Topic 8.1 Metabolism

Question 1

Metabolism

Answer 1

describes the sum total of all reactions that occur within an organism in order to maintain life

Question 2

Metabolic pathways

Answer 2

typically organized into chains or cycles of enzyme-catalyzed reactions

Question 3

Activation Energy

Answer 3

• Enzymes speed up the rate of a biochemical reaction by lowering the activation energy
• When an enzyme binds to a substrate it stresses and destabilizes the bonds in the substrate
• This reduces the overall energy level of the substrate’s transitionary state, meaning less energy is needed to convert it into a product and the reaction proceeds at a faster rate

Question 4

If the reactants contain more energy than the products…

Answer 4

the free energy is released into the system (exergonic), these reactions are usually catabolic (breaking down), as energy is released from broken bonds within a molecule

Question 5

If the reactants contain less energy than the products…

Answer 5

free energy is lost to the system (endergonic)

these reactions are usually anabolic (building up), as energy is required to synthesize bonds between molecules

Question 6

Enzyme Inhibition

Answer 6

Enzyme inhibitors prevent the formation of an enzyme-substrate complex and hence prevent the formation of product

Question 7

Normal Enzyme Reaction

Answer 7

• In a normal reaction, a substrate binds to an enzyme (via the active site) to form an enzyme-substrate complex
• The shape and properties of the substrate and active site are complementary, resulting in enzyme-substrate specificity
• When binding occurs, the active site undergoes a conformational change to optimally interact with the substrate (induced fit)
• This conformational change destabilizes chemical bonds within the substrate, lowering the activation energy
• As a consequence of enzyme interaction, the substrate is converted into product at an accelerated rate

Question 8

Competitive Inhibition

Answer 8

• Competitive inhibition involves a molecule, other than the substrate, binding to the enzyme’s active site
• The molecule (inhibitor) is structurally and chemically similar to the substrate (hence able to bind to the active site)
• The competitive inhibitor blocks the active site and thus prevents substrate binding
• As the inhibitor is in competition with the substrate, its effects can be reduced by increasing substrate concentration

Question 9

Noncompetitive Inhibition

Answer 9

• Non-competitive inhibition involves a molecule binding to a site other than the active site (an allosteric site)
• The binding of the inhibitor to the allosteric site causes a conformational change to the enzyme’s active site
• As a result of this change, the active site and substrate no longer share specificity, meaning the substrate cannot bind
• As the inhibitor is not in direct competition with the substrate, increasing substrate levels cannot mitigate the inhibitor’s effect

Question 10

Examples of enzyme inhibition

Answer 10

• An example of a use for a competitive inhibitor is in the treatment of influenza via the neuraminidase inhibitor, Relenza TM
• An example of a use for a non-competitive inhibitor is in the use of cyanide as a poison (prevents aerobic respiration)

Question 11

End-product inhibition

Answer 11

a form of negative feedback by which metabolic pathways can be controlled

Question 12

End-product inhibition functions

Answer 12

to ensure levels of an essential product are always tightly regulated

Question 13

Malaria

Answer 13

• The life cycle of the parasite requires both a human and mosquito host – hence the disease is transmitted via mosquito bites
• The maturation and development of the parasite in both human and mosquito host is coordinated by specific enzymes
• By targeting these enzymes for inhibition, new anti-malarial drugs and medications can be produced-