Active sites, inhibition, rate factors and the key digestive enzymes: flashcards and practice questions for GCSE and AP. Free, no sign-up.
Subject: biology
Which characteristic of enzymes primarily explains why cells require only tiny amounts of each enzyme to sustain metabolic processes?
Answer: They are biological catalysts that are not changed or used up by the reactions they accelerate.
Enzymes are biological catalysts that emerge unchanged from the reactions they catalyze. This reusability means a single enzyme molecule can facilitate thousands of reactions per second, making them highly efficient and requiring only small quantities within a cell.
Why is the induced fit model considered a more accurate representation of enzyme-substrate binding than the lock-and-key model?
Answer: The induced fit model explains how the active site can change shape to strain substrate bonds, facilitating the reaction.
The induced fit model refines the lock-and-key model by suggesting that the active site is not perfectly rigid. Instead, it molds itself more closely around the substrate upon binding, and this slight change in shape helps to strain the substrate's bonds, which facilitates the chemical reaction. This dynamic interaction is a key aspect of how enzymes lower activation energy.
What is the primary effect on an enzyme's structure and activity when it is exposed to temperatures significantly above its optimum?
Answer: The enzyme denatures, losing its tertiary structure and active site shape, leading to a steep and irreversible loss of activity.
Above an enzyme's optimum temperature, the excessive kinetic energy breaks the hydrogen bonds and other weak interactions that maintain the protein's tertiary structure. This causes the active site to lose its specific shape, rendering it unable to bind the substrate effectively. This process, called denaturation, is usually irreversible and results in a steep decline in enzyme activity.
How do competitive and non-competitive inhibitors differ in their binding location and the effect on an enzyme's maximum reaction rate (Vₘₐₓ)?
Answer: Competitive inhibitors bind to the active site and can be overcome by increasing substrate concentration to restore Vₘₐₓ, whereas non-competitive inhibitors bind to an allosteric site and lower Vₘₐₓ regardless of substrate concentration.
Competitive inhibitors resemble the substrate and bind directly to the active site, competing with the substrate. This competition can be overcome by increasing substrate concentration, allowing Vₘₐₓ to be reached. Non-competitive inhibitors, however, bind to an allosteric site (away from the active site), changing the enzyme's shape and distorting the active site. This type of inhibition cannot be overcome by adding more substrate, resulting in a lowered Vₘₐₓ.
How do enzymes accelerate chemical reactions?
Answer: By lowering the activation energy required to start the reaction.
Enzymes function as catalysts by lowering the activation energy of the reactions they catalyze. This means less energy is needed to destabilize existing bonds, allowing the reaction to proceed much faster. Enzymes do not change the overall energy released or absorbed (ΔG), nor do they shift the equilibrium position or supply energy.
What is the role of a cofactor in enzyme function?
Answer: Cofactors are non-protein helpers that many enzymes require to become active.
Many enzymes are inactive as bare proteins and require a non-protein helper molecule called a cofactor to function. These can be inorganic (like metal ions) or organic (called coenzymes, often derived from vitamins).
Which enzyme breaks down starch into maltose?
Answer: Amylase
Amylase is the enzyme responsible for breaking down starch into maltose, primarily found in the mouth (salivary amylase) and small intestine (pancreatic amylase).
Which enzyme acts on proteins to produce shorter peptides in the stomach?
Answer: Pepsin
Pepsin is secreted as an inactive precursor (pepsinogen) and activated in the acidic environment of the stomach to break down proteins into shorter peptides.
Which enzyme is secreted by the pancreas and acts in the small intestine to break down proteins and peptides into smaller peptides?
Answer: Trypsin
Trypsin is secreted by the pancreas as inactive trypsinogen and activated in the small intestine, where it breaks down proteins and peptides into smaller peptides.
Which enzyme breaks down lipids (fats and oils) into fatty acids and glycerol in the small intestine?
Answer: Lipase
Lipase is secreted by the pancreas and acts in the small intestine to digest lipids (fats and oils) into fatty acids and glycerol.
Which enzyme breaks down lactose into glucose and galactose in the small intestine?
Answer: Lactase
Lactase is found in the small intestine and is responsible for breaking down the disaccharide lactose into its constituent monosaccharides, glucose and galactose.
Which enzyme breaks down hydrogen peroxide (H₂O₂) into water and oxygen inside cells, especially liver cells?
Answer: Catalase
Catalase is a very fast enzyme that destroys the toxic by-product hydrogen peroxide, converting it into harmless water and oxygen.
What is a catalyst?
Answer: A substance that speeds up a reaction without being used up by it.
A catalyst, including biological catalysts like enzymes, is defined as a substance that increases the rate of a chemical reaction without being consumed or permanently altered in the process.
What is the substrate in an enzyme-catalyzed reaction?
Answer: The molecule that binds to the enzyme's active site and is acted upon.
The substrate is the specific molecule or molecules upon which an enzyme acts. It binds to the enzyme's active site, where the catalytic reaction takes place.
What is the active site of an enzyme?
Answer: A pocket on the enzyme's surface where the substrate binds and the reaction occurs.
The active site is a specific, small region on the enzyme's surface, formed by particular amino acids, where the substrate binds to form an enzyme-substrate complex and the catalytic reaction takes place.
What is an enzyme-substrate complex?
Answer: A temporary unit formed when the substrate is bound to the active site.
An enzyme-substrate complex is a transient intermediate formed when the substrate molecule physically binds to the enzyme's active site, allowing the catalytic reaction to proceed.
What is activation energy?
Answer: The energy input needed to start a reaction, which enzymes lower.
Activation energy is the initial energy barrier that must be overcome for a chemical reaction to begin. Enzymes accelerate reactions by providing an alternative pathway with a lower activation energy.
What is denaturation in the context of enzymes?
Answer: The loss of an enzyme's tertiary structure and active-site shape, e.g., by heat or extreme pH.
Denaturation refers to the process where an enzyme (a protein) loses its specific three-dimensional structure, particularly the active site, due to factors like excessive heat or extreme pH. This loss of shape renders the enzyme inactive.
What does Vₘₐₓ represent in enzyme kinetics?
Answer: The maximum reaction rate, reached when all active sites are saturated with substrate.
Vₘₐₓ (maximum velocity) is the highest reaction rate an enzyme can achieve when all its active sites are fully occupied by substrate molecules, meaning the enzyme is saturated.
What is a competitive inhibitor?
Answer: An inhibitor that resembles the substrate and binds to the active site, blocking it.
A competitive inhibitor has a similar shape to the enzyme's natural substrate and competes with it for binding to the active site, thereby reducing enzyme activity.
What is a non-competitive inhibitor?
Answer: An inhibitor that binds to an allosteric site, distorting the active site indirectly.
A non-competitive inhibitor binds to a site on the enzyme other than the active site (an allosteric site). This binding causes a conformational change in the enzyme, which distorts the active site and reduces its ability to bind substrate or catalyze the reaction effectively.
What is a coenzyme?
Answer: An organic cofactor, often derived from a vitamin.
Coenzymes are a specific type of cofactor that are organic molecules. Many are derived from vitamins, such as NAD⁺ from niacin or FAD from riboflavin.
What is a prosthetic group?
Answer: A cofactor that is permanently and tightly bound to its enzyme.
A prosthetic group is a specific type of cofactor that is distinguished by being permanently and tightly associated with its enzyme, such as the heme group in catalase.
What is the induced fit model?
Answer: A model in which the active site molds around the substrate as it binds, straining its bonds.
The induced fit model, proposed by Daniel Koshland, suggests that the active site is not perfectly rigid but rather undergoes a slight conformational change to mold more closely around the substrate upon binding. This dynamic adjustment helps to optimize the fit and strain the substrate's bonds, facilitating the reaction.
What is an allosteric site?
Answer: A binding site on an enzyme away from the active site.
An allosteric site is a regulatory binding site on an enzyme that is distinct from the active site. Binding of molecules (like non-competitive inhibitors or allosteric regulators) to this site can cause conformational changes that affect the active site's function.
What is the optimum temperature for an enzyme?
Answer: The temperature at which an enzyme's rate is highest.
The optimum temperature is the specific temperature at which an enzyme exhibits its maximum catalytic activity. Beyond this point, higher temperatures lead to denaturation and a rapid decrease in activity.
A biological catalyst that speeds up a chemical reaction without being changed or used up by it is called an {0}.
Answer: enzyme
An enzyme is a biological catalyst that remains unchanged after a reaction, allowing it to catalyze many reactions.
A substance that speeds up a chemical reaction without being used up by it is known as a {0}.
Answer: catalyst
A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process.
The molecule an enzyme acts upon is called its {0}.
Answer: substrate
The substrate is the specific molecule that an enzyme binds to and acts upon during a chemical reaction.
The small pocket on an enzyme's surface where catalysis occurs and the substrate binds is called the {0}.
Answer: active site
The active site is the specific region on an enzyme where the substrate binds and the chemical reaction takes place.
The initial input of energy required to start a chemical reaction is known as the {0}.
Answer: activation energy
Enzymes work by lowering the activation energy, which is the energy needed to destabilize existing bonds so a reaction can proceed.
The loss of an enzyme's tertiary structure and active-site shape, often due to heat or extreme pH, is called {0}.
Answer: denaturation
Denaturation causes an enzyme to lose its specific shape, particularly that of its active site, rendering it inactive.
The model where the active site molds itself more closely around the substrate as it binds is known as the {0} model.
Answer: induced fit
The induced fit model suggests that the active site is flexible and changes shape slightly to accommodate the substrate, facilitating the reaction.
An inhibitor that has a shape similar to the substrate and binds directly to the active site, blocking it, is a {0}.
Answer: competitive inhibitor
Competitive inhibitors compete with the substrate for binding to the active site, reducing enzyme activity.
An inhibitor that binds to an allosteric site, away from the active site, and distorts the active site's shape is a {0}.
Answer: non-competitive inhibitor
Non-competitive inhibitors bind to a site other than the active site, causing a conformational change that reduces the enzyme's ability to bind substrate or catalyze the reaction.
Many enzymes require a non-protein helper molecule called a {0} to function.
Answer: cofactor
Cofactors are non-protein chemical compounds or metallic ions that are required for an enzyme's activity as a catalyst.
Organic cofactors, often derived from vitamins, are specifically called {0}.
Answer: coenzyme
Coenzymes are organic cofactors that assist enzymes in catalyzing reactions, with many being derived from vitamins.
The temperature at which an enzyme's reaction rate is highest is known as its {0}.
Answer: optimum temperature
At the optimum temperature, enzyme activity is maximal due to frequent collisions without denaturation.
loading your study session...