Energetics and Enzymes Flashcards
Define Gibbs free energy
(Gibb’s) Free Energy is defined as the amount of energy within a molecule that could perform useful work at a constant temperature.
What happens if Gibbs free energy is negative
A reaction can only occur spontaneously if Delta G is negative.
What happens if Gibbs free energy is positive
Conversely, a reaction cannot occur spontaneously if DG for the reaction is positive.
Pathways within the cell that synthesise molecules are generally energetically unfavourable e.g. peptide synthesis How do they then take place within cells?
COUPLED REACTIONS They take place because they are coupled to an energetically favourable one. Providing that the sum of the DG for the overall reaction is still negative, the reaction will proceed.
When glucose reacts with fructose to make sucrose, delta G is + 23 kJ/mole. The reaction for ATP to become ADP has a delta G of -31 kJ/mole How would glucose be converted to sucrose in a cell?
COUPLED REACTIONS add pic
How do enzymes act as catalysts for reactions?
Lower activation energy.
The transition state is the particular conformation of the substrate in which the atoms of the molecule are rearranged both geometrically and electronically so that the reaction can proceed. Enzymes work by bending their substrates in such a way that the bonds to be broken are stressed and the substrate molecule resembles the transition state. Enzyme bind one or more substrate molecules tightly within a part of a protein known as a active site. Enzymes arrange the bonds in such a way that the bonds are strained.
What is the lock and key model?
In this model, the shape of the substrate (key) matches that of the active site (lock) of the enzyme. This model explains the specificity of most enzymes for a single substrate.
What is the induced fit model?
Induced Fit Model (Daniel Koshland Jnr) In this model, the substrate induces a change in the conformation of the enzyme which results in the formation of the active site. Upon release of products, the enzyme reverts back to its original conformation.
What is a Lysozyme
Lysozyme is a component of tears and nasal secretions and is one of the first lines of defence against bacteria. It catalyses the hydrolysis of sugar molecules within bacterial cell walls that are necessary for their structure. With this bond broken, the bacteria lyse and die.
Draw a graph to show the effect of pH on reactions catalysed by enzymes?
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Draw a graph to show the effect of temperature on reactions catalysed by enzymes?
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Draw a graph to show the effect of substrate concentration on reactions catalysed by enzymes?
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Define coenzyme
a non-protein compound that is necessary for the functioning of an enzyme
Explain the role of coenzyme NAD in reactions catalysed by dehydrogenases
NAD+ catalyses the dehydrogenation of substrates by readily accepting a hydrogen atom and two electrons. add pic
