Chapter 3 CARBOHYDRATE METABOLISM BREAKDOWN OF GLUCOSE TO
Chapter 3 CARBOHYDRATE METABOLISM
BREAK-DOWN OF GLUCOSE TO GENERATE ENERGY - Also known as Respiration. - Comprises of these different processes depending on type of organism: I. Anaerobic Respiration II. Aerobic Respiration
ANAEROBIC RESPIRATION Comprises of these stages: glycolysis: glucose 2 pyruvate + NADH fermentation: pyruvate lactic acid or ethanol cellular respiration:
AEROBIC RESPIRATION Comprises of these stages: Oxidative decarboxylation of pyruvate Citric Acid cycle Oxidative phosphorylation/ Electron Transport Chain(ETC)
Brief overview of catabolism of glucose to generate energy STARCHY FOOD α – AMYLASE ; MALTASES Glucose converted to glu-6 -PO 4 Start of cycle Glycolysis in cytosol Cycle : anaerobic 2[Pyruvate+ATP+NADH] Anaerobic condition Lactic Acid fermentation in muscle. Only in yeast/bacteria Anaerobic respiration or Alcohol fermentation Aerobic condition; in mitochondria Pyruvate enters as Acetylco. A - Krebs Cycle - E transport chain
GLYCOLYSIS Show time. .
GLYCOLYSIS 1 st stage of glucose metabolism → glycolysis An anaerobic process, yields 2 ATP (additional energy source) Glucose will be metabolized via gycolysis; pyruvate as the end product The pyruvate will be converted to lactic acid (muscles → liver) Aerobic conditions: the main purpose is to feed pyruvate into TCA cycle for further rise of ATP
The breakdown of glucose to pyruvate as summarized: Glucose (six C atoms) → 2 pyruvate (three C atoms) 2 ATP + 4 ADP + 2 Pi → 2 ADP + 4 ATP (phosphorylation) Glucose + 2 ADP + 2 Pi → 2 Pyruvate + 2 ATP (Net reaction) Fig. 17 -1, p. 464
Fig. 17 -2, p. 465
Louis Pasteur - French biologist - did research on fermentation which led to important discoveries in microbiology and chemistry
HOW 6 -CARBON GLUCOSE CONVERTED TO THE 3 CARBON GLYCERALDEHYDE-3 -PHOSPHATE? Preparation phase Step 1 Glucose is phosphorylated to give gluc-6 -phosphate p. 467
Fig. 17 -3, p. 468
Table 17 -1, p. 469
Fig. 17 -4, p. 470
Step 2 Glucose-6 -phosphate isomerize to give fructose-6 phosphate p. 470 a
Step 3 Fructose-6 -phosphate is phosphorylated producing fructose-1, 6 -bisphosphate p. 470 b
Fig. 17 -6, p. 471
Step 4 Fructose-1, 6 -bisphosphate split into two 3 -carbon fragments p. 471 a
Step 5 Dihydroxyacetone phosphate is converted to glyceraldehyde-3 -phosphate p. 471 b
HOW IS GLYCERALDEHYDE-6 -PHOSPHATE CONVERTED TO Payoff phase PYRUVATE Step 6 Glyceraldehyde-6 -phosphate is oxidized to 1, 3 -bisphoglycerate p. 472
Fig. 17 -7, p. 473
p. 474 a
Fig. 17 -8, p. 475
Step 7 Production of ATP by phosphorylation of ADP p. 476
Step 8 Phosphate group is transferred from C-3 to C-2 p. 477 a
Step 9 Dehydration reaction of 2 -phosphoglycerate to phosphoenolpyruvate p. 477 b
Step 10 Phosphoenolpyruvate transfers its phosphate group to ADP → ATP and pyruvate p. 478
Control points in glycolysis Fig. 17 -10, p. 479
HOW IS PYRUVATE METABOLIZED ANAEROBICALLY? Conversion of pyruvate to lactate in muscle p. 479
Fig. 17 -11 b, p. 481
Pyruvate decarboxylase Fig. 17 -11 a, p. 481
Fig. 17 -12, p. 482
Acetaldehyde + NADH → Ethanol + NAD+ Glucose + 2 ADP + 2 Pi + 2 H+ → 2 Ethanol + 2 ATP + 2 CO 2 + 2 H 2 O p. 482
Chapter 3 (cont. ) Carbohydrate metabolism
Gluconeogenesis Conversion of pyruvate to glucose Biosynthesis and the degradation of many important biomolecules follow different pathways There are three irreversible steps in glycolysis and the differences bet. glycolysis and gluconeogenesis are found in these reactions Different pathway, reactions and enzyme ST EP 1 p. 495
is the biosynthesis of new glucose from non-CHO precursors. this glucose is as a fuel source by the brain, testes, erythrocytes and kidney medulla comprises of 9 steps and occurs in liver and kidney the process occurs when quantity of glycogen have been depleted - Used to maintain blood glucose levels. Designed to make sure blood glucose levels are high enough to meet the demands of brain and muscle (cannot do gluconeogenesis). promotes by low blood glucose level and high ATP inhibits by low ATP occurs when [glu] is low or during periods of fasting/starvation, or intense exercise pathway is highly endergonic *endergonic is energy consuming
STEP 2
The oxalocetate formed in the mitochondria have two fates: - continue to form PEP - turned into malate by malate dehydrogenase and leave the mitochondria, have a reaction reverse by cytosolic malate dehydrogenase Reason?
Controlling glucose metabolism • found in Cori cycle • shows the cycling of glucose due to gycolysis in muscle and gluconeogenesis in liver • This two metabolic pathways are not active simultaneously. • when the cell needs ATP, glycolisys is more active • When there is little need for ATP, gluconeogenesis is more active As energy store for next exercise Fig. 18 -12, p. 502
Cori cycle requires the net hydrolysis of two ATP and two GTP.
Fig. 18 -13, p. 503
The Citric Acid cycle Cycle where 30 to 32 molecules of ATP can be produced from glucose in complete aerobic oxidation Amphibolic – play roles in both catabolism and anabolism The other name of citric acid cycle: Krebs cycle and tricarboxylic acid cycle (TCA) Takes place in mitochondria
Fig. 19 -2, p. 513
Steps 3, 4, 6 and 8 – oxidation reactions Fig. 19 -3 b, p. 514
5 enzymes make up the pyruvate dehydrogenase complex: ü ü ü pyruvate dehydrogenase (PDH) Conversion of pyruvate Dihydrolipoyl transacetylase to acetyl-Co. A Dihydrolipoyl dehydrogenase Pyruvate dehydrogenase kinase Pyruvate dehydrogenase phosphatase
Step 1 Formation of citrate p. 518
Step 2 Isomerization Table 19 -1, p. 518
cis-Aconitate as an intermediate in the conversion of citrate to isocitrate Fig. 19 -6, p. 519
Step 3 Formation of αketoglutarate and CO 2 – first oxidation Fig. 19 -7, p. 521
Step 4 Formation of succinyl-Co. A and CO 2 – 2 nd oxidation p. 521
Step 5 Formation of succinate p. 522
Step 6 Formation of fumarate – FAD -linked oxidation p. 523 a
Step 7 Formation of L-malate p. 524 a
Step 8 Regeneration of oxaloacetate – final oxidation step p. 524 b
Krebs cycle produced: • 6 CO 2 • 2 ATP • 6 NADH • 2 FADH 2 Fig. 19 -8, p. 526
Table 19 -3, p. 527
Fig. 19 -10, p. 530
Fig. 19 -11, p. 531
Fig. 19 -12, p. 533
Fig. 19 -15, p. 535
Overall production from glycolysis, oxidative decarboxylation and TCA: Oxidative decarboxylation Glycolysis TCA cycle - 2 ATP 2 NADH 6 NADH , 2 FADH 2 2 CO 2 2 Pyruvate 4 CO 2 Electron transportation system
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