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Copyright 2009, John Wiley & Sons, Inc.
Chapter 25: Metabolism and Nutrition
Copyright 2009, John Wiley & Sons, Inc.
Metabolism
Metabolism – refers to all chemical reaction occurring in body Catabolism – break down complex molecules
Exergonic – produce more energy than they consume Anabolism – combine simple molecules into
complex ones Endergonic – consume more energy than they produce
Adenosine triphosphate (ATP) “energy currency” ADP + P + energy ↔ ATP
Copyright 2009, John Wiley & Sons, Inc.
Role of ATP in linking anabolic and catabolic reactions
Copyright 2009, John Wiley & Sons, Inc.
Energy transfer
Oxidation-reduction or redox reactions Oxidation – removal of electrons
Decrease in potential energy Dehydrogenation – removal of hydrogens Liberated hydrogen transferred by coenzymes
Nicotinamide adenine dinucleotide (NAD) Flavin adenine dinucleotide (FAD)
Glucose is oxidized
Reduction – addition of electrons Increase in potential energy
Copyright 2009, John Wiley & Sons, Inc.
3 Mechanisms of ATP generation1. Substrate-level phosphorylation Transferring high-energy phosphate group
from an intermediate directly to ADP2. Oxidative phosphorylation Remove electrons and pass them through
electron transport chain to oxygen3. Photophosphorylation Only in chlorophyll-containing plant cells
Copyright 2009, John Wiley & Sons, Inc.
Carbohydrate metabolism
Fate of glucose depends on needs of body cells ATP production or synthesis of amino acids,
glycogen, or triglycerides GluT transporters bring glucose into the cell
via facilitate diffusion Insulin causes insertion of more of these
transporters, increasing rate of entry into cells Glucose trapped in cells after being
phosphorylated
2/20/2011
2
Copyright 2009, John Wiley & Sons, Inc.
Glucose catabolism / cellular respiration
1. Glycolysis Anaerobic respiration – does not require
oxygen2. Formation of acetyl coenzyme A3. Krebs cycle reactions4. Electron transport chain reactions Aerobic respiration – requires oxygen
Copyright 2009, John Wiley & Sons, Inc.
Overview of cellular respiration
1NADH + 2 H+
GLYCOLYSIS2
2
2 Pyruvic acid
1 Glucose
ATP1
NADH + 2 H+GLYCOLYSIS
+ 2 H+NADH
CO2FORMATIONOF ACETYLCOENZYME A
2
2
2
2
2 Acetylcoenzyme A
2 Pyruvic acid
1 Glucose
ATP
2
1NADH + 2 H+
GLYCOLYSIS
+ 2 H+NADH
CO2FORMATIONOF ACETYLCOENZYME A
KREBSCYCLE
+ 6 H+
CO2
FADH2
NADH
2
4
6
2
2
2
2
2
2 Acetylcoenzyme A
2 Pyruvic acid
1 Glucose
ATP
ATP
2
3
1NADH + 2 H+
GLYCOLYSIS
+ 2 H+NADH
CO2FORMATIONOF ACETYLCOENZYME A
KREBSCYCLE
+ 6 H+
CO2
FADH2
NADH
2
4
6
2
ELECTRONTRANSPORTCHAIN
e–
e–
e–
32 or 34
O26
6
2
2
2
2
H2O
Electrons
2 Acetylcoenzyme A
2 Pyruvic acid
1 Glucose
ATP
ATP ATP
2
3
4
Copyright 2009, John Wiley & Sons, Inc.
Glycolysis
1. Glycolysis Splits 6-carbon glucose into 2 3-carbon
molecules of pyruvic acid Consumes 2 ATP but generates 4 10 reactions Fate of pyruvic acid depends on oxygen
availability If oxygen is scarce (anaerobic), reduced to lactic acid
Hepatocytes can convert it back to pyruvic acid If oxygen is plentiful (aerobic), converted to acetyl
coenzyme A
Copyright 2009, John Wiley & Sons, Inc.
Cellular respiration begins with glycolysis
Copyright 2009, John Wiley & Sons, Inc.
The 10 reactions of glycolysis
2/20/2011
3
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
ATP
H H
H
HHO
1
H
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
OH2CP
ATP
H
HO
H
H
HH
H
H
H
HO
1
2
H
H
Phosphofructokinase
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
ADP
P
OH2CP
ATP
ATP
OH
H
HO
H
H
HH
H H
H
H
HO
H
HO
1
2
3
H
H
Phosphofructokinase
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
CH2O
Fructose 1, 6-bisphosphate
O
OH
H
OH2C
ADP
PP
P
OH2CP
ATP
ATP
OH
H
HO
H
H
HH
H
H
H
H
H
H
HO
HO
H
HO
OH
1
2
3
4
H
H
Phosphofructokinase
Dihydroxyacetonephosphate
CH2OH
CH2OC O
Glyceraldehyde3-phosphate
HCOHCH2O
OHC
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
CH2O
Fructose 1, 6-bisphosphate
O
OH
H
OH2C
ADP
PP
P
P
P
OH2CP
ATP
ATP
OH
H
HO
H
H
HH
H
H
H
H
H
H
HO
HO
H
HO
OH
1
2
3
4
5
H
H
+ 2H+NADH
HCOHC
CH2O
OO 1, 3-Bisphosphoglyceric acid
(2 molecules)
2
P
P
Phosphofructokinase
Dihydroxyacetonephosphate
CH2OH
CH2OC O
Glyceraldehyde3-phosphate
HCOHCH2O
OHC
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
CH2O
Fructose 1, 6-bisphosphate
O
OH
H
OH2C
ADP
PP
P
P
P
OH2CP
ATP
ATP
OH
H
HO
H
H
HH
H
H
H
H
H
H
HO
HO
H
HO
OH
1
2
3
4
5
6
H
H
2 NAD+ + 2 P
+ 2H+NADH
HCOHC
CH2O
O
COOH
O
2
2 ADP
HCOHCH2O
1, 3-Bisphosphoglyceric acid(2 molecules)
2
3-Phosphoglyceric acid(2 molecules)
P
P
P
Phosphofructokinase
Dihydroxyacetonephosphate
CH2OH
CH2OC O
Glyceraldehyde3-phosphate
HCOHCH2O
OHC
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
CH2O
Fructose 1, 6-bisphosphate
O
OH
H
OH2C
ADP
PP
P
P
P
OH2CP
ATP
ATP
ATP
OH
H
HO
H
H
HH
H
H
H
H
H
H
HO
HO
H
HO
OH
1
2
3
4
5
6
7H
H
2 NAD+ + 2 P
+ 2H+NADH
HCOHC
CH2O
O
COOH
O
2
2 ADP
HCOHCH2O
1, 3-Bisphosphoglyceric acid(2 molecules)
2
3-Phosphoglyceric acid(2 molecules)
COOH
CH2OHHCO 2-Phosphoglyceric acid
(2 molecules)P
P
P
P
Phosphofructokinase
Dihydroxyacetonephosphate
CH2OH
CH2OC O
Glyceraldehyde3-phosphate
HCOHCH2O
OHC
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
CH2O
Fructose 1, 6-bisphosphate
O
OH
H
OH2C
ADP
PP
P
P
P
OH2CP
ATP
ATP
ATP
OH
H
HO
H
H
HH
H
H
H
H
H
H
HO
HO
H
HO
OH
1
2
3
4
5
6
7
8
H
H
2 NAD+ + 2 P
+ 2H+NADH
HCOHC
CH2O
O
COOH
O
2
2 ADP
HCOHCH2O
1, 3-Bisphosphoglyceric acid(2 molecules)
2
3-Phosphoglyceric acid(2 molecules)
COOH
CH2OHHCO 2-Phosphoglyceric acid
(2 molecules)
COOH
CH2
C O Phosphoenolpyruvic acid(2 molecules)
P
P
P
P
P
Phosphofructokinase
Dihydroxyacetonephosphate
CH2OH
CH2OC O
Glyceraldehyde3-phosphate
HCOHCH2O
OHC
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
CH2O
Fructose 1, 6-bisphosphate
O
OH
H
OH2C
ADP
PP
P
P
P
OH2CP
ATP
ATP
ATP
OH
H
HO
H
H
HH
H
H
H
H
H
H
HO
HO
H
HO
OH
1
2
3
4
5
6
7
8
9
H
H
2 NAD+ + 2 P
+ 2H+NADH
2 NAD+ + 2
HCOHC
CH2O
O
COOH
O
2
2 ADP
P
HCOHCH2O
1, 3-Bisphosphoglyceric acid(2 molecules)
2
3-Phosphoglyceric acid(2 molecules)
COOH
CH2OHHCO 2-Phosphoglyceric acid
(2 molecules)
Pyruvic acid(2 molecules)
COOH
CH2
2
2 ADP
C O Phosphoenolpyruvic acid(2 molecules)
COOH
CH3
C O
P
P
P
P
P
Phosphofructokinase
Dihydroxyacetonephosphate
CH2OH
CH2OC O
Glyceraldehyde3-phosphate
HCOHCH2O
OHC
ADP
O
Glucose (1 molecule)
CH2OH
OH
OH
OH4 1
3 2
5
6
Glucose 6-phosphate
O
OH
OH
OH
CH2OH
Fructose 6-phosphate
O
OH
H
OH2C 6
5
4 3
2
1
CH2O
Fructose 1, 6-bisphosphate
O
OH
H
OH2C
ADP
PP
P
P
P
OH2CP
ATP
ATP
ATP
ATP
OH
H
HO
H
H
HH
H
H
H
H
H
H
HO
HO
H
HO
OH
1
2
3
4
5
6
7
8
9
10
H
H
Copyright 2009, John Wiley & Sons, Inc.
Formation of Acetyl coenzyme A
2. Formation of Acetyl coenzyme A Each pyruvic acid converted to 2-carbon acetyl
group Remove one molecule of CO2 as a waste product
Each pyruvic acid also loses 2 hydrogen atoms NAD+ reduced to NADH + H+
Acetyl group attached to coenzyme A to form acetyl coenzyme A (acetyl CoA)
Copyright 2009, John Wiley & Sons, Inc.
Fate of pyruvic acid
Copyright 2009, John Wiley & Sons, Inc.
The Krebs cycle
3. The Krebs cycle Also known as citric acid cycle Occurs in matrix of mitochondria Series of redox reactions 2 decarboxylation reactions release CO2
Reduced coenzymes (NADH and FADH2) are the most important outcome
One molecule of ATP generated by substrate-level phosphorylation
Copyright 2009, John Wiley & Sons, Inc.
The Krebs Cycle
Copyright 2009, John Wiley & Sons, Inc.
The Eight reactions of the Krebs cycle
2/20/2011
4
1
CCH2
COOHO
Oxaloacetic acid
COOHCitric acid
H2C COOHCOOHHOC
H2C COOH
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
H2O
CO2
NAD+
KREBSCYCLE
NADH
CoA
CoA
1
CCH2
COOHO
Oxaloacetic acid
COOH
Isocitric acid
H2C COOH
HOC COOHHC COOH
H
Citric acid
H2C COOHCOOHHOC
H2C COOH
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
H2O
CO2
NAD+
KREBSCYCLE
NADH
CoA
CoA
2
1
To electrontransport chain
CO2
+ H+
CCH2
COOHO
Oxaloacetic acid
COOH
Alpha-ketoglutaric acid
H2C COOHHCH
C COOH
Isocitric acid
H2C COOH
HOC COOHHC COOH
H
Citric acid
H2C COOHCOOHHOC
H2C COOH
NAD+
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
H2O
CO2
NAD+
KREBSCYCLE
NADH
NADH
CoA
CoA
2
3
O
1
To electrontransport chain
CO2
+ H+NADH
CO2
+ H+
CCH2
COOHO
Oxaloacetic acid
COOH
Succinyl CoA
H2C COOHCH2
C S CoA Alpha-ketoglutaric acid
H2C COOHHCH
C COOH
Isocitric acid
H2C COOH
HOC COOHHC COOH
H
Citric acid
H2C COOHCOOHHOC
H2C COOH
NAD+
NAD+
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
H2O
CO2
NAD+
KREBSCYCLE
NADH
NADH
O
CoA
O
CoA
2
3
4
1
To electrontransport chain
CO2
+ H+NADH
CO2
+ H+
CCH2
COOHO
Oxaloacetic acid
COOH
H2C COOHH2C COOHSuccinic acid
Succinyl CoA
H2C COOHCH2
C S CoA Alpha-ketoglutaric acid
H2C COOHHCH
C COOH
Isocitric acid
H2C COOH
HOC COOHHC COOH
H
Citric acid
H2C COOHCOOHHOC
H2C COOH
NAD+
NAD+
GDP
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
ADP
H2O
CO2
NAD+
KREBSCYCLE
NADH
NADH
ATP
GTP
O
CoA
CoA
O
CoA
2
3
4
5
1
To electrontransport chain
CO2
+ H+NADH
CO2
+ H+
To electrontransportchain
CCH2
COOHO
Oxaloacetic acid
COOH
H2C COOHH2C COOHSuccinic acid
Succinyl CoA
H2C COOHCH2
C S CoA Alpha-ketoglutaric acid
H2C COOHHCH
C COOH
Isocitric acid
H2C COOH
HOC COOHHC COOH
H
Citric acid
H2C COOHCOOHHOC
H2C COOH
Fumaric acid
NAD+
NAD+
GDP
FAD
HCCH
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
ADP
FADH2
COOH
COOH
H2O
CO2
NAD+
KREBSCYCLE
NADH
NADH
ATP
GTP
CoA
CoA
O
CoA
2
3
4
5
6
O
1
To electrontransport chain
CO2
+ H+NADH
CO2
+ H+
To electrontransportchain
CCH2
COOHO
Oxaloacetic acid
COOH
HCOHCH2
COOH
COOH
H2C COOHH2C COOHSuccinic acid
Malic acid
Succinyl CoA
H2C COOHCH2
C S CoA Alpha-ketoglutaric acid
H2C COOHHCH
C COOH
Isocitric acid
H2C COOH
HOC COOHHC COOH
H
Citric acid
H2C COOHCOOHHOC
H2C COOH
Fumaric acid
NAD+
NAD+
GDP
FAD
HCCH
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
ADP
FADH2
COOH
COOH
H2O
H2O
CO2
NAD+
KREBSCYCLE
NADH
NADH
ATP
GTP
CoA
CoA
O
CoA
2
3
4
5
6
7
O
1
To electrontransport chain
CO2
+ H+NADH
CO2
+ H+
To electrontransportchain
CCH2
COOHO
Oxaloacetic acid
COOH
+ H+NADH
HCOHCH2
COOH
COOH
H2C COOHH2C COOHSuccinic acid
Malic acid
Succinyl CoA
H2C COOHCH2
C S CoA Alpha-ketoglutaric acid
H2C COOHHCH
C COOH
Isocitric acid
H2C COOH
HOC COOHHC COOH
H
Citric acid
H2C COOHCOOHHOC
H2C COOH
Fumaric acid
NAD+
NAD+
GDP
FAD
NAD+
HCCH
+ H+Pyruv ic
acidAcetyl
coenzyme A
CCH3
OCH3
CCOOH
O
To electrontransport chain
ADP
FADH2
COOH
COOH
H2O
H2O
CO2
NAD+
KREBSCYCLE
NADH
NADH
ATP
GTP
CoA
CoA
O
CoA
2
3
4
5
6
7
8
O
Copyright 2009, John Wiley & Sons, Inc.
Electron transport chain
4. Electron transport chain Series of electron carriers in inner mitochondrial
membrane reduced and oxidized As electrons pass through chain, exergonic
reactions release energy used to form ATP Chemiosmosis
Final electron acceptor is oxygen to form water
Copyright 2009, John Wiley & Sons, Inc.
Chemiosmosis Carriers act as proton pumps to expel H+ from
mitochondrial matrix Creates H+ electrochemical gradient – concentration
gradient and electrical gradient Gradient has potential energy – proton motive force As H+ flows back into matrix through membrane,
generates ATP using ATP synthase
Energy fromNADH + H+
H+
Low H+ concentration inmatrix of mitochondrion
Innermitochondrialmembrane
Matrix
High H+ concentrationbetween inner andouter mitochondrialmembranes
Outer membraneInner membrane
H+
channel
Electrontransport
chain(includes
proton pumps)
1 Energy fromNADH + H+
H+
H+
Low H+ concentration inmatrix of mitochondrion
Innermitochondrialmembrane
Matrix
High H+ concentrationbetween inner andouter mitochondrialmembranes
Outer membraneInner membrane
H+
channel
Electrontransport
chain(includes
proton pumps)
1
2
Energy fromNADH + H+
H+
H+
ADP +
ATP synthaseLow H+ concentration inmatrix of mitochondrion
Innermitochondrialmembrane
Matrix
High H+ concentrationbetween inner andouter mitochondrialmembranes
Outer membraneInner membrane
H+
channel
Electrontransport
chain(includes
proton pumps)
P
ATP
1
2
3
Copyright 2009, John Wiley & Sons, Inc.
The actions of the three proton pumps and ATP synthase in the inner membrane of mitochondria
Space between outerand inner mitochondrialmembranes
Innermito-chondrialmembrane
Mitochondrialmatrix
H+ channel
NADH dehydrogenasecomplex: FMN andfive Fe-S centers
NAD
e–
H++ + + + + + +
– – – – – – –
Q
NADH+ H+
1
Space between outerand inner mitochondrialmembranes
Innermito-chondrialmembrane
Mitochondrialmatrix
H+ channel
NADH dehydrogenasecomplex: FMN andfive Fe-S centers
Cytochrome b-c1complex: cyt b, cyt c1, and an Fe-S center
NAD
e–
e–
e–
H++ + + + + + +
– – – – – – –
Q
Cyt c
NADH+ H+H+
1 2
Space between outerand inner mitochondrialmembranes
Innermito-chondrialmembrane
Mitochondrialmatrix
H+ channel
NADH dehydrogenasecomplex: FMN andfive Fe-S centers
Cytochrome b-c1complex: cyt b, cyt c1, and an Fe-S center
Cytochrome oxidasecomplex: cyt a, cyt a3,and two Cu
NAD1 1/2 O2
e–
e–
e–
e–
e–
H+ H+H+
+ + + + + + +
– – – – – – –
H2O
Q
Cyt c
NADH+ H+H+
3
ADP +
ATP synthase
P
ATP1 2 3
3
Copyright 2009, John Wiley & Sons, Inc.
Summary of cellular respiration
2/20/2011
5
Copyright 2009, John Wiley & Sons, Inc.
Glucose anabolism
Glucose storage: glycogenesis Polysaccharide that is the only stored carbohydrate in
humans Insulin stimulates hepatocytes and skeletal muscle cells
to synthesize glycogen
Glucose release: glycogenolysis Glycogen stored in hepatocytes broken down into
glucose and release into blood
Copyright 2009, John Wiley & Sons, Inc.
Glycogenesis and glycogenolysis
Copyright 2009, John Wiley & Sons, Inc.
Formation of glucose from proteins and fats: gluconeogenesis
Glycerol part of triglycerides, lactic acid, and certain amino acids can be converted by the liver into glucose
Glucose formed from noncarbohydrate sources
Stimulated by cortisol and glucagon
Copyright 2009, John Wiley & Sons, Inc.
Lipid metabolism
Transport by lipoproteins Most lipids nonpolar and
hydrophobic Made more water-soluble
by combining them with proteins to form lipoproteins
Proteins in outer shell called apoproteins (apo) Each has specific functions All essentially are transport
vehicles
Copyright 2009, John Wiley & Sons, Inc.
Apoproteins Apoproteins categorized and named according to density (ratio of
lipids to proteins) Chylomicrons
Form in small intestine mucosal epithelial cells Transport dietary lipids to adipose tissue
Very low-density lipoproteins (VLDLs) Form in hepatocytes Transport endogenous lipids to adipocytes
Low-density lipoproteins (LDLs) – “bad” cholesterol Carry 75% of total cholesterol in blood Deliver to body cells for repair and synthesis Can deposit cholesterol in fatty plaques
High-density lipoproteins (HDLs) – “good” cholesterol Remove excess cholesterol from body cells and blood Deliver to liver for elimination
Copyright 2009, John Wiley & Sons, Inc.
Lipid Metabolism
2 sources of cholesterol in the body Present in foods Synthesized by hepatocytes
As total blood cholesterol increases, risk of coronary artery disease begins to rise Treated with exercise, diet, and drugs
Lipids can be oxidized to provide ATP Stored in adipose tissue if not needed for ATP
Major function of adipose tissue to remove triglycerides from chylomicrons and VLDLs and store it until needed 98% of all body energy reserves
2/20/2011
6
Copyright 2009, John Wiley & Sons, Inc.
Lipid Metabolism
Lipid catabolism: lipolysis Triglycerides split into glycerol and fatty acids Must be done for muscle, liver, and adipose tissue
to oxidize fatty acids Enhanced by epinephrine and norepinephrine
Lipid anabolism: lipogenesis Liver cells and adipose cells synthesize lipids from
glucose or amino acids Occurs when more calories are consumed than
needed for ATP production
Copyright 2009, John Wiley & Sons, Inc.
Pathways of lipid metabolism
Copyright 2009, John Wiley & Sons, Inc.
Protein metabolism Amino acids are either oxidized to produce
ATP or used to synthesize new proteins Excess dietary amino acids are not excreted
but converted into glucose (gluconeogenesis) or triglycerides (lipogenesis)
Protein catabolism Proteins from worn out cells broken down into
amino acids Before entering Krebs cycle amino group must be
removed – deamination Produces ammonia, liver cells convert to urea,
excreted in urine
Copyright 2009, John Wiley & Sons, Inc.
Various points at which amino acids enter the Krebs cycle for oxidation
Copyright 2009, John Wiley & Sons, Inc.
Protein anabolism Carried out in ribosomes of almost every cell in the body 10 essential amino acids in the human
Must be present in the diet because they cannot be synthesized
Complete protein – contains sufficient amounts of all essential amino acids – beef, fish, poultry, eggs
Incomplete protein – does not – leafy green vegetables, legumes, grains
10 other nonessential amino acids can be synthesized by body cells using transamination
Copyright 2009, John Wiley & Sons, Inc.
Key molecules at metabolic crossroads
3 molecules play pivotal roles in metabolism Stand at metabolic crossroads – reactions
that occur or not depend on nutritional or activity status of individual
1. Glucose 6-phosphate Made shortly after glucose enters body cell 4 fates – synthesis of glycogen, release of
glucose into blood stream, synthesis of nucleic acids, glycolysis
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Copyright 2009, John Wiley & Sons, Inc.
Key molecules at metabolic crossroads2. Pyruvic acid
If there is enough oxygen, aerobic cellular respiration occurs
If there is not enough oxygen, anaerobic reactions can produce lactic acid, produce alanine or gluconeogenesis
3. Acetyl Coenzyme A When ATP is low and oxygen plentiful, most pyruvic acid
goes to ATP production via Acetyl CoA Acetyl CoA os the entry into the Krebs cycle Can also be used for synthesis of certain lipids
Copyright 2009, John Wiley & Sons, Inc.
Metabolic adaptations
During the absorptive state ingested nutrients are entering the blood stream Glucose readily available for ATP production
During postabsorptive state absorption of nutrients from GI tract complete Energy needs must be met by fuels in the body Nervous system and red blood cells depend on
glucose so maintaining steady blood glucose critical
Effects of insulin dominate
Copyright 2009, John Wiley & Sons, Inc.
Metabolism during absorptive state
Soon after a meal nutrients enter blood Glucose, amino acids, and triglycerides in chylomicrons
2 metabolic hallmarks Oxidation of glucose for ATP production in all body cells Storage of excess fuel molecules in hepatocytes,
adipocytes, and skeletal muscle cells
Pancreatic beta cells release insulin Promotes entry of glucose and amino acids into cells
Copyright 2009, John Wiley & Sons, Inc.
Principal metabolic pathways during the absorptive state
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
1
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
HEPATOCYTES IN LIVER
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Fatty acids
Triglycerides
Glyceraldehyde3-phosphate Glycogen
Glucose
+ H2O +CO2 ATP
1
2
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
HEPATOCYTES IN LIVER
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fatty acids
Triglycerides
Glyceraldehyde3-phosphate Glycogen
Glucose
+ H2O +CO2 ATP
1
2
3
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
GLUCOSE
HEPATOCYTES IN LIVER
SKELETALMUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Fattyacids
Triglycerides
Glyceraldehyde3-phosphate
Glucose
Fatty acids
Triglycerides
Glyceraldehyde3-phosphate Glycogen
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4
4
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
GLUCOSE
HEPATOCYTES IN LIVER
SKELETALMUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fattyacids
Triglycerides
Glyceraldehyde3-phosphate
Glucose
Fatty acids
Triglycerides
Glyceraldehyde3-phosphate Glycogen
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4 5
4
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
GLUCOSE
HEPATOCYTES IN LIVER
SKELETALMUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fattyacids
Triglycerides
Glyceraldehyde3-phosphate
Glucose
Keto acids
Fatty acids
Triglycerides
Glyceraldehyde3-phosphate Glycogen
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4 5
6
4
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
GLUCOSE
HEPATOCYTES IN LIVER
SKELETALMUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fattyacids
Triglycerides
Glyceraldehyde3-phosphate
Glucose
Keto acids
Fatty acidsProteins
Triglycerides
Glyceraldehyde3-phosphate Glycogen
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4 5
67
4
AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINALTRACT
GLUCOSE
HEPATOCYTES IN LIVER
SKELETALMUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fattyacids
Triglycerides
Glyceraldehyde3-phosphate
Glucose
Keto acids
Fatty acidsProteins
Triglycerides
Glyceraldehyde3-phosphate Glycogen
Glucose
GlycogenGlycogen
ProteinsProteins
+ H2O +CO2 ATP
1
2
3
4 5
67
8
4
Copyright 2009, John Wiley & Sons, Inc.
Metabolism during postabsorptive state About 4 hours after the last meal absorption in
small intestine nearly complete Blood glucose levels start to fall Main metabolic challenge to maintain normal blood
glucose levels Glucose production Breakdown of liver glycogen, lipolysis,
gluconeogenesis using lactic acid and/or amino acids
Glucose conservation Oxidation of fatty acids, lactic acid, amino acids,
ketone bodies and breakdown of muscle glycogen
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Copyright 2009, John Wiley & Sons, Inc.
Principal metabolic pathways during the postabsorptive state
1
Liver glycogen
Glucose
LIVER
Blood
HEARTADIPOSE TISSUESKELETAL MUSCLE TISSUE
OTHER TISSUES
1
Liver glycogen
Glucose
LIVER
Glycerol
Blood
HEART
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
SKELETAL MUSCLE TISSUE
OTHER TISSUES
2
Fatty acids
1
Liver glycogen
Glucose
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
SKELETAL MUSCLE TISSUE
OTHER TISSUES3
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Muscle proteins
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
Fasting orstarvation
SKELETAL MUSCLE TISSUE
OTHER TISSUES
ProteinsAmino acids
Amino acids
4
4
3
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
Fasting orstarvation
SKELETAL MUSCLE TISSUE
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acidsFatty acids
ATP
ATP
ATP
4
5
5
4
3
5
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
Fasting orstarvation
SKELETAL MUSCLE TISSUE
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acidsFatty acids
Lactic acidATP
ATP
ATP
ATP
4
5
5
6
4
3
5
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
Fasting orstarvation
SKELETAL MUSCLE TISSUE
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acidsFatty acids
Lactic acidATP
ATPATP
ATP
ATP
4
5
5
67
4
3
5
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Fatty acids
Lactic acid
Ketone bodies
Glycerol
Blood
NERVOUSTISSUE Ketone
bodiesGlucose
Starvation
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
Fasting orstarvation
SKELETAL MUSCLE TISSUE
Ketone bodies
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acidsFatty acids
Ketone bodies
Lactic acidATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP ATP
4
5
8
5
6
88
7
4
3
5
4
2
8
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Fatty acids
Lactic acid
Ketone bodies
Glycerol
Blood
NERVOUSTISSUE Ketone
bodiesGlucose
Starvation
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
TriglyceridesADIPOSE TISSUE
Fasting orstarvation
SKELETAL MUSCLE TISSUE
Ketone bodies
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Glucose6-phosphate
Pyruvic acid
Lacticacid
Muscle glycogen
(aerobic) (anaerobic)
Amino acidsFatty acids
Ketone bodies
Lactic acidATP
O2
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP ATP
+ O2–
4
5
8
5
6
88
7
4
3
9
5
4
2
8
Copyright 2009, John Wiley & Sons, Inc.
Hormones and autonomic nervous system regulate metabolism during postabsorptive state As blood glucose decline, insulin secretion falls
Glucagon – increases release of glucose into blood via gluconeogenesis and glycogenolysis
Sympathetic nerve endings of ANS release norepinephrine and adrenal medulla releases epinephrine and norepinephrine Stimulate lipolysis, glycogen breakdown
Copyright 2009, John Wiley & Sons, Inc.
Heat and energy balance
Heat – form of energy that can be measured as temperature and can be expressed in calories calorie (cal) – amount of heat required to raise 1 gram of
water 1°C Kilocalorie (kcal) or Calorie (Cal) is 1000 calories
Metabolic rate – overall rate at which metabolic reactions use energy Some energy used to make ATP, some lost as heat Basal metabolic rate (BMR) – measurement with body in
quiet, resting, fasting condition
Copyright 2009, John Wiley & Sons, Inc.
Body temperature homeostasis
Despite wide fluctuations in environmental temperatures, homeostatic mechanisms maintain normal range for internal body temperature
Core temperature (37°C or 98.6°F) versus shell temperature (1-6°C lower)
Heat produced by exercise, some hormones, sympathetic nervous system, fever, ingestion of food, younger age, etc.
Copyright 2009, John Wiley & Sons, Inc.
Heat and engery balance
Heat can be lost through Conduction to solid materials in contact with body Convection – transfer of heat by movement of a
gas or liquid Radiation – transfer of heat in form of infrared
rays Evaporation exhaled air and skin surface
(insensible water loss) Hypothalamic thermostat in preoptic area Heat-losing center and heat-promoting center
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Copyright 2009, John Wiley & Sons, Inc.
Thermoregulation
If core temperature declines Skin blood vessels constrict Release of thyroid hormones, epinephrine and
norepinephrine increases cellular metabolism Shivering
If core body temperature too high Dilation of skin blood vessels Decrease metabolic rate Stimulate sweat glands
Copyright 2009, John Wiley & Sons, Inc.
Negative feedback mechanisms that conserve heat and increase increase production
Copyright 2009, John Wiley & Sons, Inc.
Nutrition Nutrients are chemical substances in food that body
cells use for growth, maintenance, and repair 6 main types
1. Water – needed in largest amount2. Carbohydrates3. Lipids4. Proteins5. Minerals6. Vitamins
Essential nutrients must be obtained from the diet
Copyright 2009, John Wiley & Sons, Inc.
Guidelines for healthy eating
We do not know with certainty what levels and types of carbohydrates, fat and protein are optimal
Different populations around the world eat radically different diets adapted to their particular lifestyle
Basic guidelines Eat a variety of foods Maintain a healthy weight Choose foods low in fat, saturated fat and cholesterol Eat plenty of vegetables, fruits and grain products Use sugars in moderation only
Copyright 2009, John Wiley & Sons, Inc.
MyPyramid
Copyright 2009, John Wiley & Sons, Inc.
Minerals
Inorganic elements that occur naturally in Earth’s crust
Eat foods that contain enough calcium, phosphorus, iron and iodine
Excess amounts of most minerals are excreted in urine and feces
Major role of minerals to help regulate enzymatic reactions
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Copyright 2009, John Wiley & Sons, Inc.
Vitamins
Organic nutrients required in small amounts to maintain growth and normal metabolism
Do not provide energy or serve as body’s building materials Most are coenzymes Most cannot be synthesized by the body Vitamin K produced by bacteria in GI tract Some can be assembled from provitamins No single food contains all the required vitamins 2 groups
Fat-soluble – A, D, E, K Water-soluble – several B vitamins and vitamin C
Copyright 2009, John Wiley & Sons, Inc.
End of Chapter 25
Copyright 2009 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.
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