Topic 8.1: Metabolism Flashcards
Definition of metabolism
Web of all the enzyme-catalysed reactions in a cell
Metabolic pathways
Consist of chains and cycles of enzyme-catalysed reactions
Example of chains of enzyme catalyzed reactions
Glycolysis
Example of cycle of enzyme catalyzed reactions
Krebs cycle
Calvin cycle
Definition of activation energy
Required amount of energy for a chemical reaction to proceed
How do enzymes speed up the rate of a biochemical reaction?
a) Lowering the activation energy
b) Stressing and destabilising the bonds in the substrate
Types of enzymatic reactions
a) Exergonic (Release of energy to the environment)
b) Endergonic (Absorbance of energy from the environment)
Definition of enzyme inhibitor
Molecule that disrupts the normal reaction pathway between an enzyme and a substrate
Normal enzyme reaction (3)
a) A substrate binds to an enzyme
b) The active site undergoes a conformational change to optimally interact with the substrate
c) Substrate is converted into product at an accelerated rate
Competitive inhibition (2)
a) Molecule, other than substrate, blocking the active site, preventing substrate from binding to it.
b) Its effects can be reduced by increasing substrate concentration.
Noncompetitive inhibition (2)
a) Molecule binding to an allosteric site, causing a conformational change in the active site and substrate cannot bind to it
b) Its effects cannot be mitigated by increasing substrate concentration.
Example of competitive inhibition
a) Treatment of influenza (Relenza)
b) Relenza competitively binds to the neuraminidase active site and prevents the cleavage of the protein4
Example of noncompetitive inhibition
a) Cyanide is a poison which prevents ATP production via aerobic respiration, leading to eventual death
b) By changing the shape of the active site, cytochrome oxidase can no longer pass electrons to the final acceptor (oxygen)
Definition of end-product inhibition
Negative feedback by which metabolic pathways can be controlled
Process of end-product inhibition
a) The final product in a series of reactions inhibits an enzyme from an earlier step in the sequence
b) The product binds to an allosteric site and temporarily inactivates the enzyme
Purpose of end-product inhibition
Ensure levels of an essential product are always tightly regulated
End-product inhibition of the pathway that converts threonine to isoleucine
a) Isoleucine may be synthesised from threonine in a five-step reaction pathway
b) First, threonine is converted into an intermediate compound by an enzyme.
c) Isoleucine can bind to an allosteric site on this enzyme and function as a non-competitive inhibitor
Competitive inhibition and maximum rate of enzyme activity
It can still be achieved by increasing substrate concentration
Noncompetitive inhibition and maximum rate of enzyme activity
The maximum rate of enzyme activity is reduced although substrate concentrations increase
Lock and Key Model
a) Active site complements the substrate precisely
b) Explains specificity
Induced Fit Model
a) Active site undergo conformational change when exposed to a substrate to improve binding.
b) Explains broad specificity and catalysis
