Chapter #4: Enzymes and Energy

Review Questions

Catalyst

A substance that increases the rate of a chemical reaction without itself undergoing any change

How does an enzyme increase the rate of a reaction?

By lowering activation energy

To what extent does an enzyme participate in a reaction?

Enzymes bind to the substrates and then the reaction occurs

Active site

Pockets in the enzymes where the reaction occurs

Conformation

A characteristic 3D shape of each enzyme

Substrate

The reactants that fit into the active sites

Product

The result from the reaction

Enzyme activity

The rate its substrates are converted to products

What are the factors that affect enzymatic activity?

Temperature, pH, concentration of cofactors and coenzymes, concentration of enzyme and substrate, and possible stimulatory or inhibitory effects of products on enzyme function

How is enzyme activity used clinically?

Used to diagnose and monitor diseases by measuring activity in bodily fluid

How are most enzymes named?

“-ase”

Phosphatase

Remove phosphate groups

Kinase

Add phosphate groups

Amylase

Breakdown starch

What is the function of a cofactor?

Changes the conformation of the active site, allowing for a better fit between the enzyme and its substrates

What is the function of a coenzyme?

Participates in temporary bonding between the enzyme and its substrates

Are enzyme always active?

No

How are enzymes activated and deactivated?

Many are activated by phosphorylation and deactivated by dephosphorylation

How are enzymes affected by the substrate concentration?

As the substrate concentration increases, so will the enzymatic activity

Are all enzymatic reactions reversible?

Only some

In a reversible reaction, what determines the direction in which the reaction is catalyzed by the enzyme?

Depends on which side of the reaction has the higher concentration

Metabolic pathways

Sequences of enzymatic reactions that begin with initial substrate, progress through intermediates and end with a final product

How are enzymes involved in metabolic pathways?

Typically more than one enzyme is working as the pathways are mostly branched

How does end-product inhibition work?

Occurs when 1 product in a divergent pathways inhibits activity of the branch-point enzyme

Allosteric inhibition

Product binds to enzyme causing it to change to an inactive shape

What happens to a metabolic pathway when an enzyme in that pathway is defected?

Increases in intermediates or decreases in products

First law of thermodynamics

Energy cannot be destroyed or created, only transformed

Second law of thermodynamics

Energy is lost with each transformation in the form of heat

Endergonic reactions

Require input of energy to proceed

Exergonic reactions

Release energy as they proceed with the reaction

How are endergonic and exergonic reactions coupled to each other?

As exergonic reactions release energy, endergonic reactions gain that energy

Reducing agent

Donates electrons

Oxidizing agent

Accepts electrons

Describe the function of NAD and FAD as oxidizing and reducing agents

NAD can accept two electrons but can only bind with one protons making it the oxidizing agent; FAD accepts two electrons and binds with two protons making it the reducing agent