Transcript Prolonged starvation

BIOC 460 - DR. TISCHLER
LECTURE 21
METABOLISM: BASIC CONCEPTS
OBJECTIVES
1. Identify the three major forms in which energy is stored
and the four primary circulating fuels.
2. Distinguish between G and G, and explain the
relationship between mass action effect and G.
3. Define high-energy phosphate transfer potential, and
explain its significance in terms of the formation of ATP
via substrate-level phosphorylation.
4. Define the absorptive (well-fed), postabsorptive (fasting),
starvation (gluconeogenic) and prolonged starvation
nutritional states and identify the primary sources of
glucose in each of these.
GENERAL INFORMATION ABOUT METABOLISM
Catabolism: breakdown of fuels – used to produce energy
Anabolism: synthesis and storage of fuels
Most cells use oxidative metabolism (varying degrees)
Red blood cells lack mitochondria = entirely anaerobic
ATP: most common direct energy source
OVERVIEW OF METABOLIC PATHWAYS
AND SYSTEMS OF ENERGY METABOLISM
Nucleic
Acids
GLYCOGEN
PROTEIN
Ribose-5-P
Glucose
Lactate
Glucose-6-P
TRIACYLGLYCEROLS
Urea
Amino
Acids
Pyruvate
Free Fatty Acids
Acetyl-CoA
Ketone
Bodies
ATP
Figure 1. Energy systems
PHYSIOLOGICAL FREE ENERGY
G = G + 2.3 log [products/reactants]
G = actual free energy difference of reaction in cell;
must be negative for reaction to proceed
G = point of reference
"mass action effect"
change G by altering ratio of products/substrates
product and/or reactant lowers G
reaction proceeds better towards product
O
O
O
PHOSPHOCREATINE
ATP
O
*
- P-O-P-O-POCH2
O
Adenine
O
O- O - O-
g
b
a
-7.3 -6.6
-
O-
CPK
OH OH
NH
P*N-C N CH2 COO
O-
CH3
-10.3
Kcal
-14.8
O
CH2
Kcal
-10.1
O
O
O-
P* O C
O-
OH
O
CH CH2 O P
-
O-
O P *O C
O-
COO-
O-
1,3-bisPHOSPHOGLYCERATE
PHOSPHOENOLPYRUVATE
(TWO HIGH ENERGY INTERMEDIATES OF THE GLYCOLYTIC PATHWAY)
Figure 2. Structures of important compounds having high-energy
phosphate bonds. ATP formed by substrate-level phosphorylation
SUMMARY OF CARBOHYDRATE PATHWAYS
GLYCOGEN
Glycogenolysis
Glycogenesis
NADPH formation
GLUCOSE
Glucose-6-P
PPP Nucleic acid synthesis
Glycolysis
Gluconeogenesis
Acetyl CoA
Pyruvate
LACTATE
anaerobic
metabolism
aerobic
metabolism
Citric Acid
Cycle
CO2
PPP = pentose phosphate pathway
Figure 3. Summary of carbohydrate pathways. Pyruvate
metabolism to acetyl CoA and carbon dioxide is irreversible.
Table 1. Summary of Nutritional States
Nutritional
State
Description
period within no more than 4 hours after the last meal
Absorptive commenced during which food is digested and absorbed; also
called well-fed state
Postabsorptive
period after food is completely digested and absorbed up until
18 to 24 hours afterwards; also referred to as a fasting state
Starvation
period of time from about 24 hours after the last meal and
onwards until refeeding or death; early starvation is
approximately the first 5 days
Prolonged
starvation
period of time one week and longer after food deprivation
BLOOD GLUCOSE HOMEOSTASIS

maintenance of blood glucose concentration

brain depends on glucose; >50% of total

prolonged starvation has <25% decline in glucose

hyperglycemia – too little insulin

hypoglycemia – too little intake or too much insulin
Table 2. Primary sources and fates of glucose,
and the major fuel for the brain in each phase
Nutritional Absorptive
status
(Well-fed)
Postabsorptive
(Fasting)
Early
Starvation
Liver
gluconeogenesis
Prolonged
Starvation
Sources of
Blood
Diet
Glucose
Liver
glycogen
Tissues
Using
Glucose
(fates)
All
Primarily
Brain and red
brain and red
blood cells
blood cells
Red blood
cells only
Primary
Brain Fuel
Glucose
Glucose
Ketone
bodies
Glucose
Liver
gluconeogenesis