C1.1  Enzymes and Metabolism

Theme:  Interaction and Interdependence

Interaction is the physical and chemical contact between molecules that allows life to function.

• The fundamental interaction between enzyme and substrate occurs at the active site.  The Induced Fit Model describes how the enzyme and substrate interact dynamically, changing shape slightly to improve the binding and lower the activation energy.
• ​Interactions aren't always productive. Competitive inhibitors interact with the active site, while non-competitive inhibitors interact with allosteric sites, changing the enzyme's shape and functionality.

Individual enzymatic reactions are interdependent on each other.

• Reactions rarely happen in a single step. They are interdependent sequences (chains or cycles) where the product of one enzyme becomes the substrate for the next. 
  
• End-product inhibition occurs when the final product of a pathway acts as an inhibitor for the first enzyme in that pathway. This creates a negative feedback loop, ensuring the cell does not waste energy creating more of a substance than it needs.

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• In what ways do variations in form allow diversity of function in carbohydrates and lipids?
• How do carbohydrates and lipids compare as energy storage compounds?

​
​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• How can compounds synthesized by living organisms accumulate and become carbon sinks?
• What are the roles of oxidation and reduction in biological systems?

Key Terms to Know: * higher level only

Activation Energy
Active Site
Allosteric Site*
Amino Acid
Anabolic
Antibiotic Resistance*
Bird (as endothermic)*
Calvin Cycle*
Catabolic
Catalyst
Cell Respiration
Collision Theory
Competitive Inhibitor*
Concentration
Condensation Reaction
Conformation*
Cyclical metabolism*

Denaturation
Digestion
Enzyme
Extracellular*
Feedback Inhibition*
Globular Protein
Glycogen
Glycolysis*
Heat*
Hydrolysis
Immobilized
Induced-Fit
Intracellular*
Isoleucine*
Kreb'S Cycle*
Linear metabolism*
Macromolecule

Mammal (as endothermic)*
Mechanism-Based Inhibition*
Metabolism
Molecular Motion
Monomer
Non-Competitive Inhibitor*
Oxidation
Penicillin*
pH
Photosynthesis
Protein Synthesis
Reaction Rate
Specificity
Statin*
Substrate
Temperature
Transpeptidase*

C1.1.1— Enzymes as catalysts.

• Define catalyst.
• State the role of enzymes in the chemical reactions on which life is based. ​
• State that enzymes speed up chemical reactions without being altered, so can be reused.
  

C1.1.2— Role of enzymes in metabolism.

• Define metabolism.
• Define specificity in relation to enzyme structure and function. 
• Outline how control of metabolism is regulated by enzymes.

C1.1.3—  Anabolic and catabolic reactions.

• Contrast anabolic and catabolic reactions.
• List three examples of anabolic processes. 
• List three examples of catabolic processes.

C1.1.4— Enzymes as globular proteins with an active site for catalysis.

• Outline properties of globular proteins. 
• Explain the relationship between enzyme structure and enzyme specificity, including the structure and function of the active site.​

C1.1.5— Interactions between substrate and active site to allow induced-fit binding.

• Outline the stages of enzyme catalysis of a chemical reaction.
• Describe the induced fit model of enzyme binding.​

C1.1.6- Role of molecular motion and substrate-active site collisions in enzyme catalysis.

• Explain the role of random collisions in the binding of the substrate with the enzyme active site.
• Compare enzyme and substrate movement involved in reactions that occur in the cytoplasm, with large substrates and with immobilized enzymes.

C1.1.7- Relationships between the structure of the active site, enzyme–substrate specificity and denaturation.

• Discuss variation in specificity of different enzymes. 
• Define denaturation.
• Outline the causes and effects of denaturation on enzyme structure and function.

C1.1.8- Effects of temperature, pH and substrate concentration on the rate of enzyme activity.

• Explain the effects of temperature, pH and substrate concentration on enzyme structure and function with reference to collision theory, temporary and permanent denaturation. 
• Draw and interpret graphs showing the effects of temperature, pH and substrate concentration of the activity of enzymes.

C1.1.9- Measurements in enzyme-catalyzed reactions.

• Identify the manipulated (independent), responding (dependent) and controlled variation in experiments of enzyme catalyzed reactions.
• State the unit for enzyme reaction rate.
• State two methods for determining the rate of enzyme reaction rates.
• Describe three investigative techniques for measuring the activity of an example enzyme.

C1.1.10- Effect of enzymes on activation energy. 

• Define activation energy.
• State that activation energy is used to break or weaken bonds in the substrate. 
• Explain the role of enzymes in lowering the activation energy of a reaction.
• Interpret graphs showing the effect of lowering the activation energy by enzymes.

AHL ​​​C1.1.11- Intracellular and extracellular enzyme-catalyzed reactions.

• Compare the location of synthesis of enzymes used within and outside of a cell. 
• State an example of an intracellular metabolic reaction  and an extracellular metabolic reaction.

AHL ​​​C1.1.12- Generation of heat energy by the reactions of metabolism.

• Outline the generation of heat energy by the reactions of metabolism. 
• Describe how birds and mammals maintain a body temperature greater than that of their environment.
• Outline an example of maintaining temperature homeostasis using heat generated by reactions of metabolism.

AHL ​​​C1.1.13- Cyclical and linear pathways in metabolism.

• State the reason for metabolic pathways.
• Contrast linear metabolic pathways with cyclical reaction pathways.
• State and example of a linear metabolic pathway and a cyclic  metabolic pathway.

AHL ​​​C1.1.14- Allosteric sites and non-competitive inhibition.

• Outline the structure and function of an allosteric site. 
• Define enzyme inhibitor.
• Describe mechanism of action of non-competitive enzyme inhibitors.

AHL ​​​C1.1.15- Competitive inhibition as a consequence of an inhibitor binding reversibly to an active site.

• Describe mechanism of action of competitive enzyme inhibitors. 
• Outline the function of statins as an example of a competitive inhibitor.
• Explain why the rate of reaction with increasing substrate concentration is lower with a non-competitive inhibitor compared to a competitive inhibitor.​

AHL ​​​C1.1.16- Regulation of metabolic pathways by feedback inhibition.

• Outline the mechanism and benefit of feedback inhibition.
• Illustrate end-product inhibition of the threonine to isoleucine metabolic pathway.​

AHL ​​​C1.1.17- Mechanism-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor.

• Compare reversible and irreversible enzyme inhibition.
• Outline the cause and consequence of mechanism-based inhibition.
• Illustrate mechanism-based inhibition using penicillin as an example.​