Basic Concepts of Metabolism Flashcards
Why do we need energy?
1) Muscle contraction and cellular movements
2) Active transport of molecules and ions
3) Synthesis of macromolecules and other biomolecules
Why is ATP the “energy currency” of the cell?
It has 3 high-energy bonds in the form of phosphoanhydride linkages, breaking this bond releases a lot of energy. It also has a central position in the phosphoryl transfer potential, allowing it to transport and transfer phosphoryl groups.
What is phosphoryl transfer potential?
The capacity the compound has to transfer the phosphoryl group.
The more reduced a molecule is to begin with, the more
free energy is released by its oxidation
ATP is an activated carrier of
phosphoryl groups
NAD+ is an activated carrier of electrons for fuel oxidation
The reactive part of NAD+: nicotinamide ring, which accepts a hydrogen ion and 2e-, which are equivalent to a hydride ion (H:-)
The reduced form of this carrier is NADH
NAD+ is an e- acceptor in redox dehydrogenation rxns -> protons accompany the e-, 1proton 2e-
Derived from: vitamin nicacin = B3
FAD is also an activated carrier of electrons for fuel oxidation
Reduced form is FADH2
Acts as the e- acceptor in a rxn that removes 2H and creates a double bond.
Carries 2e-.
Derived from vitamin riboflavin
NADPH is the activated carrier of electrons for the synthesis of biomolecules
Reductive biosynthesis: reducing power + ATP
The precursors are more oxidized than the products
NADPH vs NADH
NADPH is used almost exclusively for reductive biosynthesis
NADH is primarily used for the generation of ATP
Coenzyme A (CoA-SH) is the activated carrier of two-carbon fragments, specifically acyl groups
Acyl groups are essential for catabolism (ox of fatty acids) and in anabolism (synthesis of membrane lipids).
The acyl group often linked to CoA is acetyl unit = acetyl CoA
The terminal sulfhydryl group is the reactive group.
Derived from vitamin pantothenate = B5
Metabolism is regulated through the control of:
1) The amounts of enzymes
2) The catalytic activities of enzymes
3) The accessibility of the substrates
The amounts of enzymes are regulated by
controlling the rate of synthesis of enzymes and their rate of degradation
The catalytic activities of enzymes are controlled in several ways:
- Allosteric control = feedback inhibition (product molecule can inhibit its own synthesis)
- Activation and deactivation of enzymes by reversible covalent modification (phosphorylation, regulation of enzymes with phosphorylation i.e kinases)
The accessibility of substrates is controlled by
compartmentalization. The transfer of substrates from one compartment of a cell to another can be a control point. Compartmentalization segregates opposed rxns.
