Enzymes and Metabolism Flashcards
What is an enzyme?
Enzyme: A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold (i.e. a biological catalyst) without being consumed in the process
What is metabolism?
Metabolism is the complex network of interdependent and interacting chemical reactions that occur in living organisms.
Most of these reactions happen inside cells but some are also extracellular reactions
They form pathways in which one type of molecule is transformed into another by a series of small steps. Most of these pathways are chains of reactions
Enzyme specificity
Each enzyme catalyzes one specific reaction, or a specific group of reactions
Because of enzyme specificity, living organisms have to make large numbers of ATP Formation different enzymes.
What is anabolism?
Anabolism is reactions that build up larger molecules from smaller ones. In order to do this, energy is required usually in the form of ATP
Examples of anabolic reactions
Protein synthesis, DNA replication, photosynthesis and synthesis of complex carbohydrates
What is catabolism?
Catabolism involves the breakdown of larger molecules into smaller ones. In the process, energy is released and is sometimes captured as ATP which can be used in the cell.
Examples of catabolism reactions
Digestion and cell respiration.
Importance of the shape of the enzyme
For a reaction to be catalyzed, the substrate must bind to the active site on the surface of the enzyme (The shapes must fit each other)
Typically, just a few amino acids at the active site are essential to create the chemical conditions that change the substrates enough to convert them into products
The 3-D structure of the enzyme is crucial and if altered, the structure of the active site may change and catalysis is unlikely to happen
How does enzymes induced fit model work?
An enzyme is a dynamic protein molecule that changes shape to better accommodate the substrate.
Some enzymes can catalyze multiple reactions. As the substrate approaches the enzyme, it induces a conformational change in the active site - it changes shape to fit the substrate. This stresses the substrate, reducing the activation energy of the reaction.
What is denaturation?
A denatured protein or enzyme does not return to its former structure - the denaturation is permanent.
Enzymes are proteins and denaturation is a key to how enzyme activity is affected by temperature and pH.
What causes denaturation?
Heat can cause denaturation: vibrations within the molecule breaks intermolecular bonds or interactions.
Extremes of pH can cause denaturation: charges on R groups are changed, breaking ionic bonds within the protein or causing new ionic bonds to form.
Effects of temperature on enzymes
Low temperatures result in insufficient thermal energy for the activation of a given enzyme-catalyzed reaction to be achieved.
Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity.
This is because a higher kinetic energy will result in more frequent collisions between the substrate and the active site. At an optimal temperature (differs for different enzymes), the rate of enzyme activity will be at its peak.
At high temperatures enzymes are denatured and stop working permanently. This is because heat causes vibrations inside enzymes which break bonds needed to maintain the structure of the enzyme.
Effects of pH on enzymes
At the optimal pH (a) and (b) the maximum rate of reaction is achieved. Above and below the optimal pH the rate decreases.
The change in rate is because bonds are made and broken which change the shape of the active site and therefore, decrease the rate of reaction.
This is why cell compartmentalization is important
Effects of substrate (reactant) concentration
Enzyme activity increases as the substrate concentration increases because the enzyme and the substrate encounter each other more frequently
After a certain point, adding more substrate does not increase the reaction rate because all the enzymes are saturated
