Bioenergetics and Biochemical Reaction Types

Photosynthetic autotrophs Heterotrophs

bioenergeticsbioenergetics is the study of the balance between energy intake in the form of food and energy utilization by is the study of the balance between energy intake in the form of food and energy utilization by organisms for life-sustaining processes- tissue synthesis, osmoregulation, digestion, respiration, reproduction, organisms for life-sustaining processes- tissue synthesis, osmoregulation, digestion, respiration, reproduction, locomotion, etc.locomotion, etc.

Autotrophs

Use CO2 as sole carbon source

Photoautotrophs: Energy from sunlight (photosynthesis)

Chemoautotrophs: Energy from oxidation of inorganic compounds e.g.,Fe ++-----> Fe+++

Heterotrophs: Use combined forms of carbon (sugars) for energy

Energy

The measurement of energy requires converting it from one form to anotherThe measurement of energy requires converting it from one form to another

The basic unit of energy is the calorieThe basic unit of energy is the calorie

international unit: the joule - 1.0 joule = 0.239 calories or 1 calorie = 4.184 jouleinternational unit: the joule - 1.0 joule = 0.239 calories or 1 calorie = 4.184 jouleEnergy content of a substanceEnergy content of a substance

Gross energy represents the energy present in dry matter (DM)-Gross energy represents the energy present in dry matter (DM)-

Laws of Thermodynamics1. Conservation of energy. Energy may change form or be transported but cannot be

created or destroyed.2. Entropy. In all natural processes, the entropy of the universe increases.

Animals are not engines and can’t use heat to perform work Animals are not engines and can’t use heat to perform work

Cells are isothermal (Const temp and pressure)Cells are isothermal (Const temp and pressure)

Cells obtain their energy from chemical bonds, Cells obtain their energy from chemical bonds,

Free energy G- amt of energy capable of work at const temp and pressureFree energy G- amt of energy capable of work at const temp and pressure

Enthalpy H-Heat content of the system.

Entropy S- expression of randomness in the system-

G=H-TS G’o = -RTlnK’eq (Std free energy change of a reaction) (pH7, 25C, 1M reactant/product, 1Atm)

Std versus actual

Std free energy change G’o tells us direction of a reaction and how far it will go to reach equilibrium WHEN Initial conc of reactant and product is 1M, pH is 7, temp is 25C, pressure is 1Atm.

G’o is a constant for that reaction

ACTUAL CHANGE

A+B <-----> C+D

G = G’o + RTln [C][D][A][B]

A---->B G’o = +13.8 kJ/molB---->C G’o =-30.5 kJ/molA---->C

Sum= -16.7 kJ/mol (reaction is spontaneous because the two are coupled)

Keq and Go

ATP+H2O---->ADP+ Pi -7.3Kcal/molATP+H2O---->AMP+PPi -10.9Kcal/molPPi+H2O---->2Pi -4.6Kcal/mol

ReviewEnergy transduction in cells are via chemical reactions- bond formation/breakage

Covalent bonds share electronsHomolytic cleavage- each atom leaves the bond with on electronHeterolytic cleavage-one atom retains both electrons

Nucleophiles-groups rich in and capable of donating electron (attracted to nucleus)Electrophile- group deficient in electron (attracted to electron)

Non-bonded electrons (dots) are moved in direction of arrows

Carbonyl

Chemical reaction that occur during metabolism

Carbonyl bonds play a key role in C-C bond formation and breakage

Rearrangements in electrons

Grp transfer- transfer of acyl/phosphoryl from one nucleophile to another

Biological oxidation (loss of electron)-Oxidation releases energy.

Every oxidation is accompanied by a reduction (electron acceptor acquires electrons removed by oxidation).

Metabolism= Catabolism and Anabolism

Converge and Diverge

Catabolism• Generate ATP

• Generate building blocks forbiosynthesis Anabolism

• Utilize energy

• Generate biomolecules

Different enzymes mediate catabolic and anabolic pathways.Catabolic and anabolic pathways employ different enzymes which are regulated separatelySome key steps in each pathway are unidirectional

Themes

Allosteric regulation- metabolic intermediate (ATP)

Synthesis/degradation of enzyme Control enzyme levels

Covalent Modification of enzyme- Phosphorylation (integrated via growth factors/hormones)

Compartmentalization•One way to allow reciprocal regulation of catabolic and anabolic processes•Cytosol Vs mitochondria

Specialization of organs• Regulation in higher eukaryotes• Organs have different metabolic roles

Liver = gluconeogenesis (glucose)Muscle = glycolysis

Availability of substrate-(intracellular conc of substrate is often below Km of enzyme- rate is proportional to substrate conc)

Glucose

Glucose

Glycolysis(every cell)

Pyruvate

Hexose shunt(every cell)

NADPH

AcetylCoA

Fatty acids(liver, adipose)

Glycogen(liver muscle)Amino acids

(Liver)

Gluconeogenesis(every cell)

ATP ATP ATP

Heterotrophic cells obtain free energy from catabolism of nutrients forming ATP

Hydrolysis of ATP has a high negative DG- -30.5kJ/mol. This means that ATP has a strong tendency to transfer terminal phosphate to water.

ATP hydrolysis in water only produces heat

In cells ATP hydrolysis involves covalent participation of ATP. ATP provides energy by grp transfer (Substrate Level Phosphorylation).

ATP hydrolysis is exogermic (negative G). This is coupled with endogermic (positive G) reactions in cells allowing these reactions to proceed.

Some processes do involve direct ATP hydrolysis providing energy that changes protein conformation producing mechanical motion

High energy bond

Why is ATP PO4 bond high energy bond? It is not breaking of bond - it is difference in free energy between reactant and product.

ATP + H2O <-------> ADP + Pi DGo’ = -30.5 kJ/mol

Why does ATP have strong tendency to transfer its terminal phosphate?

Electrostatic repulsion

Resonance stabilization-

Hydration-

Oxidation and Reduction

Oxidation - loss of electronsReduction - gain of electrons

Electrons can be transferred from one mol to anotherdirectly as an electron (one electron)as hydrogen atoms (one proton + one electron) as hydride ion (:H-) (two electron) (NAD)

direct combination with oxygen

In aerobic organismsOxidation of carbon (loss of electrons from carbon) is used to generate ATPThe final acceptor of electrons is oxygen producing CO2

ReducedHigh energy

OxidizedLow energy

Fatty acids are more energy rich compared to glucose because carbon in fatty acids is more reduced

Oxidation

Biological Oxidation Involves loss of electrons from carbon

In cells Carbon (or another atom like nitrogen) exists in a range of oxidation states because:Carbon shares electrons with another atom (Oxygen, nitrogen, sulphur, hydrogen)The more electronegative atom “OWNS” the bonded electrons it shares

C ON

C

H

C

C

C

In the C-O bond, the C has partially lost the electron and has undergone oxidationIn the C-N bond, the C has partially lost the electron and has also undergone oxidation even when no oxygen is involved!Electron is not Fully transferred

Conjugate redox pairs

AH2 <--------> A + 2e- + 2H+ (redox pair)

B+2e- + 2H+ <-----> BH2 (redox pair)

Two conjugate redox pairs together in soln- electron transfer from electron donor of one pair to electron acceptor of another pair

AH2 + B <-----> A + BH2

AH2 + NAD+ -----> A + NADH + H+

Electron donating mol is called reducing agentElectron accepting mol is called oxidising agent

(In a buffer you have proton donor <---------> proton acceptor+ H+)

Overview

Glucose Glycolysis AcetylCoA Krebs cycleElectronTransportchain

CytosolMitochondria

ATP NADHFADH ATP

H2O

CO2 O2

Glycolysis and Anaerobic respiration

Glucose

2 Pyruvate

2ATP

2ADP

2NAD

2NADH

4ADP

4ATP

Acetaldehyde

Ethanol

Lactate

Muscle

Yeast

Krebs

CO2

Krebs cycle

Pyruvate

AcetylCoA

3NAD

ADP

3NADH

FADFADH2

ATP3 CO2

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