Untitled Flashcards Set

Activation Energy Basics

Q: What is activation energy (EA)? A: The initial energy input required to get a chemical reaction started, even for energy-releasing reactions. It's the energy needed to reach the transition state.

Q: What is the transition state? A: A high-energy, unstable state that reactant molecules must reach before they can proceed to products. Molecules are contorted/deformed in this state.

Q: Why do exergonic reactions still need activation energy? A: Because chemical bonds in reactants must be broken before new bonds can form in products. Breaking bonds requires energy input to reach the unstable transition state.

Q: Is activation energy always positive? A: Yes, EA is always positive regardless of whether the overall reaction is endergonic or exergonic, because the transition state is always higher energy than reactants.

Q: What provides the activation energy for most reactions? A: Heat (thermal energy) from the surroundings. This speeds up molecular motion, increases collision frequency and force, and helps break bonds.

Activation Energy and Reaction Rate

Q: How does activation energy affect reaction rate? A: Higher activation energy = slower reaction rate. Fewer molecules have enough energy to overcome a high barrier at any given moment.

Q: What is catalysis? A: The process of speeding up a reaction by reducing its activation energy. This increases the reaction rate without being consumed.

Q: What is a catalyst? A: A substance that lowers the activation energy of a reaction, thereby increasing reaction rate. Biological catalysts are called enzymes.

Q: Why don't high-activation-energy reactions proceed at room temperature? A: Because very few molecules have enough thermal energy to overcome the large energy barrier required to reach the transition state.

Enzyme Fundamentals

Q: What are enzymes? A: Biological catalysts (usually proteins) that speed up chemical reactions by lowering activation energy without being consumed in the process.

Q: How do enzymes work? A: They provide an alternative reaction pathway with lower activation energy, allowing more molecules to reach the transition state at a given temperature.

Q: What is the active site? A: The specific region of an enzyme where substrate molecules bind and the catalytic reaction occurs. It has a specific shape and chemical environment.

Q: What is a substrate? A: The reactant molecule(s) that bind to an enzyme's active site and undergo the catalyzed reaction.

Q: What is the enzyme-substrate complex (ES complex)? A: The temporary intermediate formed when a substrate binds to an enzyme's active site before the reaction proceeds.

Enzyme Models and Mechanisms

Q: What is the lock-and-key model? A: An early model proposing that enzymes have rigid active sites that exactly complement the substrate shape, like a lock and key.

Q: What is the induced-fit model? A: The current model stating that enzyme active sites are flexible and change shape when substrate binds, optimizing the fit and catalytic efficiency.

Q: Why is the induced-fit model more accurate? A: Because it explains how enzymes can stabilize the transition state better than the substrate, and how conformational changes contribute to catalysis.

Q: What happens after the enzyme-substrate complex forms? A: The enzyme facilitates bond breaking/forming, converts substrate to product(s), then releases the product(s) and returns to its original state.

Cofactors and Coenzymes

Q: What are cofactors? A: Non-protein helper molecules (metal ions or organic molecules) that some enzymes require for proper function.

Q: What are coenzymes? A: Organic cofactors, often derived from vitamins, that participate in enzyme-catalyzed reactions by accepting/donating chemical groups.

Q: What's the difference between cofactors and coenzymes? A: Cofactors include both metal ions and organic molecules; coenzymes are specifically organic cofactors, often vitamin-derived.

Q: Give examples of metal ion cofactors. A: Mg²⁺, Zn²⁺, Fe²⁺, Cu²⁺, Mn²⁺. These help with enzyme structure or participate directly in catalysis.

Q: Give examples of coenzymes. A: NAD⁺/NADH, FAD/FADH₂, Coenzyme A, thiamine pyrophosphate, biotin. Many are derived from B vitamins.

Six Classes of Enzymes

Q: What are the six main classes of enzymes? A: 1) Oxidoreductases 2) Transferases 3) Hydrolases 4) Lyases 5) Isomerases 6) Ligases

Q: What do oxidoreductases do? A: Catalyze oxidation-reduction reactions (electron transfer). Examples: dehydrogenases, oxidases, reductases.

Q: What do transferases do? A: Transfer functional groups from one molecule to another. Examples: kinases (transfer phosphate), transaminases (transfer amino groups).

Q: What do hydrolases do? A: Break bonds using water (hydrolysis reactions). Examples: digestive enzymes like pepsin, lipases, nucleases.

Q: What do lyases do? A: Add or remove groups to form double bonds, or break bonds without using water. Examples: aldolase, decarboxylases.

Q: What do isomerases do? A: Rearrange atoms within a molecule to form isomers. Examples: phosphoglucose isomerase, triose phosphate isomerase.

Q: What do ligases do? A: Join two molecules together using ATP energy. Examples: DNA ligase, aminoacyl-tRNA synthetases.

Enzyme Environment and Regulation

Q: How does temperature affect enzyme activity? A: Low temperature = low activity (insufficient kinetic energy). Optimal temperature = maximum activity. High temperature = denaturation and loss of function.

Q: How does pH affect enzyme activity? A: Each enzyme has an optimal pH range. Extreme pH values can denature enzymes or change the ionization state of key amino acids.

Q: What is enzyme denaturation? A: Loss of enzyme structure and function due to disruption of weak bonds, typically caused by extreme temperature, pH, or chemical conditions.

Q: How do competitive inhibitors work? A: They compete with substrate for the active site, reducing enzyme activity. Can be overcome by increasing substrate concentration.

Q: How do non-competitive inhibitors work? A: They bind to a site other than the active site (allosteric site), changing enzyme shape and reducing activity. Cannot be overcome by more substrate.

Q: What is allosteric regulation? A: Regulation of enzyme activity through binding of molecules at sites other than the active site, causing conformational changes that affect activity.

Enzyme Kinetics

Q: What is Vmax? A: The maximum reaction rate achieved when all enzyme active sites are saturated with substrate.

Q: What is Km (Michaelis constant)? A: The substrate concentration at which the reaction rate is half of Vmax. It indicates enzyme affinity for substrate.

Q: What does a low Km value indicate? A: High enzyme affinity for substrate (enzyme binds substrate tightly and at low concentrations).

Q: What does a high Km value indicate? A: Low enzyme affinity for substrate (requires high substrate concentration to achieve significant binding).

Q: What is enzyme turnover number (kcat)? A: The number of substrate molecules converted to product per enzyme molecule per unit time when enzyme is saturated.

Non-Enzymatic Protein Functions

Q: What are some non-enzymatic functions of proteins? A: Structural support, transport, storage, hormones, defense, motor proteins, and regulatory functions.

Q: Give examples of structural proteins. A: Collagen (connective tissue), keratin (hair, nails), elastin (elastic fibers).

Q: Give examples of transport proteins. A: Hemoglobin (oxygen transport), albumin (blood protein transport), membrane channels and carriers.

Q: Give examples of storage proteins. A: Ferritin (iron storage), casein (milk protein), albumin (amino acid storage).

Q: Give examples of hormone proteins. A: Insulin, growth hormone, glucagon, thyroid hormones.

Q: Give examples of defense proteins. A: Antibodies (immunoglobulins), complement proteins, fibrinogen (blood clotting).

Q: Give examples of motor proteins. A: Myosin (muscle contraction), kinesin and dynein (intracellular transport), flagellar proteins.

Application and Clinical Connections

Q: Why are enzymes important in medicine? A: Enzyme deficiencies cause diseases, enzymes are drug targets, and enzyme levels are used as diagnostic markers.

Q: What are some enzyme deficiency diseases? A: Phenylketonuria (PKU) - phenylalanine hydroxylase deficiency, Tay-Sachs disease - hexosaminidase A deficiency.

Q: How are enzymes used as diagnostic tools? A: Elevated enzyme levels in blood can indicate tissue damage (e.g., cardiac enzymes after heart attack, liver enzymes in hepatitis).

Q: What are some enzyme inhibitors used as drugs? A: Aspirin (COX inhibitor), statins (HMG-CoA reductase inhibitors), ACE inhibitors (angiotensin-converting enzyme inhibitors).

Q: Why don't we just increase body temperature to speed up reactions? A: Because proteins denature at high temperatures, losing their structure and function. Enzymes provide a better solution by lowering activation energy.They speed up reactions without the detrimental effects of increased heat.