Carbohydrates PDF

C6H12O6 JOENNE O. CAJARA, LPT CARBOHYDRATES  Which contain the elements  Most abundant carbon, hydrogen, and biomolecule found in oxygen nature  It forms a class of organic compounds that includes  Can yield 4 s...

C6H12O6 JOENNE O. CAJARA, LPT CARBOHYDRATES  Which contain the elements  Most abundant carbon, hydrogen, and biomolecule found in oxygen nature  It forms a class of organic compounds that includes  Can yield 4 sugars, starches, and kilocalorie/gram upon cellulose. hydrolysis  Are now defined as polyhydroxyaldehydes or polyhydroxyketones or substances that yield these compounds on hydrolysis. Four key function of Carbohydrates in the body  Provide energy  Spare proteins  Assist in the breakdown of fats  Provide bulk in the diet  Provide Energy  Carbohydrates provide 4 kilocalories per gram  Body’s preferred source of energy  So if I have a food with 10 grams of carbohydrates, how many calories would that food provide?  Spare Proteins  Proteins build and maintain cell structure  If you do not eat enough carbohydrates, your body will begin to use proteins for energy  If proteins are used as energy, they can’t be used to build and maintain cell structure Help in the Breakdown of Fats  If you don’t consume enough carbohydrates, your body cannot completely break down fats  Your body will begin to breakdown it’s own stored fat for energy  This may lead to ketosis and this could cause a person to slip into a coma and die  Too Little Carbohydrate  Ketosis  Associated with low carbohydrate diets o Glucose is the preferred source of energy. When that is not available, the body begins to draw on fat stores for energy o Symptoms include: o tiredness, headache, feeling thirsty all the time, bad breath, metallic taste in the mouth, weakness, dizziness, nausea or stomach ache, sleep problems CLASSIFICATI ON 1. Monosaccharides 2. Disaccharides 3. Oligosaccharides 4. Polysaccharides MONOSACCHARIDES  Monomers or building blocks of carbohydrates  They can be classified according to:  The number of carbon atoms  The functional group (aldehyde or ketone)  They can be linked by glycosidic bonds to create larger structures  Different Sugar Conformations In organic chemistry the carbons are labeled 1-6  Isomers and Epimers  Compounds that have the same molecular formula but have different structures are called isomers  Fructose, glucose, mannose, and galactose are all isomers of each other, having the same chemical formula, C6H12O6  Carbohydrate isomers that differ in configuration around only one specific carbon atom are defined as epimers of each other.  Enantiomers  A special type of isomerism is found in the pairs of structures that are mirror images of each other.  These mirror images are called enantiomers, and the two members of the pair are designated as a D- and an L-sugar  The vast majority of the sugars in humans are D- sugars.  In the D isomeric form, the –OH group on the asymmetric carbon (a carbon linked to four different atoms or groups) farthest from the carbonyl carbon is on the right, whereas in the L-isomer it is on the left. glyceraldehyde * CH2CHCH O an aldotriose OH OH CHO CHO H OH HO H CH2OH CH2OH D-(+)-glyceraldehyde L-(-)-glyceraldehyde D & L are used to relate configuration of the chiral center most removed from the reducing group ( C=O ). If the -OH is on the right in the Fischer projection, then it is D, if the -OH is on the left, then it is L  Joining of Monosaccharides  Monosaccharides can be joined to form disaccharides, oligosaccharides, and polysaccharides.  Important disaccharides include lactose (galactose + glucose), sucrose (glucose + fructose), and maltose(glucose + glucose). Polysaccharides  Important polysaccharides include branched glycogen (from animal sources); glycogen is formed in the body cells from molecules of glucose it is called glycogenesis while glycogen is hydrolyzed into glucose it is called glycogenolysis.  starch (plant sources) and unbranched cellulose (plant sources); each is a polymer of glucose  The bonds that link sugars are called glycosidic bonds  These are formed by enzymes known as glycosyltransferases Polysaccharides  Dextrin is produced during the hydrolysis of starch. It is used when digestion might be a problem as with infants and elderly persons.  Heparin is used as a blood anticoagulant. It accelerates the inactivation of thrombin and other blood-clotting agents.  Dextran is used as blood extenders to hold water in the bloodstream and help prevent drops in blood volume and blood pressure and are Important component of dental plaque. Carbohydrates have a wide range of function  They provide a significant fraction of the dietary calories for most organisms  They act as a storage form of energy in the body  They serve as cell membrane components that mediate some forms of intercellular communication  They serve as a structural component of many organisms, including the cell walls of bacteria, the exoskeleton of many insects, and the fibrous cellulose of plants.  Digestion of Dietary Carbohydrates  The principal sites of dietary carbohydrate digestion are the mouth and intestinal lumen.  This digestion is rapid and is catalyzed by enzymes known as glycoside hydrolases (glycosidases) that hydrolyze glycosidic bonds.  The final products of carbohydrate digestion are the monosaccharides, glucose, galactose and fructose, which Carbohydrate Digestion in  the GI Tract Digestion of carbohydrate begins in the mouth  Further digestion of carbohydrates by pancreatic enzymes occurs in the small intestine  Finalcarbohydrate digestion by enzymes synthesized by the Digestion of carbohydrate begins in the mouth  The major dietary polysaccharides are of plant (starch, composed of amylose and amylopectin) and animal (glycogen) origin.  During mastication, salivary α-amylase acts briefly on dietary starch and glycogen, hydrolyzing random α(1→4) bonds.  Because branched amylopectin and glycogen also contain α(1→6) bonds, which α-amylase cannot hydrolyze, the digest resulting from its action contains a mixture of short, branched and unbranched oligosaccharides known as dextrins  Carbohydrate digestion halts temporarily in the stomach, because the high acidity inactivates Further digestion of carbohydrates by pancreatic enzymes occur in small intestine  When the acidic stomach contents reach the small intestine, they are neutralized by bicarbonate secreted by the pancreas, and pancreatic α- amylase continues the process of starch digestion. Carbohydrate Absorption  The duodenum and upper jejunum absorb the bulk of the dietary sugars  Differentsugars have different mechanisms of absorption  Galactose and glucose- sodium-dependent glucose cotransporter (SGLT-1)  Fructose- sodium- independent monosaccharide Abnormal degradation of disaccharides  The overall process of carbohydrate digestion and absorption is so efficient in healthy individuals that ordinarily all digestible dietary carbohydrate is absorbed by the time the ingested material reaches the lower jejunum.  However, because it is monosaccharides that are absorbed, any defect in a specific disaccharidase activity of the intestinal mucosa causes the passage of undigested carbohydrate into the large intestine.  As a consequence of the presence of this osmotically active material, water is drawn from the mucosa into the large intestine, causing osmotic diarrhea.  This is reinforced by the bacterial fermentation of the remaining carbohydrate to two- and three-carbon compounds (which are also osmotically active) plus large volumes of CO2  Digestive enzyme deficiencies  Genetic deficiencies of the individual disaccharidases result in disaccharide intolerance.  Alterations in disaccharide degradation can also be caused by a variety of intestinal diseases, malnutrition, or drugs that injure the mucosa of the small intestine  Lactose Intolerance  More than three quarters of the world’s adults are lactose intolerant  This is particularly manifested in certain populations. For example, up to 90% of adults of African or Asian descent are lactase-deficient and, therefore, are less able to metabolize lactose than individuals of Northern European origin.  The age-dependent loss of lactase activity represents a reduction in the amount of enzyme rather than a modified inactive enzyme.  Due to small variations in the DNA sequence of a region on chromosome 2 that controls expression of the gene for lactase  Sucrase-isomaltase deficiency  This deficiency results in an intolerance of ingested sucrose  The disorder is found in about 10% of the Inuit people of Greenland and Canada, whereas 2% of North Americans are heterozygous for the deficiency  Treatment includes the dietary restriction of sucrose, and enzyme replacement therapy.  Diagnosis  Identification of a specific enzyme deficiency can be obtained by performing oral tolerance tests with the individual disaccharides.  Measurement of hydrogen gas in the breath is a reliable test for determining the amount of ingested carbohydrate not absorbed by the body, but which is metabolized instead by the intestinal flora Maintaini ng Blood Glucose Homeosta sis QUALITATIVE DETECTION OF CARBOHYDRA TES Reducing sugars  A carbohydrate that is oxidized by Tollen’s, Fehling’s or Benedict’s solution. Tollen’s: Ag+  Ag (silver mirror) Fehling’s or Benedict’s: Cu3+ (blue)  Cu2+ (red ppt)  These are reactions of aldehydes and alpha-hydroxyketones  All monosaccharides (both aldoses and ketoses) and most disaccharides are reducing sugars.  Sucrose (table sugar), a disaccharide, is not a reducing sugar. Reducing sugars Qualitative Detection of Carbohydrates Molisch Test It is a usefultest for identifying any compound which can be dehydrated to furfuralor hydroxymethylfurfural in the presence of H2SO4. Alpha- naphthol reacts with the cyclic aldehyde to form purple colored condensationproducts. A positive test is indicated by the formation of a purple product at the interface of the two layers. Monosaccharides (-) (+) give a rapid positive test. Disaccharidesand polysaccharides react slower. Qualitative Detection of Carbohydrates Iodine Test Iodine test distinguishes starch and glycogen (polysaccharides) from monosaccharides, disaccharides, and other polysaccharides. Amylose,in the starch,is responsible for the reaction with iodine. Its helicesbind iodine atomsin the solution and produce amylose-iodine complex. Iodine slides into amylose coilto form a complex thatgives a blue-black color. A bluish black color is a positive test for starch. Glycogen, the common polysaccharidein animals, has a slight difference in structure and produces only (+) (-) an intermediate colorreaction. Glycogen reacts with the reagentto give a brown- black color. Other polysaccharidesand monosaccharides yield yellow-orange color, which is a negative result. Specific Qualitative Detection of Carbohydrates Barfoed’s Test Barfoed’s testis a chemicaltest used to detect the presence ofmonosaccharides which detects reducing monosaccharides in the presence of disaccharides.This reaction can be used for disaccharides,but the reaction would be very slow. The Barfoed reagent is made up of copper acetate in a dilute solution of acetic acid.Since acidic pH is unfavorable for reduction, monosaccharides,which are strong reducing agents, react in about 1-2 min. However,the reducing disaccharidestake a longer time of about 7-8 minutes, having first to get hydrolyzed in the acidic solution and then reactwith the reagent.Once the reaction takes place, thin red precipitate forms atthe bottom ofthe sides of the tube. The difference in the time of appearance ofprecipitate thus helps distinguish reducing monosaccharides from reducing disaccharides. Specific Qualitative Detection of Carbohydrates Seliwanoff’s Test Seliwanoff’s testis used to differentiate between sugars that have a ketone group (ketose) and sugars that have an aldehyde group (aldoses). This test is a timed color reaction specific to ketohexoses. The reagentof this testconsists ofresorcinoland concentrated HCl. The acid hydrolysis of polysaccharides and oligosaccharides yields simpler sugars.Ketoses are more rapidly dehydrated than aldoses. Ketoses undergo dehydration in the presence of concentrated acid to yield 5- hydroxymethylfurfural. The dehydratedketose (+) (-) reacts with two equivalents of resorcinol in a series of condensation reactions to produce a complex (not a precipitate),termed xanthenoid,with deep cherry red color. Aldoses may react slightly to produce a faint pink to cherry red color if the test is prolonged. Specific Qualitative Detection of Carbohydrates Phenylhydrazine Test/Osazone Test Osazone test is a chemical test used to detect reducing sugars. This test even allows the differentiation of different reducing sugars on the basis of the time of appearance of the complex. The reagent for this test consists of phenylhydrazine in acetate buffer. This test is based on the fact that carbohydrates with free or potentially free carbonylgroups react with phenylhydrazine to form osazone. The condensation-oxidation-condensation reaction between three molecules of phenylhydrazine and carbon one and two of aldoses and ketoses yields 1, 2- diphenyhydrazone,which is known as osazone.  LABORATORY TEST HOSPITAL SETTING  BLOOD SUGAR TEST (FASTING BLOOD SUGAR or FBS) A blood glucose test is used to find out if your blood sugar levels are in a healthy range. It is often used to help diagnose and monitor diabetes. What happens during a blood glucose test?  A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. How long do I have to fast before the test? You usually need to fast for 8–12 hours before a test. Most tests that require fasting are scheduled for early in the morning. That way, most of your fasting time will be overnight. Can I drink anything besides water during a fast?  No. Juice, coffee, soda, and other beverages can get in your bloodstream and affect your results. In addition, you should not: Chew gum Smoke Exercise  These activities can also affect your results.  But you can drink water. It's actually good to drink water before a blood test. It helps keep more fluid in your veins, which can make it easier to draw blood. What if I make a mistake and have something to eat or drink besides water during my fast?  Tell your health care provider before your test. He or she can reschedule the test for another time when you are able to complete your fast. Is there anything else I need to know about fasting before a blood test?  Be sure to talk to your health care provider if you have any questions or concerns about fasting.  You should talk to your provider before taking any lab test. Most tests don't require fasting or other special preparations. For others, you may need to avoid certain foods, medicines, or activities. Taking the right steps before testing helps ensure your results will be accurate. Symptoms of high blood glucose levels include: Increased thirst and urination (peeing) Blurred vision Fatigue Sores that don't heal Weight loss when you're not trying to lose weight Numbness or tingling in your feet or hands  Symptoms of low blood glucose levels include: Feeling shaky or jittery Hunger Fatigue Feeling dizzy, confused, or irritable Headache A fast heartbeat or arrhythmia (a problem with the rate or rhythm of your heartbeat) Having trouble seeing or speaking clearly Fainting or seizures  Summary  Monosaccharides (simple sugars) containing an aldehyde group are called aldoses and those with a keto group are called ketoses  Disaccharides, oligosaccharides, and polysaccharides consist of monosaccharides linked by glycosidic bonds.  Compounds with the same chemical formula are called isomers.  If two monosaccharide isomers differ in configuration around one specific carbon atom (with the exception of the carbonyl carbon), they are defined as epimers of each other.  If a pair of sugars are mirror images (enantiomers), the two members of the pair are designated as D- and L-sugars. Summary  When a sugar cyclizes, an anomeric carbon is created from the aldehyde group of an aldose or keto group of a ketose. This carbon can have two configurations, α or β.  If the aldehyde group on an acyclic sugar gets oxidized as a chromogenic agent gets reduced, that sugar is a reducing sugar.  A sugar with its anomeric carbon linked to another structure is called a glycosyl residue  Sugars can be attached either to an –NH2 or an –OH group, producing N- and O-glycosides  Summary  Salivary α-amylase acts on dietary polysaccharides (glycogen, amylose, amylopectin), producing oligosaccharides  Pancreatic α-amylase continues the process of polysaccharide digestion. The final digestive processes occur at the mucosal lining of the small intestine  Several disaccharidases [for example, lactase (β- galactosidase), sucrase, maltase, and isomaltase] produce monosaccharides (glucose, galactose, and fructose).  These enzymes are secreted by and remain associated with the luminal side of the brush border membranes of intestinal mucosal cells.  Absorption of the monosaccharides requires specific transporters Summary  If carbohydrate degradation is deficient (as a result of heredity, intestinal disease, malnutrition, or drugs that injure the mucosa of the small intestine), undigested carbohydrate will pass into the large intestine, where it can cause osmotic diarrhea.  Bacterial fermentation of the compounds produces large volumes of CO2 and H2 gas, causing abdominal cramps, diarrhea, and flatulence  Lactose intolerance, caused by a lack of lactase, is by far the most common of these METABOLISM OF CARBOHYDRA TES How do organisms survive? Living cells require energy from outside sources Some animals obtain energy by eating plants, and some animals feed on other organisms that eat plants PHOTOSYNTHESIS  Plants pick up carbon dioxide from the air and water from the soil and combine them to form carbohydrates in a process called photosynthesis.  Enzymes, chlorophyll and sunlight are necessary. During photosynthesis, oxygen is given off into the air, thus renewing our vital supply of this element.  Carbohydrates produced in reaction of glucose, is a monosaccharide.  Photosynthesisgenerates O2 and organic molecules, which are used in cellular respiration  Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work  Autotrophs  Organisms that use light energy from the sun  Plants, protists, cyanobacteria  Heterotrophs  Organisms that cannot use the sun’s energy to make food  Animals and most microorganisms  ATP  Adenosine triphosphate  Energy used by all cells  Organic molecule containing high energy phosphate bonds  Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic CO2  H2O molecules  O2 Cellular respiration in mitochondria ATP powers ATP most cellular work Heat energy  Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose OXYGEN-CARBON DIOXIDE CYCLE IN NATURE C6H12O6 + 6O2  Animals oxidize carbohydrates in their 6CO2 + 6H2O + bodies to yield carbon dioxide, water and energy energy  Again, this reaction is not a simple as it appears; many different enzymes are required. Cellular Respiration  Cellular Respiration  A series of reactions where fats, proteins, and carbohydrates, mostly glucose, are broken down to make CO2, water, and energy. C6H12O6 + 6O2 6CO2 + 6H20 + e- + 36- 38ATP’s The Stages of Aerobic Respiration  Harvestingof energy from glucose has three stages 1. Glycolysis (breaks down glucose into two molecules of pyruvate) 2. Citric acid cycle (completes the breakdown of glucose) 3. Oxidative phosphorylation (accounts for most of the ATP synthesis)  Where does it happen?  The process take place in two parts of the cell  Glycolysis occurs in the cytoplasm  Krebs cycle and ETC occur in the mitochondria  matrix and cristae  Review of Mitochondrial Structure  Smooth outer membrane  Folded inner membrane  Folds are called cristae  Space inside is called matrix  Intermembrane Space Contains respiratory enzymes Several identical copies of mito genome, ribosomes, tRNAs Various enzymes for expression of mito genes  Intermembrane Space Proteins: 1. Carry out oxidation reactions of the respiratory chain 2. ATP synthase 3. Specific transport proteins  Intermembrane Space w/ porin, permeable to all molecules 0f 5000d or < Enzymes involved in mitochondrial lipid synthesis Enzymes that convert lipid substrates  Intermembrane Space Contains several enzymes that use the ATP passing out of the matrix to phosphorylate other nucleotides Structure of Mitochondrion  Cellular Respiration  Respiration occurs in all cells and can take place with or without oxygen  Aerobic and anaerobic respiration  Anaerobic Respiration  Occurs when no oxygen is available to the cell  Alcoholic and Lactic Acid Fermentation  Much less ATP is produced than aerobic respiration Anaerobic Respiration  Lactic acid fermentation: occurs in muscle cells  Lactic acid is produced in the muscles during rapid exercise when the body cannot supply enough oxygen to the glucose lactic acid + carbon tissues dioxide + 2 ATP  First step in anaerobic respiration is also glycolysis Anaerobic Cytoplasm Respiration Alcoholic C6H12O6 fermentation glycolys Bacteria, Yeast 2 is Lactic acid ATP glucose fermentation Muscle cells 2 ATP 36 ATP Kreb ET Aerobic s C Respiration Cycl Mitochondri e a Glycolysis  Glycolysis  A series of reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates.  An ancient metabolic pathway that it evolved long ago, and it is found in the great majority of organisms alive today.  Glycolysis doesn’t require oxygen, and many anaerobic have this pathway. Step 1 A phosphate group is transferred from ATP to glucose to form glucose-6-phosphate  Step 2  Glucose-6-phosphate is converted to its isomer, fructose-6-phosphate  Step 3 Aphosphate group is transferred from ATP to fructose-6-phosphate to form fructose 1,6- bisphosphate  Step 4  Fructose-1,6-bisphosphate splits to form two three- carbon sugars: dihydroxyacetone phosphate and glyceraldehyde-3- phosphate.  Step 5  DHAPis converted into glyceraldehyde-3- phosphate, until all DHAP is converted.  Step 6  Two half reactions occur simultaneously: 1) Glyceraldehyde-3-phosphate is oxidized, and 2) NAD+ is reduced to NADH releasing energy that is then used to phosphorylate the molecule, forming 1,3-bisphosphoglycerate.  Step 7  1,3-bisphosphoglycerate donates one of its phosphate groups to ADP to make ATP and turning into 3-phosphoglycerate in the process.  Step 8  3-phosphoglycerateis converted into its isomer, 2-phosphoglycerate  Step 9  2-phosphoglycerate loses a molecule of water, becoming phosphoenolpyruvate (PEP)  Step 10  PEPreadily donates its phosphate group, making a second molecule of ATP. As it loses its phosphate, PEP is converted to pyruvate, the end product of glycolysis Summary What happens to pyruvate and NADH?  Products of Glycolysis  Two NADH, two pyruvate, and a net total of 2 ATPs  If oxygen is present, the pyruvate enters the Krebs cycle  NADH needs to be converted back to NAD+ to keep glycolysis going.  Aerobic respiration, NADH enters electron transport chain  Anaerobic, NADH undergoes fermentation to regenerate NAD+  Fermentation and Anaerobic Respiration  Some prokaryotes- bacteria and archaea that live in low oxygen environments rely on anaerobic respiration to break down fuels.  methanogens, sulfate-reducing bacteria  Fermentation is an anaerobic process that regenerate NAD+, producing alcohol or lactic acid as by-products  Lactic acid fermentation  NADH transfers its electrons directly to pyruvate generating lactate as the by-product.  Muscle cells also carry out this process  Alcohol fermentation  NADH donates its electrons to a derivative of pyruvate, producing ethanol  Two-step process:  Caboxyl is removed from pyruvate to form acetaldehyde, CO2 is produced  NADH passes its electrons to acetaldehyde, regenerating NAD+ Krebs Cycle A Little Krebs Cycle History  Discovered by Hans Krebs in 1937  He received the Nobel Prize in physiology or medicine in 1953 for his discovery  Forced to leave Germany prior to WWII because he was Krebs Cycle  Also known as citric acid cycle  Requires oxygen (Aerobic)  Cyclical series of oxidation reactions that give off CO2 and produce one ATP per cycle  Turns twice per glucose molecule  Takes place in matrix of mitochondria Oxidation of Pyruvate to Acetyl CoA  Before the citric acid cycle can begin, pyruvate must be converted to acetyl Coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle  This step is carried out by a multienzyme complex that catalyzes three reactions After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed  MITOCHONDRION CYTOSOL CO2 Coenzyme A 1 3 2 NAD NADH + H Acetyl CoA Pyruvate Transport protein Initial step: Pyruvate is converted to Acetyl-CoA  The Citric Acid Cycle The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO2 The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn Figure 9.11 Pyruvate CO2 NAD  CoA NADH + H Acetyl CoA CoA CoA Citric acid cycle 2 CO2 FADH2 3 NAD FAD 3 NADH + 3 H ADP + P i ATP  The Citric Acid Cycle The citric acid cycle has eight steps, each catalyzed by a specific enzyme The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain Step 1  Acetyl-CoA combines with four-carbon acceptor molecule, oxaloacetate to form six-carbon molecule, citrate Step 2 Citrate is converted to its isomer, isocitrate Step 3 Isocitrate is oxidized and releases a molecule of CO2 leaving behind a five- carbon molecule, α- ketoglutarate. During this step, NAD+ is reduced to form NADH Step 4 α-ketoglutarate is oxidized, reducing NAD+ to NADH and releasing CO2 in the process The remaining four-carbon molecule picks up picks up CoA forming succinyl CoA Step 5 The CoA of succinyl is replaced by a phosphate group which is transferred to ADP to make ATP. Succinate is formed as a product Step 6 Succinate is oxidized, forming another four- carbon molecule called fumarate. Two hydrogen atoms, with their electrons are transferred to FAD, producing FADH2 Step 7 Water is added to the four-carbon molecule fumarate, converting it into another four-carbon molecule, malate. Step 8 In the last step of the citric acid cycle, oxaloacetate, the starting four-carbon compound, is regenerated by oxidation of malate. Another molecule of NAD+ is reduced to NADH in the process  Products of the Krebs Cycle  Each turn of the Krebs Cycle also produces 3NADH, 1FADH2, 1 ATP, and 2CO2  Therefore, for each Glucose molecule, the Krebs Cycle produces 6NADH, 2FADH2, 2ATP, and 4CO2  The Krebs cycle does not produce much ATP directly however, it can make a lot of ATP indirectly, by the way of NADH and FADH2 it generates, which participate in the electron transport chain. Figure 9.12-4 Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric 3 NADH acid + H cycle CO2 CoA-SH -Ketoglutarate 4 CO2 NAD NADH Succinyl + H CoA Figure 9.12-8 Acetyl CoA CoA-SH NADH + H 1 H2O NAD 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric 3 NADH 7 acid + H H2O cycle CO2 Fumarate CoA-SH -Ketoglutarate 6 4 CoA-SH FADH2 5 CO2 NAD FAD Succinate Pi NADH GTP GDP Succinyl + H CoA ADP ATP  Electron Transport Chain  Electron Transport Chain A series of proteins and organic molecules found in the inner membrane of the mitochondria. Electrons are passed from one member of the transport chain to another in a series of redox reactions.  Electron Transport Chain 1. Located in the inner membrane of the mitochondria. 2. Oxygen pulls the electrons from NADH and FADH2 down the electron transport chain to a lower energy state 3. Process produces 34 ATP or 90% of the ATP in the body.  Electron Transport Chain 4. Requires oxygen, the final electron acceptor. 5. For every FADH2 molecule – 2 ATP’s are produced. 6. For every NADH molecule – 3 ATP’s are produced. 7. Chemiosmosis – the production of ATP using the energy of H+ gradients across membranes to phosphorylate ADP.  ATP Synthase  A protein in the inner membrane in the mitochondria.  Uses energy of the ion gradient to power ATP synthesis.  For every H+ ion that flows through ATP synthase, one ATP can be formed from ADP  Electrons are transferred from NADH or FADH2 to the electron transport chain Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2 The electron transport chain generates no ATP directly It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space H+ then moves back across the membrane, passing through the proton, ATP synthase ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work  Electron Transport Hydrogen Ion Movement Mitochondrion Channel Intermembrane Space ATP synthase Inner Membrane Matrix ATP Production Overview of Oxidative Phosphorylation Products of Oxidative Phosphorylation  32 ATP Produced, H2O Produced  Occurs Across Inner Mitochondrial membrane  Uses coenzymes NAD+ and FAD+ to accept e- from glucose  NADH = 3 ATP’s  FADH2 = 2 ATP’s Copyright Cmassengale Total energy yield  Glycolysis  2 ATP  2 NADH  4-6 ATP (Depends on how this NADH molecule gets to the ETC. To make things simple we will say that these two NADH’s make 4 ATP )  Formation of Acetyl CoA  2 NADH  6 ATP Total energy yield  Krebs Cycle  2 ATP  6 NADH  18 ATP  2 FADH2  4 ATP Grand Total = 36 ATP Summary of Cellular Respiration Figure 9.6-1 Electrons carried via NADH Glycolysis Glucose Pyruvate CYTOSOL MITOCHONDRION ATP Substrate-level phosphorylation Figure 9.6-2 Electrons Electrons carried carried via NADH and via NADH FADH2 Pyruvate Glycolysis Citric oxidation acid Glucose Pyruvate Acetyl CoA cycle CYTOSOL MITOCHONDRION ATP ATP Substrate-level Substrate-level phosphorylation phosphorylation Figure 9.6-3 Electrons Electrons carried carried via NADH and via NADH FADH2 Pyruvate Oxidative Glycolysis Citric phosphorylation: oxidation acid electron transport Glucose Pyruvate Acetyl CoA cycle and chemiosmosis CYTOSOL MITOCHONDRION ATP ATP ATP Substrate-level Substrate-level Oxidative phosphorylation phosphorylation phosphorylation THANK YOU!