Chemistry of life · Topic 7 of 17

Metabolism & Enzymes

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Biology · chemistry of life

Metabolism is every reaction in a cell: anabolism builds and uses energy, catabolism breaks down and releases it, ATP carries it, enzymes speed it.

01 · Two directionsAnabolic builds · catabolic breaks down

02 · Energy currencyATP = the cell's energy currency

03 · EnzymesEnzymes lower activation energy

Metabolism = all the chemical reactions in a cell must know

ATP = the cell's energy currency (adenine + ribose + 3 phosphates) must know

Activation energy = the energy needed to start a reaction

Each enzyme is specific to its substrate (shape fit)

Lock-and-key, refined by induced fit: the active site reshapes slightly

Denatured = shape lost → the enzyme stops working

ATP → ADP + phosphate releases energy for cell work

ADP + phosphate + energy from food → ATP (rebuilding costs energy)

Substrate binds the enzyme's active site → enzyme–substrate complex

Enzymes speed up reactions by lowering activation energy must know

Enzymes are reusable (not used up by the reaction)

Heat speeds enzymes up to an optimum; too hot → denatured

Each enzyme has an optimal pH; extreme pH denatures it

Glucose breakdown = catabolic; building protein from amino acids = anabolic

Anabolism builds (uses energy); catabolism breaks down (releases energy) must know

Commonly confused

	Anabolism	Catabolism
What it does	Builds large molecules from small ones	Breaks large molecules into small ones
Energy	Requires an energy input	Releases energy
Example	Amino acids → protein	Glucose broken down for ATP
ATP	Spends ATP	Its released energy is used to make ATP

Trap: enzymes don't change the energy a reaction releases, only its start-up barrier

Show 6 more facts

Optima fit the site: many human enzymes ~37 °C; pepsin ~pH 1.5; trypsin ~pH 8

Exergonic releases energy; endergonic needs energy

Competitive inhibitor blocks the active site; noncompetitive binds elsewhere

Cofactors = ions (Mg²⁺, Zn²⁺); coenzymes = organic, often from vitamins

Feedback inhibition: the end product shuts down an early enzyme

Energy coupling: ATP hydrolysis powers work (e.g. the Na⁺/K⁺ pump)

Pearl

Anabolism assembles, catabolism takes apart, and enzymes only lower the hill a reaction must climb to start.

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