Enzymes Flashcards
(35 cards)
List some examples of enzymes in food. [7]
- Amylase
- Cellulase
- Invertase
- Lactase
- Pectic enzymes
- Proteases
- Lipases
Also - Novozymes (company that sells enzymes for just about any industry you can imagine)
Describe the use in the food industry.
Amylases
- Hydrolysis of starch in the production of HFCS (syrups)
- Increase sugar content for yeast fermentation (baked goods)
Describe the use in the food industry.
Cellulases
- Hydrolysis of cell-wall cellulose during drying of beans (coffee)
- Peeling of apricots, tomatoes (fruits)
Describe the use in the food industry.
Invertase
- Conversion of sucrose to glucose and fructose (artificial honey)
Describe the use in the food industry.
Lactase
- Prevents crystallization of lactose, which makes ice cream have a sandy or grainy texture (ice cream)
- Removal of lactose (lactose removal)
Describe the use in the food industry.
Pectic enzymes
- Improve yield of press juices, prevent cloudiness (fruit juice)
Describe the use in the food industry.
Proteases
- Tenderization (meats and fish)
- Casein coagulation; aging (cheese)
- Production of soy milk
Describe the use in the food industry.
Lipases
- Aging, ripening, development of flavour (cheese)
Describe naming convensions for enzymes.
- Systematic name: name of substrate + nature of chemical reaction & ending in ‘ase’ (e.g., polyphenol oxidase; peptidase; lipase; lactase)
- Trivial name: common use name (e.g., pepsin; papain; trypsin)
- EC number: classification scheme established by the enzyme commission
What are enzymes?
- Debate about the nature of enzymes (1920 - 1930): colloidal particles; lipids; CHO; proteins; other?
- 1st crystallization of urease (1926) and then pepsin (1930) used to prove the protein nature of enzymes
- James Sumner and John Northrup won the Nobel prize in 1946 for showing this.
What are ribozymes?
- Ribosome = rRNA + protein
- rRNA = ribozyme = peptidyl transferase
- Hammerhead ribozome = RNA cleavage and joining
How do enzymes work?
- Enzyme binds substrate (binding is thermodynamically driven - bound form is lower energy than unbound form)
- Enzyme also binds transition state; lowers the activation barrier
- Enzymes have less affinity for the product and unbind.
Describe catalytic power.
- Notice how catalase increases the speed of the reaction by 1.5 billion times.
Describe how enzymes have evolved.
Enzymes are evolved to better stabilize the transition state as compared to the substrate.
What is the issue if the enzyme binds/stabilizes the substrate equally well as to the transition state?
- Net effect on the energy barrier would be zero (would have no effect on overall reaction)
Describe basic enzyme kinetics: basic mechanism and Michaelis-Menten equation.
- KD = Koff/Kon (dissociation constant; measure of binding affinity of enzyme for substrate)
- Km = (Koff + Kcat)/Kon (breakdown of enzyme-substrate complex; often Kcat is «< Koff so Km ~ Kd)
How is kcat, Km measured?
- Doubling substrate concentration doubles reaction rate
- At high substrate concentration, the initial reaction rate approximates max reaction rate.
- When substrate concentration = Km, then Km is the substrate concentration that gives 1/2 Vmax.
How do enzymes stabilize the transition state?
- Active site favours substrate distortion
- Dynamic networks
- Electric field effects
Still an unresolved question; many possible factors.
Describe the dynamics of enzymes.
‘Enzymes flex to function’
Which factors in the environment affect protein (enzyme) fuction? [5]
- Temperature
- Salt
- pH
- Pressure
- Effect of force (shaking; blending; extrusion)
What is the effect of temperature on enzymes?
- Affects molecular dynamics (mainly entropic)
What is the effect of salt and pH on enzyme functions?
- Affect electrostatic interactions of protein, surface charges, and protein hydration.
What is the effect of pressure on enzyme function?
- folded proteins exclude H2O from inner core
- pressure favours state with lowest excluded volume
What is the effect of force on enzyme function?
shaking; blending; extrusion; etc.
- incorporation of air bubbles
- air is more hydrophobic than water
- proteins adsorb to air-liquid interface and denature, exposing their hydrophobic groups to the air
