energy / enzymes

Energy

Capacity to do work or cause change

Relationship between energy and work

Energy is required to perform work

1st law of thermodynamics

Energy cannot be created or destroyed, only changed from one form to another

1st law example from lecture

Glucose chemical energy converted to ATP and heat; total energy stays constant

Potential energy

Stored energy available to do work based on position or structure

Examples of potential energy

Chemical bonds in glucose, concentration gradients across a membrane

Kinetic energy

Energy of motion

Examples of kinetic energy

Thermal (Brownian) motion, muscle contraction, active transport

"Cells do work to fight entropy"

Cells spend ATP to maintain organization, repair structures, and keep gradients intact against the tendency toward disorder

2nd law of thermodynamics

Every energy transfer or transformation increases the entropy of the universe; some usable energy is always lost as heat

2nd law example from lecture

Cellular metabolism is inefficient; energy is lost as heat during respiration

Which has more potential energy: glucose or CO2?

Glucose, due to its high-energy C-H and C-C bonds (CO2 is fully oxidized)

Where is potential energy stored in a molecule?

In the arrangement of chemical bonds, not molecular motion

Endergonic reaction

Requires net energy input; products have higher potential energy than reactants (e.g., photosynthesis)

Exergonic reaction

Releases energy spontaneously; products have lower potential energy than reactants (e.g., cellular respiration, ATP hydrolysis)

How enzymes "facilitate" a reaction

Speed it up by lowering the activation energy barrier without being consumed

Catalyst

Chemical agent that speeds up a reaction without being permanently altered or consumed

Activation energy

Initial energy input needed to break chemical bonds and start a reaction

Enzyme active site

Specific pocket on the enzyme where substrate binds and the reaction occurs

Competitive inhibitor

Blocks the active site by competing with the normal substrate; not changed by the enzyme

Non-competitive inhibitor

Binds away from the active site and changes the enzyme's shape so the active site binds substrate less effectively