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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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
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.
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
A+B <-----> C+D
DG = DG’o + RTln [C][D]
A---->B DG’o = +13.8 kJ/mol
B---->C DG’o =-30.5 kJ/mol
Sum= -16.7 kJ/mol (reaction is spontaneous because the two are coupled)
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)
Non-bonded electrons (dots) are moved in direction of arrows
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).
• Generate ATP
• Generate building blocks for
• 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
Allosteric regulation- metabolic intermediate (ATP)
Synthesis/degradation of enzyme Control enzyme levels
Covalent Modification of enzyme- Phosphorylation (integrated via growth factors/hormones)
•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)
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
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?
Fatty acids are more energy rich compared to glucose because carbon in fatty acids is more reduced
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
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
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
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+)