Chp 6 Metabolism
Transcript of Chp 6 Metabolism
MetabolismMetabolism::
Key wordsKey words• Metabolism – definition• Catabolism and anabolism – definition, example• Identify/distinguish structure of coenzymes• Identify structure of ATP
What is Metabolism?What is Metabolism?• Definition: Metabolism is the sum total of the
chemical reactions of biomolecules in an organism• Metabolism consists of
1.1. Catabolism: Catabolism: the breakdown of larger molecules into smaller ones, an oxidative process releases energyreleases energy
2.2. Anabolism: Anabolism: the synthesis of larger molecules from smaller ones, a reductive process that requires energy
• Catabolism:Catabolism: the oxidative breakdown of nutrients
• Anabolism:Anabolism: the reductive synthesis of biomolecules
Terminology in MetabolismTerminology in Metabolism
• Metabolic pathway: A sequence of reactions, where the product of one reaction becomes the substrate for the next reaction.- either linear pathway or cyclic pathway- metabolic pathways proceed in many stages, allowing for efficient use of energy
• Metabolites: intermediat es in metabolic pathway
Eg. 6 CO2(g) + 6 H2O(l) → C6H12O6(aq) + 6 O2(g)
C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O
light
photosynthesis
respiration
Metabolic Metabolic pathwaypathway
Metabolic pathway: linear or cyclicMetabolic pathway: linear or cyclic
A Comparison of Catabolism and A Comparison of Catabolism and AnabolismAnabolism
• Metabolism is the sum total of the chemical reactions of biomolecules in an organism
MetabolismMetabolism• Metabolism involves the energy flow in the cell• Photoautotroph via photosynthesis transfers the
energy to heterotrophs• Heterotrophs obtain the energy through
oxidation/reduction of organic compounds (carbohydrate, lipid and proteins)
• Food supplies the energy• Energy = ATP
The Role of Oxidation and Reduction in The Role of Oxidation and Reduction in MetabolismMetabolism
• Oxidation-Reduction (redox) reactions are those in which electrons are transferred from a donor to an acceptor– oxidation:oxidation: the loss of electrons; the substance that loses
the electrons is called a reducing agentreducing agent– reduction:reduction: the gain of electrons; the substance that gains
the electrons is called an oxidizing agentoxidizing agent• Carbon in most reduced form- alkane• Carbon in most oxidized form- CO2 (final product of
catabolism)Reduced Oxidized
Oxidation and Reduction in MetabolismOxidation and Reduction in Metabolism
CH3CH2OH + 2H+ + 2e-
Ethanol Acetaldehyde
NAD+ + H+ + 2e- NADH
CH3CH2OH + NAD+ + NADH +H+
CH3CHO
CH3CHO
CH3CHCOO-OH
+ 2H+ + 2e-
Pyruvate Lactate
NAD+NADH + H+ + 2e-
+ H++ NADH CH3CHCOO-OH
+ NAD+
CH3CCOO-O
CH3CCOO-O
Oxidation of ethanol by NAD+
Reduction of pyruvate by NADH
Oxidation – less e
Reduction – gain e
Oxidizing agent – e acceptor
reducing agent – e donor
Metabolism: FeaturesMetabolism: Features
Metabolic pathway:1. Enzymes – multienzymes 2. Coenzymes3. ATP – produced or used
Regulation of metabolic pathway:– Feedback inhibition or – Feed-forward activation
Metabolism: RegulationMetabolism: Regulation
• Regulation of metabolic pathway: 1. Feedback inhibition = product (usually ultimate product)
of a pathway controls the rate of synthesis through inhibition of an early step (usually the first step)
A B C D E P
2. Feed-forward activation = metabolite produced early in pathway activates enzyme that catalyzes a reaction further down the pathway
A B C D E P
E1 E2 E3 E4 E5
E1 E2 E3 E4 E5
—
+
CoenzymesCoenzymes
Coenzymes in metabolism:• NAD+/NADH • NADP+/NADPH• FAD+/FADH2
• Coenzyme A (CoASH) – activation of metabolites
Electron carriers
NADNAD++/NADH: An Important Coenzyme/NADH: An Important Coenzyme• Nicotinamide adenine
dinucleotide (NAD+) is an important coenzyme
• Acts as a biological oxidizing agent
• The structure of NAD+/NADH is comprised of a nicotinamide portion.
• It is a derivative of nicotinic acid
• NAD+ is a two-electron oxidizing agent, and is reduced to NADH
Reduced form, NADH carries 2 electrons
NADPNADP++/NADPH: /NADPH: Also comprised of nicotinamide portionAlso comprised of nicotinamide portion
• Nicotinamide adenine dinucleotide phosphate (NADP+) – oxidizing agent
• NADPH involves in reductive biosynthesis
• Differ with NAD+ at ribose (C2 contain a phosphoryl group, PO3
2-
• As electron carrier in photosythesis and pentose phosphate pathway
Reduced form, NADPH carries 2 electrons Anabolism
The Structures Flavin Adenine The Structures Flavin Adenine Dinucleotide (FAD)Dinucleotide (FAD)
• FAD is also a biological oxidizing agent
• FAD – can accept one-electron or two-electron
FADH carries 1 electron, FADH2 carries 2 electrons
The terminal e acceptor (O2) can accept only unpaired e (e must be transferred to O2 one at a time)
FAD/FADHFAD/FADH22
• FADH (semiquinone form) carries 1 electron,
• FADH2 (fully reduced hydroquinone form) carries 2 electrons
1
1
*
Formation of fully reduced hydroquinone form bypass the semiquinone form
Coenzyme A in Activation of Metabolic Coenzyme A in Activation of Metabolic PathwaysPathways
• A step frequently encountered in metabolism is activation– activationactivation:: the formation of a more reactive
substance – A metabolite is bonded to some other molecule
and the free-energy change for breaking the new bond is negative.
– Causes next reaction to be exergonic
Coenzyme A (CoASH)Coenzyme A (CoASH)• Coenzyme A – functions as a
carrier of acetyl and other acyl groups
• Has sulfhydryl/thiol group
Thioester bond
Acetyl-CoA: is a “high-energy” compound because of the presence of thioester bond – hydrolysis will release energy
CoASH
• ATP is essential high energy bond-containing compound
• Phosphorylation of ADP to ATP requires energy
• Hydrolysis of ATP to
ADP releases energyPhosphorylation: the addition of phosphoryl (PO3
2-) group/Pi (inorganic phosphate)
ATP- high energy compoundATP- high energy compound
nucleotide
MetabolismMetabolism::
(2)(2)
• ATP is essential high energy bond-containing compound
• Phosphorylation of ADP to ATP requires energy
• Hydrolysis of ATP to
ADP releases energyPhosphorylation: the addition of phosphoryl (PO3
2-) group/Pi (inorganic phosphate)
ATP- high energy compoundATP- high energy compound
nucleotide
• “High Energy” bonds- bonds that require or release convenient amounts of energy, depending on the direction of the reaction
• Couple reactions: the energy released by one reaction, such as ATP hydrolysis, provides energy for another reactions to completion – in metabolic pathway
The Phosphoric Anhydride Bonds in ATP are The Phosphoric Anhydride Bonds in ATP are “High Energy” Bonds“High Energy” Bonds
Phosphoanhydride /
Couple reaction: exampleCouple reaction: example
Role of ATP as Energy CurrencyRole of ATP as Energy Currency
Phosphorylation of ADP requires energy from breakdown of nutrients (catabolism)
The energy from hydrolysis of ATP will be used in the formation of products (anabolism)
Metabolism of CarbohydrateMetabolism of Carbohydrate
Catabolism
Anabolism
Major pathways of carbohydrate metabolism.
Fig 8.1 3rd ed
Key wordsKey words• Glycolysis, the fate for pyruvate• Substrate-level phosphorylation and oxidative
phosphorylation
GlycolysisGlycolysis• Glycolysis is the first stage of glucose
metabolism
• Glycolysis converts 1 molecule of glucose to 2 units of pyruvate (three C units) and the process involves the synthesis of ATP and reduction of NAD+ (to NADH)
• The pathway has 10 steps/reactions
• Glycolysis are divided into 2 stages/phases, Phase 1=1st 5 reactionsPhase 2=2nd 5 reactions
Linear pathway
12
GlycolysisGlycolysis• Glycolysis are divided into 2 stages/phases,
1. Phase 1=1st 5 reactions - energy investment A hexose sugar (glucose) is split into
2 molecules of three-C metabolite (glyceraldehyde-3-phosphate = GAP).
2. Phase 2=2nd 5 reactions – energy recovery The two molecules of GAP are converted to
2 molecules of pyruvate with the generation of 4 ATP and 2 NADH
Overall equation –Glucose + 2 NAD+ + 2 ADP + 2Pi
2 pyruvate + 2 NADH + 2 ATP + 2 H2O + 4H+
Glycolysis has a net “profit” of 2 ATP per glucose
The Reactions of The Reactions of GlycolysisGlycolysis1. Phosphorylation of glucose to give
glucose-6-phosphate2. Isomerization of glucose-6-
phosphate to give fructose-6-phosphate
3. Phosphorylation of fructose-6-phosphate to yield fructose-1,6-bisphosphate
4. Cleavage of fructose-1,6,-bisphosphate to give glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
5. Isomerization of dihydroxyacetone phosphate to give glyceraldehyde-3-phosphate – isomerase enzyme
1
2
3
4
5
Use ATP
Use ATP
glucokinase
phosphofructokinase
The Reactions of Glycolysis (Cont’d)The Reactions of Glycolysis (Cont’d)6. Oxidation of glyceraldehyde-3-
phosphate to give 1,3-bisphosphoglycerate
7. Transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to give 3-phosphoglycerate
8. Isomerization of 3-phosphoglycerate to give 2-phosphoglycerate
9. Dehydration of 2-phosphoglycerate to give phosphoenolpyruvate
10. Transfer of a phosphate group from phosphoenolpyruvate to ADP to give pyruvate
oxidation
transfer
isomerization
dehydration
transfer
Phosphorylation of ADP to ATP
Phosphorylation of ADP to ATP
6
7
8
9
10
Electron acceptor – NAD+
Glyceraldehyde-3-P dehydrogenase
GlycolysisGlycolysis• Dephosphorylation of ATP• Phosphorylation of ADP
• Oxidation of intermediates and reduction of NAD+ to NADH by dehydrogenase reactions- step 6 - glyceraldehyde-3-phosphate dehydrogenase
By kinase enzyme at step 1, 3, 7 and 10
ATP productionATP production• ATP is produced by phosphorylation of ADP - is
through substrate-level phosphorylation• Substrate-level phosphorylation – the process of
forming ATP by phosphoryl group transfer from reactive intermediates to ADP
• 1,3-bisphosphoglycerate and phosphoenolpyruvate – “high-energy” intermediates/compounds
• Oxidative phosphorylation – the process of forming ATP via the pH gradient as a result of the electron transport chain.
Glycolysis - Step 7 and 10
Fates of Pyruvate From GlycolysisFates of Pyruvate From Glycolysis• Once pyruvate is formed, it
has one of several fates
• In aerobic metabolism-
pyruvate will enter the citric acid cycle, end product in aerobic metabolism CO2 and H2O
• In anaerobic metabolism- the pyruvate loses CO2
produce ethanol = alcoholic fermentation
produce lactate = anaerobic glycolysis
Anaerobic Metabolism of PyruvateAnaerobic Metabolism of Pyruvate• Under anaerobic conditions, the most important pathway for the
regeneration of NAD+ is reduction of pyruvate to lactate• Lactate dehydrogenase (LDH) is a tetrameric isoenzyme consisting
of H and M subunits; H4 predominates in heart muscle, and M4 in skeletal muscle In muscle, during vigorous exercise –
demand of ATP but O2 is in short supply is largely synthesized via anaerobic glycolysis which rapidly generates ATP rather than through slower oxidative phosphorylation
Alcoholic Fermentation Alcoholic Fermentation • Two reactions lead to the production of ethanol:
– Decarboxylation of pyruvate to acetaldehyde
– Reduction of acetaldehyde to ethanol
• Pyruvate decarboxylase is the enzyme that catalyzes the first reaction
• This enzyme require Mg2+ and the cofactor, thiamine pyrophosphate (TPP)
• Alcohol dehydrogenase catalyzes the conversion of acetaldehyde to ethanol
In anaerobic bacteria
NADNAD++ Needs to be Recycled to Prevent Decrease in Needs to be Recycled to Prevent Decrease in Oxidation ReactionsOxidation Reactions
Structure of cell Structure of cell
Cytoplasm/
Cytosol
TYPICAL PROKARYOTIC CELL
Cytosol
Where does the Glycolysis Take Place?Where does the Glycolysis Take Place?
Glycolysis is universal!
Citric Acid Cycle
= Krebs Cycle, Tricarboxylic acid Cycle
(TCA)
Key wordsKey words• Definition – citric acid cycle• Explain the citric acid cycle• Distinguish between glycolysis and citric acid cycle• Understand -oxidation – catabolism of lipid
Citric acid cycle Citric acid cycle
• Requires aerobic condition• Amphibolic (both catabolic & anabolic)
• Serves 2 purposes:
Citric Acid Cycle
= Krebs Cycle
= Tricarboxylic acid Cycle
(TCA)
TCATCA• Circular pathway• Two-carbon unit
needed at the start of the citric acid cycle
• The two-carbon unit is acetyl-CoA
• Involves 8 reactions• The overall reaction
from 1 acetyl-CoA produce 3 NADH, 1 FADH2, 2 CO2 and 1 GTP (equivalent to 1 ATP)
Pyruvate is converted to Acetyl-CoA – Pyruvate is converted to Acetyl-CoA – activation of pyruvateactivation of pyruvate
• Pyruvate dehydrogenase complex is responsible for the conversion of pyruvate to acetyl-CoA
• Five enzymes in complex• Requires the presence of cofactors TPP (thymine
pyrophosphate), FAD, NAD+, and lipoic acid and coenzyme A (CoA-SH)
• The overall reaction of the pyruvate dehydrogenase complex is the conversion of pyruvate, NAD+, and CoA-SH to acetyl-CoA, NADH + H+, and CO2
Thioester, high energy compound
Oxidation of pyruvate and reduction of NAD+
3C
2CPyruvate = pyruvic acid
Features of TCAFeatures of TCA• Circular pathway• Two-carbon unit needed
at the start of the citric acid cycle
• The two-carbon unit is acetyl-CoA
• Involves 8 reactions• The overall reaction from
1 acetyl-CoA produce 3 NADH, 1 FADH2, 2 CO2
and 1 GTP (equivalent to 1 ATP)
How about 1 molecule of glucose?
X 2
Electron acceptor – NAD+ and FAD
Mitochondrial matrix
Where does the Citric Acid Cycle Take Place?Where does the Citric Acid Cycle Take Place?
• In eukaryotes, cycle takes place in the mitochondrial matrix
In prokaryotes? Cytoplasm
The Central Relationship of the Citric The Central Relationship of the Citric Acid Cycle to CatabolismAcid Cycle to Catabolism
• TCA involves 8 series of reactions that oxidizes the acetyl group of acetyl-CoA to 2 molecules of CO2
and the energy is conserves in NADH, FADH2 and “high-energy” compound, GTP
• Acetyl-CoA – synthesize from pyruvate (glycolysis product)
Guanosine – Tri-Phosphate
Aerobic catabolismAerobic catabolism
• NADH, FADH2 from glycolysis and TCA will enter the Electron Transport Chain (ETC) to produce more ATP (oxidative phosphorylation)
• 1 NADH = 2.5 ATP,
• 1 FADH2 = 1.5 ATP
• ETC take place in mitochondria - inner membrane (eukaryotes)
In prokaryotes?
In ETC
Oxidation of Pyruvate Forms COOxidation of Pyruvate Forms CO22 and ATP and ATP
Aerobic metabolism is more efficient than anaerobic metabolism
Citric acid cycle - amphibolic Citric acid cycle - amphibolic • Amphibolic (both catabolic
& anabolic)• Serves 2 purposes:
1. Oxidize Acetyl-CoA to CO2 to produce energy (ATP & reducing power of NADH & FADH2)-involved in the aerobic catabolism of carbohydrates, lipids and amino acids
2. Supply precursors for biosynthesis (anabolism) of carbohydrates, lipids, amino acids, nucleotides and porphyrins
Replenish TCA- catabolism of amino a. and fatty a.
Anabolic pathway
Require aerobic condition
Differences between glycolysis & TCA Differences between glycolysis & TCA cyclecycle
• Glycolysis is a linear pathway; TCA cycle is cyclic
• Glycolysis occurs in the cytosol and TCA is in the mitochondrial matrix
• Glycolysis does / does not require oxygen; TCA requires oxygen (aerobic)
Lipids are Involved in Generation and Lipids are Involved in Generation and Storage of EnergyStorage of Energy
• The oxidation of fatty acids (FA)in triacylglycerols are the principal storage form of energy for most organisms– Their carbon chains are in a highly reduced form– The energy yield per gram of fatty acid oxidized is greater
than that per gram of carbohydrate oxidized
C6H12O6 + 6O2
CH3(CH2)14COOH + 23O2
6CO2 + 6H2O
16CO2 +16H2O
-15.9
-38.9Palmitic acid
Glucose
Energy(kJ•mol-1)
Catabolism of Lipids - triacylglycerolCatabolism of Lipids - triacylglycerol• Lipases catalyze hydrolysis of bonds between fatty acid and
the rest of triacylglycerols• Phospholipases catalyze hydrolysis of bonds between fatty
acid and the rest of phosphoacylglycerols • May have multiple sites of action
Catabolism of fatty acid - Catabolism of fatty acid - -Oxidation-Oxidation• -Oxidation:-Oxidation: a series
of reactions that cleaves carbon atoms two at a time from the carboxyl end of a fatty acid
• The complete cycle of one -oxidation requires four enzymes/steps
• Take place in mitochondria matrix
1 round of -oxidation = yield 1 NADH, 1 FADH2 and 1 acetyl-CoA
Spiral pathway
METABOLISM
REVISION
– Catabolism:Catabolism: the oxidative breakdown of nutrients
– Anabolism:Anabolism: the reductive synthesis of biomolecules• Catabolism – features
1. Release energy (ADP ATP)
2. Oxidizing agent (NAD+, FAD)
• Anabolism – features
1. Use energy (ATP ADP)
2. Reducing agent (NADH ,FADH2)
Metabolism – the sum total of biochemical reaction carried out by organism
MetabolismMetabolism• Metabolism involves the energy flow in the cell• Photoautotroph via photosynthesis transfers the
energy to heterotrophs• Heterotrophs obtain the energy through
oxidation/reduction of organic compounds (carbohydrate, lipid and proteins)
• Food supplies the energy• Energy = ATP
Major pathways of carbohydrate metabolism.
Fig 8.1 3rd ed
GlycolysisGlycolysis• Glycolysis is the first stage of glucose
metabolism
• Glycolysis converts 1 molecule of glucose to 2 units of pyruvate (three C units) and the process involves the synthesis of ATP and reduction of NAD+ (to NADH)
• The pathway has 10 steps/reactions
• Glycolysis are divided into 2 stages/phases, Phase 1=1st 5 reactionsPhase 2=2nd 5 reactions
Linear pathway
Fates of Pyruvate From GlycolysisFates of Pyruvate From Glycolysis• Once pyruvate is formed, it
has one of several fates
• In aerobic metabolism-
pyruvate will enter the citric acid cycle, end product in aerobic metabolism CO2 and H2O
• In anaerobic metabolism- the pyruvate loses CO2
produce ethanol = alcoholic fermentation
produce lactate = anaerobic glycolysis
Glycolysis – in cytoplasm
• ATP is essential high energy bond-containing compound
• Phosphorylation of ADP to ATP requires energy
• Hydrolysis of ATP to
ADP releases energyPhosphorylation: the addition of phosphoryl (PO3
2-) group/Pi (inorganic phosphate)
ATP- high energy compoundATP- high energy compound ATP – energy carrier / an
energy transfer agent
nucleotide
Coenzyme A (CoASH)Coenzyme A (CoASH)• Coenzyme A – functions as a
carrier of acetyl and other acyl groups
• Has sulfhydryl/thiol group
Thioester bond
Acetyl-CoA: is a “high-energy” compound because of the presence of thioester bond – hydrolysis will release energy
CoASH
TCATCA• Circular pathway• Two-carbon unit
needed at the start of the citric acid cycle
• The two-carbon unit is acetyl-CoA
• Involves 8 reactions• The overall reaction
from 1 acetyl-CoA produce 3 NADH, 1 FADH2, 2 CO2 and 1 GTP (equivalent to 1 ATP)
Citric acid cycle - amphibolic Citric acid cycle - amphibolic • Amphibolic (both catabolic
& anabolic)• Serves 2 purposes:
1. Oxidize Acetyl-CoA to CO2 to produce energy (ATP & reducing power of NADH & FADH2)-involved in the aerobic catabolism of carbohydrates, lipids and amino acids
2. Supply precursors for biosynthesis (anabolism) of carbohydrates, lipids, amino acids, nucleotides and porphyrins
Replenish TCA- catabolism of amino a. and fatty a.
Anabolic pathway
Require aerobic condition
Where does the Citric Acid Cycle Take Place?Where does the Citric Acid Cycle Take Place?
• In eukaryotes, cycle takes place in the mitochondrial matrix
In prokaryotes? Cytoplasm