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Fundamentals of nutritional biochemistry: nutrient functions and requirements
Overview of metabolism and energetic strategies in
human cellsA key cycle for multiple roles: the
tricarboxylic acid cycle
Russian National Research Medical University
Maxim A. Abakumov
Moscow, 2014
Main paradigm of life
• Live organisms need to spent energy to stop
entropy processes
• Energy can by obtained directly from
surrounding area (autotrophes) or from other
organisms (heterotrophes)
Main paradigm of life
• Metabolism is the set of life-sustaining chemical
transformations within the cells of living organisms
• Metabolism is divided onto anabolism and
catabolism
• Catabolism is the set of metabolic pathways that
breaks down molecules into smaller units to
release energy
• Anabolism is the set of metabolic pathways that
construct molecules from smaller units
Catabolic and anabolic pathways
BioenergeticsEnergy containing
nutrients Carbohydrates Proteins Fats
Energy depleted end products
CO2
H2O NH3
Precursor molecules
Aminoacids Sugars Fatty acids Nitrogen bases
Cell macromolecules
Proteins Lipids Polysaccharides Nucleic acids
Catabolism
Anabolism
ADP+Pi
NAD+
FAD
ATPNADH2
FADH2
Ingestion
Nutrients
• Carbohydrates• Proteins• Lipids• Inorganic
Digestion, transport
Metabolic reaction
Molecular and cellular action
Main nutrients
Carbohydrates Proteins Lipids
Digestion DigestionDigestion
Sugars Aminoacids Fatty acids + glycerol
Carbohydrates metabolic pathway
Digestion
AbsorbtionGlucose
Liver
Glycolysis +TCA
Glycogenesis
Triglycerids
Energy
Storage
VLDL
Adipose tissueSystem circulation
Protein metabolic pathway
Digestion
Absorbtion
Aminoacids
Liver
Peripheraltissue (muscle)
Protein synthesis
Energy
Energy
Oxidation
Oxidation
Lipid methabolic pathway
Digestion
Absorbtion
TriacylgliceridsIn chylomicrons
Glycerol
Fatty acid
Lipase
Liver
MuscleEnergy
Adipose tissue
Glucose
Fat (storage)
Nutrients, Organs, and Circulation
Matthews et al 2003 Fig 23.1
Two condition of organism
Fed state Fasting state
• Overnight fasting• Prolonged fasting• Long term physical• activity
Distihguish them
Fed state Fasting state
•Blood glucose level is low
•Liver glycogen is used
•Overall energy supply is
unsufficient
• Action is required
• Mostly catabolic pathways
are activated
•Blood glucose level is high
•Liver glycogen is restored
•Energy supply is effecient
•Storage processes are activated
•Mostly anabolic pathways are
activated
Hormonal control• Insulin and glucagon are two main hormones
controlling glucose methabolism
• Insulin – fed state hormone
• Insuline provides glycolysis, glicogen and fatty
acid synthesis
• Glucagon – fasting state hormone
• Glucagon provides gluconeogenesis, glicogen
and fatty acids decomposition
Major Events: Storage, Retrieval, & Use of “Fuels”
Matthews et al 2003 Fig 23.4
Major metabolic pathways
1. Fuel oxidation2. Fuel storage3. Synthetic pathways4. Waste-disposal pathway
Energy value of foodBiofuels
•Carbonydrates•Lipids•Proteins
Digestion
Waste products:CO2
H2ONH4
+
ADP + Pi
ATP
Ready-to-use energy mostly is used as an ATP
What is ATP?
Adenosine Triphosphate (ATP)
• ATP + H2O ADP + Pi G°´ = -30.5 kJ mol-1
• ATP + H2O AMP + PPi G°´ = -45.6 kJ mol-1
ATP as an energy equivalent. Energy coupling
ATP provides energy by the process of group transfers and not by simple hydrolysis.
OH
COOH
CH
CH2
CH2
CO
NH2
+ NH3
ATP ADP+Pi
NH2
COOH
CH
CH2
CH2
CO
NH2
O
COOH
CH
CH2
CH2
CO
NH2
P
O
OHOH
ATP
ADP+Pi NH3
Reaction ΔG (kJ/mol)
Glu + Pi = Glu-6-P +14 (unfavorable)
ATP = ADP +Pi -31 (favorable)
Glu+ ATP=Glu-6-P + ADP -17 (favorable)
Total reaction
Glu+ ATP + NH3=Gln + ADP + Pi
ATP role in cell
• ATP supplies energy for biosynthesis processes
• ATP supplies energy for movement and muscle contraction
• ATP provide energy for transmembrane transport
• ATP used for DNA/RNA synthesis• ATP used for heat emission
Basal metabolic rate (BMR)• Rate of energy expenditure by humans and
other animals at rest• Measured in kJ per hour per kg body mass
Basal metabolic
rate
Thermogenesis
Activity
Total energy consumption
Basal metabolic rate (BMR)
Function BMR,%
Service
Kidney (Na+ transport) 6-7
Heart 9-11
Nervous system 15-20
Respiration 6-7
Repair
Protein resynthesis 10-15
Triacylglycerol resynthesis 1-2
Transmembrane potential (Na+ transport ) 20-25
BMR calculationThe Original Harris-Benedict Equation:
For men
For women
The Katch-McArdle Formula (Resting Daily Energy Expenditure):
The Mifflin St Jeor Equation:
, where s is +5 for males and −161 for females.
, where LBM is the lean body mass in kg
Energy transformation
• Energy of chemical bonds must be transformed into energy rich compounds (ATP, creatine-P)
• 1) C6H12O6 + O2 = 6CO2 +6H2O +Q → no cash energy
• 2) C6H12O6 + O2 +36ADP + 36Pi → 6CO2 +H2O +36ATP + Q → 36 ATP cash energy
Energy flow in cell
Lehninger 2002 Fig III.1
Energy containingnutrients
Carbohydrates Proteins Fats
Energy depleted end products
CO2
H2O NH3
Precursor molecules
Aminoacids Sugars Fatty acids Nitrogen bases
Cell macromolecules
Proteins Lipids Polysaccharides Nucleic acids
Catabolism
Anabolism
ADP+Pi
NAD+
FAD
ATPNADH2
FADH2
Energy flow in cell
• 1) C6H12O6 + O2 = 6CO2 +6H2O +Q• 2) C6H12O6 + O2 +36ADP + 36Pi = 6CO2 +H2O
+36ATP + Q → 36 ATP cash energy• 1st pathway can be easily realized→ no cash
energy• 2nd pathway requiers multireaction pathway →
36 ATP cash energy
Energy flow in cell
Glicolysis
TCA cycle
Electron transfer chainOxidative phosphorilation
Lipids Carbohydrates Proteins
FA + Glycerol Glucose Aminoacids
Pyruvate
AcetylCoenzymeA
СО2
TCA
H+ + ē ETC + ATP synthase
ADP+ P
ATP
+ О2
I. Preparation stage
II.Intermediate stage
III.Terminal stage
Н2О
- NH3
Acetyl-CoA (AcCoA)
http://2012books.lardbucket.org/books/introduction-to-chemistry-general-organic-and-biological/s23-03-overview-of-stage-ii-of-catabo.html
High energy bond
Acetyl-CoA methabolic pathways
http://2012books.lardbucket.org/books/introduction-to-chemistry-general-organic-and-biological/s23-03-overview-of-stage-ii-of-catabo.html
Glucose can not be synthesized from AcCoA
PDH
Pyruvate dehydrogenase
NAD+ NADH
COOH
CH3
O HS-CoA
S-CoA
CH3
O CO2+C C +
PDH regulation
PDH
PDH P
Active
Inactive
PDH phosphorylasePDH kinase+++ • Insulin
• Ca2+
+++• ATP• AcCoA• NADH
TCA cycle• TCA cycle – tricarboxylic acids cycle, Krebs cycle,
citric acid cycle
• Main instrument for fuel transformation into ATP
• Pyruvate (actually acetate) from glycolysis is
degraded to CO2
• Some ATP is produced
• More NADH is made
• NADH goes on to make more ATP in electron
transport and oxidative phosphorylation
TCA cycle• Anapleurotic pathway (both catabolic and
anabolic pathways)• Takes place in mitochondria matrix• Stars from AcCoA obtained from pyruvate or
other sourses
3NAD+ + FAD + GDP + Pi + acetyl-CoA →
3NADH + FADH + GTP + CoA + 2CO2
Overall reaction
TCA cycle
• Pyruvate enters TCA cycle as an AcCoA
• Pyruvate is oxidatively decarboxylated to form
acetyl-CoA by pyruvate dehydrogenase (PDH)
• Pyruvate dehydrogenase uses TPP, CoASH,
lipoic acid, FAD and NAD
• NADH & succinyl-CoA are allosteric inhibitors
Step 1 – Citrate Synthase• Only step in TCA cycle that involves the formation of a
C-C bond
CH3S
O
CoA
O
OH
O
O
OHO OH
O
OHOH
O
OH
+
OH2
SH CoA
Acetyl-CoA
Oxaloacetate
Citrate
Step 2 - Aconitase
Citrate Cis-aconitate Iso-citrate
CH2
C
CH2HOOC
OHHOOC
COOHCH2
C
CHHOOC
HOOC
COOH
OH
CH2
CH
CHHOOC
HOOC
COOHOH2
OH2
Step 2 - AconitaseAconitase uses an iron-sulfur cluster
Step 3 – Isocitrate Dehydrogenase
• Classic NAD+ chemistry (hydride removal)
followed by a decarboxylation
• Isocitrate dehydrogenase is a link to the
electron transport pathway because it makes
NADH
Step 3 – Isocitrate Dehydrogenase
Isocitrate Oxalosuccinate α-Ketoglutarate
OH
CH2
CH
CHHOOC
HOOC
COOH
O
CH2
CH
CHOOC
HOOC
COOHNAD+ NADH,H+ CO2
O
CH2
CH2
CHOOC
COOH
Step 4 -α-Ketoglutarate Dehydrogenase
• Similar to pyruvate dehydrogenase - structurally and mechanistically
• Five coenzymes used - TPP, CoASH, Lipoic acid, NAD+, FAD
COOH
CH2
CH2
COOH
O
NADH+CO2
COOH
CH2
CH2
S-CoA
Oα-Ketoglutarate Dehydrogenase
α-Ketoglutarate Succinyl-CoA
Step 5 - Succinyl-CoA Synthetase
• A nucleoside triphosphate is made• Its synthesis is driven by hydrolysis of a CoA
ester
GDP + Pi → GTP + CoA
S C
CH2
CH2
COOH
OCoAOH C
CH2
CH2
COOH
OSuccinyl-CoA Synthetase
Succinyl-CoA Succinate
Step 6 - Succinate Dehydrogenase
• Mechanism involves hydride removal by FAD
and a deprotonation
• This enzyme is actually part of the electron
transport pathway in the inner mitochondrial
membrane
• The electrons transferred from succinate to FAD
(to form FADH2) are passed directly to
ubiquinone (UQ) in the electron transport
pathway
OH C
CH2
CH2
COOH
O
OH C
CH
CH
COOH
O
Step 6 - Succinate Dehydrogenase
FAD FADH2
Succinate dehydrogenase
Succinate Fumarate
Step 7 - Fumarase
H2O
Fumarase
OH
OH C
CH2
CH
COOH
O
OH C
CH
CH
COOH
O
Fumarate Malate
Step 8 - Malate Dehydrogenase
• This reaction is energetically expensive (ΔGo' = +30 kJ/mol )
OH
OH C
CH2
CH
COOH
O
O
OH C
CH2
C
COOH
O
Malate Oxaloacetate
NAD+ NADH2
Malate Dehydrogenase
AcCoA fate in TCA
TCA total ATP outcome
• Acetyl-CoA + 3 NAD+ + Q + GDP + Pi +2 H20
HS-CoA + 3NADH + QH2 + GTP + 2 CO2 + 2 H+
• Isocitrate Dehydrogenase 1 NADH=2.5 ATP
• α-ketoglutarate Dehydrogenase 1 NADH=2.5 ATP
• Succinyl-CoA Synthetase 1 GTP=1 ATP
• Sunccinate Dehydrogenase 1 QH2=1.5 ATP
• Malate Dehydrogenase 1 NADH=2.5 ATP
• Total of 10 ATPs gained from oxidation of 1 Acetyl-CoA
TCA total ATP outcome
Glucose
2x Pyruvate2 NADH 52 ATP
ATP equivalentsATP equivalents
2x Acetyl CoA 2 NADH 5
TCA6 NADH 15
2 ATP or GTP
Substrate levelphosphorylation
Oxidativephosphorylation
Total: 32 ATP28 ATP4 ATP
Sequence of reactions
+ Pyruvate
Glucose
Aerobic and anaerobic glycolysis ATP production
Anaerobic Glycolisis
CoA2x + CO2
Aerobic Glycolisis
TCA, ETC, OP
Lactate
32 ATP 2 ATP
Regulation of the TCA Cycle
• Citrate synthase - ATP, NADH, citrate and succinyl-
CoA inhibit
• Isocitrate dehydrogenase - ATP inhibits, ADP and
NAD+ activate
· α -Ketoglutarate dehydrogenase - NADH and
succinyl-CoA inhibit, AMP activates
• Pyruvate dehydrogenase: ATP, NADH, acetyl-CoA
inhibit, NAD+, CoA activate
• NADH/NAD+ strongly affects on TCA cycle
Regulation of the TCA Cycle
Inhibition
Activation
Citrate
NADH
Ca2+
Isocitrate
α-ketoglutarate
Succinyl-CoASuccinate
Fumarate
Malate
OxaloacetateO
OH C
CH2
C
COOH
O
CH2
CCH2
HOOC
OHHOOC
COOH
OH
CH2
CH
CHHOOC
HOOC
COOH
O
CH2
CH2
CHOOC
COOH
S C
CH2
CH2
COOH
OCoA
OH C
CH2
CH2
COOH
O
OH C
CH
CH
COOH
O
OH
OH C
CH2
CH
COOH
O
ATP
ADP
Pyruvate 1
2
3
4
Irreversible steps of TCA cycle1. Pyruvate dehydrogenase2. Citrate synthase3. Isocitrate dehydrogenase4. α-ketoglutarate dehydrogenase
Aminoacids income into TCA cycle
SerineAlanineTryptophanTyrosineCysteine
Glycine Threonine
AsparagineAspartate
ArginineGlutamineHistidineProline
FumarateGlutamateα-Ketoglutarate
Acetyl CoA
Pyruvate
LeucineLysinePhenylalanineThreonineTryptophanTyrosine