Chapter 2: Enzymes Flashcards
What are the 6 major enzyme classifications?
- oxidoreductases
- transferases
- hydrolases
- lyases
- isomerases
- ligases
transferases
catalyze the movement of a functional group from one molecule to another
A + BX → AX + B
kinases
transfer phosphate groups from ATP to another molecules
a type of transferase
ligases
catalyze the joining of 2 molecules
A + B → AB
what enzyme joins the 2 DNA strands?
DNA ligase
oxidoreductases
catalyze REDOX reactions; transfer electrons between biological molecules
2 classes of oxidoreductases
oxidase: oxidize molecules (remove electrons)
reductase: reduce molecules (add electrons)
isomerases
catalyze the rearrangement of bonds within a molecule
A → B
convert molecules from 1 isomer to another
hydrolases
catalyze the cleavage of a compound into 2 molecules by adding water
A + H2O → B + C
lyases
catalyze the cleavage of a single molecule into 2 products (without using water or oxidation/reduction)
A → B + C
lipases
catalyze the hydrolysis of fats
phosphatases
remove phosphate
a type of transferase
phosphorylases
transfer of a phosphate group from a donor (not ATP) to an acceptor molecule (often glucose)
Typical features of cofactors and coenzymes:
small
ions
concnetrated in an area?
charged?
Apoenzymes vs holoenzymes
apoenzymes: no cofactors or coenzymes
holoenzymes: cofactors or coenzymes
Prosthetic groups
permanently attached cofactors/coenzymes? commonly metal ions
Michaelis-Menton equation (with vMax and with Kcat)
V = Vmax [S] / Km + [S]
V = Kcat [E] [S] / Km + [S]
Catalytic efficiency
Kcat / Km
large Kcat = efficient; small Km = efficient
Hill’s coefficient
describes cooperativity
1 = no cooperativiy
greater than 1 = positive cooperativity (binding of substrate to one unit increases affinity in others)
less than 1 = negative cooeprativity
Effect of temperature on enzyme activity
velocity increases at a fairly constant rate as temperature is increased UNTIL the ideal temp is reached after which further temp increase will drop the velocity significantly as enzymes are denatured
How does negative feedback work?
the products of a mechanism will inhibit an enzyme earlier in the mechanism
What are the 4 types of reversible inhibition?
competitive, noncompetitive, uncompetitive, mixed
Competitive inhibition
bind to active site
v max is same
km changes
noncompetitive inhibition
bind to allosteric site
v max changes
km stays same (substrate still has same affinity for unaffected enzyme)
mixed inhibition
km may increase or decrease
inhibitor has different affinities for enzyme and ES complex
higher affinity for ES complex = greater lower km (increases affinity of substrate for enzyme)
uncompetitive inhibition
relatively permanent changes
3 regulated enzymes:
zymogens, allosteric enzymes, covalently modified enzymes
Describe allosteric enzymes
have allosteric sites
Describe covalently modified enzymes
Describe zymogens
inactive and must be activated
What is Km
affinity of substrate for enzyme; amount of substrate bound at half Vmax?
How do enzymes alter delta G (gibbs free energy change)?
it does NOT
exergonic vs endergonic reactions; their respective delta G values
endergonic: consumes/requires energy (positive delta G, non spontaneous)
exergonic: releases energy (negative delta G, spontaneous)
lock and key theory vs induced fit model
lock and key: enzyme has active site that perfectly matches substrate
induced fit: binding of substrate causes conformation change of enzyme to then have perfect fit with substrate (ES complex is a better fit than enzyme alone)
