Oxidative Phosphorylation and Substrate Level Phosphorylation in Cell Energy Production, Exercises of Biological Sciences

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OXIDATIVE PHOSPHORYLATION

Direct transfer of a phosphate group from a substrate to ADP for the

formation of high energy ATP is known as substrate level phosphorylation.

This reaction is mostly catalyzed by the enzyme kinases. Phosphate group

donor directly donates or transfers a phosphate group to ADP without the

involvement of an intermediate between the donor and ADP. While

technically the transfer is PO3, or a phosphoryl group, convention in

biological sciences is to refer to this as the transfer of a phosphate group.

In cells, it occurs primarily and firstly in the cytoplasm (in glycolysis) under

both aerobic and anaerobic conditions.

The phosphate group is transferred from the first molecule and received by

the second molecule. The energy released during the breakage of the

phosphate group is used to phosphorylation of ADP in substrate level

phosphorylation, and it is known as reaction coupling.

SUBSTRATE LEVEL PHOSPHORYLATION

Substrate Level Phosphorylation 1,3 Bisphosphoglycerate Phosphoenol Pyruvate (^) Pyruvate 3 phosphoglycerate

responsible for identifying and purifying Factor 1 (F1), the first part of the ATP synthase enzyme to be characterised. F1 is only a part of a larger ATP synthase complex known as Complex V. It is a peripheral membrane protein attached to component Fo, which is integral to the membrane.

Localization of metabolic functions within the mitochondrion (1) Outer membrane: Phospholipid synthesis; Fatty acid desaturation; Fatty acid elongation; (2) Intermembrane space: Nucleotide phosphorylation; (3) Inner membrane: Electron transport; Oxidative phosphorylation; Metabolite transport; (4) Matrix: Pyruvate oxidation;TCA cycle;? oxidation of fats; DNA replication; RNA transcription; Protein translation

OXIDATIVE PHOSPHORYLATION IN EUKARYOTES TAKES PLACE IN MITOCHONDRIA Two membranes: outer membrane inner membrane (folded into cristae) Two compartments: (1) the intermembrane space (2) the matrix

• Inner mitochondrial membrane: Electron transport chain ATP synthase
• Mitochondrial matrix: Pyruvate dehydrogenase complex Citric acid cycle Fatty acid oxidation Location of mitochondrial complexes The outer membrane is permeable to small molecules and ions because it contains pore- forming protein (porin). The inner membrane is impermeable to ions and polar molecules. Contains transporters (translocases).

THE ELECTRON TRANSPORT CHAIN

Series of enzyme complexes (electron carriers)

embedded in the inner mitochondrial membrane, which

oxidize NADH +H+ and FADH

2

and transport electrons to

oxygen is called respiratory electron-transport chain

(ETC).

The sequence of electron carriers in ETC

cyt b NADH FMN Fe-S Co-Q Fe-S cyt c 1 cyt c cyt a cyt a 3 O 2 succinate FAD Fe-S

Oxidative phosphorylation matrix inner membrane outer membrane inter- membrane space mitochondrion cristae

H

transport results in an electrochemical gradient Proton motive force: energy released by flow of H

down its gradient is used for ATP synthesis ATP synthase: H

channel that couples energy from H

flow with ATP synthesis

INHIBITORS OF OXIDATIVE PHOSPHORYLATION