makes the whole molecule less stable, i.e. more likely to react or break down into smaller molecules. These reactions are based on the hydrolysis of an ATP molecule in an exergonic reaction (a reaction that releases energy into the environment).
STOP! Checkpoint Time! 1. The molecule that is oxidised in a redox reaction: a. b. c. d. Gains electrons and gains potential energy Loses electrons and loses potential energy Gains electrons and loses potential energy Loses electrons and gains potential energy 2. In any redox reaction, when there is a gain of electrons by one reacting particle, it implies that another reactant must have undergone: a. b. c. d. Reduction Oxidation Production of water Cellular respiration
Understandings/Objectives 2.8.U3: Anaerobic cell respiration gives a small yield of ATP from glucose. Define anaerobic respiration. List 3 situations in which anaerobic respiration is useful. Compare anaerobic respiration in yeast and humans. 2.8.A1: Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking. Outline how anaerobic respiration in yeast is used in baking. Outline how anaerobic respiration in yeast is used in ethanol production. 2.8.A2: Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions. State the condition in which humans would perform anaerobic respiration. Outline production of lactate in humans during anaerobic respiration.
Lactic Acid in Your Muscles (ck12.org) When we exercise, our muscles are metabolizing too fast for the blood to provide enough oxygen. This causes the muscles to switch from aerobic to anaerobic metabolism. Anaerobic metabolism creates lactate and an excess of hydrogen ions. The increase in hydrogen ions causes an increase in acidity called lactic acidosis. Lactic acidosis causes the burning sensations, nausea, and stomach cramps than can accompany intense exercise. This can be alleviated with water! Water dilutes the acid and flushes it from the muscles.
Aerobic Respiration: Overview/Objectives 2.8.U4: Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose. Compare the total amount of ATP made from anaerobic and aerobic respiration. State the location of aerobic respiration. Pea Respiration Lab: 2.8.S1: Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer. Outline the use of a respirometer to measure cellular respiration rate. 2.8.NOS: Assessing the ethics of scientific research - the use of invertebrates in respirometers experiments. List ethical questions that must be considered before using animals in experiments.
Aerobic Cell Respiration Yields far more ATP than under anaerobic conditions. All four steps (that we discussed earlier) are completed...anaerobic respiration is only glycolysis. Glucose (6-carbon molecule) is gradually broken down to 6 CO2 molecules. Potential energy is then converted into ATP in the ETC (electron transport chain).
Running Aerobically It s much more efficient to respire aerobically than anaerobically. Long distance runners try to maintain an aerobic speed. If they use up the available oxygen, muscles will start anaerobically respiring, which produces lactate.
STOP! Checkpoint time! Anaerobic Respiration Aerobic Respiration
The Mitochondria 8.2.U12: The structure of the mitochondrion is adapted to the function it performs. Outline how mitochondria structure could evolve through natural selection. State evidence that suggests mitochondria were once free living prokaryotes. 8.2.S2: Annotations of a diagram of a mitochondrion to indicate the adaptations to its function. Draw and label a diagram of the mitochondria. State the function of the following mitochondrial structures: outer membrane, inner membrane, cristae, intermembrane space, matrix, ribosome, mtdna 8.2.A1: Electron tomography used to produce images of active mitochondria. State that electron tomography enables scientists to view the dynamic nature of mitochondrial membranes.
The Mitochondrion Each reaction within the mitochondrion has specific requirements; such as ph, concentration gradients, and membrane structures. Evolutionary driving force behind the mitochondrion s structure: The need for concentration gradients and compartmentalisation of various reactions. Increased surface area. Able to produce more ATP, evolutionary advantage in poor niches. Evolved over billions of years. You need to be able to annotate a diagram of the mitochondrion based on an electron micrograph, and indicate how it is adapted to its function.
The Mitochondrion
The Mitochondrion
STOP! Checkpoint Time! In red, outline the outer membrane. In blue, outline the inner membrane. In black, outline the intermembrane space. In red, indicate the cristae In blue, indicate the matrix
Linking Reaction Review Decarboxylation: Loss of a carbon atom from a carbon chain. Oxidation: Loss of electrons. Reduction: Gain of electrons. Pyruvate is converted into Acetyl-CoA Reactant: Pyruvate Products: Acetyl CoA, CO2, NADH
Krebs Cycle 8.2.U7: In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of electron carriers, liberating carbon dioxide. State that NADH and FADH2 are electron carriers formed during the Krebs cycle. Outline the events of the Krebs cycle, referencing the formation of NADH and FADH2, formation of ATP and decarboxylation of acetyl groups. 8.2.S1: Analysis of diagrams of the pathways of aerobic respiration to decide where decarboxylation and oxidation reactions occur. State that decarboxylation of glucose occurs in the linking reaction and Krebs cycle of aerobic respiration.
Krebs Cycle
Krebs Cycle Named after Hans Krebs, sometimes referred to as the Citric Acid Cycle because the first step of this cycle involves citric acid. Takes place in the mitochondrial matrix. You do NOT need to know the names of the intermediates, just the overall results!
Key Points about the Krebs Cycle 1. 2. 3. 4. The acetyl group that enters the Krebs cycle is successively oxidised as it loses hydrogen atoms (and electrons). The hydrogen atoms lost are picked up by hydrogen carriers, either NAD or FAD, which are themselves reduced in this process. The oxidation of the acetyl group is coupled with a loss of carbon dioxide (i.e. decarboxylation). One glucose yields 2 pyruvates, so Krebs happens twice per glucose. You should be able to indicate where oxidation or decarboxylation is occurring in the Krebs cycle reaction pathway. 3 decarboxylation reactions (loss of CO2): 1 in the link reaction, 2 in Krebs.
STOP! Checkpoint Time! 1. 2. How many carbon atoms are fed into the Krebs cycle as a result of the oxidation of one molecule of pyruvate? Carbon dioxide (CO2) is released during which of the following stages of cellular respiration? a. b. c. d. 3. Glycolysis Oxidation of pyruvate to Acetyl CoA and the Krebs Cycle The Krebs Cycle Oxidation of pyruvate to Acetyl CoA What is needed for the link reaction to proceed? i. ii. iii. Pyruvate CO2 NADH + H+
Which molecules are represented by the letters W, X, Y, and Z?
Electron Transport Chain 8.2.U8: Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD. State that NAD+ is reduced to become NADH in the link reaction and Krebs cycle. State that FAD is reduced to become FADH2 in the Krebs cycle. State that NADH and FADH2 carry electrons to the ETC on the mitochondrial inner membrane. 8.2.U9: Transfer of electrons between carriers in the ETC in the membrane of the cristae is coupled to proton pumping. State that at the ETC, FADH2, and NADH transfer electrons to electron carrier proteins. State that the movement of electrons through electron carrier proteins in the ETC is used to pump protons (H+) across the inner mitochondrial membrane into the intermembrane space.
Electron Transport Chain 8.2.U11: Oxygen is needed to bind with the free protons to maintain the hydrogen gradient, resulting in the formation of water. State that oxygen is the final electron acceptor in aerobic cellular respiration. State that the formation of water in the matrix at the end of the ETC helps to maintain the hydrogen gradient between the intermembrane space and the matrix.
Electron Transport Chain (ETC) Electron carriers = NAD and FAD The reduced forms of these carriers carry the energy released by the oxidation reactions to the cristae, where they give off their e- and H+ (hydrogen ions) to protein complexes. Each NADH molecule can give rise to 3 ATP molecules. Each FADH2 molecule can give rise to 2 ATP molecules (donates its e- at a later step). ATP Synthase = In the inner mitochondrial membrane. Uses a hydrogen ion (proton) gradient to synthesize ATP. CHEMIOSMOSIS
ATP Synthase and Gradients & ETC ATP Synthase and Gradients The Electron Transport Chain
ETC
ETC The electrons (e-) are transferred from one e- carrier to another along the ETC, until they reach cytochrome oxidase, and are combined with oxygen and hydrogen to form water. Since O2 (oxygen) is the final electron acceptor, this process is called oxidative phosphorylation. The transfer of e- along the ETC involves a drop in the energy state of electrons (energy is released). This energy is used to pump H+ ions across the inner membrane into the intermembrane space.
Chemiosmosis 8.2.U10: In chemiosmosis protons diffuse through ATP synthase to generate ATP. Define oxidative phosphorylation and chemiosmosis. 8.2.NOS: Paradigm shift- chemiosmotic theory led to a paradigm shift in the field of bioenergetics. State that Peter Mitchell s proposal of the chemiosmotic hypothesis in 1961 lead to a major shirt if our understanding of cellular processes.
Chemiosmosis Movement of ions across a semipermeable membrane, down an electrochemical gradient. Pumping protons into intermembrane space. Uses energy released from ETC. Followed by diffusion of protons into matrix, down the concent. gradient through ATP synthase. Produces ATP.
Nature of Science New evidence can cause a change in a basic concept. It was known that there was a ph gradient across the mitochondrial inner membrane and it was believed that this was used by soluble enzymes to form ATP. In 1961, Peter Mitchell proposed the now accepted chemiosmotic theory in which he theorised that a proton gradient across the mitochondrial inner membrane drove ATP synthesis through membrane-bound ATPase molecules. His findings have now been modified by new evidence.
STOP! Checkpoint Time! 1. During aerobic respiration, which sequence do electrons follow? a. b. c. d. 2. 3. Where are the proteins of the ETC located? In cellular respiration, the energy for most ATP synthesis is supplied by: a. b. c. d. 4. food citric acid cycle ATP NAD+ food NADH electron transport chain oxygen glucose pyruvate ATP oxygen glucose ATP electron transport chain NADH High-energy phosphate bonds in organic molecules. A proton gradient across a membrane. Converting oxygen to ATP. Transferring electrons from organic molecules to pyruvate. What happens to oxygen during aerobic cell respiration? a. b. c. d. Oxygen is reduced by accepting electrons at the end of the ETC. Oxygen is oxidised by accepting electrons at the end of the ETC. Oxygen is reduced by accepting hydrogen at the start of the ETC. Oxygen is oxidised by accepting hydrogen at the end of the ETC.