L7 - Energy, ATP, & Enzymes

Potential energy

Stored energy — like a stretched rubber band or a concentration gradient.

Kinetic energy

Energy in motion — doing work right now.

First Law of Thermodynamics

Energy can't be created or destroyed — only changed from one form to another.

Second Law of Thermodynamics

Every energy change increases disorder (entropy) — some energy is always lost as heat.

Entropy

Disorder or randomness — the universe always trends toward more of it.

Gibbs free energy (G)

The energy in a system available to do work.

ΔG (delta G)

Products' energy minus reactants' energy — tells if a reaction is spontaneous.

Exergonic

Releases energy (negative ΔG) — happens on its own.

Endergonic

Needs energy input (positive ΔG) — won't happen by itself.

Catabolic reaction

Breaks things down — releases energy.

Anabolic reaction

Builds things up — needs energy.

Spontaneous

Can happen without energy input — but does NOT mean fast!

Activation energy (Ea)

The push needed to get a reaction started — the energy "hill" to climb.

Transition state

The shaky, in-between moment where bonds are breaking and forming.

Enzyme

A protein that speeds up reactions by lowering activation energy — names end in "-ase."

Ribozyme

An enzyme made of RNA instead of protein.

Catalyst

Something that speeds up a reaction without being used up.

Substrate

The molecule an enzyme works on.

Active site

The special pocket on an enzyme where the substrate fits.

Induced fit

The enzyme changes shape slightly to hug the substrate tightly and strain its bonds.

Molecular complementarity

Enzyme and substrate fit together because of matching shape AND chemistry.

Cofactor

A helper (like a metal ion, e.g., Mg2+) that some enzymes need to work.

Enzyme-substrate complex

The enzyme and substrate stuck together during the reaction.

Denaturation

When heat or pH ruins an enzyme's shape so it stops working.

Optimum pH/temperature

The pH or temperature where an enzyme works best.

Competitive inhibitor

A fake substrate that blocks the active site — adding more real substrate can kick it out.

Allosteric regulation

A molecule binds somewhere OTHER than the active site and changes the enzyme's shape — turns it on or off.

Feedback inhibition

The end product of a pathway blocks the first enzyme — like a factory shutting down when there's enough product.

Metabolic pathway

A chain of reactions where each step is done by a different enzyme.

ATP (adenosine triphosphate)

The cell's main energy currency — has 3 phosphates.

ADP (adenosine diphosphate)

What ATP becomes after losing one phosphate — 2 phosphates left.

Hydrolysis

Using water to break a bond — ATP + H2O → ADP + Pi.

Phosphorylation

Adding a phosphate group to a molecule — often "turns on" a protein.

Coupling

Hooking an energy-releasing reaction to an energy-needing one so both can happen.

High-energy phosphate bond

A bond that releases lots of energy when broken because the phosphates repel each other.

Activated carrier

A molecule that carries energy (like ATP) or electrons (like NAD+, FAD) between reactions.

Na+/glucose symporter

Glucose rides into the cell for free by hitching a ride with sodium flowing down its gradient.

Diffusion rate factors

Bigger molecules move slower; higher temperature = faster; bigger gradient = faster.