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Flashcards in Energetics and Enzymes Deck (14):

Concept of free energy

The amount of energy within a molecule that could perform useful work at a constant temperature.


When is a reaction spontaneous?

When delta-G is negative


Why does glucose + fructose --> sucrose not take place spontaneously until coupled with ATP's reaction to form ADP?

Glucose + fructose = sucrose is +23KJ/mol - not spontaneous.
ATP -> ADP = -31KJ/mol = spontaneous
When coupled, overall delta G is 23-31= -8KJ/mol - spontaneous


How do enzymes act as catalysts?

Increase rate
Provide alternative reaction route with a lower activation energy for molecules to reach their transition state.


Graph of rate of reaction against increasing substrate concentration

Increases steadily then plateaus past point of saturation


Graph of enzyme activity against temperature

Slowly increases to peak at optimum temperature, steep decrease beyond this point


Graph of enzyme activity against pH

Increases from 0 steadily to peak at optimum pH, decreases steadily as pH increases away from optimum pH


Definition of a coenzyme

A non-protein molecule that is necessary for an enzyme to function but itself only functions after binding to a protein.


Role of NAD in reactions catalysed by dehydrogenases?

Catalyses the dehydrogenation of substrates by readily accepting a hydrogen atom and two electrons.


How can enzyme activity be measured using spectrophotometry?

Rate of reaction can be recorded by measuring and comparing absorbance at regular intervals throughout the reaction


What is Vmax?

The maximum rate once enzyme is saturated with substrate


What is Km?

The substrate concentration that corresponds to the rate of reaction equal to Vmax/2


Effect of a competitive inhibitor on Vmax and Km

Increases Km
Vmax remains the same


Effect of a non-competitive inhibitor on Vmax and Km

Km remains the same
Decreases Vmax