* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Cellular Respirationx
Amino acid synthesis wikipedia , lookup
Radical (chemistry) wikipedia , lookup
Metalloprotein wikipedia , lookup
Fatty acid synthesis wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Biosynthesis wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Mitochondrion wikipedia , lookup
Photosynthesis wikipedia , lookup
Butyric acid wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
NADH:ubiquinone oxidoreductase (H+-translocating) wikipedia , lookup
Electron transport chain wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Light-dependent reactions wikipedia , lookup
Microbial metabolism wikipedia , lookup
Nicotinamide adenine dinucleotide wikipedia , lookup
Adenosine triphosphate wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Citric acid cycle wikipedia , lookup
Cellular Respiration Releasing Stored Energy Harvesting Chemical Energy Autotrophs like plants and cyanobacteria use photosynthesis to change the sun’s light energy into chemical energy contained in the bonds within glucose molecules. Both autotrophs and heterotrophs then use this energy-rich molecule to supply the energy they need to power their cellular activities like growth, movement, or reproduction. When glucose or other large molecules are broken down into smaller molecules, the energy from the broken chemical bonds is used to make ATP from ADP and phosphate. ATP is the main energy currency of living things. The complex many-step procedure used by living things to make ATP from the breakdown of large molecules such as glucose is called cellular respiration. Cellular respiration can be divided into several smaller biochemical pathways: glycolysis fermentation aerobic respiration Glycolysis evolved very early in the Earth’s history. There was no free oxygen in the atmosphere, so the first organisms (bacteria) all used glycolysis to produce ATP. It took more than one billion years for bacteria to evolve the process of photosynthesis. Glycolysis provides enough energy for many current unicellular organisms that have limited energy needs. Larger organisms have greater energy needs and use aerobic respiration to meet those needs. Glycolysis A biochemical pathway is a series of chemical Glucose C C C C C C reactions where the 2 ATP products of one reaction become the reactants of the next reaction. 2 ADP P- C C C C C C -P 6-C Compound Glycolysis is a biochemical pathway. In glycolysis, one molecule of glucose is split in half to produce P- C C C C C C -P 2 PGAL two molecules of 2 NAD+ pyruvic acid (pyruvate) and two molecules of 2 NADH + 2H+ ATP. Glycolysis happens in P- C C C -P P- C C C -P 2 molecules of a 3-C compound the cell’s cytoplasm. All 4 ADP living things can perform glycolysis. 4 ATP Glycolysis has 10 C C C C C C chemical reactions, but 2 molecules of pyruvic acid can be summarized in (pyruvate) four steps. Step 1 – Two phosphate groups are added to the glucose molecule from 2 ATPs, making a 6-C compound that can be split. Step 2 – The 6-C compound is split into two 3-C molecules of PGAL (phosphoglyceraldehyde). Step 3 – The two PGAL molecules are oxidized and receive another phosphate group. The oxidation of PGAL accompanies the reduction of NAD+ to NADH. Step 4 – the phosphate groups are removed, producing 2 pyruvic acid molecules and 4 ATP, for a net gain of 2 ATP. Lactic Acid Fermentation In the absence of oxygen, some cells convert pyruvic acid into other compounds using one of several other biochemical pathways. These new steps do not make any more ATP. They are still necessary because glycolysis in the absence of oxygen will use up a cell’s supply of NAD+. If all of the cell’s NAD+ is gone, glycolysis will stop and the cell can no longer make ATP by splitting glucose. The combination of glycolysis and these other NAD+ regenerating steps are called fermentation. There are two main types of fermentation: lactic acid fermentation and alcoholic fermentation. In lactic acid fermentation, pyruvic acid is rearranged to form another 3-C molecule, lactic acid. As this occurs, NADH + H+ are converted back into NAD+, so glycolysis can continue. Lactic acid fermentation by bacteria makes yogurt or cheese. Lactic acid fermentation also happens in animal muscle tissue during strenuous exercise, and can result in muscle cramps. C C C C Glucose C C 2 NAD+ Glycolysis 2 NADH + 2H+ C C C C C C 2 molecules of pyruvic acid (pyruvate) 2 NADH + 2H+ 2 NAD+ C C C C C 2 molecules of lactic acid (lactate) C Lactic Acid Fermentation Alcoholic Fermentation Some plant cells, bacteria, and the unicellular fungus known as yeast use a biochemical pathway to regenerate NAD+ known as alcoholic fermentation. In this pathway, pyruvic acid is converted into a 2-C compound called ethyl alcohol (ethanol), and carbon dioxide. Like in lactic acid fermentation, these steps turn NADH and H+ back into NAD+, thus allowing glycolysis to continue. Alcoholic fermentation is important economically. It is used in the production of beers and wines. As the yeast ferment the sugars present in the mix, the ethanol content rises until it reaches a concentration high enough to kill the yeast. This is about 12%. The CO2 is released during fermentation. To make champagne, the CO2 is retained. Bread also depends on alcoholic fermentation. The bubbles of CO2 produced cause the bread to rise. The alcohol evaporates during baking, producing the wonderful smell of baking bread. C C C C C C Glucose 2 NAD+ Glycolysis 2 NADH + 2H+ C C C C C C 2 molecules of pyruvic acid (pyruvate) Alcoholic Fermentation 2 NADH + 2H+ 2 NAD+ C C C C C C 2 molecules of ethyl alcohol (ethanol) and 2 CO2 Glycolysis is not an efficient way to make ATP. Its efficiency is only about 3.5% Aerobic Respiration and Mitochondria Aerobic respiration has two major stages: the Krebs cycle and the electron transport chain. In the presence of O2, in the reactions of the Krebs cycle, glucose is completely oxidized into CO2 and H2O. As the glucose is oxidized, NAD+ is reduced to NADH and H+. In the presence of oxygen, the electron transport chain can operate. NADH is fed into the transport chain and produces large amounts of ATP as well as regenerating NAD+. Although the Krebs cycle produces a small amount of ATP, most of the ATP produced during aerobic respiration is produced by the electron transport chain. In prokaryotes, the reactions of the Krebs cycle and the electron transport chain occur in the cell’s cytosol. In eukaryotes, these reactions, happen within mitochondria. The pyruvic acid made during glycolysis diffuses through the double membrane and into the mitochondrial matrix. The mitochondrial matrix contains the enzymes needed for the Krebs cycle. When pyruvic acid enters the mitochondrial matrix, it reacts with a molecule called coenzyme A to form acetyl coenzyme A (acetyl CoA) and a molecule of CO2. One molecule of NAD+ is reduced to NADH and H+. Acetyl CoA can enter the Krebs cycle. Aerobic Respiration The Krebs Cycle Step 1 - Acetyl CoA bonds with a 4-C molecule (oxaloacetic acid) to form a The Krebs 6-C molecule (citric acid), cycle is a CoA releasing coenzyme A. Citric Acid biochemical Step 2 - Citric acid is C C C C C C C C pathway that oxidized, releasing CO2, an Acetyl CoA + forming breaks the H atom to NAD CO 2 C remaining NADH, and a 5-C compound. bonds in acetyl + NAD C C C C CoA, forming Step 3 – The 5-C Oxaloacetic acid NADH + compound becomes a 4-C CO2, H atoms, H+ compound, forming CO2, and ATP. NADH + H+ 5-C compound NADH, and ATP In eukaryotic + NAD C C C C C Step 4 – The 4-C cells, the Krebs compound changes to a 4-C compound cycle takes different 4-C compound, ADP C C C C place inside the releasing an H atom to C CO2 mitochondrial ATP FAD, which forms FADH2. NAD+ matrix. FADH2 Step 5 – The 4-C NADH + The Krebs compound changes back H+ FAD into oxaloacetic acid and Cycle has 5 C C C C forming another NADH. main steps: 4-C compound Aerobic Respiration – Electron Transport Chain The electron transport chain is the second part of aerobic respiration. In eukaryotic cells, the molecules needed for this are embedded in the inner mitochondrial membrane. In prokaryotes, the molecules for the electron transport chain are embedded in the cell membrane. The purpose of the electron transport chain is to make ATP from ADP. This happens when NADH and FADH2 are converted back into NAD+ and FAD. The electrons in the H atoms of NADH and FADH2 are high energy electrons. As these electrons are passed along the electron transport chain they lose some of their excess energy. This energy is used to pump the protons of the H atoms from the mitochondrial matrix to the other side of the inner membrane, building up a concentration gradient. As protons pass back through ATP synthase molecules located in the membrane, ATP is made from ADP. This process can only continue if the last molecule in the electron transport chain can get rid of its excess electrons. It does so by passing them off to oxygen atoms. This is why O2 is needed for aerobic respiration. The Electron Transport Chain Cytosol Intermembrane Space H+ 2e- eee- NADH eATP synthase ADP NAD+ FADH2 FAD ATP Mitochondrial Matrix O2 + 4e- + 4H+ 2H2O Cellular Respiration - Energy Output Glucose Glycolysis 2 NADH 2 ATP 6 ATP from electron transport chain (ETC) Pyruvic Acid 2 NADH 6 ATP from ETC Acetyl CoA 2 ATP produced directly Krebs cycle 6 NADH 18 ATP from ETC 2 FADH2 4 ATP from ETC Aerobic respiration is a more efficient way to produce ATP than glycolysis, with an efficiency rate of about 66%. 38 ATP