Unit 3 AP Bio

Enzyme

Protein catalyst that speeds up reactions by lowering activation energy

Activation energy

Energy needed to start a chemical reaction

Active site

Part of an enzyme where the substrate binds

Substrate

Reactant that binds to an enzyme

Enzyme-substrate complex

Temporary complex formed when a substrate binds to an enzyme

Induced fit

Enzyme changes shape slightly when substrate binds

Denaturation

Change in protein shape that reduces or destroys enzyme function

Effect of high temperature on enzymes

Can disrupt bonds, alter enzyme shape, and decrease activity

Effect of extreme pH on enzymes

Can disrupt bonds and charges, changing the active site

Optimal pH

pH at which an enzyme works most efficiently

Substrate concentration

Increasing it raises reaction rate until enzymes become saturated

Enzyme saturation

All enzyme active sites are occupied, so reaction rate levels off

Competitive inhibitor

Binds to the active site and competes with the substrate

Noncompetitive inhibitor

Binds to an allosteric site and changes enzyme shape

Allosteric site

Site other than the active site where a regulator can bind

Feedback inhibition

End product inhibits an earlier enzyme in a metabolic pathway

Negative control

Group where no effect or reaction is expected

Independent variable

Factor changed by the researcher

Dependent variable

Factor measured by the researcher

Metabolism

Sum of all chemical reactions in a cell

Catabolic pathway

Breaks down molecules and releases energy

Anabolic pathway

Builds molecules and requires energy

Exergonic reaction

Reaction that releases energy

Endergonic reaction

Reaction that requires energy

Catabolic goes with

Exergonic

Anabolic goes with

Endergonic

ATP

Main usable energy molecule of the cell

ATP hydrolysis

ATP → ADP + Pi, releasing usable energy

Phosphorylation

Addition of a phosphate group to a molecule

Energy coupling

Using energy from an exergonic reaction to power an endergonic reaction

First law of thermodynamics

Energy cannot be created or destroyed, only transferred or transformed

Second law of thermodynamics

Energy transfers increase entropy and release some energy as heat

Conserved metabolic pathways

Pathways like glycolysis found across all domains, supporting common ancestry

Overall purpose of photosynthesis

Convert light energy into chemical energy stored in carbohydrates

Photosynthesis equation

CO2 + H2O + light → carbohydrates + O2

Chloroplast

Organelle where photosynthesis occurs

Stroma

Fluid inside chloroplast where the Calvin cycle occurs

Thylakoid

Membrane sac where light reactions occur

Grana

Stacks of thylakoids

Light reactions location

Thylakoid membrane

Calvin cycle location

Stroma

Light reactions inputs

Light and water

Light reactions outputs

ATP, NADPH, and O2

Photosystem II

First photosystem in linear electron flow; receives replacement electrons from water

Photolysis

Splitting water using light energy

Why is water split in photosynthesis?

To replace electrons lost from Photosystem II

What happens to oxygen from water splitting?

It is released as a by-product

Photosynthesis ETC

Uses electron energy to create an H+ gradient across the thylakoid membrane

ATP synthase in photosynthesis

Uses H+ flow to make ATP

Photosystem I

Re-excites electrons that are eventually used to form NADPH

Linear electron flow

PSII → ETC → PSI; produces ATP and NADPH

Cyclic electron flow

Uses PSI only and produces ATP

Calvin cycle purpose

Use CO2, ATP, and NADPH to produce G3P

Calvin cycle inputs

CO2, ATP, and NADPH

Calvin cycle product

G3P

Three stages of Calvin cycle

Carbon fixation, reduction, regeneration of RuBP

Carbon fixation

CO2 is attached to RuBP

Rubisco

Enzyme that catalyzes carbon fixation

Reduction phase

ATP and NADPH help convert 3-PGA into G3P

Regeneration phase

ATP is used to regenerate RuBP

One net G3P requires

3 CO2, 9 ATP, and 6 NADPH

Photorespiration

Rubisco binds O2 instead of CO2, wasting energy and producing no sugar

Why does photorespiration increase in hot, dry conditions?

Stomata close, CO2 decreases, and O2 increases

C4 plants

Reduce photorespiration by separating carbon fixation and Calvin cycle by location

CAM plants

Reduce water loss by separating carbon fixation and Calvin cycle by time

Overall purpose of cellular respiration

Extract energy from biological molecules to make ATP

Cellular respiration equation

Glucose + O2 → CO2 + H2O + ATP

Four stages of cellular respiration

Glycolysis, pyruvate oxidation, Krebs cycle, oxidative phosphorylation

Glycolysis location

Cytosol

Glycolysis input

Glucose

Glycolysis outputs

2 pyruvate, 2 NADH, and net 2 ATP

Does glycolysis directly require oxygen?

No

Substrate-level phosphorylation

Direct transfer of phosphate to ADP to make ATP

Pyruvate oxidation

Pyruvate is converted into acetyl-CoA

Pyruvate oxidation products

Acetyl-CoA, CO2, and NADH

Citric acid cycle location

Mitochondrial matrix

What is the release date for Housewife by Tate McRae?

OCTOBER 15, 2026 😆

Main purpose of citric acid cycle

Transfer high-energy electrons to NADH and FADH2

citric acid cycle products

CO2, NADH, FADH2, and some ATP

NADH

Electron carrier that brings high-energy electrons to the ETC

FADH2

Electron carrier that brings high-energy electrons to the ETC

Oxidation

Loss of electrons

Reduction

Gain of electrons

OIL RIG

Oxidation Is Loss, Reduction Is Gain

Oxidative phosphorylation

ETC plus chemiosmosis

ETC location in mitochondria

Inner mitochondrial membrane

What does the ETC do?

Uses electron energy to pump H+ into the intermembrane space

Final electron acceptor in cellular respiration

Oxygen

Why is oxygen important?

It accepts electrons so the ETC can continue

Intermembrane space pH

Lower pH because it has more H+

Matrix pH

Higher pH because it has fewer H+

Low pH means

More H+ ions

High pH means

Fewer H+ ions

Proton gradient

Difference in H+ concentration across a membrane

Chemiosmosis

Movement of H+ through ATP synthase down its gradient

ATP synthase

Uses energy from H+ flow to make ATP

What happens if the proton gradient decreases?

Less H+ flows through ATP synthase, so less ATP is made

What happens if oxygen is removed?

ETC stops, proton gradient decreases, and ATP production drops

Cristae

Folds of inner mitochondrial membrane that increase surface area for ATP production

Approximate ATP per glucose

About 30-32 ATP