Topic 3.6 Enzymes

Question 1

3.6.1 Define enzyme and active site.

Answer 1

Enzyme: globular proteins - long chains of amino acids in specific 3D shapes. Enzymes, as catalysts, influence the rate of reactions by lowering the activation energy of reactions. They aren’t used up in reactions, and can function as catalysts numerous times.

Active site: area in 3D shape of an enzyme designed to match the enzyme substrate (it’s where the substrate attaches to in a reaction)

Question 2

3.6.2 Explain enzyme–substrate specificity.

Answer 2

Enzymes & substrates are specific for each other.

e.g. Lock & key analogy; lock = enzyme, key = substrate. 3D shape of internal portion of lock is complex & specific, so only 1 key will fit.

Question 3

3.6.3 Explain the effects of temperature, pH and substrate concentration on enzyme activity.

Answer 3

Temperature

• ↑ temperature = faster moving molecules = faster reaction rate
  
  • reactions are dependent on molecular collisions
• temperature will increase reaction rate with or without enzymes
• in reactions using enzymes, there is an upper limit:
  
  • limit is based on temperature at which enzyme (as portein) is denatured (loses shape due to intermolecular bonds being stressed and broken)
  • denaturation is often permanent (depends on whether covalent bonds in molecule have broken) but sometimes temporary until molecule re-forms its normal shape

pH

• pH of solution depends on relative # of H⁺ to OH^- in solution
• too acidic/basic, relatively large # of H⁺/OH^- can bond with (-)/(+) charges of enzyme/substrate respectively → prevents proper charge matching between these two
  
  • enzyme is less efficient; sometimes completely inactive in extreme situations
    
    • numerous H⁺ and OH^- can result in denaturation of enzyme
• Optimum pH varies depending on enzyme; pH 7 is optimum for many enzymes
• Note: pH scale is logarithmic; each whole number difference on pH scale = increase or decrease in a power of 10

Substrate concentration

• ↑ concentration = more reactant molecules to collide = faster reaction rate
• limited by enzymes → enzymes have a maximum rate at which they can work, so at some point adding more substrate will not further increase the reaction rate
• same applies to enzyme concentration; limited by substrates (when all being reacted, rate plateaus)

Salt Concentration

• each enzyme has optimum salt concentration
• changes in salt concentration may denature enzymes

Question 4

3.6.4 Define denaturation.

Answer 4

Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties. Only heat, pH, & salt are agents of denaturation.

Question 5

3.6.5 Explain the use of lactase in the production of lactose-free milk.

Answer 5

• Lactase = enzyme produced in digestive tract that allows digestion of disaccharide lactose into 2 monosaccharides (more readily absorbed into bloodstream)
• most people lose ability to produce lactase as they get older
  
  • lactose-containing foods aren’t digested
  • bacterial colonies feed on lactose → leads to symptoms like cramping, excessive gas and diarrhea
• Therefore, milk (products) can be traced with lactase before consumption
  
  • nutrients aren’t affected
  • allows person to absorb lactose as it has been pre-digested
• technology must be improved to be effective on larger scale
• some ethnic groups have higher incidence of lactose intolerance than others (example of natural variation of population)