IB TOPIC 8 | METABOLISM, CELL RESPIRATION AND PHOTYOSYNTHESIS
2016 | SYJ0014
Topic 8.1: Metabolism, cell respiration and photosynthesis – Metabolism
Metabolic reactions are regulated in response to the cell’s needs.
• Understanding: Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.
Metabolism: chemical reactions that take place in living cells of an organism
Metabolic pathway: series of chains and cycles of interconnected enzyme-catalysed biochemical reaction
Sequential nature: most chemical reaction happens in a sequence of small steps that overall form a metabolic pathway
• Understanding: Enzymes lower the activation energy of the chemical reactions that they catalyse.
Biochemical reaction: the transformation of one molecule to a different molecule inside a cell,
mediated and catalyzed by enzymes within the cell
Transition state: state that must be reached for a reaction to proceed
Activation energy: energy required for substrate to reach transition state
Substrate: substance involved in reaction with enzyme to form products
Products: substance formed in a reaction from the substrates with enzyme
Enzymes: biological catalysts that alter the rate of specific reaction reactions inside cells
Lowers activation energy: enzyme lowers the energy required for the substrate to
reach the transition state in a reaction
Increases rate of reaction: lowering activation energy increases the chance of
substrate to have sufficient energy, hence increases reaction rate
• Understanding: Enzyme inhibitors can be competitive or non-competitive.
• Skill: Distinguishing different types of inhibition from graphs at specified substrate concentration.
Inhibitors: chemical substances that reduce the activity of enzymes
Competitive inhibitors: chemical structurally similar to substrate competes directly with substrate for active site
Non-competitive inhibitors: interferes with allosteric site to result in change of shape in the enzyme prevent reaction
Allosteric site: site where regulating chemical substances binds to away from the active site
Competitive inhibitors Non-competitive inhibitors
Mechanism Interferes with the active site of the enzyme Interferes with the allosteric site of the enzyme
Diagram
y-axis: reaction rate
x-axis: substrate
concentration
Characteristics Same maximum rate (Vmax) Different maximum rate (Vmax)
Different pattern in increase (different Km) Same pattern in increase (same Km)
Description When the concentration of substrate excess the amount of Inhibitor does not compete with substrate and binds with
inhibitors, the substrate outcompetes the inhibitor and allosteric site of enzymes regardless of concentration of
maximum rate may be achieved substrates
Example Ethanol to inhibit the oxidization of methanol by alcohol Xylitol-5-phosphate that inhibits phosphorylation of
dehydrogenase (ethanol produce less toxic by-products) fructose-6-phosphate by phosphofructokinase
• Understanding: Metabolic pathways can be controlled by end-product inhibition.
The end product of a metabolic pathway often binds to the allosteric site of the first enzyme of the chain to prevent build-up of intermediates
In low quantity of end products: metabolic pathway works rapidly
In high quantity of end products: metabolic pathway is inhibited by end products
• Application: End-product inhibition of the pathway that converts threonine to isoleucine.
Process of end-product inhibition of threonine to isoleucine:
Reaction pathway: amino acid threonine is converted to isoleucine in a
reaction pathway involving series of five reaction
End product inhibition: isoleucine acts as a non-competitive inhibitor to
threonine deaminase (first enzyme of the reaction)
Concentration if isoleucine increases: isoleucine binds to allosteric site
(reversible) acting as a non-competitive inhibitor
Concentration of isoleucine decreases: isoleucine is no longer present to
inhibit threonine; pathway restarts
LAST EDITED 2017-03-17 | 1
, IB TOPIC 8 | METABOLISM, CELL RESPIRATION AND PHOTYOSYNTHESIS
2016 | SYJ0014
• Application: Use of databases to identify potential new anti-malarial drugs.
Malaria: disease caused by pathogen Plasmodium falciparum
Build-up of malaria resistance: P. falciparum is developing increasing resistance to anti-malaria drugs
Develop of malaria chemical inhibition: study involves screening of 310,000 chemicals to test for malaria chemical inhibition
19 new chemicals inhibited enzyme normal targeted by anti-malarial drugs
15 chemicals bind to a total of 61 material proteins
• Skill: Calculating and plotting rates of reaction from raw experimental results.
Determination the rate of enzyme controlled reaction:
Measure rate of disappearance of reactants (mass, volume etc.)
Measure rate of appearance of a product (mass, volume etc.)
• Nature of science: Developments in scientific research follow improvements in computing—developments in bioinformatics, such as the
interrogation of databases, have facilitated research into metabolic pathways.
• Utilization: Many enzyme inhibitors have been used in medicine. For example ethanol has been used to act as a competitive inhibitor for antifreeze
poisoning.
• Utilization: Fomepizole, which is an inhibitor of alcohol dehydrogenase, has also been used for antifreeze poisoning.
• Guidance: Enzyme inhibition should be studied using one specific example for competitive and non-competitive inhibition.
LAST EDITED 2017-03-17 | 2
2016 | SYJ0014
Topic 8.1: Metabolism, cell respiration and photosynthesis – Metabolism
Metabolic reactions are regulated in response to the cell’s needs.
• Understanding: Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.
Metabolism: chemical reactions that take place in living cells of an organism
Metabolic pathway: series of chains and cycles of interconnected enzyme-catalysed biochemical reaction
Sequential nature: most chemical reaction happens in a sequence of small steps that overall form a metabolic pathway
• Understanding: Enzymes lower the activation energy of the chemical reactions that they catalyse.
Biochemical reaction: the transformation of one molecule to a different molecule inside a cell,
mediated and catalyzed by enzymes within the cell
Transition state: state that must be reached for a reaction to proceed
Activation energy: energy required for substrate to reach transition state
Substrate: substance involved in reaction with enzyme to form products
Products: substance formed in a reaction from the substrates with enzyme
Enzymes: biological catalysts that alter the rate of specific reaction reactions inside cells
Lowers activation energy: enzyme lowers the energy required for the substrate to
reach the transition state in a reaction
Increases rate of reaction: lowering activation energy increases the chance of
substrate to have sufficient energy, hence increases reaction rate
• Understanding: Enzyme inhibitors can be competitive or non-competitive.
• Skill: Distinguishing different types of inhibition from graphs at specified substrate concentration.
Inhibitors: chemical substances that reduce the activity of enzymes
Competitive inhibitors: chemical structurally similar to substrate competes directly with substrate for active site
Non-competitive inhibitors: interferes with allosteric site to result in change of shape in the enzyme prevent reaction
Allosteric site: site where regulating chemical substances binds to away from the active site
Competitive inhibitors Non-competitive inhibitors
Mechanism Interferes with the active site of the enzyme Interferes with the allosteric site of the enzyme
Diagram
y-axis: reaction rate
x-axis: substrate
concentration
Characteristics Same maximum rate (Vmax) Different maximum rate (Vmax)
Different pattern in increase (different Km) Same pattern in increase (same Km)
Description When the concentration of substrate excess the amount of Inhibitor does not compete with substrate and binds with
inhibitors, the substrate outcompetes the inhibitor and allosteric site of enzymes regardless of concentration of
maximum rate may be achieved substrates
Example Ethanol to inhibit the oxidization of methanol by alcohol Xylitol-5-phosphate that inhibits phosphorylation of
dehydrogenase (ethanol produce less toxic by-products) fructose-6-phosphate by phosphofructokinase
• Understanding: Metabolic pathways can be controlled by end-product inhibition.
The end product of a metabolic pathway often binds to the allosteric site of the first enzyme of the chain to prevent build-up of intermediates
In low quantity of end products: metabolic pathway works rapidly
In high quantity of end products: metabolic pathway is inhibited by end products
• Application: End-product inhibition of the pathway that converts threonine to isoleucine.
Process of end-product inhibition of threonine to isoleucine:
Reaction pathway: amino acid threonine is converted to isoleucine in a
reaction pathway involving series of five reaction
End product inhibition: isoleucine acts as a non-competitive inhibitor to
threonine deaminase (first enzyme of the reaction)
Concentration if isoleucine increases: isoleucine binds to allosteric site
(reversible) acting as a non-competitive inhibitor
Concentration of isoleucine decreases: isoleucine is no longer present to
inhibit threonine; pathway restarts
LAST EDITED 2017-03-17 | 1
, IB TOPIC 8 | METABOLISM, CELL RESPIRATION AND PHOTYOSYNTHESIS
2016 | SYJ0014
• Application: Use of databases to identify potential new anti-malarial drugs.
Malaria: disease caused by pathogen Plasmodium falciparum
Build-up of malaria resistance: P. falciparum is developing increasing resistance to anti-malaria drugs
Develop of malaria chemical inhibition: study involves screening of 310,000 chemicals to test for malaria chemical inhibition
19 new chemicals inhibited enzyme normal targeted by anti-malarial drugs
15 chemicals bind to a total of 61 material proteins
• Skill: Calculating and plotting rates of reaction from raw experimental results.
Determination the rate of enzyme controlled reaction:
Measure rate of disappearance of reactants (mass, volume etc.)
Measure rate of appearance of a product (mass, volume etc.)
• Nature of science: Developments in scientific research follow improvements in computing—developments in bioinformatics, such as the
interrogation of databases, have facilitated research into metabolic pathways.
• Utilization: Many enzyme inhibitors have been used in medicine. For example ethanol has been used to act as a competitive inhibitor for antifreeze
poisoning.
• Utilization: Fomepizole, which is an inhibitor of alcohol dehydrogenase, has also been used for antifreeze poisoning.
• Guidance: Enzyme inhibition should be studied using one specific example for competitive and non-competitive inhibition.
LAST EDITED 2017-03-17 | 2
