Exam 4 Review:  Chapter 24:  Phosphorylation

phosphorylation - Any chemical reaction which adds a phosphate group (HPO4-) to an organic molecule; to create the covalent bond, chemical energy of some form must be provided; in human cells, such reactions form two categories: (1) substrate-level and (2) oxidative.

substrate-level phosphorylation - Synthesis of high energy phosphate compounds through the enzyme catalyzed (kinases) addition of low energy phosphate ions to an activated substrate, usually an organic molecule; these substrate-level phosphorylation reactions are coupled to energy yielding reactions, e.g., ATP hydrolysis, which occur in the cytoplasm of various cells; an example is the phosphorylation of creatine by ATP, catalyzed by creatine kinase, which occurs in striated muscle tissue.

oxidative phosphorylation - The phosphorylation of adenosine diphosphate (ADP) and synthesis of adenosine triphosphate (ATP) by the complex of oxidation reduction reactions localized in the electron transport chain and ATP synthetase enzymes of the inner christae membranes of the mitochondria which use the energy derived from the oxidation of nutrients such as glucose or fatty acids and delivered to the system by electron transport molecules such as FAD and NAD.

kinase - Any of various enzymes which catalyze the transfer of a phosphate group from a donor molecule, such as ADP or ATP, to an acceptor molecule; such transfers also often involve the transfer of useful chemical energy with which the cell can do work.

ATP synthase (= ATP synthetase) - An enzyme which catalyzes the covalent linking together of adenosine diphosphate (ADP) and a phosphate ion to form adenosine triphosphate (ATP) by using the energy derived from the oxidation of nutrients such as glucose or fatty acids; the enzyme is located within the inner membrane of the mitochondria and its synthetic activity is directly tied to the proton motive force (chemiosmosis) generated by the electron transport chain which receives energetic electrons from electron carriers NAD and FAD, and uses that energy to pump hydrogen ions from the mitochondrial matrix to the intermembrane space, and when those hydrogen ions follow their concentration gradient back to the matrix, they pass through a channel in this enzyme and provide the immediate source of energy for the synthesis of the ATP.

creatine phosphate - The small organic compound found in muscle cells which serves as a molecular storage depot for chemical energy in the form of high energy phosphate groups; when needed this compound transfers a high energy phosphate group to ADP to form ATP.

chemiosmosis - The theoretical mechanism which explains energy transduction (the proton motive force) in the mitochondrion; as a general mechanism, it is the coupling of one enzyme catalysed reaction to another using the transmembrane flow of an intermediate species; for example, cytochrome oxidase pumps protons across the mitochondrial inner cristae membrane and ATP synthesis is driven by re-entry of protons through the ATP synthesizing protein complex.

Follow this link for some useful animations of ATP synthesis in mitochondria.

photophosphorylation - Phosphorylation, specifically ATP synthesis, induced by radiant sunlight energy during photosynthesis which is carried out by green plants and certain photosyntheitc microorganisms.

List:

11. the three main types of phosphorylation

          substrate-level phosphorylation, oxidative phosphorylation, photophosphorylation

Describe:

8. the electron transport system and its relation to ATP synthetase.


The Electron Transport System (ETS) consists of a series of complexes which are clusters of related oxidation-reduction enzymes and associated membrane-bound electron-transfer compounds which are located as integral proteins within the inner = cristae membrane of the mitochondrion.  See the figure below.

Complex I is capable of accepting the most energetic pairs of electrons which are carried by NAD+.  As these electron pairs are transferred along the series of oxidation-reduction enzymes in the ETS pathway, some useful chemical energy is extracted from them.

Because FAD+ carries somewhat less energetic pairs of electrons, those electrons must be delivered to the ETS pathway beyond Complex I and, therefore, somewhat less useful chemical energy can be extracted from them as the complete the path.

All of the useful chemical energy extracted from these pairs of energetic electrons is used to power the active transport of hydrogen ions from the matrix in the interior of the mitochondrion to the intermembrane space.  See the figure to the right.

This extensive hydrogen pumping establishes a powerful electrochemical gradient favoring the movement of the hydrogen ions back across the inner = cristae membrane of the mitochondrion.  This gradient, its potential energy, is the proton motive force.

In the mitochondrion, the only route for hydrogen ions to return to the mitochondrial interior, the matrix, is by passing through the enzyme ATP synthetase.  In so doing, the proton motive force is used to phosphorylate ADP, producing ATP.  This is the source of the majority of ATPS produced by oxidative phosphorylation.


9. chemiosmosis.

Chemiosmosis is the theoretical mechanism which explains energy transduction (the proton motive force) in the mitochondrion; as a general mechanism, it is the coupling of one enzyme catalysed reaction to another using the transmembrane flow of an intermediate species; for example, cytochrome oxidase pumps protons across the mitochondrial inner cristae membrane and ATP synthesis is driven by re-entry of protons through the ATP synthesizing protein complex.  See also the discussion in question 8 above.