Presentation on theme: "Chapter 25 Metabolism and Nutrition"— Presentation transcript:
1 Chapter 25 Metabolism and Nutrition The food we eat is our only source of energy for performing biological work.There are three major metabolic destinations for the principle nutrients. They will be used for energy for active processes, synthesized into structural or functional molecules, or synthesized as fat or glycogen for later use as energy.
3 CoenzymesTwo coenzymes are commonly used by living cells to carry hydrogen atoms: nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD).An important point to remember about oxidation-reduction reactions is that oxidation is usually an energy-releasing reaction.
4 Mechanisms of ATP Generation ADP + P = ATPPhosphorylation isbond attaching 3rd phosphate group contains stored energyMechanisms of phosphorylationwithin animalssubstrate-level phosphorylation in cytosoloxidative phosphorylation in mitochondriain chlorophyll-containing plants or bacteriaphotophosphorylation.
5 Phosphorylation in Animal Cells In cytoplasm (1)In mitochondria (2, 3 & 4)
6 Carbohydrate ReviewIn GI tractpolysaccharides broken down into simple sugarsabsorption of simple sugars (glucose, fructose & galactose)In liverfructose & galactose transformed into glucosestorage of glycogen (also in muscle)In body cells --functions of glucoseoxidized to produce energyconversion into something elsestorage energy as triglyceride in fat
7 Fate of GlucoseGlucose can be used to form amino acids, which then can be incorporated into proteins.Excess glucose can be stored by the liver and skeletal muscles as glycogen, a process called glycogenesis.If glycogen storage areas are filled up, liver cells and fat cells can convert glucose to glycerol and fatty acids that can be used for synthesis of triglycerides (neutral fats) in the process of lipogenesis.
8 Glucose Movement into Cells In GI tract and kidney tubulesNa+/glucose symportersMost other cellsGluT facilitated diffusion transportersinsulin increases the insertion of GluT transporters in the membrane of most cellsin liver & brain, always lots of GluT transportersGlucose 6-phosphate forms immediately inside cell (requires ATP) thus, glucose is “hidden” when it is in the cell.Concentration gradient remains favorable for more glucose to enter.
10 Glucose Oxidation Cellular respiration 4 steps are involved glucose + O2 produces H2O + energy + CO2Anaerobic respirationcalled glycolysis (1)formation of acetyl CoA (2) is transitional step to Krebs cycleAerobic respirationKrebs cycle (3) and electron transport chain (4)
11 GlycolysisGlycolysis refers to the breakdown of the six-carbon molecule, glucose, into two three-carbon molecules of pyruvic acid.10 step process occurring in cell cytosoluse two ATP molecules, but produce four, a net gain of two (Figure 25.3).
12 Glycolysis of Glucose & Fate of Pyruvic Acid Breakdown of six-carbon glucose molecule into 2 three-carbon molecules of pyruvic acidPyruvic acid is converted to acetylCoA, which enters the Kreb’s Cycle.The Kreb’s Cycle will require NAD+NAD+ will be reduced to the high-energy intermediate NADH.
13 Glycolysis of Glucose & Fate of Pyruvic Acid When O2 falls short in a cellpyruvic acid is reduced to lactic acidcoupled to oxidation of NADH to NAD+NAD+ is then available for further glycolysislactic acid rapidly diffuses out of cell to bloodliver cells remove lactic acid from blood & convert it back to pyruvic acid
14 Pyruvic AcidThe fate of pyruvic acid depends on the availability of O2.
15 Formation of Acetyl Coenzyme A Pyruvic acid enters the mitochondria with help of transporter proteinDecarboxylationpyruvate dehydrogenase converts 3 carbon pyruvic acid to 2 carbon fragment acetyl group plus CO2.
16 Formation of Acetyl Coenzyme A 2 carbon fragment (acetyl group) is attached to Coenzyme A to form Acetyl coenzyme A, which enter Krebs cyclecoenzyme A is derived from pantothenic acid (B vitamin).
17 Krebs CycleThe Krebs cycle is also called the citric acid cycle, or the tricarboxylic acid (TCA) cycle. It is a series of biochemical reactions that occur in the matrix of mitochondria (Figure 25.6).
19 Krebs CycleThe large amount of chemical potential energy stored in intermediate substances derived from pyruvic acid is released step by step.The Krebs cycle involves decarboxylations and oxidations and reductions of various organic acids.For every two molecules of acetyl CoA that enter the Krebs cycle, 6 NADH, 6 H+, and 2 FADH2 are produced by oxidation-reduction reactions, and two molecules of ATP are generated by substrate-level phosphorylation (Figure 25.6).The energy originally in glucose and then pyruvic acid is primarily in the reduced coenzymes NADH + H+ and FADH2.
20 Krebs Cycle (Citric Acid Cycle) The oxidation-reduction & decarboxylation reactions occur in matrix of mitochondria.acetyl CoA (2C) enters at top & combines with a 4C compound2 decarboxylation reactions peel 2 carbons off again when CO2 is formed
21 Potential energy (of chemical bonds) is released step by step to reduce the coenzymes (NAD+NADH & FADFADH2) that store the energyReview:Glucose 2 acetyl CoA moleculeseach Acetyl CoA molecule that enters the Krebs cycle produces2 molecules of C023 molecules of NADH + H+one molecule of ATPone molecule of FADH2Krebs Cycle
22 Electron Transport Chain The electron transport chain involves a sequence of electron carrier molecules on the inner mitochondrial membrane, capable of a series of oxidation-reduction reactions.As electrons are passed through the chain, there is a stepwise release of energy from the electrons for the generation of ATP.In aerobic cellular respiration, the last electron receptor of the chain is molecular oxygen (O2). This final oxidation is irreversible.The process involves a series of oxidation-reduction reactions in which the energy in NADH + H+ and FADH2 is liberated and transferred to ATP for storage.
23 Electron Transport Chain Pumping of hydrogen is linked to the movement of electrons passage along the electron transport chain.It is called chemiosmosis (Figure 25.8.)Note location.
24 ChemiosmosisH+ ions are pumped from matrix into space between inner & outer membraneHigh concentration of H+ is maintained outside of inner membraneATP synthesis occurs as H+ diffuses through a special H+ channels in the inner membrane
26 Steps in Electron Transport Carriers of electron transport chain are clustered into 3 complexes that each act as a proton pump (expelling H+)Mobile shuttles (CoQ and Cyt c) pass electrons between complexes.The last complex passes its electrons (2H+) to oxygen to form a water molecule (H2O)
27 Proton Motive Force & Chemiosmosis Buildup of H+ outside the inner membrane creates + chargeThe potential energy of the electrochemical gradient is called the proton motive force.ATP synthase enzymes within H+ channels use the proton motive force to synthesize ATP from ADP and P
28 Summary of Aerobic Cellular Respiration The complete oxidation of glucose can be represented as follows:C6H12O6 + 6O2 => 36 or 38ATP + 6CO2 +6H2ODuring aerobic respiration, 36 or 38 ATPs can be generated from one molecule of glucose.Two of those ATPs come from substrate-level phosphorylation in glycolysis.Two come from substrate-level phosphorylation in the Krebs cycle.
29 Review Table 25.1 summarizes the ATP yield during aerobic respiration. Figure 25.8 summarizes the sites of the principal events of the various stages of cellular respiration.
30 Glycogenesis & Glycogenolysis glucose storage as glycogen4 steps to glycogen formation in liver or skeletal musclestimulated by insulinGlycogenolysisglucose release
31 Glycogenesis & Glycogenolysis glucose storage as glycogenGlycogenolysisglucose releasenot a simple reversal of stepsPhosphorylase enzyme is activated by glucagon (pancreas) & epinephrine (adrenal gland)Glucose-6-phosphatase enzyme is only in hepatocytes so muscle can not release glucose into the serum.
32 GluconeogenesisGluconeogenesis is the conversion of protein or fat molecules into glucose (Figure 25.12).
33 GluconeogenesisGlycerol (from fats) may be converted to glyceraldehyde-3-phosphate and some amino acids may be converted to pyruvic acid. Both of these compounds may enter the Krebs cycle to provide energy.Gluconeogenesis is stimulated by cortisol, thyroid hormone, epinephrine, glucagon, and human growth hormone.