bioch lec 7- intro the metabolism
What are the two things metabolic pathways consist of? (2 things)
They consist of a series of enzyme-catalyzed reactions and the resulting metabolites/intermediates formed between steps.
What varies about metabolic pathways between organisms and tissues? (2 distinctions)
Different organisms and tissues may use different pathways, but they all follow the same chemical & thermodynamic principles.
What are the two major purposes of metabolism? (2 purposes)
(1) Obtain usable chemical energy (e.g., photosynthesis or nutrient breakdown).
(2) Produce necessary biomolecules for growth and maintenance.
What defines anabolic vs catabolic pathways? (2 contrasts)
Anabolic pathways use energy and are generally reductive; catabolic pathways release energy and are generally oxidative.
What is an amphibolic pathway? (1 definition)
A pathway that can function in both anabolic and catabolic directions depending on cellular needs.
Which dietary macromolecules are major fuel sources? (3 groups)
Proteins → amino acids, polysaccharides → simple sugars, and triacylglycerols → fatty acids are the major fuels. Nucleic acids are not significant fuel.
What are the two major storage forms of excess fuels? (2 forms)
Excess carbohydrates → glycogen (liver, muscle); excess fatty acids → triacylglycerols in adipocytes.
Why do fats yield more energy upon oxidation than carbohydrates? (1 reason)
Fatty acids are more reduced, so more oxidation steps occur, releasing more energy before reaching CO₂.
What does ΔG°′ represent? (1 description)
The standard free energy change: the inherent energy difference between products and reactants under biochemical standard conditions.
How is ΔG (actual free energy) calculated? (formula)
ΔG = ΔG°′ + RT ln([products]/[reactants]). Actual values depend on concentrations.
Under what two conditions is a reaction spontaneous? (2 conditions)
When ΔG < 0, or when concentrations shift to make the RTln term negative enough to outweigh ΔG°′.
How do we classify reactions by ΔG magnitude? (3 categories)
ΔG ≪ 0 = irreversible; ΔG ~ 0 = reversible; ΔG > 0 = non-spontaneous forward.
What requirement must each step in a metabolic pathway meet to proceed forward? (1 requirement)
Each reaction must have a negative ΔG′ under cellular conditions.
What does “pathways exist in steady state” mean? (1 concept)
Intermediate concentrations stay relatively constant even though metabolites continuously flow through the pathway. (Pool analogy on slide.)
Which steps in a pathway are typically regulated—reversible or irreversible? (1 answer)
Irreversible steps are regulated; reversible steps usually are not.
What is the rate-limiting step? (1 definition)
The irreversible, regulated reaction that controls the overall flux of the pathway.
What is product inhibition? (1 definition)
When an enzyme is inhibited by the product of its own reaction.
What is feedback inhibition? (1 definition)
When an enzyme early in a pathway is inhibited by a downstream metabolite
What is feed-forward activation? (1 definition)
An enzyme is activated by an upstream metabolite to ensure coordinated pathway flow.
Why must opposing pathways be reciprocally regulated? (1 reason)
To prevent futile cycling—both pathways running simultaneously and wasting energy.
What must happen to the irreversible steps when reversing a pathway direction? (1 requirement)
They must be bypassed or replaced with alternative reactions
What are the three major classes of high-energy intermediates? (3 types)
Electron carriers, nucleoside triphosphates, and thioesters.
Which cofactors are oxidizing agents in catabolism? (2 examples)
NAD⁺ and FAD, which accept electrons.
Which cofactor is mainly used in reductive biosynthesis? (1 answer)
NADPH, which donates electrons.
What enables NAD⁺/NADP⁺/FAD to undergo redox reactions? (1 feature)
The nitrogenous base moiety that undergoes reversible reduction.
What is the difference between NAD⁺/NADP⁺ and FAD in terms of binding? (1 distinction)
NAD⁺/NADP⁺ are cosubstrates, whereas FAD is a prosthetic group tightly bound to enzymes
Why must FADH₂ be reoxidized for enzyme reuse? (1 reason)
Because FAD is enzyme-bound, it must be regenerated to FAD before another catalytic cycle (often via coenzyme Q).
Why does ATP hydrolysis release so much energy? (3 reasons)
Resonance stabilization of products,
(2) Reduced electrostatic repulsion,
(3) Solvation effects favor products.
How much ΔG°′ is released when one phosphoanhydride bond is hydrolyzed? (1 value)
Approximately −32 kJ/mol.
Why are thioesters high-energy compounds? (1 explanation)
They lack delocalization of electrons, making their hydrolysis strongly favorable.
What are the two ways ATP is generated in cells? (2 processes)
Substrate-level phosphorylation and oxidative phosphorylation.
What are three major uses of ATP? (3 uses)
Driving unfavourable reactions, powering movement, and fueling primary active transport.
What condition must be met for coupled reactions to proceed spontaneously? (1 condition)
The combined ΔG of both reactions must be negative.
What is phosphate transfer potential? (1 definition)
A measure of how much free energy of hydrolysis a phosphorylated compound can donate.
How does phosphocreatine support ATP regeneration in muscle? (1 function)
It rapidly donates a phosphate to ADP via its very negative ΔG°′ (−43 kJ/mol), providing a short-term ATP reserve.
What is the overall purpose of coupling phosphocreatine hydrolysis to ATP formation? (1 purpose)
To ensure rapid ATP availability during short bursts of intense muscle activity.