Bioenergetics

BiochemistryCollege of Life SciencesZhejiang University

Wei-Jun Yang [email protected]://marine:[email protected]/

I Introduction

II Foundations of Biochemistry

III Structure and Catalysis and

Information Pathways

V Bioenergetics and Metabolism

III Bioenergetics and Metabolism13 Principle of Bioenergetics14 Glycolysis and the Catabolism15 The Citric Acid Cycle16 Oxidation of Fatty Acid17 Amino Acid Oxidation and the Production of Urea18 Oxidative Phosphorylation and Photophosphrylation19 Carbohydrate Biosynthesis20 Lipid Synthesis 21 Biosynthesis of Amino Acids, Nucleotides, and

Related Molecules22 Integration and Hormonal Regulation of Mammalian

Metabolism

Four Functions of Metabolism:

1. To obtain chemical energy by capturing solar energy

or by degradation of energy-rich nutrients from the

environment .

2. To convert nutrient molecules into the cell's own

characteristic molecules.

3. To polymerize monomeric precursors into

macrobiomolecules (proteins, nucleic acids, lipids,

polysaccharides).

4. To synthesize and degrade biomolecules required in

specialized cellular functions.

Three Major Types of Energy Transformation

Photosynthesis Cellular respiration Biological work

Biological Work Requires Energy

Hydrothermal vent（热液口）

Two Groups of Metabolism1. Autotrophs (自养生物，such as photosynthetic

bacteria and higher plants) can use carbon dioxide from the atmosphere as their sole source of carbon, from which they construct all their carbon-containing biomolecules.

2. Heterotrophs（异养生物）cannot use atmospheric carbon dioxide and must obtain carbon from their environment in the form of relatively complex organic molecules, such as glucose, proteins.

Energy relationships between catabolic and anabolic pathways

Catabolism（异化作用）: The pathway degrade organic nutrients into simple end products in order to extract chemical energy and convert it into a form useful to the cell.Anabolism（同化作用）:The pathway start with small precursor molecules and convert them to larger and more complex molecules and require the input of energy.

Energy relationships between catabolic and anabolic pathways

Three types of molecular metabolic pathwaysa; Converging catabolic b; Diverging anabolicc; Cyclic pathway

14 Principle of Bioenergetics

*** Bioenergetics and Thermodynamics

*** Phosphoryl Group Transfers and ATP

*** Biological Oxidation-Reduction Reaction

Two Laws of Thermodynamics

The First Law;The total energy in the universe does not change

Biological Energy Transformations Follow the Laws of Thermodynamics

The second Law;The entropy (disorder) of the universe is increasing

Biological Energy Transformations

Follow the Laws of Thermodynamics

Three thermodynamic quantities;

1. Gibbs free energy (G) and free-energy change, ΔG

2. Enthalpy (H) and Enthalpy change ΔH

3. Entropy (S) and Entropy change ΔS

Gibbs Free Energy (G);

expresses the amount of energy capable of doing work

during a reaction at constant temperature and pressure.

Free-energy Change (ΔG);

When ΔG°' is negative, the products contain less free

energy than the reactants. The reaction will therefore

proceed spontaneously to form the products under

standard conditions.

When ΔG°' is positive, the products of the reaction

contain more free energy than the reactants. The reaction

will therefore tend to go in the reverse direction if we start

with 1.0 M concentrations of all components.

The units of ΔG is joules/mole or calories/mole

Enthalpy (H，焓);

is the heat content of the reacting system. It reflects the

number and kinds of chemical bonds in the reactants

and products.

Enthalpy Change (ΔH);

When a chemical reaction releases heat, it is said to be

exothermic; the heat content of the products is less

than that of the reactants and ΔH has a negative value.

Reacting systems that take up heat from their

surroundings are endothermic and have positive values

of ΔH.

The units of ΔH is joules/mole or calories/mole

Entropy (S，熵);

is a quantitative expression for the randomness or

disorder in a system.

Entropy Change (ΔS);

When the products of a reaction are less complex and

more disordered than the reactants, the reaction is said

to proceed with a gain in entropy (p. 72).

The units ΔS is joules/mole•degree Kelvin.

In Biological Systems

(at constant temperature and pressure)

ΔG = ΔH - TΔS

T is the absolute temperature.

When entropy increases, ΔS has a positive sign. When

heat is released by the system to its surroundings, ΔH

has a negative sign. Either of these conditions, which

are typical of favorable processes, will tend to make

ΔG negative. In fact, ΔG of a spontaneously reacting

system is always negative.

Actual Free energy Changes Depend on the Concentration of Reactants and Products

ΔG°' = -RT ln K'eq

ATP: Adenosin triphosphate

ADP: Adenosin diphosphate

AMP: Adenosin monophosphate

Major Function of ATP in Cells

Heterotrophic cells obtain free energy in a chemical

form by the catabolism of nutrient molecules and use

that energy to make ATP from ADP and Pi. ATP then

donates some of its chemical energy to endergonic

processes such as the synthesis of metabolic

intermediates and macromolecules from smaller

precursors, transport of substances across membranes

against concentration gradients, and mechanical

motion.

The Free-Energy Change for ATP Hydrolysis Is Large and Negative

Although its hydrolysis is highly exergonic (ΔG°' = -

30.5 kJ/mol), ATP is kinetically stable toward

nonenzymatic breakdown at pH 7 because the

activation energy for ATP hydrolysis is relatively high.

Rapid cleavage of the phosphoric acid anhydride bonds

occurs only when catalyzed by an enzyme.

The actual free energy of hydrolysis (ΔG) of ATP in living cells

is very different (not 30.5 kJ/mol).

Furthermore, the cytosol contains Mg2+, which binds to ATP

and ADP. In most enzymatic reactions that involve ATP as

phosphoryl donor, the true substrate is MgATP2- and the

relevant ΔG°' is that for MgATP2- hydrolysis.

ΔG for ATP hydrolysis in intact cells, usually designated ΔGP, is much more negative than ΔG°' in most cells ΔGP ranges from -50 to -65 kJ/mol.

Other Phosphorylated Compounds and Thioesters Also Have Large Free

Energies of Hydrolysis

1. Phosphoenolpyruvate（磷酸烯醇式丙酮酸）

2. 1,3-bisphosphoglycerate（甘油-1,3-二磷酸）

3. Phosphocreatine（磷酸肌酸）

4. Thioesters（硫酯）

Other Phosphorylated Compounds and Thioesters Also Have Large Free

Energies of HydrolysisPhosphoenolpyruvate（磷酸烯醇式丙酮酸）

1,3-bisphosphoglycerate（甘油-1,3-二磷酸）

Phosphocreatine（磷酸肌酸）

Thioesters（硫酯）

ATP Provides Energy by Group Transfers, Not by Simple Hydrolysis

Two groups of phosphate compounds in living organisms.

High-energy compounds; ΔG°' ＜ -25 kJ/mol

"low-energy" compounds; ΔG°' ＞ -25 kJ/mol

Flow of Phosphoryl Groups

The transfer of phosphate groups is one of the central

features of metabolism. Metabolic electron transfer

reactions are also of crucial importance.

The path of electron flow in metabolism is complex.

Electrons move from various metabolic intermediates

to specialized electron carriers in enzyme-catalyzed

reactions. Those carriers in turn donate electrons to

acceptors with higher electron affinities, with the

release of energy. Cells contain a variety of molecular

energy transducers, which convert the energy of

electron flow into useful work.

The Flow of Electrons Can Do Biological Work

ΔG=-nFΔE, or ΔG°'=-nFΔE'0

The energy made available to do work by this spontaneous electron flow (the free-energy change for the oxidation-reduction reaction) is proportional to ΔE:

Acetaldehyde（乙醛）is reduced by NADH:Acetaldehyde + NADH + H+ ethanol + NAD+

The relevant half reactions and their Eo values are:(1) Acetaldehyde + 2H+ + 2e- ethanol E'0 = -0.197 V (2) NAD+ + 2H+ + 2e- NADH + H+ E'0 = -0.320 V

ΔE0 = -0.197 V - (-0.320 V) = 0.123 V, and n is 2. ΔG°' = -nFΔE'0 = -2(96.5 kJ/V•mol)(0.123 V) = -23.7 kJ/mol.

Soluble Electron Carriers

1. Nicotinamide adenine dinucleotide (NAD+，

烟酰胺腺嘌呤二核苷酸)

2. Nicotinamide adenine dinucleotide

phosphate (NADP+，磷酸烟酰胺腺嘌呤二核苷酸)

3. Flavin mononucleotide (FMN，黄素单核苷酸)

4. Flavin adenine dinucleotide (FAD，黄素腺嘌呤

二核苷酸)

NADH and NADPH Act with Dehydrogenases（脱氢酶）as Soluble Electron Carriers

Flavoproteins Contain Flavin（黄素）Nucleotides

1. Glycolysis: two phases and ten steps of glycolysis

（第6组）

2. Three fates of pyruvate under aerobic and

anaerobic conditions（第7组）

3. Microbial fermentations yield alcohol and other

end products of commercial value （第8组）

4. Feeder pathways for glycolysis（第9组）

5. Regulation of carbohydrate catabolism（第10组）

6. The pentose phosphate pathway of glucose

oxidation（第11组）

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