Cellular Metabolism Chapter 3 PDF

Cellular Metabolism Chapter 3  Topic overview  Cell metabolism, introduction and application  Carbohydrate metabolism  Fat metabolism  Protein metabolism  Cellular Metabolism Cellular metabolism refers to all of the chemical processes that occur inside living cells...

Cellular Metabolism Chapter 3  Topic overview  Cell metabolism, introduction and application  Carbohydrate metabolism  Fat metabolism  Protein metabolism  Cellular Metabolism Cellular metabolism refers to all of the chemical processes that occur inside living cells.  Energy Energy can exist in two states: Kinetic energy – energy of motion. Potential energy – stored energy. Chemical energy – potential energy stored in bonds, released when bonds are broken. Energy can be transformed form one state to another.  Energy The ultimate source of energy for most living things is the sun.  Ground work  The goal of cellular respiration is to produce energy in the form of ATP  It’s actually a breakdown process of macromolecules (carbohydrates, protein and lipids) from bigger molecule, into smaller molecules, and harvesting energy along the line.  Energy investment will also be made in order to produce energy  It is a series of processes, that happened one after another, under certain circumstances.  Cellular Respiration Cellular respiration – the oxidation of food molecules to obtain energy. Electrons are stripped away. Different from breathing (respiration).  Cellular Respiration Aerobic versus Anaerobic Metabolism Heterotrophs Aerobes: Use molecular oxygen as the final electron acceptor Anaerobes: Use other molecules as final electron acceptor Energy yield much lower ATP yield  Cellular Respiration When oxygen acts as the final electron acceptor (aerobes): Almost 20 times more energy is released than if another acceptor is used (anaerobes). Advantage of aerobic metabolism: Smaller quantity of food required to maintain given rate of metabolism.  Aerobic Respiration  In aerobic respiration, ATP forms as electrons are harvested, transferred along the electron transport chain and eventually donated to O2 gas. Oxygen is required! Glucose is completely oxidized. C6H12O6 + 6O2 6CO2 + 6H2O + energy (heat Glucose Oxygen Carbon Water or ATP) Dioxide  Cellular Respiration - 3 Stages  Food is digested to break it into smaller pieces – no energy production here.  Glycolysis – coupled reactions used to make ATP. Occurs in cytoplasm Doesn’t require O2  Oxidation – harvests electrons and uses their energy to power ATP production. Only in mitochondria More powerful  Anaerobic Respiration Anaerobic respiration occurs in the absence of oxygen. Different electron acceptors are used instead of oxygen (sulfur, or nitrate). Sugars are not completely oxidized, so it doesn’t generate as much ATP.  Glycolysis Glycolysis – the first stage in cellular respiration. A series of enzyme catalyzed reactions. Glucose converted to pyruvic acid. Small number of ATPs made (2 per glucose molecule), but it is possible in the absence of oxygen. All living organisms use glycolysis.  Glycolysis  Uphill portion primes the fuel with phosphates.  Uses 2 ATPs  Fuel is cleaved into 3-C sugars which undergo oxidation.  NAD+ accepts e-s & 1 H+ to produce NADH  NADH serves as a carrier to move high energy e-s to the final electron transport chain.  Downhill portion produces 2 ATPs per 3-C sugar (4 total).  Net production of 2 ATPs per glucose molecule.  Harvesting Electrons form Chemical Bonds When oxygen is available, a second oxidative stage of cellular respiration takes place. First step – oxidize the 3-carbon pyruvate in the mitochondria forming Acetyl-CoA. Next, Acetyl-CoA is oxidized in the Krebs cycle.  Producing Acetyl-CoA  The 3-carbon pyruvate loses a carbon producing an acetyl group.  Electrons are transferred to NAD+ forming NADH.  The acetyl group combines with CoA forming Acetyl-CoA.  Ready for use in Krebs cycle.  The Krebs Cycle The Krebs cycle is the next stage in oxidative respiration and takes place in the mitochondria. Acetyl-CoA joins cycle, binding to a 4-carbon molecule to form a 6-carbon molecule. 2 carbons removed as CO2, their electrons donated to NAD+, 4-carbon molecules left. 2 NADH produced. More electrons are extracted and the original 4-carbon material is regenerated. 1 ATP, 1 NADH, and 1 FADH2 produced.  The Krebs Cycle Each glucose provides 2 pyruvates, therefore 2 turns of the Krebs cycle. Glucose is completely consumed during cellular respiration. Using Electrons to Make ATP NADH & FADH2 contain energized electrons. NADH molecules carry their electrons to the inner mitochondrial membrane where they transfer electrons to a series of membrane bound proteins – the electron transport chain.  Building an Electrochemical Gradient In eukaryotes, aerobic metabolism takes place in the mitochondria in virtually all cells. The Krebs cycle occurs in the matrix, or internal compartment of the mitochondrion. Protons (H+) are pumped out of the matrix into the intermembrane space.  Producing ATP- Chemiosmosis A strong gradient with many protons outside the matrix and few inside is set up. Protons are driven back into the matrix. They must pass through special channels that will drive synthesis of ATP. Oxidative phosphorylation Review of Cellular Respiration 1 ATP generated for each proton pump activated by the electron transport chain. NADH activates 3 pumps. FADH2 activates 2 pumps. The 2 NADH produced during glycolysis must be transported across the mitochondrial membrane using 2 ATP. Net ATP production = 4 Glucose + 2 ATP + 36 ADP + 36 Pi + 6 O2 6CO2 + 2 ADP + 36 ATP + 6 H2O  Fermentation In the absence of oxygen, the end-product of glycolysis, pyruvate, is used in fermentation. During glycolysis, all the NAD+ becomes saturated with electrons (NADH). When this happens, glycolysis will stop. 2 NADH and 2 ATP produced. Pyruvate is used as the electron acceptor resetting the NAD+ for use in glycolysis.  Fermentation – 2 Types  Animals add extracted electrons to pyruvate forming lactate. Reversible when oxygen becomes available. Muscle fatigue  Yeasts, single-celled fungi, produce ethanol. Present in wine & beer. Alcoholic fermentation  Metabolism of Lipids Triglycerides are broken down into glycerol and 3 fatty acid chains. Glycerol enters glycolysis. Fatty acids are oxidized and 2-C molecules break off as acetyl-CoA. Oxidation of one 18-C stearic acid will net 146 ATP. Oxidation of three glucose (18 Cs) nets 108 ATP. Glycerol nets 22 ATP, so 1 triglyceride nets 462 ATP.  Metabolism of Proteins Proteins digested in the gut into amino acids which are then absorbed into blood and extracellular fluid. Excess proteins can serve as fuel like carbohydrates and fats. Nitrogen is removed producing carbon skeletons and ammonia. Carbon skeletons oxidized.  Metabolism of Proteins Ammonia is highly toxic, but soluble. Can be excreted by aquatic organisms as ammonia. Terrestrial organisms must detoxify it first.  Regulating Cellular Respiration Rate of cellular respiration slows down when your cells have enough ATP. Enzymes that are important early in the process have an allosteric (regulating) site that will bind to ATP. When lots of ATP is present, it will bind to this site, changing the shape of the enzyme, halting cellular respiration.