Enzymes Lecture 1
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49 Terms
Why are biological catalysts necessary for life?
uncatalyzed rxns too slow to sustain life
What are the two types of biological catalysts?
enzymes (proteins) and ribozymes (RNA)
What is the primary biological catalyst used in cells?
enzymes
Why did ribozymes take longer to discover?
RNA is unstable
What makes enzymes superior catalysts?
high catalytic power & specificity, work under mild temp and pH, function in aqueous environments
What role do enzymes play in metabolism?
catalyze every step
Is glucose oxidation thermodynamically favorable?
Yes, highly exergonic
Why can glucose sit on a shelf for years without reacting?
reaction is thermodynamically favorable but kinetically slow because it has a high activation energy
What are the three characteristics that define enzymes?
Catalytic Power
Specificity
Regulation
What is catalytic power?
ability of an enzyme to accelerate a reaction compared with the uncatalyzed reaction
What is the range of catalytic power for enzymes?
10^5 to 10^17
Which enzyme has the highest catalytic power?
Orotidine Monophosphate Decarboxylase
What conditions do enzymes work under?
mild temp, mild pH, aqueous
How do you calculate catalytic power?
catalyzed rate / uncatalyzed rate
What is enzyme specificity?
ability of an enzyme to recognize a specific substrate and produce a specific product
What determines enzyme specificity?
Complementary interactions between the substrate and active site
What properties must match between substrate and active site?
shape, polarity, charge
What is a cofactor?
non-protein component required by some enzymes for activity
What are metal ions?
cofactors
What is a coenzyme?
organic or organometallic cofactor involved directly in catalysis
What is a prosthetic group?
tightly bound or covalently attached coenzyme
What is a holoenzyme?
active enzyme w/ cofactor
What is an apoenzyme?
inactive enzyme w/o cofactor
Where do many coenzymes come from?
vitamins from diet
What reaction do oxidoreductases catalyze?
redox rxns
What type of enzyme is Lactate Dehydrogenase?
Oxidoreductase
What reaction does lactate dehydrogenase catalyze?
lactate → pyruvate (NAD+/NADH)
What do transferases do?
transfer functional groups
What class of enzyme is Phosphofructokinase?
Transferase
What class of enzyme is Hexokinase?
Transferase
What class of enzymes are kinases?
Transferases
What do hydrolases do?
break covalent bonds using water
Examples of hydrolases?
Urease, Trypsin
What do lyases do?
Add groups to double bonds
Remove groups to create double bonds
What do isomerases do?
Rearrange atoms within molecules
What do ligases do?
Form new bonds using energy from ATP hydrolysis
What class of enzymes is Pyruvate Carboxylase?
ligase
What is the MOST common enzyme class?
Oxidoreductase
What is the LEAST common enzyme class?
Ligases
What is the lock and key hypothesis?
enzyme active site perfectly matches the substrate
What is wrong with the lock and key model?
Enzymes are flexible, not rigid
What is the induced fit hypothesis?
Substrate binding causes the enzyme to change shape to create a better fit
What happens when a substrate binds?
enzyme undergoes a conformational change
What is E.C.1.?
Oxidoreductase
What is E.C.2.?
Transferase
What is E.C.3.?
Hydrolase
What is E.C.4.?
Lyase
What is E.C.5.?
Isomerase
What is E.C.6.?
Ligase