All Study Guides Biological Chemistry I Unit 5
🔬 Biological Chemistry I Unit 5 – Enzymes – Kinetics and RegulationEnzymes are protein catalysts that speed up chemical reactions in living organisms. They're essential for life processes, operating under mild conditions and catalyzing reactions up to 10^17 times faster than uncatalyzed reactions.
Enzyme structure determines function, with the active site binding specific substrates. Enzyme kinetics studies reaction rates, using models like Michaelis-Menten. Factors like temperature, pH, and inhibitors affect enzyme activity, which is tightly regulated in cells.
Got a Unit Test this week? we crunched the numbers and here's the most likely topics on your next test What Are Enzymes?
Enzymes are biological catalysts that speed up chemical reactions in living organisms
Composed of proteins folded into specific three-dimensional structures
Catalyze reactions by lowering the activation energy required for the reaction to occur
Highly specific, each enzyme catalyzes a particular reaction or set of related reactions
Essential for life, involved in processes such as digestion, metabolism, and DNA replication
Operate under mild conditions (physiological temperature and pH) unlike many industrial catalysts
Capable of catalyzing reactions at rates up to 10^17 times faster than uncatalyzed reactions
Produced by living cells and can be isolated and used in various applications (food processing, medicine, biotechnology)
Enzyme Structure and Function
Enzymes are primarily composed of amino acids linked together by peptide bonds
Amino acid sequence determines the unique three-dimensional structure of each enzyme
Active site is the region where the substrate binds and the catalytic reaction occurs
Shaped to fit the specific substrate, often described as a "lock and key" or "induced fit" model
Contains amino acid residues that interact with the substrate and facilitate the reaction
Cofactors are non-protein molecules that some enzymes require for catalytic activity
Can be inorganic (metal ions like Fe^2+, Mg^2+, Zn^2+) or organic (coenzymes such as vitamins)
Enzymes are not consumed during the reaction and can catalyze multiple rounds of the same reaction
Enzyme activity can be affected by factors such as temperature, pH, and the presence of inhibitors or activators
Some enzymes have regulatory sites distinct from the active site that modulate their activity
Enzyme Kinetics Basics
Enzyme kinetics is the study of the rates of enzyme-catalyzed reactions
Reaction rate depends on the concentration of enzyme, substrate, and any cofactors or inhibitors
Initial reaction rate (v 0 v_0 v 0 ) is measured when the substrate concentration is much higher than the enzyme concentration
Michaelis-Menten kinetics describes the relationship between substrate concentration and reaction rate for many enzymes
Assumes a simple two-step reaction: E + S ⇌ ES → E + P
K m K_m K m (Michaelis constant) is the substrate concentration at which the reaction rate is half of the maximum rate (V m a x V_max V m a x )
Lineweaver-Burk plot (double reciprocal plot) is used to determine V m a x V_max V m a x and K m K_m K m from experimental data
Turnover number (k c a t k_cat k c a t ) represents the maximum number of substrate molecules converted to product per enzyme molecule per unit time
Catalytic efficiency (k c a t / K m k_cat/K_m k c a t / K m ) is a measure of how efficiently an enzyme converts substrate to product
Michaelis-Menten Equation
The Michaelis-Menten equation describes the kinetics of many enzyme-catalyzed reactions:
v = V m a x [ S ] K m + [ S ] v = \frac{V_max[S]}{K_m + [S]} v = K m + [ S ] V m a x [ S ]
v v v is the reaction rate, V m a x V_max V m a x is the maximum rate, [ S ] [S] [ S ] is the substrate concentration, and K m K_m K m is the Michaelis constant
Assumes a simple two-step reaction mechanism: E + S ⇌ ES → E + P
E is the enzyme, S is the substrate, ES is the enzyme-substrate complex, and P is the product
At low substrate concentrations, the reaction rate is approximately proportional to the substrate concentration (first-order kinetics)
At high substrate concentrations, the reaction rate approaches V m a x V_max V m a x and is independent of substrate concentration (zero-order kinetics)
The Michaelis constant K m K_m K m is equal to the substrate concentration at which the reaction rate is half of V m a x V_max V m a x
A lower K m K_m K m indicates a higher affinity of the enzyme for the substrate
The turnover number k c a t k_cat k c a t is related to V m a x V_max V m a x by the equation: V m a x = k c a t [ E ] T V_max = k_cat[E]_T V m a x = k c a t [ E ] T , where [ E ] T [E]_T [ E ] T is the total enzyme concentration
Factors Affecting Enzyme Activity
Temperature influences enzyme activity by affecting the kinetic energy of molecules and the stability of the enzyme structure
Optimal temperature is the temperature at which the enzyme exhibits maximum activity
Higher temperatures can denature enzymes, causing a loss of activity
pH affects enzyme activity by altering the ionization state of amino acid residues in the active site and the enzyme structure
Optimal pH is the pH at which the enzyme exhibits maximum activity
Extreme pH values can denature enzymes or alter the ionization of key residues
Ionic strength and the presence of salts can affect enzyme activity by influencing the solubility and stability of the enzyme and substrate
Substrate concentration affects the reaction rate, as described by the Michaelis-Menten equation
Product concentration can influence the reaction rate through product inhibition or by shifting the equilibrium of reversible reactions
Enzyme concentration directly affects the reaction rate, with higher concentrations leading to faster rates until the substrate becomes limiting
Presence of inhibitors or activators can modulate enzyme activity by binding to the enzyme and altering its structure or function
Enzyme Inhibition and Activation
Enzyme inhibitors are molecules that decrease enzyme activity by binding to the enzyme
Competitive inhibitors bind to the active site, competing with the substrate
Increase the apparent K m K_m K m without affecting V m a x V_max V m a x
Can be overcome by increasing the substrate concentration
Non-competitive inhibitors bind to a site other than the active site, altering the enzyme's structure and function
Decrease V m a x V_max V m a x without affecting K m K_m K m
Cannot be overcome by increasing the substrate concentration
Uncompetitive inhibitors bind only to the enzyme-substrate complex, not to the free enzyme
Decrease both V m a x V_max V m a x and K m K_m K m
Mixed inhibitors can bind to both the free enzyme and the enzyme-substrate complex
Affect both V m a x V_max V m a x and K m K_m K m , depending on the relative affinities for the free enzyme and the complex
Enzyme activators are molecules that increase enzyme activity by binding to the enzyme
Allosteric activators bind to a site other than the active site, inducing a conformational change that enhances activity
Some activators are required for enzyme function, such as certain metal ions or coenzymes
Enzyme Regulation in Cells
Enzyme activity is tightly regulated in cells to maintain homeostasis and respond to changing conditions
Allosteric regulation involves the binding of effector molecules to sites other than the active site, modulating enzyme activity
Allosteric enzymes often have multiple subunits and exhibit cooperative binding of substrates or effectors
Positive cooperativity occurs when the binding of one substrate molecule enhances the binding of subsequent molecules
Negative cooperativity occurs when the binding of one substrate molecule reduces the affinity for subsequent molecules
Covalent modification, such as phosphorylation or acetylation, can regulate enzyme activity by altering the enzyme's structure or function
Feedback inhibition is a common regulatory mechanism in metabolic pathways
The end product of a pathway inhibits the activity of an earlier enzyme in the pathway, preventing excessive production
Compartmentalization of enzymes within the cell can control their access to substrates and regulate their activity
Gene expression can be regulated to control the amount of enzyme produced in response to cellular needs
Induction is the increased expression of an enzyme in response to the presence of its substrate or other signals
Repression is the decreased expression of an enzyme when its activity is not needed
Real-World Applications
Industrial biocatalysis uses enzymes to catalyze reactions in the production of chemicals, pharmaceuticals, and food ingredients
Enzymes offer high specificity, mild reaction conditions, and reduced environmental impact compared to traditional chemical processes
Examples include the use of lipases in detergents, proteases in leather processing, and glucose isomerase in high-fructose corn syrup production
Medical applications of enzymes include diagnostic tests, enzyme replacement therapies, and targeted drug delivery
Diagnostic tests measure the activity of specific enzymes to detect diseases (liver function tests, cardiac markers)
Enzyme replacement therapies provide functional enzymes to treat genetic disorders (Gaucher disease, Fabry disease)
Enzymes can be conjugated to drugs or antibodies for targeted delivery to specific tissues or cells
Biotechnology and genetic engineering use enzymes for DNA manipulation, protein production, and metabolic engineering
Restriction enzymes are used to cut DNA at specific sequences for cloning and gene manipulation
DNA polymerases are used in polymerase chain reaction (PCR) to amplify DNA fragments
Engineered enzymes can be produced in recombinant organisms for various applications (biofuels, bioremediation)
Enzymes in agriculture and food processing improve crop yields, food quality, and shelf life
Cellulases and amylases are used in animal feed to improve nutrient availability and digestion
Pectinases and other enzymes are used in fruit juice clarification and wine production
Transglutaminases are used to modify the texture and stability of dairy products and processed meats