Biological Energy Processes: Exam Prep
Unit 2 Overview
Chapters & Assignments:
Chapters 6 and 7 (1 assignment)
Chapter 8 (1 assignment)
Test Information:
Midterm test on Tuesday, October 14th
Labs on Biomolecules, Calorimetry, and Photosynthesis
No class on October 7th
Midterm will take place on Thursday, October 16th at 5:30 PM
Lab Attendance Policy:
Students must reach out if they have or believe they will miss 2 or more labs
Missing more than 2 labs may result in failing the course
Encourage communication with the instructor for class and lab attendance issues.
Chapters 6 and 7
6.1 Life and the Flow of Energy
Definition of Energy:
Energy is the ability to do work or cause change.
Importance of Energy for Life:
Constant supply of energy is required for:
Growth
Response to stimuli
Metabolism
Reproduction
Solar Energy Dependence:
Life on Earth ultimately depends on solar energy.
Photosynthesis plays a critical role by providing nutrients for most organisms.
Forms of Energy
Energy occurs in two forms:
Kinetic Energy: Energy of motion (example: a ball rolling down a hill).
Potential Energy: Stored energy (example: food has stored energy).
Types of Energy
Chemical Energy: Stored in chemical bonds.
Mechanical Energy: Energy of motion (example: movement when walking).
Two Laws of Thermodynamics
The First Law of Thermodynamics
Law Statement: Energy cannot be created or destroyed but can be converted from one form to another.
Known as the law of conservation of energy.
The Second Law of Thermodynamics
Law Statement: Energy transformations are never completely efficient; some energy is always lost as heat.
Implication in Ecosystems:
Examples of energy transformation in ecosystems include photosynthesis and cellular respiration.
A leaf cell utilizes but does not create solar energy; energy is transformed into carbohydrates but some is lost as heat (not destroyed).
Cells and Entropy
Entropy Definition: Refers to the relative amount of disorder or disorganization in a system.
Every energy transformation increases the total entropy of the universe.
Living organisms need constant energy from the sun to power cellular processes, e.g. transport or biosynthesis.
Energy Transformations and Metabolism
Metabolism: Sum of all chemical reactions occurring in a cell, involving:
Catabolism: Breakdown of molecules.
Anabolism: Building of molecules.
Reactants and Products:
Reactants are substances participating in a reaction; products are what forms as a result of the reaction.
Free Energy (ΔG): Amount of energy available, calculated as the difference between the free energy of products and reactants.
A negative ΔG indicates a spontaneous reaction.
Types of Reactions
Exergonic Reactions:
Spontaneous and release energy.
Products possess less free energy than reactants (ΔG is negative).
Endergonic Reactions:
Require an input of energy.
Products have more free energy than reactants (ΔG is positive).
ATP: Energy for Cells
ATP (Adenosine Triphosphate): The main energy currency for cells generated from ADP and inorganic phosphate.
Formed by the breakdown of glucose.
It powers various cellular reactions, via its breakdown.
Structure of ATP
ATP comprises:
Adenine (nitrogen-containing base)
Ribose (5-carbon sugar)
Three phosphate groups
Energy is stored in the bonds between the phosphate groups.
ATP is unstable and possesses high potential energy.
Function of ATP
Uses of ATP in Cells include:
Chemical Work: Synthesizing macromolecules (anabolism).
Transport Work: Pumping substances across membranes.
Mechanical Work: Driving muscle contractions and cellular movement.
Coupled Reactions
Definition: The energy released from an exergonic reaction drives an endergonic reaction.
This commonly occurs through ATP breakdown, which supplies energy for these reactions.
Phosphorylation: Transfer of a phosphate group, enabling ATP to energize or alter the shape of reactants.
Examples of ATP-powered reactions:
Synthesis of macromolecules
Maintenance of internal conditions
Muscle contraction mechanisms
6.3 Enzymes and Metabolic Pathways
Definition of Metabolic Pathways: Series of linked biochemical reactions, where products of one serve as reactants for another.
Enzymes: Typically proteins acting as catalysts to expedite chemical reactions.
Types of Enzymes: Ribozymes (RNA catalysts).
Enzymes do not influence the direction of the reaction; free energy dictates that.
Energy of Activation:
Definition: Minimum energy required to initiate a reaction; necessary even in exergonic reactions.
Role of Enzymes: They lower the energy of activation needed, thus increasing reaction rates without altering the end products.
Enzyme Functioning
Enzymes bind with substrates forming an enzyme-substrate complex.
The active site is the region where substrates bind.
Reactions may involve degradation or synthesis of substrates.
Induced Fit Model: Enzymes undergo minor shape changes to better fit substrates, further facilitating reactions.
Factors Affecting Enzymatic Speed
Enzyme activity is influenced by:
Substrate Concentration: Increased substrates lead to more active site occupancy, heightening reaction rate until saturation.
Temperature & pH: Higher temperatures enhance collisions, whereas extremes can denature enzymes. Different enzymes have preferred pH levels (e.g., pepsin prefers low pH).
Enzyme Activation: Enzymes can be regulated by turning genes on or off and attaching/removing phosphates.
Enzyme Inhibition: Regulation occurs when a substrate cannot bind to an enzyme's active site. Feedback inhibition is a common form, where abundant products block enzyme activity.
6.4 Oxidation-Reduction Reactions and Metabolism
Oxidation and Reduction Process:
Oxidation: Loss of electrons.
Reduction: Gain of electrons.
Together, they are referred to as redox reactions.
Example: In a redox reaction between oxygen and magnesium, magnesium is oxidized (loses electrons), while oxygen is reduced (gains electrons).
Photosynthesis and Cellular Respiration
Chloroplast Function:
Convert solar energy to ATP; use it to reduce carbon dioxide to form carbohydrates.
Mitochondria Function:
Oxidize carbohydrates to build ATP; utilizes oxygen and produces CO2 and water.
Relationship: Products of photosynthesis serve as substrates for cellular respiration and vice versa.
Cellular Respiration Overview
Concept: Release of energy from glucose that is then used to synthesize ATP; requires oxygen (aerobic process).
Net ATP Production from Respiration:
Breakdown of glucose yields 36-38 ATP molecules.
Coenzymes: NADH and FADH2 play key roles in transporting electrons to the electron transport chain.
Phases of Cellular Respiration
Main Phases:
Glycolysis
Preparatory Reaction
Krebs Cycle (Citric Acid Cycle)
Electron Transport Chain (ETC)
Glycolysis occurs in the cytoplasm; the others in mitochondria.
Glycolysis
Definition: Breakdown of glucose into two pyruvate molecules; does not require oxygen (anaerobic).
Steps:
Energy Investment Steps: Two ATP are used to activate glucose, producing two G3P molecules.
Energy-Harvesting Steps: Oxidation of G3P yields NADH and direct ATP synthesis, resulting in a total of four ATP but net gain of two ATP.
Fermentation
If oxygen is lacking, fermentation provides a means of generating energy with two forms existing:
Lactic Acid Fermentation: Pyruvate reduces to lactate with a net gain of two ATP.
Alcohol Fermentation: Pyruvate reduces to ethanol and CO2, also yielding two ATP.
Comparison: Fermentation generates significantly less energy than cellular respiration (only two ATP compared to up to 38 ATP).
Citric Acid Cycle
Process:
The acetyl CoA combines with oxaloacetate to form citrate and completes two cycles for each glucose molecule.
Outputs: Produces NADH, FADH2, and a small amount of ATP along with CO2 as a waste product.
Electron Transport Chain
Located in the cristae of mitochondria, where electrons from NADH and FADH2 are passed along a series of carriers.
Generates a proton gradient used by ATP synthase to produce ATP through chemiosmosis.
Overall Energy Yield: Breakdown of glucose can yield a total of 36-38 ATP, accounting for substrate-level phosphorylation in glycolysis and Krebs cycle, and oxidative phosphorylation in ETC.