Chapter 6 Flashcards
vitalism
belief that living things are different from non-living
protease
pre-digest proteins
lipase
together with protease, break down substances into smaller water soluble substances
carbohydrase
convert starch syrup to sugar syrup
isomerase
convert glucose to fructose (sweeter)
co-factors
inorganic ions required by some enzymes for activity
co-enzymes
vitamins required by some enzymes for activity
prosthetic group
tightly associated with enzyme (like glued)
apoenzyme
lack of extra factor
holoenzyme
apoenzyme with extra factor
6 classifications of enzymes
- oxidoreductases
- transferases
- hydrolases
- lyases
- isomerases
- ligases
chemical catalysts…
require extremes of temp, pressure, pH
enzymes function at…
physiological conditions
enzymes have a ________.
high degree of specificity
Active sites can change…
pKa
Substrates are bound to enzymes by…
weak interactions (H bonding, electrostatic, hydrophobic, vdW)
specificity of substrate depends on….
arrangement of atoms in the active site
substrate binding can cause…
induced fit or conformation selection
hand
substrate
glove
enzyme
P < S
spontaneous
binding effects
interaction between enzyme and substrate
chemical effects
accepting/donating protons; forming covalent linkages
Induced fit during E+S causes…
active site to become more complimentary toward transition state
Substrate binding promotes reaction by…
- reducing entropy
- removal of water molecules to expose reactive groups
- alignment of reactive functional groups of enzyme with substrate
- distortion of substrates
- induced fit as a response
Increased interactions of enzyme and substrate occurs in….
transition state
enzymes have higher affinity for ….
transition state than substrates
transition state analogs
stable compounds whose structures resemble unstable transition states
catalytic antibodies
- abzymes
- generated against a transition state analog may bind to substrate, catalyzing rex by promoting formation of transition state
What participates in enzymatic catalysis?
- polar, ionizable residues (Asp, Glu, His, Cys, Tyr, Lys, Arg, Ser)
- anions and cations of certain amino acids
two commonly observed mechanisms of catalysis
- acid/base
- covalent
for most enzymes, greatest activity at…
physiological pH 7.4 and 37 degrees
steady state equation
rate of formation of ES complex is equal ti rate of its breakdown
Km
amount of substrate required for enzyme to function at half maximal velocity
[S] < Km
enzymes are highly sensitive to change in substrate conc., but have very little activity
[S] > Km
enzymes have high activity but are insensitive to changes in substrate concentration.
[S] = Km
enzyme has significant activity and is responsive to changes in substrate concentration
kcat
-enzyme turnover number
the number of molecules of substrate converted to product per unit time by a single enzyme
how to calculate kcat
Vmax/[E]t
reversible enzyme inhibitors
bind to enzyme by non-covalent interactions
- competitive
- uncompetitive
- non-competitive
competitive inhibitors
resemble substrate
- binds only to enzyme
- increase Km
uncompetitive
- bind to ES
- decrease Vmax and Km
non-competitive
- bind to E and ES
- decrease Vmax
irreversible enzyme inhibitors
- highly stable covalent bonds with enzymes
- permanently inactivates enzyme
what are serine protease
- digestive enzyme
- mediate turnover of self proteins
- in pancreas as inactive zymogens
- both covalent and acid/base catalysis
zymogens
prevent damage to cellular proteins, activated by selective proteolysis
trypsin cleaves
Lys and Arg
chymotrypsin cleaves
Phe, Tyr
Elastase cleaves
Gly, Ala
papain
cuts all peptide bonds
catalytic triad
His, Asp, Ser
catalytic triad - His
removes H from Ser hydroxyl to make it a strong nucleophile and donate electrons and activating a water molecule to regenerate the free enzyme – acid/case catalysis
catalytic triad - Asp
stabilize the positively-charged His to facilitate serine ionization
catalytic triad - Ser
acts as nucleophile (tendency to donate e-) attaching the carbonyl grouop of the polypeptide substrate – covalent catalysis
enzyme can be regulated by:
- controlling amount present (long term)
- adjusting activity of a constant quantity (short term)
enzymatic pathways often controlled through
negative feedback by final product
final product often inhibits…
first step; conserving material and energy and prevent accumulation of intermediates
negative feedback is…
a branched pathway
allosteric enzymes do not….
obey michaelis-mentin kinetics and have signoidal curves
allosteric enzyme binding of substrate disrupts R to T equilibrium in favour of…
R
cooperatively/threshold effect
Allosteric enzymes transition from a less active state to a more active state within a narrow range of substrate concentration. They are sensitive near the Km than M-M enzymes of the same Vmax. Below this sensitivity there is little zctivity, after the threshold, the enzyme activity rapidly increases.
PEP is an ____________ of PFK-1
allosteric inhibitor
ADP is an _________ of PFK-1
allosteric activator
When ration of [PEP]/[ADP] is low….
PFK is activated and glycolysis produces more ATP
glycogen synthase
-anabolic, catalyzes production of glycogen from glucose
glycogen phosphorylase
-catabolic, catalyze breakdown of glycogen into glucose
phosphorylation favours….
breakdown of glycogen into glucose in response to glucagon and epinephrine (anabolic inactive)
dephospho rylation favours….
storage of glucose as glycogen in response to insulin (catabolic inactive)
