AP Biology Unit 3 – Cellular Energetics: Ultimate Study Notes (CED aligned)

Enzyme Structure and Function

Enzyme Properties

Structure Determines Function

• Enzymes are proteins with specific 3D shapes

• The active site binds the substrate

• Shape determines specificity

• Cause → Effect

  • Change in enzyme shape → reduced binding → decreased activity

Catalysis and Activation Energy

Lowering Activation Energy

• Enzymes speed up reactions by lowering activation energy

• Do not change overall energy of reaction (ΔG)

• Do not get used up

• Cause → Effect

  • Lower activation energy → faster reaction rate

Environmental Impacts on Enzymes

Temperature, pH, and Concentration

• Temperature increase → more collisions → higher rate (up to optimum)

• Extreme temperature → denaturation → loss of function

• pH changes → disrupt bonds → alter shape

• Substrate concentration → increases rate until saturation

• Tips

  • Always mention denaturation when discussing high temperature

  • Use term: optimal conditions

Cellular Energy and ATP

Role of ATP

Energy Transfer

• ATP stores energy in phosphate bonds

• ATP → ADP + Pi releases energy

• Powers cellular work (active transport, synthesis, movement)

• Cause → Effect

  • ATP hydrolysis → energy released → drives cellular processes

Coupled Reactions

Energy Coupling

• Exergonic reactions release energy

• Endergonic reactions require energy

• ATP couples these reactions

• Cause → Effect

  • Energy from ATP → drives unfavorable reactions

• Tips

  • Phrase: “ATP provides energy for…”

  • Know: exergonic = releases, endergonic = requires

Photosynthesis

Light Reactions

Energy Capture

• Occur in thylakoid membranes

• Light excites electrons in chlorophyll

• Water is split → releases oxygen

• Produces ATP and NADPH

• Cause → Effect

  • Light energy → excited electrons → ATP and NADPH production

Calvin Cycle

Carbon Fixation

• Occurs in stroma

• CO₂ is fixed into organic molecules

• Uses ATP and NADPH to produce G3P (sugar precursor)

• Cause → Effect

  • ATP and NADPH → drive sugar production

Factors Affecting Photosynthesis

Environmental Factors

• Light intensity

• CO₂ concentration

• Temperature

• Cause → Effect

  • Increased light → increased rate (until limit reached)

  • Limited CO₂ → reduced sugar production

• Tips

  • Remember: Light reactions = energy, Calvin cycle = sugar

  • Common FRQ: predict effect of changing light or CO₂

Cellular Respiration

Glycolysis

Glucose Breakdown

• Occurs in cytoplasm

• Glucose → pyruvate

• Produces small amount of ATP and NADH

• Does not require oxygen

Krebs Cycle

Energy Extraction

• Occurs in mitochondria

• Releases CO₂

• Produces NADH and FADH₂

Electron Transport Chain

ATP Production

• Located in inner mitochondrial membrane

• Electrons passed through proteins

• Creates proton gradient

• ATP synthase produces ATP

• Cause → Effect

  • Electron movement → proton gradient → ATP production

Oxygen’s Role

Final Electron Acceptor

• Oxygen accepts electrons at end of ETC

• Forms water

• Cause → Effect

  • No oxygen → ETC stops → no proton gradient → no ATP

Fermentation

Anaerobic Conditions

• Occurs without oxygen

• Regenerates NAD⁺

• Allows glycolysis to continue

• Produces less ATP

• Tips

  • Common FRQ: “What happens without oxygen?”

  • Answer:

    • ETC stops

    • ATP production decreases

    • Fermentation occurs

Energy Flow and Metabolism

Energy Transformations

First and Second Laws of Thermodynamics

• Energy cannot be created or destroyed

• Energy transformations are inefficient (heat lost)

• Cause → Effect

  • Energy loss as heat → limits efficiency of processes

Metabolic Pathways

Regulation and Feedback

• Cells regulate pathways using enzymes

• Feedback inhibition slows pathways

• Cause → Effect

  • End product accumulates → inhibits enzyme → slows pathway

• Tips

  • Use term: feedback inhibition

  • Helps maintain homeostasis