Post on 16-Jul-2020
Enzymes (p.36-40)
1.3 Biochemical Reactions
Chemical reaction
Activation energy:
certain amount of energy required to begin any
chemical reaction
Enzyme
name usually ends in –ase (eg. Amylase)
protein catalyst
speeds up a chemical reaction without being
consumed
reduces the activation energy
Activation Energy is reduced by:
Bring two substrates together in correct position
stretch/bend bonds
Transfer electrons
Add/remove hydrogen ion
destabilize
substrate
Enzyme Structure
very specific
Specific 3-D shape allows binding to one specific substrate
Specific function for specific biochemical reaction
Enzyme + Substrate Enzyme-substrate complex
Induced-Fit Model
1. substrate binds to the active siteof enzyme
2. functional groups come close
3. enzyme protein change its shape better grip
4. Forms enzyme-substrate complex
5. reaction occurs
6. products less affinity for enzyme released
7. enzyme returns to original shape recycled
Factors affecting Enzyme activity
1. Temperature
2. pH
3. Enzyme concentration
4. Substrate concentration
1. Temperature
Too low: bonds not flexible enough for substrate to
fit properly
Too high: enzyme denatures
2. pH
Bonds sensitive to H+ concentration
3. Enzyme concentration
More enzymes
more likely to
collide with substrates
increased rate of
reaction
Can saturate
4. Substrate Concentration
More substrates
increased rate of
reaction
Until Point of saturation
(all enzymes of occupied)
Enzyme - Regulation Mechanisms
Cofactors/Coenzymes
Competitive inhibitors
Non-Competitive
inhibitors
Allosteric Changes
Feedback Inhibition
Cofactors/Coenzymes
Cofactors:
nonprotein
inorganic substances
Zn2+, Mn2+
Coenzyme:
organic substances
NAD+
derivative of Vitamin B3
electron carrier in cellular respiration
NADP+
electron carrier in photosynthesis
Cofactors/Coenzymes
placed within the
active site of the
enzyme
helps to draw
electrons from the
substrate molecules.
Competitive Inhibitors
similar to substrate
block active site
reversible
overcome by
increasing [substrate]
Noncompetitive Inhibitors
not compete for active site
bind to another site on enzyme (allosteric site)
change shape
prevents substrate from binding
DDT, poison, inhibits enzymes of nervous system
Video: Competitive and non-competitive inhibition.mp4.mp4
Allosteric Changes
Allosteric site:
receptor site some distance away from the active site
Allosteric activator:
stabilizes active form of enzyme
Allosteric inhibitor:
stabilizes inactive form of enzyme
Feedback Inhibition
for a series of sequential reactions
each step has specific enzymes
a product in later steps inhibits enzyme for earlier step
binds to allosteric site of enzyme using weak bonds
Feedback Inhibition
Cells use this process to
prevent overproduction
of a certain product