AP Bio: Unit 3

UNIT 3: CELLULAR ENERGETICS

TABLE OF CONTENTS

• ENZYMES

• ENVIRONMENTAL IMPACTS ON ENZYME FUNCTION

• CELLULAR ENERGY

• PHOTOSYNTHESIS

• CELLULAR RESPIRATION

3.1 ENZYMES

Topic 3.1 Objectives/EKS

BIG IDEA 2

• Energetics: Biological systems use energy and molecular building blocks to grow, reproduce, and maintain dynamic homeostasis.

LEARNING OBJECTIVE 3.1.A

• Explain how enzymes affect the rate of biological reactions.

ESSENTIAL KNOWLEDGE

3.1.A.1

• Structure and Function of Enzymes:

  • Enzymes are proteins that act as biological catalysts.

  • They facilitate chemical reactions in cells by lowering activation energy.

3.1.A.2

• Enzyme-Substrate Interaction:

  • For a reaction to occur, the substrate's shape and charge must be compatible with the enzyme’s active site, illustrated by the enzyme-substrate complex model.

METABOLISM

• Definition: The sum of all chemical reactions in a cell or organism.

• Metabolic Pathway: A sequence that begins with a specific molecule and ends with a product, with each step catalyzed by a specific enzyme.

Catabolic Pathways

• Release energy by breaking down complex molecules into simpler compounds.

• Example: Cellular respiration (breaking down glucose in the presence of oxygen).

Anabolic Pathways

• Consume energy to build complex molecules from simpler ones.

• Example: Protein synthesis from amino acids.

• Bioenergetics: Study of how organisms manage energy.

ENZYMES

• Enzymes accelerate metabolic reactions by lowering energy barriers.

• Catalyst Definition: A chemical agent that speeds up a reaction without being consumed.

• Example: Hydrolysis of sucrose by sucrase.

ACTIVATION ENERGY

• Definition: The initial energy needed to start a chemical reaction is called free energy of activation or activation energy (EA).

• Generally supplied through thermal energy absorbed from surroundings.

  • Energonic Reactions: Require net input of energy.

  • Exergonic Reactions: Result in net loss of energy.

• Enzymes catalyze reactions by lowering the EA barrier without affecting the change in free energy (ΔG); they speed up reactions that would occur eventually anyway.

3.1 PRACTICE FRQ

Experiment with Human Salivary Enzyme α-amylase

• Setup:

  1. 10 mL of concentrated starch solution.

  2. 1.0 mL of α-amylase solution.

  3. Test tube inverted to mix and incubated at 25°C.

  4. Measure maltose production every 10 minutes for 1 hour.

• Maltose Concentration (uM):

  • Time (minutes): 0, 10, 20, 30, 40, 50, 60

  • Concentration (0, 10, 5.1, 8.6, 10.4, 11.1, 11.2, 11.5).

Questions

• (a) Graph the data and calculate reaction rate from 0 to 30 minutes.

• (b) Explain the observed change in reaction rate after 30 minutes.

• (c) Predict graph results if α-amylase concentration was doubled, explaining predictions.

• (d) Identify TWO environmental factors that could change enzyme reaction rates and explain their effects.

3.2 ENVIRONMENTAL IMPACTS ON ENZYME FUNCTION

Topic 3.3 Objectives/EKS

LEARNING OBJECTIVE 3.2.A

• Explain how changes to the structure of an enzyme may affect its function.

ESSENTIAL KNOWLEDGE

3.2.A.1

• Changes in molecular structure can alter enzyme function or efficiency.

  • Denaturation: Disruption of protein structure by temperature, pH, or chemicals—leading to loss of catalytic ability.

  • Denaturation may be reversible in some cases.

3.2.A.2

• Environmental conditions outside the optimal range can disrupt hydrogen bonds, affecting enzyme efficiency.

LEARNING OBJECTIVE 3.2.B

• Explain how the cellular environment affects enzyme activity.

ESSENTIAL KNOWLEDGE

3.2.B.1

• The relative concentrations of substrates and products affect reaction efficiency.

3.2.B.2

• Higher temperatures increase molecular speed, collision frequency, and reaction rates until optimal temperature is exceeded.

3.2.B.3

• Inhibition:

  • Competitive Inhibitors: Bind to active sites, competing with substrates.

  • Noncompetitive Inhibitors: Bind elsewhere, altering enzyme shape/activity.

ENZYME DENATURATION

• Enzymes lose their shape under certain conditions, termed denaturation.

• Denatured enzymes are inactive and cannot catalyze reactions.

• Optimal temperature and pH conditions are crucial for enzyme function.

EFFECTS OF TEMPERATURE, pH, AND CONCENTRATIONS

• pH: Affects enzyme structure by altering proton concentration, disrupting H-bonds leading to loss of secondary/tertiary structure.

• Temperature: Increases kinetic energy, increasing reaction rates until denaturation occurs.

ENZYME INHIBITION

• Cells manage resource use via negative feedback, where product of a pathway inhibits its own production.

• Regulatory molecules can affect enzyme function through allosteric interactions—inhibiting or stimulating activity based on molecular binding.

3.3 CELLULAR ENERGY

Topic 3.3 Objectives/EKS

LEARNING OBJECTIVE 3.3.A

• Describe the role of energy in living organisms.

ESSENTIAL KNOWLEDGE

3.3.A.1

• All living systems require an input of energy.

3.3.A.2

• Life requires a highly ordered system without violating the first and second laws of thermodynamics.

  • Energy input must exceed energy loss to maintain order and support processes.

  • Cellular processes that release energy can coupled with energy-requiring processes.

  • Significant energy loss or disorganization leads to death.

3.3.A.3

• Energy pathways are sequential for controlled energy transfer.

LAWS OF THERMODYNAMICS

• First Law: Energy of the universe is constant. Transfers occur; energy cannot be created or destroyed.

• Second Law: Every transfer increases entropy; systems lose usable energy, often as heat.

CELLULAR THERMODYNAMICS

• Cells are open systems not in equilibrium, experiencing constant material flow.

• Catabolic pathways release free energy in reactions.

• Cellular work types: transport work, mechanical work, and chemical work.

CELLULAR WORK

• Cells manage energy through energy coupling, using exergonic processes to drive endergonic ones.

• ATP (adenosine triphosphate): The cell's energy shuttle composed of ribose, adenine, and three phosphate groups.

  • Hydrolysis of terminal phosphate bond releases energy for work.

REGENERATION OF ATP

• ATP is renewed by adding a phosphate to ADP, with energy for this process sourced from catabolic reactions.

• ATP Cycle: Continuous transfer of energy from catabolic to anabolic pathways.

CONSERVATION OF METABOLIC PATHWAYS

• Core metabolic pathways are conserved across life domains indicating a shared ancestry.

• Examples: Glycolysis and oxidative phosphorylation.

3.3 PRACTICE FRQ

Example Question:

• Discuss the role of green plants in the energy transformation from the Sun into a form usable by other organisms.

3.4 PHOTOSYNTHESIS

Topic 3.4 Objectives/EKS

LEARNING OBJECTIVE 3.4.A

• Describe photosynthesis processes and chloroplast features for energy capture and storage.

ESSENTIAL KNOWLEDGE

3.4.A.1

• Photosynthesis Definition: Series of reactions transforming CO₂ and H₂O into carbohydrates and O₂ using light energy.

  • Photosynthesis first evolved in prokaryotes and resulted in an oxygenated atmosphere.

3.4.A.2

• Chloroplast Structure: Stroma and thylakoids are integral to photosynthetic processes.

  • Stroma: Fluid in chloroplast, site for the Calvin cycle.

  • Thylakoids: Membranes with chlorophyll for light reactions, organized into grana.

LEARNING OBJECTIVE 3.4.B

• Explain how cells capture light energy and store it biologically.

ESSENTIAL KNOWLEDGE

3.4.B.1

• Light reactions result in ATP and NADPH production from captured solar energy, feeding the Calvin cycle.

3.4.B.2

• Electron Transport Chain (ETC): Electrons transfer through thylakoids, generating NADPH while protons create a gradient for ATP synthesis.

PHOTOSYNTHESIS

• Converts solar energy to chemical energy; sustains life by producing organic molecules from inorganic sources.

• Autotrophs synthesize nutrients through photosynthesis and play a crucial role in food webs.

• The process evolved first in prokaryotes, leading to an increase in atmospheric oxygen.

BIOCHEMISTRY OF PHOTOSYNTHESIS

• Equation: $6CO<em>2 + 12H</em>2O + ext{Light energy} <br>ightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2 + 6H_2O$

• Electrons flow from water to glucose; redox process with water oxidized and carbon dioxide reduced, powered by light energy.

TWO STAGES OF PHOTOSYNTHESIS

1. Light Reactions (thylakoids):

   • Split H₂O, release O₂, reduce NADP⁺ to NADPH, generate ATP.

2. Calvin Cycle (stroma):

   • Fixes CO₂ into organic molecules using ATP and NADPH.

LIGHT REACTIONS

• Convert sunlight into ATP and NADPH energy forms.

• Pigment Function: Absorb specific wavelengths, chlorophyll reflects and transmits green light.

• Photosystem: Reaction-center complex around which pigmented molecules transfer photon energy.

PHOTOSYSTEMS

• Photosystem Structure: Light-harvesting complexes transfer energy to reaction centers where a primary electron acceptor captures electrons, initiating the light reactions.

LIGHT REACTIONS STEPS

1. PSII (P680) oxidizes water, releasing oxygen.

2. Excited electrons travel through the ETC, establishing a proton gradient.

3. Electrons are re-excited in PSI (P700), resulting in NADPH formation.

4. ATP Synthase utilizes the proton gradient to convert ADP and inorganic phosphate to ATP via chemiosmosis.

CALVIN CYCLE

• Uses ATP and NADPH to convert CO₂ into sugar, regenerating molecules in the process.

• Three main phases:

  1. Carbon fixation (catalyzed by rubisco).

  2. Reduction phase.

3.4 PRACTICE FRQ

Example Question:

• Discuss the role of green plants in transforming solar energy into usable forms for heterotrophs.

3.5 CELLULAR RESPIRATION

Topic 3.5 Objectives/EKS

LEARNING OBJECTIVE 3.5.A

• Describe processes/structural features of mitochondria for energy use from biological macromolecules.

ESSENTIAL KNOWLEDGE

3.5.A.1

• Cellular respiration extracts energy from macromolecules to synthesize ATP.

3.5.A.2

• Aerobic cellular respiration in eukaryotes involves enzyme-catalyzed reactions that capture energy.

3.5.A.3

• Electron Transport Chain (ETC): Establishes a proton gradient, with oxygen as the final electron acceptor.

LEARNING OBJECTIVE 3.5.B

• Explain how cells obtain energy from macromolecules for cellular functions.

ESSENTIAL KNOWLEDGE

3.5.B.1

• Glycolysis releases energy from glucose, forming ATP and NADH.

3.5.B.2

• Pyruvate oxidation occurs in mitochondria, generating CO₂ and reducing NAD + to NADH.

3.5.B.3

• Krebs cycle releases CO₂ and synthesizes ATP, with electrons transferred to NADH and FADH₂.

FERMENTATION AND CELL RESPIRATION

• Both processes transfer energy from biological macromolecules to ATP.

• Aerobic respiration uses O₂ for energy release; Fermentation occurs without O₂, partially oxidizing sugars.

STAGES OF CELL RESPIRATION

1. Glycolysis

2. Pyruvate Oxidation

3. Citric Acid Cycle (Krebs Cycle)

4. Oxidative Phosphorylation

ATP PRODUCTION

• Regenerated via substrate-level phosphorylation or oxidative phosphorylation.

• Glycolysis occurs in the cytosol; enzymes for the Krebs cycle primarily in the mitochondria.

OXIDATIVE PHOSPHORYLATION

• Involves the ETC, where NADH and FADH2 donate electrons, establishing a proton gradient across the inner mitochondrial membrane, leading to ATP synthesis via ATP synthase.

FERMENTATION

• Allows ATP production without oxygen, tapping into glycolysis coupled with fermentation to regenerate NAD+.

• Types of fermentation include alcohol fermentation (e.g., yeast) and lactic acid fermentation (common in muscle cells).

3.5 PRACTICE FRQ

Example Question:

• Describe contributions to ATP synthesis from glycolysis and the Krebs cycle, citing specific functions.