Post on 17-Dec-2015
Chapter 7
IntroductionEnergy
HeatMechanicalElectricalChemicalStored in food and body
MetabolismRelease of energy(ATP), water, and carbon
dioxide
Chemical Reactions in the BodyEnergy metabolism
ways the body obtains & uses energy from foodSite of Metabolic rxns
Cell (non-stop metabolic work)Liver cells
Anabolism [ana= (build) up]Requires energy
Catabolism [kata=(break)down]Releases energy
Chemical Reactions in the Body
Chemical Reactions in the Body• Transfer of energy in reactions – ATP
• Released during breakdown of glucose, fatty acids, and amino acids
• Form of phosphate groupso Negative charge – vulnerable to hydrolysis
• Provides energy for all cell activities• Coupled reactions
o Efficiency & Heat losso 50% from food to ATP; 50% lost as heat
Chemical Reactions in the BodyEnzymes
Facilitators of metabolic reactionsCoenzymes
OrganicAssociate with enzymesWithout coenzyme, an enzyme cannot function
Breaking Down Nutrients for EnergyDigestion
Carbohydrates – glucose (& other monosaccharides)
Fats (triglycerides) – glycerol and fatty acidsProteins – amino acids
Molecules of glucose, glycerol, amino acids, and fatty acidsCatabolism
Carbon, nitrogen, oxygen, hydrogen
Breaking Down Nutrients for EnergyTwo new compounds
Pyruvate 3-carbon structure Can be used to make glucose
Acetyl CoA 2-carbon structure Cannot be used to make glucose
TCA cycle and electron transport chain
Breaking Down Nutrients for Energy – Glucose Glucose-to-pyruvate
Glycolysis 2 pyruvate molecules Hydrogen atoms carried to electron transport chain
Pyruvate can be converted back to glucose Liver cells and kidneys (to some extent)
Breaking Down Nutrients for Energy – Glucose Pyruvate’s options
Quick energy needs – anaerobic Pyruvate-to-lactate
Slower energy needs – aerobic Pyruvate-to-acetyl CoA
Breaking Down Nutrients for Energy – Glucose Pyruvate-to-lactate
Pyruvate accepts hydrogens Converts pyruvate to lactate
Occurs to a limited extent at restProduces ATP quickly
Mitochondrial abilityAccumulation of lactate in muscles
Effects Cori cycle
Breaking Down Nutrients for Energy – Glucose Pyruvate-to-Acetyl CoA
Pyruvate enters mitochondria of cell Carbon removed – becomes carbon dioxide 2-carbon compound joins with CoA becoming acetyl
CoA – irreversible
Breaking Down Nutrients for Energy – Glucose Acetyl CoA’s options – 2 functions
Synthesize fatsGenerate ATP through TCA cycle
Hydrogens – electron transport chain
Breaking Down Nutrients for Energy – Glucose
Breaking Down Nutrients for Energy – Glycerol and Fatty Acids Glycerol-to-pyruvate
Glycerol can be converted Glucose Pyruvate
Fatty acids-to-Acetyl CoAFatty acid oxidation
2-carbon units at a time then join with CoA Hydrogens and electrons carried to electron
transport chain
Breaking Down Nutrients for Energy – Amino AcidsDeamination of amino acids Amino acids-to-energy
Several entry points in energy pathway Converted to pyruvate (glucogenic) Converted to acetyl CoA (ketogenic) Enter TCA cycle directly (glucogenic)
Amino acids-to-glucose
Breaking Down Nutrients for Energy – Glucose
Final Steps of CatabolismTCA Cycle
Inner compartment of mitochondriaCircular path
Acetyl CoA Oxaloacetate – made primarily from pyruvate
Carbon dioxide releaseHydrogen atoms and their electrons
Niacin and riboflavin
Final Steps of CatabolismElectron transport chain
Energy captures in ATPSeries of proteins
Electron “carriers” Inner membrane of mitochondria
Electrons passed to next carrier Join oxygen at end of chain – water released ATP synthesis
Energy Balance – Feasting Metabolism favors fat formation
Regardless of excess from protein, fat, or carbohydrates Dietary fat to body fat is most direct and efficient
conversion Carbohydrate and protein have other roles to fulfill
before conversion to body fat
Energy Balance – Transition from Feasting to Fasting Glucose, glycerol, and fatty acids are used
then storedFasting state draws on these stores
Glycogen and fat are released
Fasting—Inadequate EnergyGlucose is needed for the brain and nerve cells.Protein meets glucose needs through amino acids that
provide pyruvate.The shift to ketosis occurs when the brain becomes
fueled by ketone bodies.Ketones produced when glucose is not available.
Ketosis causes a suppression of the appetite.Hormones slow metabolism.Symptoms of Starvation:
Muscle wasting. Decreased heart rate, respiratory rate, metabolic rate, and
body temperature. Impaired vision, Organ failure, Decreased immunity. Depression, anxiety, and food-related dreams.
Low-Carbohydrate DietsMetabolism similar to fastingResult in changes in metabolism similar to
what occurs during fasting.Ketones will be present in the urine when
glycogen depletion has occurred.When a dieter returns to a well-balanced diet,
the body will retain depleted nutrients.