Bioenergetics

Is the study of energy changes associated with biochemical reactions, It is the study of how energy is captured and transformed from one type to another It studies utlization of energy

Total energy change in a system that is available for doing work.that is the useful energy , known as chemical potential ^G=G of products-G of reactants

Negative ~> there is net lose of energy The reaction is spontaneous Exergonic reaction Positive ~> there is net gain of energy The reaction is not spontaneous Endergonic reaction that need energy to happen

That the reactants are in equilibrium state where the reaction happens in both directions at the same rate

Vital endergonic reactions such as synthetic one need energy so it obtain it by coupling to an exergonic reaction and is named coupled exergonic endergonic system where the overall net change is exergonic Vital exergonic reactions are catabolism Vital endergonic reactions are anabolism

Catabolic reactions give energy which can be stored in the form of ATP that anabolic reactions can utilise it later through hydrolysis of ATP

It has 3 components 1- nitrogenous base ( adenine) 2- sugar ( ribose) 3- 3 phosphoryl groups joined to ribose by phosphate ester bond ( covalent one) and to each other by phospho anhydride bonds

-7.3 kcal / mol

breakdown of either phospho anydride bonds releases energy

1- substrate level phosphorylation • the conversion of ADP TO ATP by the use of high energy phosphate metabolites • Some of the common phosphate-containing compounds found in cells and the energy released by hydrolysis of their phosphate bonds under standard conditions must have ^ G >7.3 2- oxidative phosphorylation Approximately 40% of the released energy is partly converted into useful form . ATP formation in this process depends on the principles of oxidation- reduction reactions (redox) reactions that occur mainly in the mitochondria.

• Redox reactions occurs • Hydrogen removel of one electron is accompanied by a release of energy • Instead of releasing a massive energy in form of heat which may destroy the living cells , hydrogen tranfers electron through different components of the redox chain ( that get more electropositive )so it is liberated in steps and small utilizable amounts • Part of this amounts can be captured and stored by the production of ATP and this is called oxidative phosphorylation

Dehydrogenase is used and according to the type of hydrogen carrier dehydrogenase is classified into 1- NAD LINKED DEHYDROGENASE it is the electron acceptor in oxidation of hydroxlyted carbon atoms 2- FAD LINKED DEHYDROGENASE It is the electron acceptor in oxidation of two adjacent carbons ( carbon -carbon double bond ) 3- NADPH LINKED DEHYDROGENASE It is a major source of reducing power for biosynthetic pathways. In contrast to NADH, that is generated and used primarily in the mitochondria; most of the NADPH is formed and used in extra-mitochondrial reactions.

it is the final common pathway in aerobic cells by which electrons carried in NADH+H AND FADH2 are transfered to oxygen to form water The energy relaesd at specific steps in ETC is used to synthesize ATP by oxidative phosphorylation

Inner mitochondrial membrane

5 complexes 1- FMN ,FE-s Transfer2 e from NADH+H to CoQ 2- FAD ,FE-S. transfer2 e from succinate to CoQ 3- Cytochrome b , c1 , FE-S. transfer 2 e from reduced CoQ to cytochrome c 4- cytochrome a, a3 , CuA , CuB. Transfer 2 e from cytochrome c to oxygen forming h2o

the tendency of a compound to be reduced (gaining electron)

The lowest electron affinity / the lowest reduction potential and vice versa

Hydrogen has the lowest Oxygen has the highest

Stronger electron acceptors have positive reduction potential. (higher electron affinity ) Stronger electron donors have negative reduction potential -(lower electron affinity ) Electrons will be transferred from more elecronegative to more electropositive compounds.

^E=E acceptor -Edonor

^G = -n F ^E

By changing its products and reactants concentration

Are equal

Cytosol Mitochondria