Energy and Enzymes

Define matter and energy + Differentiate between kinetic and potential energy and give examples of each.

• Matter — anything that has mass and takes up space. Atoms, molecules, cells — all matter.

• Energy — the ability to do work or cause change. Energy has no mass and takes up no space.

Two forms of energy:

• Kinetic energy — energy of motion. Anything actively moving has kinetic energy.

• Potential energy — stored energy based on position or structure. Not moving yet but has the capacity to do work.

Define the first and second laws of thermodynamics and apply them to living systems.

First Law — Conservation of Energy

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

• Total energy in a system always stays the same

• Example: your body doesn't create energy from nothing — it converts chemical energy in food into movement, heat, and other forms

Second Law — Entropy

• Every energy conversion produces some heat (unusable energy)

• The universe tends toward increasing disorder (entropy)

• No energy conversion is 100% efficient — some energy is always lost as heat

Distinguish between exergonic and endergonic reactions.

	Exergonic	Endergonic
Energy	Releases energy	Requires energy input
Free energy change	Negative (−ΔG)	Positive (+ΔG)
Spontaneous	Yes	No
Examples	Cellular respiration, burning wood	Photosynthesis, building proteins

• Free energy (G) = energy available to do work

• Exergonic = energy exits = products have less energy than reactants = energy released

• Endergonic = energy enters = products have more energy than reactants = energy required

Define an enzyme and explain what is meant by “specific” and “catalyst” in terms of enzyme function.

• Enzyme — a protein that speeds up a chemical reaction without being consumed or changed itself. A biological catalyst.

• Catalyst — something that speeds up a reaction without being used up

• Specific — each enzyme only works on one particular molecule called its substrate

Explain how an enzyme functions. Include in your explanation a definition of “activation energy” and how an enzyme affects activation energy.

• Activation energy — the energy required to start a chemical reaction. Like the push needed to get a boulder rolling.

Without an enzyme:

• Reactions require a large amount of activation energy to get started

• Reactions happen slowly or not at all at body temperature

With an enzyme:

• Enzyme lowers the activation energy required

• Reaction happens faster at the same temperature

• Enzyme doesn't change the final outcome — just speeds up getting there

List the factors that affect enzyme function and, for each, explain how it affects function.

Four main factors:

1. Temperature

• Higher temp = faster enzyme activity up to a point

• Too high = enzyme denatures (loses its shape) = stops working permanently

• Each enzyme has an optimal temperature — for human enzymes ~37°C (body temp)

2. pH

• Each enzyme has an optimal pH

• Too acidic or too basic = enzyme denatures = stops working

• Example: stomach enzyme pepsin works best at pH 2. Salivary amylase works best at pH 7.

3. Substrate Concentration

• More substrate = faster reaction up to a point

• Once all active sites are occupied the reaction rate plateaus — enzyme is saturated

4. Enzyme Concentration

• More enzymes = faster reaction up to a point

• Once all substrate is being used adding more enzymes makes no difference

Differentiate between competitive and noncompetitive inhibitors, and reversible and irreversible inhibitors.

	Competitive	Noncompetitive
Where it binds	Active site	Different site (allosteric site)
How it works	Blocks substrate from binding	Changes shape of enzyme so active site no longer works
Can it be overcome	Yes — add more substrate	No — more substrate doesn't help

Also need to know:

	Reversible	Irreversible
Binding	Temporary	Permanent
Effect	Enzyme can recover	Enzyme permanently destroyed
Example	Most drug interactions	Nerve agents, some antibiotics

Differentiate between catabolic and anabolic reactions.

	Catabolic	Anabolic
What it does	Breaks large molecules DOWN into smaller ones	Builds large molecules UP from smaller ones
Energy	Releases energy (exergonic)	Requires energy (endergonic)
Examples	Digestion, cellular respiration	Building proteins, DNA replication

Define a redox reaction by differentiating between reduction and oxidation.

• Redox = Reduction + Oxidation — they always happen together

	Oxidation	Reduction
Electrons	Loses electrons	Gains electrons
Charge	Becomes more positive	Becomes more negative

• When one molecule loses electrons (oxidized) another molecule gains them (reduced)

• They always happen together — you can't have one without the other

• In cellular respiration glucose gets oxidized (loses electrons) and oxygen gets reduced (gains electrons)

List the purposes for breaking large molecules (polymers) down to small molecules (monomers).

• Energy extraction — breaking bonds in molecules like glucose releases energy the cell can use to make ATP

• Building new molecules — monomers from broken down polymers become raw materials to build new different polymers

  • Example: amino acids from digested protein can be reassembled into your own proteins

• Recycling damaged molecules — old or damaged proteins and organelles get broken down so their parts can be reused

Describe the mechanisms that control metabolic pathways:

1. Function of ubiquitin and proteasomes

2. Autophagy

3. Feedback inhibition

1. Ubiquitin & Proteasomes

• Ubiquitin — a small protein that tags damaged or unneeded proteins for destruction. Like putting a sticky note on something that says "throw this away"

• Proteasome — the cellular "shredder" that destroys tagged proteins and breaks them into amino acids for recycling

2. Autophagy

• "Self eating" — the cell breaks down its own damaged organelles and large molecules

• Cell wraps damaged components in a membrane bubble → delivers them to lysosome → lysosome digests them

• Like the cell's internal cleanup and recycling program

3. Feedback Inhibition

• The end product of a metabolic pathway inhibits an enzyme earlier in the pathway

• When enough product has been made the pathway shuts itself off automatically

• Like a thermostat shutting off the heat when the room reaches the right temperature