lecture intro to metabolism

Study Tip

• Review the role of inhibitors and activators in enzyme regulation before next class.

• Pay special attention to the differences between competitive and non-competitive inhibitors.

Upcoming Assignment

• Please be prepared for a quiz on enzyme function and regulation next week.

LECTURE

Energy Reactions: Exergonic vs. Endergonic

Exergonic Reactions

• These are reactions where substrates have a higher energy level than the products.

• Energy Flow:

  • Energy is released as the reaction proceeds.

  • The reaction is spontaneous.

• Example: The breakdown of glucose in cellular respiration.

• Graph Representation:

  • Substrates: 100 energy units.

  • Products: 50 energy units.

  • Energy released: 50 units (Exergonic reaction).

Endergonic Reactions

• These are reactions where the products have a higher energy level than the substrates.

• Energy Flow:

  • Energy must be supplied for the reaction to occur.

• Example: Photosynthesis.

• Graph Representation:

  • Substrates: 50 energy units.

  • Products: 100 energy units.

  • Energy absorbed: 50 units (Endergonic reaction).

Cellular Respiration

• Location: Cellular respiration occurs in the mitochondria.

• Process: It converts glucose and oxygen into carbon dioxide, water, and ATP (energy).

• Glucose breakdown:

  • From a 6-carbon chain (glucose) to 6 carbon dioxide molecules.

  • Energy is released as chemical bonds are broken.

  • This process is an example of an Exergonic Reaction.

Photosynthesis

• Location: Photosynthesis occurs in the chloroplasts.

• Process: It converts carbon dioxide and water into glucose and oxygen, using light energy.

• Glucose formation:

  • 6 molecules of carbon dioxide are converted into a glucose molecule.

  • Bonds are formed, requiring energy input.

  • This process is an example of an Endergonic Reaction.

Concepts of Energy Reactions

Exergonic Reactions

• Energy Flow: Energy is released.

• Characteristics:

  • These reactions are spontaneous.

  • They can occur without additional energy input.

• Example: Cellular respiration (breaking down glucose to produce ATP).

Endergonic Reactions

• Energy Flow: Energy is absorbed.

• Characteristics:

  • These reactions are nonspontaneous.

  • They require an energy supply to proceed.

• Example: Photosynthesis (building glucose from carbon dioxide and water).

Energy Coupling

• This process refers to when energy released from exergonic reactions is used to drive endergonic reactions.

• Example: Energy from cellular respiration can be used in photosynthesis.

Real-World Examples

• Breaking Down Food:

  • Leaving a piece of food, such as chicken tenders, on the table will cause the proteins and carbohydrates to naturally break down over time.

  • This process is an example of an Exergonic reaction.

• Making a Cake:

  • Combining eggs, flour, and milk requires energy to create a cake.

  • This process is Endergonic because energy is needed to form bonds and create the cake.

Activation Energy and Chemical Reactions

Activation Energy

• Exergonic reactions release energy but may require an initial energy input.

• Definition: The energy required to start a chemical reaction, acting as a barrier to be overcome for the reaction to proceed.

• Activation Energy and Energy Release:

  • Even in exergonic reactions, activation energy is needed to begin the reaction.

• Examples:

  • In an exergonic reaction that releases 50 calories of energy, 10 calories of activation energy is required. After the activation energy is supplied, 40 calories of energy are released.

  • Energy Input Analogy: If someone gives $10 today and gets $20 later, it’s a good investment. If the return is only $10, it’s not worth it. If the return is $5, it’s a bad deal.

Chemical Reaction Comparison

• The reaction will proceed if the activation energy is less than or equal to the energy released.

• Activation Energy and Reactions:

  • Example: If 100 calories of activation energy are required but only 50 calories are released, the reaction will not occur.

  • If the activation energy is less than or equal to the energy released, the reaction will proceed.

Ways to Speed Up Reactions

Enzymes

• Catalysts that help speed up chemical reactions.

• Role of Enzymes:

  • They lower the activation energy required for reactions to occur.

  • Example: In digestion, enzymes in the stomach lower the activation energy required to break down food.

• Catalysts:

  • Substances that increase the rate of a chemical reaction by lowering the activation energy.

  • Example of Enzyme Action:

    • Without enzymes: A chemical reaction might require 10 calories of activation energy.

    • With enzymes: The same reaction may only require 1 calorie of activation energy.

Enzymes and Catalysis in Chemical Reactions

Gluten and Its Effects

• Gluten is a protein, and while it often gets a bad reputation, it’s a natural part of many foods.

• Some people can’t digest gluten due to a lack of enzymes, leading to digestive issues.

Enzymes and Catalysts

• Enzymes:

  • A type of catalyst that speeds up biochemical reactions by lowering activation energy.

• Catalysts:

  • Any substance that starts or speeds up a chemical reaction.

• Other types of catalysts:

  • Heat

  • pH

• Without enzymes, processes like digestion would be inefficient and slow.

Enzyme Action and Lactose Intolerance

Lactose Intolerance

• Occurs when a person lacks the enzyme lactase, which breaks down lactose.

• The lactose stays in the digestive system, causing discomfort until it is eventually broken down.

How Enzymes Work

• Enzymes bind to substrates to form an enzyme-substrate complex, which then produces the final product.

• After the product is formed, the enzyme is free to start the process again.

Enzyme Shape and Function

• The enzyme’s active site must match the shape of the substrate.

• If the shape of the active site changes (denaturation), the enzyme will no longer work effectively, and the reaction will not occur.

Denaturation and Temperature Effects

Denaturation

• A process that alters the enzyme's shape, making it ineffective.

• Heat: Can cause denaturation by breaking the bonds that hold the enzyme's shape.

• Optimal Temperature: Enzymes work best at a certain temperature, and too much heat will reduce their effectiveness.

Collision Theory and Reaction Rate

Collision Theory:

• The concept that molecules must collide to react.

• Increasing temperature speeds up the movement of molecules, leading to more frequent collisions and an increased reaction rate.

• However, excessive heat can break the enzyme's bonds, leading to denaturation and a decreased reaction rate.

Impact of Heat on Enzyme Activity

• Increase in reaction rate: As heat increases, molecules move faster and collide more often, speeding up the reaction.

• Decrease in reaction rate: Too much heat causes the enzyme to denature, losing its shape and its ability to bind with the substrate, which slows down the reaction.

Enzyme Regulation and Energy Conservation

Denaturation and its Effects

• Denaturation: Changes in the enzyme’s shape that prevent it from binding to substrates and carrying out reactions.

• Heat and pH: Both can alter the shape of the enzyme, affecting its ability to function.

Impact of pH on Enzyme Activity

• Optimal pH: Enzymes work best at specific pH levels. Deviating from this optimal range can slow down or stop the reaction.

• Acidic vs. Alkaline pH: Different enzymes have varying preferences for pH:

  • Some work better in acidic environments.

  • Others work best in alkaline or neutral environments.

Acid Reflux and its Impact on the Body

• Acid reflux: Occurs when stomach acid moves up into the esophagus, causing discomfort and potentially leading to long-term issues like esophageal cancer.

• Medication for acid reflux: Medications like Tums neutralize stomach acid, but excessive use can disrupt the enzyme activity required for digestion.

Enzyme Regulation via Allosteric Sites

• Allosteric site: A region of the enzyme separate from the active site that can regulate enzyme activity.

• Activation or inhibition: The binding of molecules to the allosteric site can turn the enzyme "on" or "off," controlling its activity.

Energy Conservation in the Body

• Enzyme activation: Enzymes require energy to perform their functions, and the body regulates enzyme activity to conserve energy.

• Turning off unnecessary enzymes: The body "turns off" enzymes that are not needed at the moment, much like turning off lights to conserve electricity.

Enzyme Inhibitors

Inhibitors

• Molecules that bind to enzymes to stop their activity.

• Competitive inhibitors: Compete with the substrate for the enzyme’s active site.

• Non-competitive inhibitors: Bind to a site other than the active site, changing the enzyme’s shape and preventing it from working.

Enzyme Regulation: Inhibitors and Activators

Allosteric Inhibition

• Allosteric inhibitors: Bind to the allosteric site (a site separate from the active site).

• Effect: Cause a conformational change in the enzyme, preventing substrate binding to the active site, stopping enzyme activity.

• Reversibility: When more substrate (e.g., lactose) is needed, the inhibitor is removed, and the enzyme returns to active form to perform its function.

Allosteric Activation

• Activator molecules: Bind to the allosteric site.

• Effect: Enable the enzyme to bind with the substrate and catalyze the reaction, turning on the enzyme when it's normally in an "off" state.

Competitive Inhibition

• Competitive inhibitors: Compete with the substrate for binding to the active site.

• Mechanism: Mimic the substrate's shape and trick the enzyme into binding to them instead.

• Effect: Prevent the substrate from binding to the enzyme and stop the enzyme from catalyzing the reaction.

• Example: Medications like acetaminophen (Tylenol) reduce pain by inhibiting enzymes involved in pain production.

Non-Competitive Inhibition

• Non-competitive inhibitors: Bind to the allosteric site (not the active site).

• Effect: Even if the substrate binds to the active site, the enzyme’s activity is reduced due to structural changes.