BIO 100 - Topic 7: Metabolism

Metabolism

The sum of all chemical reactions in the body that sustain life.

Two main types of metabolism

Anabolism (building molecules) and Catabolism (breaking down molecules).

Anabolic pathway

A metabolic process that builds complex molecules from simpler ones; requires energy.

Catabolic pathway

A metabolic process that breaks down complex molecules into simpler ones; releases energy.

Example of an anabolic reaction

Synthesis of proteins from amino acids.

Example of a catabolic reaction

Breakdown of glucose during cellular respiration.

Energy

The capacity to do work or cause change.

Kinetic energy

Energy associated with motion.

Potential energy

Stored energy due to position or structure.

Chemical energy

Potential energy stored in chemical bonds of molecules.

Bioenergetics

The study of how organisms acquire, transform, and use energy.

Thermodynamics

The study of energy transformations.

First Law of Thermodynamics

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

Second Law of Thermodynamics

Every energy transfer increases the entropy (disorder) of the universe.

Entropy

A measure of disorder or randomness; increases in spontaneous processes.

Spontaneous reaction

A reaction that occurs naturally without input of energy; increases entropy.

Free energy (G)

Energy in a system available to do work.

ΔG

Change in free energy between products and reactants in a reaction.

Negative ΔG

Indicates an exergonic (energy-releasing) reaction; spontaneous.

Positive ΔG

Indicates an endergonic (energy-requiring) reaction; nonspontaneous.

Exergonic reaction

Releases free energy; products have less energy than reactants.

Endergonic reaction

Requires input of energy; products have more energy than reactants.

Coupled reactions

Use the energy released from exergonic reactions to drive endergonic ones.

ATP (adenosine triphosphate)

Main energy currency of the cell; provides energy for cellular processes.

Structure of ATP

Adenine (nitrogen base), ribose (sugar), and three phosphate groups.

ATP hydrolysis

Breaking ATP into ADP and inorganic phosphate (Pi); releases energy.

Why ATP releases energy

Breaking the unstable bond between the last two phosphate groups releases usable energy.

ATP regeneration

ATP is regenerated by adding a phosphate to ADP using energy from catabolism.

Phosphorylation

Adding a phosphate group to a molecule, often using ATP; increases molecule’s energy.

Role of ATP in cells

Provides energy for mechanical work, transport work, and chemical work.

Enzyme

A biological catalyst that speeds up chemical reactions by lowering activation energy.

Catalyst

A substance that speeds up a chemical reaction without being consumed.

Activation energy (Ea)

The initial energy needed to start a chemical reaction.

How enzymes lower Ea

Enzymes stabilize the transition state and reduce the energy needed for the reaction to proceed.

Substrate

The specific molecule that an enzyme binds and acts upon.

Active site

The region of the enzyme where the substrate binds and the reaction occurs.

Induced fit

When the substrate binds, the enzyme changes shape slightly to fit more snugly.

Enzyme specificity

Each enzyme works on a specific substrate due to the shape of its active site.

Effect of temperature on enzymes

Too much heat can denature (unfold) the enzyme, reducing activity.

Effect of pH on enzymes

Each enzyme has an optimal pH range; outside that range, activity drops.

Denaturation

When an enzyme loses its shape (and function) due to heat or pH.

Cofactor

A non-protein helper (like metal ions) that assists enzyme activity.

Coenzyme

An organic cofactor (like vitamins) that helps enzymes function.

Inhibitor

A molecule that reduces enzyme activity.

Competitive inhibitor

Binds to the active site, blocking the substrate from binding.

Noncompetitive inhibitor

Binds to a different site, changing the enzyme’s shape so the active site is less effective.

Allosteric regulation

When a molecule binds to a site other than the active site, affecting enzyme function.

Feedback inhibition

A process where the end product of a pathway inhibits an early enzyme in the pathway.

Why feedback inhibition is useful

It prevents the cell from wasting resources by making too much of a product.

Energy coupling

The use of energy from one reaction (usually ATP hydrolysis) to power another.

Three types of cellular work

Chemical (building molecules), transport (pumping ions), and mechanical (muscle contraction).

How enzymes help reactions

They speed up reactions without being used up themselves.

How cells control metabolism

Through enzyme regulation, compartmentalization, and feedback mechanisms.

What happens if an enzyme is missing

A metabolic pathway may be blocked or slowed; the organism may have a disease or disorder.

Why metabolism is organized in steps

Each step is controlled and regulated, allowing for energy capture and use at each point.

How enzyme activity is measured

By the rate at which products are made or substrates are used up.