CHAPTER 6 EMOTION & AFFECT © 2014 Wadsworth Cengage Learning.
2009 Cengage-Wadsworth Chapter 3 Carbohydrates.
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Transcript of 2009 Cengage-Wadsworth Chapter 3 Carbohydrates.
2009 Cengage-Wadsworth
Chapter 3
Carbohydrates
2009 Cengage-Wadsworth
Structural Features
• Simple carbohydrates– Monosaccharides– Disaccharides
• Complex carbohydrates– Oligosaccharides– Polysaccharides
2009 Cengage-Wadsworth
Simple Carbohydrates
• Monosaccharides– Steroisomerism
• Chiral carbon - have 4 different atoms or groups attached to them
• Stereoisomers - have 2 or more chiral carbon atoms with same 4 groups attached but are not mirror images of each other
2009 Cengage-Wadsworth
Simple Carbohydrates
– Ring structures - molecules cyclize & form another chiral carbon
– Haworth models– Pentoses– Reducing sugars
2009 Cengage-Wadsworth
Simple Carbohydrates
• Disaccharides– Maltose– Lactose– Sucrose
2009 Cengage-Wadsworth
Complex Carbohydrates
• Oligosaccharides– Raffinose– Stachyoses– Verbascose
• Polysaccharides– Starch– Glycogen– Cellulose
2009 Cengage-Wadsworth
Digestion
• Polysaccharides– Salivary -amylase - mouth– Pacreatic -amylase - small intestine– Resistant starches
• Digestion of disaccharides– Disaccharidases - active in microvilli
of enterocytes
2009 Cengage-Wadsworth
Absorption, Transport, & Distribution
• Absorption of glucose & galactose– Into cell: active transport - SGLT1– Into blood: diffusion, GLUT2
• Absorption of fructose– Into cell: facilitated transport - GLUT5– Into blood: GLUT2– Limited in 60% of adults
2009 Cengage-Wadsworth
Absorption, Transport, & Distribution
• Monosaccharide transport & cellular uptake
• Glucose transporters– GLUT isoforms
• Integral proteins• Each has specific combining site• Undergoes a conformational change upon
binding the molecule• Can reverse this change when unbound
2009 Cengage-Wadsworth
Absorption, Transport, & Distribution
– Specificity of GLUTs• GLUT1 - basic supply of glucose to cells• GLUT2 - low infinity transporter; glucose
from enterocyte to blood• GLUT3 - high-affinity for brain & other
glucose-dependent tissues• GLUT4 - insulin sensitive, in muscle &
adipose tissues• GLUT5 - for fructose
2009 Cengage-Wadsworth
Absorption, Transport, & Distribution
• Insulin– Role in cellular glucose absorption
• Binds to membrane receptor• Stimulates GLUT4 to move to membrane
• Maintenance of blood glucose levels
2009 Cengage-Wadsworth
Glycemic Response to Carbohydrates
• Glycemic index– Increase in blood glucose during 2-
hour period after consumption of a certain amount of CHO compared with equal CHO from reference food
• Glycemic load– GI x g of CHO in 1 serving of food
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
• Glycogenesis– Conversion of glucose to glycogen
• Glycogenolysis– Breakdown of glycogen to glucose– Phosphorolysis process– Regulation of phosphorylase
• Covalent - glucagon, epinephrine• Allosteric - AMP
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
• Glycolysis - degradation of glucose to pyruvate– Hexokinase/glucokinase reaction– Glucose phosphate isomerase– Phosphofructokinase reaction– Aldolase reaction– Glyceraldehyde 3-phosphate &
dihydroxyacetone phosphate
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
– Oxidation of glyceraldehyde 3-phosphate to carboxylic acid, incorporation of inorganic phosphate into high-energy anhydride bond
– Substrate-level phosphorylation of ADP– Phosphoglyceromutase– Dehydration of 2-phosphoglycerate– Phophoenolpyruvate (PEP) donates
phosphate group to ADP– Lacate dehydrogenase reaction
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
– Fructose enters pathway– Galactose is phophorylated– Galactose 1-phosphate converted to
glucose 1-phosphate– Glucose 6-phosphate enters
hexosemonophophate shunt– Glucose 1-phosphate enteres
glycogenesis– Glucose can enter glycolysis
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
• Substrate-level phosphorylation• The tricarboxylic acid cycle
– TCA pathway• Formation of citrate from oxaloacetate & acetyl
CoA• Isomerization of citrate to isocitrate• Dehydrogenation catalyzed by isocitrate
dehydrogenase• Decarboxylation & dehydrogenation of -
ketoglutarate
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
• Hydrolysis of thioester bond of acetyl CoA drives phosphorylation of guanosine diphosphate (GDP)
• Succinate dehydrogenase reaction
• Fumerase incorporates H2O across double bond of fumarate to form malate
• Malate converted to oxaloacetate
– ATPs produced by complete glucose oxidation
• C6H12O6 + 6O2 6CO2 + 6H2O + energy
• Yields 12 ATPs + 2 mol acetyl CoA per 1 mol glucose = 24 ATPs
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
– Acetyl CoA oxidation and tricarboxylic acid cycle intermediates
– NADH in anaerobic & aerobic glycolysis: the shuttle systems• Glycerol 3-phosphate shuttle system• Malate-aspartate shuttle system
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
• Formation of ATP– Biological oxidation & the electron
transport chain• Electron transport chain = sequential
reduction-oxidation• Oxidative phosphorylation = oxidation of
a metabolite by O2 through electron transport + phosphorylation of ADP
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
– Anatomical site for oxidative phosphorylation
– Components of the oxidative phosphorylation chain• Complex I NADH-coenzyme Q
oxidoreductase• Complex II• Complex III coenzyme Q-cytochrome c
oxidoreductase• Complex IV
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
– Phosphorylation of ADP to form ATP– Translocation of H+ – ATP synthase
2009 Cengage-Wadsworth
Integrated Metabolism in Tissues
• The hexosemonophosphate shunt (pentose phosphate pathway)– Pentose phosphates– Reduced cosubstrate NADPH
• Gluconeogenesis– Synthesis of glucose from non-CHO– Reversal of glycolytic pathway– Lactate utilization– Efficient glycogenesis
2009 Cengage-Wadsworth
Regulation of Metabolism
• 4 mechanisms:– Negative or positive modulation of
allosteric enzymes– Hormonal activation by covalent
modification/induction– Directional shifts in reactions– Translocation of enzymes within cells
2009 Cengage-Wadsworth
Regulation of Metabolism
• Allosteric enzyme modulation– AMP, ADP, & ATP as allosteric
modulators– AMP’s positive modulation
• Causes shift from inactive to active form of phosphorylase b
• Stimulates phosphofructokinase
2009 Cengage-Wadsworth
Regulation of Metabolism
• Regulatory effect of NADH:NAD+ ratio
• Hormonal regulation– Glycolytic enzymes– Bifunctional enzymes– Gluconeogenic enzymes
• Directional shifts in reversible reactions
2009 Cengage-Wadsworth
Perspective 3
Hypoglycemia: Fact or Fall Guy?
2009 Cengage-Wadsworth
Hypoglycemia
• Preprandial vs. postprandial serum glucose levels
• Types:– Fasting hypoglycemia
• Usually caused by insulin, sulfonylureas
– Fed (reactive) hypoglycemia• Impaired glucose tolerance, idiopathic
postprandial syndrome