Enzymes and Metabolism Flashcards
End-Product Inhibition
The product of the last reaction of the metabolic pathway inhibits the enzyme that catalyzes the first reaction of the pathway
An example of Negative Feedback Inhibition
Can be reversible once concentration of end product decreases
Lock and Key Model
Enzyme can only bind to 1 substrate
The enzyme’s active site has a shape complementary to the substrate’s shape
The substrate binds to the enzyme perfectly forming enzyme-substrate complex
Products are released, while enzyme is unchanged and ready for another reaction
How Temperature Affects Reactions
At low temperatures, the enzyme and substrate molecules have little kinetic energy, this makes them move slowly and collide less frequently leading to lower rate of reaction
As temperature increases, kinetic energy increases and enzyme and substrate collide with each other more often which raises rate of reaction
The temperature at which the enzyme works most rapidly is optimum temperature
Right after optimum temperature, however, the temperature is too high and it changes the tertiary 3D structure of the enzyme, causing the substrate to no longer fit. At this point the enzyme is said to be denatured, and can no longer catalyze reactions
How Substrate Concentration Affects Reactions
As substrate concentration increases, collisions between enzyme and substrate increases, and therefore the faster the rate of reaction
However, at high substrate concentrations, it stops affecting the enzyme as it is saturated with substrate, and therefore no more active sites are available, leading the rate to remain constant
Advantages of End-Product Inhibition
If there is too much of an end product, the whole metabolic pathway stops working and less of the end product is produced
When levels of end product decrease, the inhibitor can release and allow the metabolic pathway to work and create end product again
Penicillin and Transpeptidase
Penicillin kills bacteria by irreversibly binding to the transpeptidase enzyme which is responsible for the cross linking of peptidoglycan during the formation of the cell wall
Without the cell wall, the bacteria is vulnerable to the external environment and dies quickly
Bacteria can also develop mutations to resist penicillin, which can change the active site of the transpeptidase enzyme which increases its resistance against penicillin
Difference between Anabolism and Catabolism
Anabolism is the synthesis of a complex molecule from simple molecules
Catabolism is the breakdown of a complex molecule into simpler molecules
Anabolism involves condensation reactions where H2O is released
Catabolism involves hydrolysis reactions where H2O is required
Energy is required in Anabolism
Energy is released in Catabolism
Activation Energy
The minimum amount of energy required in order to start a reaction
The higher the activation energy, the slower the reaction
Enzymes reduce activation energy by distorting the shape of the substrate when it binds to the active site
Substrate
The reactant in enzyme-catalyzed reactions
Mechanism-Based Inhibition (MBIs)
MBIs are molecules that irreversibly bind to the active site of the enzyme and make permanent chemical changes, making it never work as a catalyst again
Some living organisms create MBIs in order to kill another organism
Induced Fit Model
Enzyme can bind to multiple substrates
The enzyme’s active site doesn’t have a rigid shape and isn’t complementary to the substrate’s shape either
Active site and substrate change their shape slightly in order to have a perfect fit, forming enzyme-substrate complex
Products are released, while enzyme returns to original shape once the reaction is done
Factors Affecting Enzyme-Catalyzed Reactions
Temperature
pH
Substrate Concentration
Inhibitor
A substance that slows down the rate at which an enzyme works
How pH Affects Reactions
Each enzyme has an optimum pH
If this pH changes, this can cause a disturbance in their ionic bonds which can lead to a change in tertiary structure, which means the substrate can’t bind, therefore denaturing the enzyme
Difference with Endothermic and Exothermic Reaction
Endothermic is Anabolic
Exothermic is Catabolic
Endothermic requires energy
Exothermic releases energy
Energy of products is more than energy of reactants in Endothermic
Energy of products is less than energy of reactants in Exothermic
Benefits of Enzyme Specificity
Allows organisms to control metabolism
Prevents unwanted side reactions at a particular active site
Interaction between Substrate and Active Site
As the substrate grows closer to the active site, the chemical properties of the enzyme attract the substrate towards the active site to bind
The interactions between the substrate and active site cause bond lengths and angles to change, therefore changing both their 3D structures
Importance of Random Motion
Catalysis only happens when substrate is in liquid, so it needs random motion
Random motion increases the chances of collision between substrate and active site of enzyme
Role of Enzyme in Metabolism
Metabolism is the sum of all chemical reactions, with each chemical reaction being interdependent on one another
They usually form pathways which are organized into chains or cycles
Each chemical reaction in the pathway is unique and is controlled by a specific enzyme, and because of enzyme specificity, living organisms require many different enzymes in order to control metabolism
Variation in Molecular Motion of Substrates and Enzymes
Usually, the substrate is smaller than the active site so it moves more than the enzyme
Some substrates are very large and don’t move a lot, therefore enzymes move in relation to substrate
Some enzymes are embedded into the membrane and can’t move, in this case the substrate needs to do all the movement
Features of a Non-Competitive Inhibitor
Has a different structure to the substrate
Binds to the allosteric site of the enzyme, therefore changing the enzyme shape and preventing substrates from binding to the active site
Increasing substrate concentration won’t help
Rate will never reach maximum
Features of a Competitive Inhibitor
Has a similar structure to the normal substrate
Binds with the active site, and therefore competes with the substrate for the active site, thus reducing the number of enzyme-substrate complexes
Can be overcome with increasing substrate concentration
Rate will eventually reach maximum
Generation of Heat Energy
Endotherms (Warm-Blooded Animals) use the heat generated by metabolism to keep a stable internal body temperature
Some of the heat released by metabolism is used for cellular activities
Ectotherms (Cold-Blooded Animals) change their body temperature in response to the environment
Characteristics of Enzymes
Enzyme is a globular protein that acts as a biological catalyst
Enzymes are three dimensional with a hydrophilic R group on the outside to ensure solubility
Enzymes speed up a metabolic reaction
Enzymes are made of living things
Enzymes have specific shape and chemical properties to allow binding of specific substrate
Intracellular Enzymes and Extracellular Enzymes
Intracellular Enzymes: Catalyse the reactions in the cells, which are usually synthesized by free ribosomes
Extracellular Enzymes: Catalyse the reactions outside the cell, which are usually synthesized by ribosomes attached to the RER
Benefits of Increasing Rate of Reaction in Cells
Less time for product formation which enhances metabolism
Can enhance energy production to support various life processes
Active Site
A region on the surface of the enzyme which the substrate binds to and gets catalyzed
