Enzymes Flashcards
Chapter 9
What are enzymes?
Enzymes are biological catalysts that speed up chemical reactions in living cells by lowering the activation energy required for the reaction.
How do enzymes function?
A: Enzymes function by reducing the activation energy of reactions, thereby increasing the reaction rate.
What is a substrate?
A substrate is the specific substance or chemical that an enzyme acts upon.
What is the enzyme-substrate complex?
It is the intermediate formed when an enzyme binds to its substrate, facilitating the reaction and leading to product formation.
List three properties of enzymes.
Enzymes are highly specific.
They remain unchanged at the end of a reaction.
They are affected by pH, temperature, and concentration.
What is activation energy?
Activation energy is the energy required to initiate a reaction. Enzymes lower this energy.
Describe the lock and key hypothesis.
The lock and key hypothesis states that the enzyme’s active site has a specific shape that fits the substrate perfectly, similar to a key fitting into a lock.
List three factors affecting enzyme activity.
Temperature
pH
Substrate concentration
How does temperature affect enzyme activity?
Enzyme activity increases with temperature up to an optimum point (37°C-40°C for mammals) but decreases when the temperature exceeds this range due to denaturation.
What happens to enzymes at low temperatures?
At low temperatures, enzymes become inactivated but regain functionality when the temperature rises to the optimum range.
How does pH affect enzyme activity?
Enzymes have an optimum pH range, and deviations from this range can lead to denaturation and loss of activity due to disruption of ionic bonds.
How does substrate concentration affect enzyme activity?
Increased substrate concentration raises reaction rates until active sites are saturated, beyond which the rate plateaus.
What happens when enzyme concentration increases?
The reaction rate increases proportionally, provided the substrate is in excess.
What is feedback inhibition?
A regulatory mechanism where the end product of a reaction inhibits the activity of an enzyme earlier in the pathway.
Define competitive inhibition.
Competitive inhibition occurs when an inhibitor competes with the substrate for the enzyme’s active site, reducing reaction rate.
Define noncompetitive inhibition.
Noncompetitive inhibition occurs when an inhibitor binds to an allosteric site, altering the enzyme’s shape and reducing its activity, independent of substrate concentration.
What is uncompetitive inhibition?
Uncompetitive inhibition occurs when inhibitors bind permanently to the enzyme, either at the active site or elsewhere, causing irreversible inhibition.
What are enzyme cofactors?
Enzyme cofactors are non-protein components required for efficient enzyme activity:
-inorganic ions
-prosthetic groups
-coenzymes.
What are inorganic ions
The ion required to form a coordinate bond at the enzyme active site
Name an example of an inorganic ion as a cofactor.
Zn²⁺
-Chloride ions enhance the activity of salivary amylase.
What is a prosthetic group?
A prosthetic group is a tightly bound organic molecule that assists enzymes in catalysis, e.g., FAD in the respiratory chain.
What are coenzymes?
Coenzymes are organic molecules derived from vitamins that bind temporarily to enzymes during catalysis, e.g., NAD, ATP, and Coenzyme A.
What are oxidoreductases?
Enzymes that catalyze oxidation-reduction reactions, e.g., pyruvate dehydrogenase.
What are transferases?
Enzymes that transfer functional groups between molecules, e.g., transaminase.
What are hydrolases?
Enzymes that catalyze hydrolysis reactions by breaking chemical bonds with water, e.g., lipases and peptidases.
What are lyases?
nzymes that break chemical bonds or form double bonds by adding or removing atoms, e.g., aldolases.
What are isomerases?
Enzymes that catalyze structural changes within a molecule, e.g., phosphoglucomutase.
What are ligases?
Enzymes that join two molecules together, e.g., DNA ligase.
What are allosteric enzymes?
Enzymes regulated by molecules binding to allosteric sites, which alter the enzyme’s activity.
Define denaturation.
Denaturation is the loss of an enzyme’s functional shape due to factors like high temperature or extreme pH.
How do heavy metal ions act as enzyme inhibitors?
Heavy metal ions like Hg²⁺ and Ag⁺ bind to enzyme sulfhydryl groups, leading to irreversible inhibition.
Give an example of a metabolic poison acting as an enzyme inhibitor.
Arsenic binds permanently to enzyme groups, disrupting catalysis.
