Week 3: Pre 1: Introduction to Metabolism

Catabolic reactions vs. anabolic reactions

Catabolic: Metabolic pathways that break down complex molecules into simpler molecules, releasing energy.

• Example: Cellular respiration.

• Generally exergonic (ΔG < 0).

Anabolic: Metabolic pathways that build complex molecules from simpler molecules, requiring energy.

• Example: Protein synthesis.

• Generally endergonic (ΔG > 0).

Metabolism

Metabolism is the sum of all chemical reactions that occur in a cell or organism to maintain life.

Each metabolic pathway is catalyzed by an _____

enzyme

Kinetic energy:

relative motion of objects 

Thermal energy:

Thermal energy is the energy associated with the random movement of atoms and molecules in a substance.

• More molecular movement → Higher temperature.

• Less molecular movement → Lower temperature.

• Thermal energy can be transferred between objects as heat.

Potential energy:

energy stored in an object due to its relative position 

Chemical energy:

Chemical energy is potential energy stored in the chemical structure of molecules, which can be released or used during chemical reactions.available energy to do work

Thermodynamics

The study of energy and its transformation

First law of thermodynamics:

Energy can be transferred and transformed, but it cannot be created or destroyed  

Second law of thermodynamics:

Every energy transfer or transformation increases the entropy (i.e., measure of disorder) of the universe 

What is entropy?

Entropy is a measure of how dispersed/disordered (spread out) energy is within a system.

Enthalpy

Enthalpy is the total heat content of a system at constant pressure.

Change in enthalpy (ΔH) tells us whether a reaction absorbs or releases heat.

Gibbs free energy refers to what

energy available in a system to do useful work

formula for change in free energy

∆G = ∆H - T∆S  OR ∆G = Gfinal – Ginitial 

Symbol	Meaning	Simple Explanation
ΔG	Change in free energy	Determines whether a reaction is spontaneous
ΔH	Change in enthalpy	Heat energy released or absorbed
T	Temperature	Temperature in Kelvin (K)
ΔS	Change in entropy	Change in disorder or energy dispersal

Endothermic reaction

An endothermic reaction is a chemical reaction that absorbs heat energy from its surroundings.

• ΔH > 0 (positive) → Heat is absorbed.

• Surroundings become cooler because heat is taken in.

• Products have higher enthalpy than reactants.

Exothermic reactions 

An exothermic reaction is a chemical reaction that releases heat energy into its surroundings.

• ΔH < 0 (negative) → Heat is released.

• Surroundings become warmer because heat is released.

• Products have lower enthalpy than reactants.

Activation Energy (Ea) 

The energy required to start a chemical reaction, determines rate of reaction. (amount of energy required for the reactants to reach the transition state) 

do enzymes have an impact on enthalpy

no they only effect how much activation energy is required

What is the difference between exergonic and endergonic reactions?

• Exergonic: Releases free energy (ΔG < 0). Spontaneous. - reactants have higher energy

• Endergonic: Requires energy input (ΔG > 0). Nonspontaneous. - Products have higher energy

Gibbs free energy (G) is positive

products have more free energy therefore energy is absorbed/needed; endergonic

Transition state

The transition state is the highest-energy, unstable point during a chemical reaction, when bonds are breaking and forming.

Catalysts:

molecules that speed up reactions but aren't consumed in them by decreasing activation energy without impacting ΔG (Delta G) = Change in Gibbs Free Energy

Enzymes:

macromolecules that act as biological catalysts 

Substrate:

substrate is the molecule that an enzyme binds to and acts on during a chemical reaction.

Enzyme substrate specificity:

An enzyme only works with specific substrates because its active site has a matching shape and charge. 

what is needed for the entropy of a system to decrease

It means you can't lower a system's entropy for free. You have to put in energy or dump heat out.

Order in a system costs energy; entropy can go down only if the surroundings take on more entropy.

Induced fit:

Induced fit occurs when an enzyme slightly changes shape as a substrate binds to its active site, allowing a better fit and helping the reaction occur.

Enzymes lower activation energy by:

• Orienting substrates correctly.

• Straining or weakening bonds.

• Providing a suitable chemical environment.

• Temporarily bonding with substrates.

Gibbs free energy is negative

products have less energy than reactants therefore energy is released; exergonic and spontaneous

Where does endergonic reactions get their ATP

from exergonic reactions

Enzyme activity is influenced by _______ and ___

temperature & pH

Cofactor vs. coenzyme

Feature	Cofactor	Coenzyme
Definition	Non-protein substance that helps an enzyme function	Organic molecule that helps an enzyme function
Type	Can be inorganic or organic	Always organic
Example	Mg²⁺, Zn²⁺, Fe²⁺	NAD⁺, FAD, Coenzyme A

How does enzyme localization help regulate chemical reactions?

Enzymes are located in specific areas of the cell, allowing reactions to occur efficiently and controlling where enzymes interact with substrates.

Competitive inhibitors:

changes shape of active site that decreases enzyme activity

Noncompetitive inhibitors:

An inhibitor binds somewhere other than the active site, decreasing enzyme activity.

Allosteric regulation

• Allosteric activation:

• Allosteric inhibition:

Allosteric regulation occurs when a molecule binds to an enzyme at a site other than the active site, changing the enzyme's shape and activity.

• Allosteric activation: Increases enzyme activity.

• Allosteric inhibition: Decreases enzyme activity.

Feedback inhibition:

Feedback Inhibition: The final product of a metabolic pathway binds to an enzyme earlier in the pathway, stopping further production.

What are the three types of work cells perform using ATP?

• Chemical: Building molecules.

• Transport: Moving substances against their concentration gradient.

• Mechanical: Producing movement.

What is energy coupling?

Energy coupling is when energy released from an exergonic (catabolic)(ΔG < 0) reaction (like ATP hydrolysis) is used to drive an endergonic (anabolic) reaction (ΔG > 0).

How are bond breaking/forming, catabolism, anabolism, exergonic/endergonic reactions, and energy coupling related?

• Bond breaking: Requires energy.

• Bond forming: Releases energy.

• Catabolism: Breaks down molecules, generally releasing free energy (exergonic, ΔG < 0).

• Anabolism: Builds molecules, generally requiring free energy (endergonic, ΔG > 0).

• Energy coupling: Uses energy from exergonic reactions (often through ATP) to power endergonic reactions.

Catabolism releases energy → ATP transfers energy → Anabolism uses energy.

How does ATP hydrolysis provide energy for cellular work?

ATP is hydrolyzed into ADP + Pi, releasing free energy (exergonic) that is coupled to energy-requiring (endergonic) cellular processes..