2 - Energetics and enzymes Flashcards
define an enzyme
a protein that acts as a catalyst to induce chemical changes in other substances, itself remaining apparently unchanged by the process
What is the first law of thermodynamics?
energy can neither be created nor destroyed, but can be simply converted from one form to another
What is the second law of thermodynamics?
in any isolated system, the degree of disorder can only increase (entropy increases)
i.e. reactions proceed spontaneously towards products with greater entropy
Define Gibbs Free Energy
Δ
the amount of energy within a molecule that could perform useful work at a constant temperature
measured in kJ/mole
How is Gibbs Free Energy calculated?
free energy of products - free energy of reactants
a reaction occurs spontaneously if ΔG is ___
negative
Which ATP bonds are considered to be higher energy bonds?
Why?
phosphoanhydride bonds
because they have a large negative ΔG of hydrolysis
what are coupled reactions used for?
usually, the pathways within a cells that synthesise molecules are energetically unfavourable, but they take place because they are coupled with energetically favourable reactions
What is the condition for favourable reactions to occur?
the overall ΔG is negative
How do enzymes work?
- substrate molecules bind tightly to the enzyme active sight
- enzymes arrange substrates so the bonds are strained (this can be in the form of oxidation or reduction reactions)
What is the transition state?
a particular conformation of the substrate in which the atoms of the molecules are rearranged both geometrically and electronically so the reaction can proceed
where are lysozymes found?
a component of tears and nasal secretions
How do lysozymes it act as one of the first line of defence against bacteria?
catalyse the hydrolysis of sugar molecules within the bacterial cell wall, so the bacteria lyse and die
What is the mechanism of action of of lysozymes hydrolysing the sugar molecule within the bacterial cell wall?
they hydrolyse alternating polysaccharide copolymers of N-acetyl glucosamine (NAG) and N-actetyl muramic acid (NAM) which represent the ‘unit’ polysaccharide structure of many bacterial cell walls
Give the order of sequence of the hydrolysis of sugar molecules by the lysozymes Glu-35 and Asp-52
- Glu-35 protonates the oxygen in the glycosidic bond, thus breaking it
- Asp-52 stabilises the positive charge in the transition state
- a water molecule enters and is deprotonated by by Glu-35, so it returns to its original state
- the hydroxide ion (from the water molecule) attacks the remaining sugar molecule, adding an OH group to it
