Metabolism 2: Energetics and Enzymes Flashcards
Laws of Thermodynamics
First Law - Energy can neither be created nor destroyed, simply converted from one form to another.
Second Law - In any isolated system, the degree of disorder can only increase. Entropy increases.
what is gibbs free energy
the amount of energy within a molecule that could perform useful work at a constant temperature. (measured in kj/mole)
When is the reaction spontaneous
The reaction can occur SPONTANEOUSLY if DG = NEGATIVE
Why do coupled reaction take place
Pathways within a cell that synthesise molecules are generally energetically unfavourable.
They take place because they’re coupled with an ENERGETICALLY FAVOURABLE reaction.
Provided that the sum of DG of the overall reaction is NEGATIVE, the reaction will proceed.
How do enzymes work?
Substrate molecules bind tightly to enzyme active site.
Enzymes arrange substrates in such a way that the bonds are strained.
This can be in the form of oxidation reactions (removal of electrons from molecule) or reduction reactions (gain of electrons).
NOTE: As cellular environment is generally aqueous, molecule gains an electron and simultaneously gains a proton.
What is the transition state
- particular conformation of the substrate in which the atoms of the molecule are rearranged both geometrically and electronically so the reaction can proceed.
Enzymes bend the substrates in such a way that the bonds to be broken are stressed and the substrate molecule resembles transition state. This makes them more likely to react.
Describe lysozymes and their function
Component of tears and nasal secretions.
One of the first lines of defence against bacteria.
Catalyses the hydrolysis of sugar molecules within the bacterial cell wall that are necessary for their structure. With this bond broken, bacteria lyse and die.
Lysozyme hydrolyzes alternating polysaccharide copolymers of N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM) which represent the “unit” polysaccharide structure of many bacterial cell walls.
Lysozyme cleaves at the b(1-4) glycosidic linkage, connecting the C1 carbon of NAM to the C4 carbon of NAG.
How does Glu 35 and Asp 52 act as catalysts in breaking down a glycosidic link
=Glu-35 protonates the Oxygen in the glycosidic link between the two sugars thus breaking the glycosidic bond.
A water molecule enters and is deprotonated by Glu-35.
Asp-52 stabilises the positive charge in the transition state.
Hydroxide ion attacks the remaining sugar molecule adding an OH group to it.
Proton is transferred to Glu-35 to return it to it’s original state.
Glu-35 and Asp-52 are both in their original state to continue catalysis.
What is NAD+ (Nicotinamide adenine dinucleotide)
VITAL COMPONENT OF MANY DEHYDROGENATION REACTIONS.
It is a co-enzyme, it has no catalytic activity of its own and only functions after binding to an enzyme.
NAD+ catalyses dehydrogenation reactions by readily accepting A PROTON AND TWO ELECTRONS.
Explain the formation of Lactate
During intense exercise, skeletal muscles have to respire anaerobically.
Pyruvate is converted to Lactate.
This generates free NAD+.
Lactate moves to the liver where high levels of NAD+ is used to convert lactate back to pyruvate.
What does Glucose-6-phosphatase do?
Removal of phosphate group from Glucose-6-phosphate
Found in the liver
What is Glucose-6-phosphatase deficiency known as
Von gierke’s dieases
Symptoms: low blood sugar levels Slow growth large liver short stature
