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Summary IB Biology Topic 8: Metabolism, Cell Respiration and Photosynthesis
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  • Module
  • Biology SL and HL
  • Institution
  • International Baccalaureate Diploma
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  • IB Biology Course Book

Detailed objective-by-objective summary notes for Topic 8: Metabolism, Cell Respiration and Photosynthesis for IB Biology SL/HL. Contains information on everything you need to know from 8.1 to 8.3, according to each understanding, application or skill. Written by a IB HL Biology student who gradua...

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  • March 5, 2019
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  • 2016/2017
  • Summary

Subjects

  • biology
  • ib biology
  • metabolism
  • cell respiration
  • photosynthesis
  • topic 8
  • ib
  • international baccalaureate
  • hl
  • sl

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  • International Baccalaureate Diploma
  • Biology SL and HL
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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

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