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.