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ASHLEY M BOMMARITOCHEMISTRY DEPARTMENT
EAST STROUDSBURG UNIVERSITY
A Brief Look into the Biochemistry of Fasting,
Starvation & Anorexia Nervosa
Metabolism
Set of chemical reactions that occur in organisms to maintain life
Two categories Catabolism – “Destructive metabolism” Anabolism – “Constructive metabolism”
Organized into metabolic pathways Enzymes couple energy-requiring reactions with
energy-releasing reactionsOnly focusing on humans and similar
mammals
General Catabolism
3 main stages Food broken down to smaller components; occurs
outside cells Digestive enzymes: proteases, glycoside hydrolases,
lipases Smaller molecules taken into cells; broken down more
Acetyl Coenzyme A (acetyl-CoA), releases some energy Acetyl group oxidized to H2O and CO2
Via citric acid cycle and electron transport chain Coenzyme NAD+ NADH; releases much more energy
TCA Cycle Overview
http://www.dnatube.com/video/278/Citric-Acid--TCA--Krebs-Cycle
Metabolism
Catabolism and Anabolism always coexistOne process may dominate over the other
Awake: catabolism Sleep: anabolism
With regular rest and healthy diet – balanced
Fasting, Starvation & Anorexia Nervosa
Fasting Voluntarily abstaining from all or most food
Starvation Extended fasting Involuntary
Anorexia Poor appetite, due to many causes
Anorexia Nervosa Eating disorder – low body weight, distorted body
image Some food is still eaten, often only certain
“categories”
General Effects
Inadequate carbohydrate consumption Body shifts to catabolic state
Body’s materials broken down – provides glucose to maintain life
Only materials required for survival are generated Catabolism > anabolism
Specific Effects – Amino Acids
Alanine level decline
Alanine to Pyruvate ratio downshift
Increase in oxidation of Alanine to obtain Pyruvate
PyruvateOxygen Carbon Hydrogen
AlanineOxygen Carbon Hydrogen
Nitrogen
Specific Effects – Amino Acids
Glutamate level decline
Glutamate to α-ketoglutarate ratio downshift
Oxidation of Glutamate increase
Specific Effects – Amino Acids
GlutamateOxygen Carbon Hydrogen
Nitrogen
α-ketoglutarateOxygen Carbon Hydrogen
Specific Effects – Amino Acids
Specific Effects : Pyruvate
Influx of carbons from acetyl CoA versus influx of carbons from pyruvate 14H: double 66H: triple
PEP carboxykinase vs. TCA cycle flux Seven-fold higher, 18H fast
Pyruvate recycling vs TCA cycle flux Five-fold higher, 18H fast
Specific Effects – Pyruvate
PyruvateOxygen Carbon Hydrogen
Acetyl CoAOxygen Carbon Hydrogen
Sulfur CoA
PyruvateOxygen Carbon Hydrogen Oxaloacetate
Oxygen Carbon Hydrogen
PEP
GlucoseOxygen Carbon Hydrogen
PhosphoenolpyruvateOxygen Carbon Hydrogen
Phosphorous
Summary
Metabolism – usually well balanced cycles Catabolism – break down, provides energy
Fasting, Starvation & Anorexia – Different forms of malnutrition
Effects - Body must adapt, still requires glucose for some cells while other cells can use different energy forms General – Body shifts to catabolic state Specifics – Amino Acids (ex, alanine & glutamate)
from muscles used to propel TCA cycle & fund glucose requirements
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