Chap 19

Question 1

What is an enzyme

Answer 1

• Organic catalyst – decreases the activation energy

Question 2

Turnover

Answer 2

• Number of cycles in a unit of time

Question 3

six classes of enzymes

Answer 3

• Oxidoreducatases – redox reactions
• Transferases – transfer groups of acids (AB + C&raquo_space; A + BC)
• Hydrolases – Hydrolysis (AB +H2O&raquo_space; A+B) – digestive enzymes
• Isomerases – interconvert isomers (fructose&raquo_space; glucose)
• Lyases – add/remove atoms to form double bonds
• Lygases - use ATP to combine 2 molecules

Question 4

lock and key vs induced fit

Answer 4

• Lock and key – must be the right shape to fit and allow reaction (old model)
• Induced fit – conformational changes to allow reaction (new model)

Question 5

the three main catalytic mechanisms that allow enzymes to lower the EActivation

Answer 5

• Migration of the substrate into the enzyme
• Substrate is forced into a less stable state
• Bonding electrons are drawn away and activation energy is decreased

Question 6

Catalytic triad

Answer 6

• Ser, His and Asp
• H+ transfers from serine to histidine
• Serine side chains bonds to the peptide bond carbon
• Peptide bond is broken and the new NH2 leaves the active site

Question 7

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

Answer 7

• Increased concentration = increased activity
• Optimal temperature increases activity
• Optimal pH increases activity.

Question 8

Different types of enzyme regulations

Answer 8

• Allosteric – binding of a regulator affects proteins ability to bind another
  - Feedback/feedforward – alteration of enzymes activity by the products of an earlier or later product in the pathway
  - Competitive vs. noncompetitive – competitive binding of the inhibitor to the active site on the enzyme prevents binding of the substrate. Noncompetitive – something binds to the enzyme, changing the shape making the substrate unable to bond to the active site. More effective at inhibiting.
  
  • Reversible vs. irreversible -
• Covalent modification: zymogens (proenzymes) – becomes active after undergoing a chemical change. – Phosphorylation: kinases use ATP to phosphates to catalyze the reaction.