Bioenergetics and biochemical reaction types
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bioenergetics 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, locomotion, etc. Bioenergetics and Biochemical Reaction Types.

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Bioenergetics and Biochemical Reaction Types

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Bioenergetics and biochemical reaction types

  • bioenergetics 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, locomotion, etc.

Bioenergetics and Biochemical Reaction Types

Photosynthetic autotrophs

Heterotrophs


Bioenergetics and biochemical reaction types

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 another

  • The basic unit of energy is the calorie

  • international unit: the joule - 1.0 joule = 0.239 calories or 1 calorie = 4.184 joule

  • Energy content of a substance

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

Energy

Laws of Thermodynamics

1.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.


Bioenergetics and biochemical reaction types

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

  • Cells are isothermal (Const temp and pressure)

  • Cells obtain their energy from chemical bonds,

  • Free 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-

  • DG=DH-TDS

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


Std versus actual

Std free energy change DG’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.

DG’o is a constant for that reaction

ACTUAL CHANGE

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

DG = DG’o + RTln [C][D]

[A][B]

A---->B DG’o = +13.8 kJ/mol

B---->C DG’o =-30.5 kJ/mol

A---->C

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

Std versus actual


Keq and d g o

Keq and DGo

ATP+H2O---->ADP+ Pi-7.3Kcal/mol

ATP+H2O---->AMP+PPi-10.9Kcal/mol

PPi+H2O---->2Pi-4.6Kcal/mol


Review

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

Covalent bonds share electrons

Homolytic cleavage- each atom leaves the bond with on electron

Heterolytic 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)

Review

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


Carbonyl

Carbonyl


Chemical reaction that occur during metabolism

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

Metabolism= Catabolism and Anabolism


Converge and diverge

Converge and Diverge

Catabolism

• Generate ATP

• Generate building blocks for

biosynthesis

Anabolism

• Utilize energy

• Generate biomolecules

Different enzymes mediate catabolic and anabolic pathways.

Catabolic and anabolic pathways employ different enzymes which are regulated separately

Some key steps in each pathway are unidirectional


Themes

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


Bioenergetics and biochemical reaction types

(Liver)

Glycogen

(liver muscle)

Glucose

Amino acids

Hexose shunt

(every cell)

Glycolysis

(every cell)

Gluconeogenesis

(every cell)

NADPH

Pyruvate

AcetylCoA

Fatty acids

(liver, adipose)


Atp atp atp

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 DG). This is coupled with endogermic (positive DG) 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

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 + PiDGo’ = -30.5 kJ/mol

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

Electrostatic repulsion

Resonance stabilization-

Hydration-


Oxidation and reduction

Oxidation and Reduction

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

Reduced

High energy

Oxidized

Low energy

Oxidation - loss of electrons

Reduction - gain of electrons

Electrons can be transferred from one mol to another

directly 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 organisms

Oxidation of carbon (loss of electrons from carbon) is used to generate ATP

The final acceptor of electrons is oxygen producing CO2


Oxidation

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

O

C

N

C

C

C

H

In the C-O bond, the C has partially lost the electron and has undergone oxidation

In 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

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 agent

Electron accepting mol is called oxidising agent

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


Overview

Overview

Cytosol

Mitochondria

H2O

Electron

Transport

chain

Krebs cycle

AcetylCoA

Glucose

Glycolysis

O2

CO2

NADH

FADH

ATP

ATP


Glycolysis and anaerobic respiration

Glycolysis and Anaerobic respiration

Lactate

4ADP

2NAD

2ATP

Muscle

Glucose

2 Pyruvate

Krebs

Yeast

2ADP

2NADH

4ATP

CO2

Acetaldehyde

Ethanol


Krebs cycle

Krebs cycle

3NAD

3NADH

ADP

Acetyl

CoA

Pyruvate

3 CO2

ATP

FADH2

FAD


Xxxxxxx

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