2.4 Enzymes and Biochemical Reactions

Enzymes are protein powerhouses that speed up chemical reactions in living things. They work by lowering the energy needed for reactions to happen, making life processes possible. Without enzymes, our bodies couldn't function properly.

These biological catalysts have specific active sites where they bind to substrates. Enzymes can be activated or inhibited, and they're sensitive to their environment. Understanding enzymes is key to grasping how our bodies work at the molecular level.

Enzyme Structure and Function

Enzymes as biological catalysts

Top images from around the web for Enzymes as biological catalysts

• 

  Energy, Matter, and Enzymes | Microbiology View original

  Is this image relevant?

• 

  Enzymes · Biology View original

  Is this image relevant?

• 

  Enzymes | OpenStax Biology 2e View original

  Is this image relevant?

• 

  Energy, Matter, and Enzymes | Microbiology View original

  Is this image relevant?

• 

  Enzymes · Biology View original

  Is this image relevant?

1 of 3

Top images from around the web for Enzymes as biological catalysts

• 

  Energy, Matter, and Enzymes | Microbiology View original

  Is this image relevant?

• 

  Enzymes · Biology View original

  Is this image relevant?

• 

  Enzymes | OpenStax Biology 2e View original

  Is this image relevant?

• 

  Energy, Matter, and Enzymes | Microbiology View original

  Is this image relevant?

• 

  Enzymes · Biology View original

  Is this image relevant?

1 of 3

• Enzymes are proteins that act as biological catalysts in living organisms
• Speed up chemical reactions by lowering the activation energy required for the reaction to occur
• Do not get consumed in the reaction and can be reused multiple times
• Highly specific to their substrates (reactants) due to unique active sites

Active sites and substrates

• Active site is the region of an enzyme where the substrate binds and the reaction takes place
• Shape and chemical properties of the active site are complementary to the substrate (lock and key model)
• Substrates are the molecules that enzymes act upon, converting them into products
• Enzyme-substrate complex forms when the substrate binds to the active site, facilitating the reaction

Catalytic efficiency of enzymes

• Enzymes are highly efficient catalysts that can increase reaction rates by up to 10^20 times compared to uncatalyzed reactions
• Catalytic efficiency is due to the precise orientation and proximity of substrates in the active site
• Enzymes can catalyze reactions under mild conditions (normal body temperature and pH) compared to industrial catalysts that often require high temperatures and pressures

Enzyme Activation and Inhibition

Activation energy and enzyme catalysis

• Activation energy is the minimum energy required for a chemical reaction to occur
• Enzymes lower the activation energy by stabilizing the transition state of the reaction
• Lower activation energy allows more substrate molecules to have sufficient energy to react, increasing the reaction rate
• Enzymes provide an alternative reaction pathway with a lower energy barrier (activation energy)

Cofactors and coenzymes

• Some enzymes require additional non-protein components called cofactors for proper functioning
• Cofactors can be inorganic ions (metal ions like Fe^2+, Mg^2+, Zn^2+) or organic molecules (coenzymes)
• Coenzymes are organic molecules that are loosely bound to the enzyme and often derived from vitamins (NAD+, FAD, coenzyme A)
• Cofactors and coenzymes assist in the catalytic function of enzymes by participating in the reaction or maintaining the enzyme's structure

Enzyme inhibition

• Enzyme inhibitors are molecules that decrease or stop enzyme activity by binding to the enzyme
• Competitive inhibitors resemble the substrate and compete for the active site, preventing substrate binding (reversible)
• Non-competitive inhibitors bind to a site other than the active site (allosteric site), altering the enzyme's conformation and decreasing its activity (reversible or irreversible)
• Inhibitors are important in regulating metabolic pathways and are used as drugs to treat various diseases (ACE inhibitors for hypertension, protease inhibitors for HIV)

Enzyme Denaturation

Factors affecting enzyme structure and function

• Enzymes are sensitive to changes in their environment, which can lead to denaturation (loss of structure and function)
• Denaturation occurs when the protein's tertiary and quaternary structures are disrupted, causing the enzyme to unfold
• Factors that can cause denaturation include extreme temperatures, pH changes, and exposure to strong chemicals (urea, detergents)
• Heat denaturation is commonly used in cooking to inactivate enzymes and alter food texture (boiling an egg denatures and coagulates egg white proteins)

Consequences of enzyme denaturation

• Denatured enzymes lose their catalytic activity as the active site is no longer properly formed
• Denaturation is often irreversible, as the unfolded protein may aggregate or form incorrect structures when cooled
• In living organisms, denatured enzymes are usually targeted for degradation and replaced by newly synthesized enzymes
• Some enzymes can renature (refold) when returned to optimal conditions, but this is not always possible, especially if the denaturation was severe or prolonged