Enzymes and Chemical Reactions (2.4)
What are the reactants and products in a chemical reaction?
Reactants are the starting substances; products are the substances formed.
Who first observed dead cells and what material were they in?
Robert Hooke, in cork (1665).
What is passive transport?
The movement of materials across the cell membrane without energy.
What molecule is the main energy currency of cells?
ATP (adenosine triphosphate).
Explain how the spatial separation of light-dependent and light-independent reactions in chloroplasts optimizes photosynthetic efficiency.
Light-dependent reactions occur in the thylakoid membrane, generating ATP and NADPH; the Calvin Cycle occurs in the stroma, where these molecules are immediately used. This ensures localized energy transfer and maintains concentration gradients of protons and substrates.
What does an enzyme do to activation energy?
It lowers the activation energy, speeding up the reaction.
State the three principles of cell theory.
All living things are made of cells; cells are the basic unit of life; new cells come from existing cells.
Define osmosis.
The diffusion of water through a selectively permeable membrane.
What’s the difference between ATP and ADP?
ATP has three phosphate groups (high energy); ADP has two (lower energy).
Describe the full pathway of electron flow starting from the photolysis of water in Photosystem II to the reduction of NADP⁺ in Photosystem I. Include all major protein complexes and electron carriers.
Photolysis of water at PS II produces electrons, protons, and O₂. Excited electrons from P680 travel via carriers to PS I. Light excites P700 in PS I, and electrons pass to ferredoxin (Fd) and then to NADP⁺ reductase, which uses them (plus H⁺) to form NADPH.
Explain the lock-and-key model of enzyme activity.
The substrate fits precisely into the enzyme’s active site, forming an enzyme–substrate complex.
What is the main function of the nucleus?
It controls cell processes and stores genetic information.
What happens to a cell in a hypertonic solution?
Water moves out; the cell shrinks.
Name two cell processes that require ATP.
Active transport and muscle contraction (motor proteins).
How does the proton gradient formed during the light-dependent reactions drive ATP synthesis, and why is this process called “photophosphorylation”?
The cytochrome complex pumps protons into the thylakoid lumen, creating a gradient (high H⁺ inside). Protons diffuse back through ATP synthase, rotating its headpiece to phosphorylate ADP + Pi → ATP. The process is driven by light-induced electron flow, hence “photo”-phosphorylation.
How do temperature and pH affect enzyme activity?
They alter enzyme shape and reaction rate; extreme conditions can cause denaturation.
Differentiate between rough and smooth endoplasmic reticulum.
Rough ER has ribosomes and modifies proteins; smooth ER makes lipids and detoxifies.
Describe how the sodium-potassium pump works.
It pumps 3 Na⁺ out and 2 K⁺ in using ATP, maintaining a negative charge.
How do cells regenerate ATP?
By using energy from glucose to add a phosphate to ADP.
Compare competitive and noncompetitive inhibition in enzyme regulation.
Competitive inhibitors block the active site; noncompetitive inhibitors bind elsewhere, changing enzyme shape.
Describe the full pathway of a protein from synthesis to secretion.
Ribosome → rough ER → vesicle → Golgi apparatus → vesicle → cell membrane (exocytosis).
Explain the difference between endocytosis and exocytosis with examples.
Endocytosis takes materials in (phagocytosis = eating, pinocytosis = drinking); exocytosis releases materials out.
Compare how autotrophs and heterotrophs obtain energy.
Autotrophs make food using sunlight; heterotrophs consume other organisms.