Enzymes
59 flashcards covering Enzymes for the MCAT Biology & Biochemistry section.
Enzymes are proteins that act as biological catalysts, speeding up chemical reactions in living organisms without being consumed in the process. They work by lowering the activation energy required for reactions, making essential processes like digestion and metabolism possible. For example, an enzyme might help break down food into smaller molecules, allowing your body to absorb nutrients efficiently. This concept is fundamental to understanding how cells function and maintain life.
On the MCAT, enzymes frequently appear in biology and biochemistry questions, often testing your knowledge of enzyme structure, function, and regulation. Expect multiple-choice questions on topics like enzyme kinetics, factors affecting activity (such as pH and temperature), and types of inhibition. Common traps include confusing competitive inhibition with non-competitive forms or overlooking allosteric regulation, so focus on applying concepts to real-world scenarios, like how enzymes relate to diseases or drug design. A solid grasp here can boost your score in passages and experiments.
Practice sketching enzyme-substrate complexes to visualize their interactions.
Terms (59)
- 01
Enzyme
A protein that acts as a biological catalyst, speeding up chemical reactions in cells by lowering the activation energy without being altered or consumed in the process.
- 02
Substrate
The specific molecule that an enzyme binds to and acts upon during a chemical reaction, fitting into the enzyme's active site to form an enzyme-substrate complex.
- 03
Active site
The specific region on an enzyme where the substrate binds and the catalytic reaction occurs, shaped to complement the substrate's structure.
- 04
Catalyst
A substance, such as an enzyme, that increases the rate of a chemical reaction by providing an alternative reaction pathway with lower activation energy, while remaining unchanged at the end.
- 05
Activation energy
The minimum energy required to start a chemical reaction, which enzymes reduce to make reactions proceed faster in biological systems.
- 06
Lock and key model
A model of enzyme action where the enzyme's active site is a rigid structure that exactly matches the substrate, like a key fitting into a lock, allowing for specific binding.
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Induced fit model
A model of enzyme-substrate interaction where the enzyme's active site changes shape slightly upon substrate binding, enhancing the fit and facilitating the reaction.
- 08
Enzyme specificity
The ability of an enzyme to catalyze reactions only with particular substrates, due to the unique shape and chemical properties of its active site.
- 09
Cofactor
A non-protein chemical component, such as a metal ion, that is required for an enzyme's full activity and often assists in the catalytic process.
- 10
Coenzyme
An organic molecule, often derived from vitamins, that acts as a cofactor by carrying chemical groups or electrons during enzymatic reactions.
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Apoenzyme
The protein portion of an enzyme that requires a cofactor or coenzyme to become active and perform its catalytic function.
- 12
Holoenzyme
The complete, active form of an enzyme, consisting of the apoenzyme bound to its necessary cofactor or coenzyme.
- 13
Optimum pH
The specific pH level at which an enzyme exhibits its maximum activity, as deviations can alter the enzyme's shape and function.
- 14
Optimum temperature
The temperature at which an enzyme functions most efficiently, typically around body temperature for human enzymes, beyond which denaturation may occur.
- 15
Denaturation
The process by which an enzyme loses its functional shape due to factors like heat or pH changes, rendering it unable to catalyze reactions.
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Enzyme inhibition
The reduction of an enzyme's activity by another molecule, which can be reversible or irreversible and serves as a regulatory mechanism in cells.
- 17
Competitive inhibition
A type of enzyme inhibition where an inhibitor molecule competes with the substrate for binding to the active site, reducing the enzyme's effectiveness.
- 18
Non-competitive inhibition
Inhibition where the inhibitor binds to a site on the enzyme other than the active site, altering the enzyme's shape and reducing its activity regardless of substrate presence.
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Uncompetitive inhibition
A form of enzyme inhibition where the inhibitor binds only to the enzyme-substrate complex, decreasing both the apparent Km and Vmax.
- 20
Allosteric inhibition
Inhibition that occurs when a molecule binds to an allosteric site on the enzyme, causing a conformational change that reduces the enzyme's activity.
- 21
Feedback inhibition
A regulatory mechanism where the end product of a metabolic pathway inhibits an enzyme earlier in the pathway, preventing overproduction.
- 22
Zymogen
An inactive precursor form of an enzyme that is activated by cleavage, such as in digestive enzymes to prevent self-digestion.
- 23
Michaelis-Menten kinetics
A model describing the rate of enzymatic reactions, where the reaction velocity increases with substrate concentration until reaching a maximum rate.
- 24
Km (Michaelis constant)
A measure of the substrate concentration at which an enzyme achieves half of its maximum velocity, indicating the enzyme's affinity for the substrate.
- 25
Vmax (maximum velocity)
The highest rate of an enzymatic reaction when the enzyme is fully saturated with substrate, reflecting the enzyme's maximum catalytic capacity.
- 26
Lineweaver-Burk plot
A graphical representation of enzyme kinetics, plotting the inverse of reaction velocity against the inverse of substrate concentration to determine Km and Vmax.
- 27
Turnover number
The number of substrate molecules converted to product per enzyme molecule per unit time, indicating the enzyme's catalytic efficiency.
- 28
Oxidoreductase
An enzyme class that catalyzes oxidation-reduction reactions, such as transferring electrons between molecules.
- 29
Transferase
An enzyme that catalyzes the transfer of a functional group, like a methyl or phosphate, from one molecule to another.
- 30
Hydrolase
An enzyme that speeds up hydrolysis reactions, breaking bonds in molecules by adding water, such as in digestion.
- 31
Lyase
An enzyme that catalyzes the addition or removal of groups to form double bonds, without hydrolysis or oxidation.
- 32
Isomerase
An enzyme that catalyzes the rearrangement of atoms within a molecule, converting it to its isomer form.
- 33
Ligase
An enzyme that joins two molecules together, often using ATP to form new bonds, such as in DNA replication.
- 34
DNA polymerase
An enzyme that synthesizes DNA by adding nucleotides to a growing chain, using a template strand during replication.
- 35
RNA polymerase
An enzyme that transcribes DNA into RNA by synthesizing a complementary RNA strand from a DNA template.
- 36
Lactase
An enzyme that breaks down lactose into glucose and galactose in the digestive system, with deficiency leading to lactose intolerance.
- 37
Amylase
An enzyme that catalyzes the hydrolysis of starch into sugars, found in saliva and pancreatic secretions.
- 38
Protease
An enzyme that breaks down proteins by hydrolyzing peptide bonds, important in digestion and protein turnover.
- 39
Lipase
An enzyme that hydrolyzes lipids into fatty acids and glycerol, aiding in fat digestion.
- 40
Kinase
An enzyme that transfers phosphate groups from ATP to other molecules, often activating proteins in signaling pathways.
- 41
Phosphatase
An enzyme that removes phosphate groups from molecules, often deactivating proteins in cellular regulation.
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Allosteric site
A specific location on an enzyme, distinct from the active site, where binding of a molecule causes a conformational change affecting activity.
- 43
Cooperativity
A phenomenon in some enzymes where the binding of a substrate to one site affects the affinity of other sites, either positively or negatively.
- 44
Hill coefficient
A value that measures the degree of cooperativity in enzyme kinetics, with values greater than 1 indicating positive cooperativity.
- 45
Transition state
The highest-energy state in a chemical reaction that enzymes stabilize to lower the activation energy and speed up the reaction.
- 46
Gibbs free energy
A thermodynamic measure that enzymes influence by lowering the activation energy barrier, making spontaneous reactions occur more readily.
- 47
Enzyme assay
A laboratory method to measure the activity of an enzyme by quantifying the rate of product formation or substrate consumption.
- 48
Initial velocity
The rate of an enzymatic reaction at the start, when substrate concentration is high and product accumulation is low, used in kinetics studies.
- 49
Mixed inhibition
A type of enzyme inhibition where the inhibitor binds to both the free enzyme and the enzyme-substrate complex, affecting both Km and Vmax.
- 50
Enzyme regulation
The control of enzyme activity through mechanisms like phosphorylation, allosteric modulation, or covalent modification to maintain cellular homeostasis.
- 51
Isozymes
Different forms of an enzyme that catalyze the same reaction but have variations in structure, kinetics, or regulation, such as lactate dehydrogenase variants.
- 52
pH and enzyme activity
The relationship where extreme pH levels can denature enzymes or alter ionization states, affecting their catalytic efficiency.
- 53
Temperature and enzyme activity
The effect where increasing temperature initially boosts enzyme activity up to the optimum, after which it declines due to denaturation.
- 54
Strategy for enzyme kinetics questions
When analyzing enzyme kinetics on the MCAT, first identify if the graph is Michaelis-Menten or Lineweaver-Burk, then determine how inhibitors alter Km and Vmax to predict outcomes.
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Common trap in inhibition identification
Students often confuse competitive and non-competitive inhibition; remember, competitive affects Km but not Vmax, while non-competitive affects Vmax but not Km.
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Example of feedback inhibition
In glycolysis, ATP inhibits phosphofructokinase, slowing the pathway when energy is abundant, preventing unnecessary glucose breakdown.
This helps cells conserve resources by regulating metabolic flux.
- 57
Enzyme immobilization
A technique where enzymes are attached to a solid support for repeated use in industrial or lab settings, maintaining activity while easing separation.
- 58
Restriction enzymes
Bacterial enzymes that cut DNA at specific sequences, used in molecular biology for techniques like gene cloning.
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Enzyme efficiency
A measure of how effectively an enzyme converts substrate to product, often quantified by the ratio of kcat to Km, indicating catalytic prowess.