Chapter 6 – Energy, Enzymes & Metabolism
Energy – The ability to do work.
Kinetic energy – Energy of motion.
Potential energy – Stored energy.
Entropy – Measure of disorder.
Free energy – Usable energy for work.
Electron transport chain – Series of proteins that transfer electrons to make ATP.
ATP – Main energy molecule in cells.
Enzyme – Protein that speeds up chemical reactions.
Ribozymes – RNA molecules that act as enzymes.
Substrate – The molecule an enzyme acts on.
Active site – Part of an enzyme where the substrate binds.
Activation energy – Energy needed to start a reaction.
Cofactors – Helpers (ions or molecules) for enzymes.
Half-life – Time for half of a substance to break down.
Autophagy – Process where cells break down their own parts for recycling.
6.1 Energy and Chemical Reactions
First law of thermodynamics – Energy cannot be created or destroyed, only transferred.
Second law of thermodynamics – Energy transfer increases disorder (entropy).
Endergonic vs. Exergonic reactions – Endergonic reactions absorb energy, exergonic reactions release energy.
Oxidation-reduction (redox) reactions – Transfer of electrons; oxidation loses electrons, reduction gains electrons.
Free energy equation (H = G + TS) – H = total energy, G = free energy, T = temperature, S = entropy.
6.2 Enzymes and Ribozymes
Enzyme properties – Reusable; forms enzyme-substrate complex to speed up reactions.
How enzymes lower activation energy – By stabilizing the transition state and making reactions easier.
What affects enzyme activity – Temperature, pH, and chemicals can change enzyme function.
Noncompetitive vs. Competitive inhibition – Competitive inhibitors block the active site; noncompetitive inhibitors bind elsewhere to change enzyme shape.
6.3 Overview of Metabolism
Catabolic vs. Anabolic pathways – Catabolic breaks molecules down, anabolic builds them up.
How to make ATP – Substrate-level phosphorylation (direct transfer of phosphate) and chemiosmosis (using a proton gradient).
Chapter 8 – Photosynthesis
Photosynthesis – Process where plants make food using light.
Biosphere – All living things on Earth.
Heterotroph – Organism that eats others for food.
Autotroph – Organism that makes its own food.
Photoautotroph – Uses light to make food (plants, algae).
Pigments – Molecules that absorb light.
Accessory pigments – Extra pigments that help absorb more light.
Stomata – Openings on leaves for gas exchange.
Chloroplasts – Organelles where photosynthesis happens.
Thylakoids – Flattened sacs in chloroplasts where light reactions occur.
Granum – Stack of thylakoids.
Stroma – Fluid in chloroplast where the Calvin cycle happens.
Photons – Light particles.
Ground state – Low-energy state of electrons.
Excited state – High-energy state of electrons after absorbing light.
Photosystem – Protein-pigment complex that captures light.
Rubisco – Enzyme that fixes CO₂ in the Calvin cycle.
Photorespiration – Wasteful process where rubisco binds oxygen instead of CO₂.
8.1 Overview of Photosynthesis
Groups that carry out photosynthesis – Plants, algae, cyanobacteria.
Chemical equation of photosynthesis –
6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
Reactants and products – Reactants: CO₂, H₂O, light. Products: Glucose, O₂.
Two stages of photosynthesis – Light reactions (make ATP & NADPH) and Calvin cycle (makes sugar).
8.2 Reactions That Harness Light Energy
Main photosynthetic pigment – Chlorophyll a.
Where photosynthesis occurs – In the chloroplasts.
Where the light reactions occur – In the thylakoid membranes.
What is produced & byproducts – ATP, NADPH (used in Calvin cycle), O₂ (waste).
Steps of light reactions & photosystems –
1. Photosystem II – Absorbs light, splits water, releases O₂, excites electrons.
2. Electron Transport Chain – Electrons move, making ATP.
3. Photosystem I – Absorbs light, re-energizes electrons, makes NADPH.
Noncyclic vs. Cyclic electron flow – Noncyclic makes ATP & NADPH; cyclic makes only ATP.
8.4 Synthesizing Carbohydrates via the Calvin Cycle
Where carbon reactions occur – In the stroma.
What is produced & byproducts – Glucose (product), ADP & NADP⁺ (recycled).
Steps of carbon reactions –
1. Carbon fixation – Rubisco fixes CO₂.
2. Reduction – ATP & NADPH convert molecules into sugars.
3. Regeneration – RuBP is reformed to continue the cycle.
8.5 Variations in Photosynthesis
C3 vs. C4 plants – C3 uses regular photosynthesis; C4 plants store carbon in a different way to reduce water loss.
CAM plants – Open stomata at night to save water in dry environments.