Chp 20 Enzymes Flashcards
are globular proteins with a unique three-dimensional shape that recognizes and binds a small group of reacting molecules, called substrates
enzymes
have a tertiary structure that includes a region called the active site where one or more small groups of substrates bind to create a chemical reaction.
enzymes
have specific amino acid residues within the active site that interact with functional groups of the substrate to form hydrogen bonds, salt bridges, and hydrophobic interactions
enzymes
has a rigid substrate binding to a rigid enzyme, much like a key fitting into a lock
lock-and-key model
more dynamic model of enzyme action, states that the active site is flexible enough to adapt to the shape of the substrate
induced-fit model
The induced-fit model has the substrate and enzyme working together to acquire a geometrical arrangement that lowers the activation energy
Enzymes like lactase have an ____ where the substrate fits for catalysis to occur. The quaternary structure of lactase consists of four subunits. The substrate, lactose (gray), is held in place in the active site by hydrogen bonds with amino acid R groups.
active site
Some enzymes show absolute specificity by catalyzing ___ reaction for one specific substrate
only one
The combination of an enzyme and a substrate forms a
enzyme–substrate (ES) complex
The ES provides an alternative pathway for the reaction with
lower activation energy
Within the active site, amino acid R groups catalyze the reaction to form an
enzyme–product (EP) complex
oxidoreductases
catalyze redox rxns
Oxidases catalyze oxidation of a substrate
Dehydrogenases catalyze removal or addition of two H atoms
Transferase
catalyzes the transfer of a functional group between two compounds
Hydrolases
catalyzes hydrolysis (adds H20) rxn that split into two producs
Lyases
catalyze the addition or removal of a gruop without hydrolyssi
isomerases
catalyze the rearrangement of atoms within a substrate
Ligases
joiing of two substrates, using ATP
The activity of an enzyme describes how fast an enzyme catalyzes the reaction and is strongly affected by reaction conditions, such as
temperature.
pH.
concentration of the enzyme and substrate.
lose activity at ___ temperatures as denaturation occurs
high
most active at an ___temperature (usually 37°C in humans).
show little activity at low temperatures.
optimum
most active at optimum pH, where proper ___ structure of the protein is maintained
tertiary
An increase in enzyme concentration
increases the rate of reaction (at constant substrate concentration).
binds more substrate with enzyme
An increase in substrate
concentration
increases the rate of reaction (at constant enzyme concentration).
eventually saturates an enzyme with substrate to give maximum activity
type of covalent modification that activates or deactivates an enzyme.
Phosphorylation
A kinase activates an inactive enzyme by
phosphorylation
A phosphatase activates an inactive enzyme by ___ of a phosphate
removal
bind with a regulator molecule at the allosteric site that is different from the active site.
change the shape of the enzyme, which causes a change in the shape of the active site
Allosteric enzymes
can be a___ that changes the shape of the active site to allow the substrate to bind more effectively
positive regulator
allosteric enzymes
can be a ____ that changes the shape of the active site to prevent the proper binding of the substrate, which decreases the rate of the catalyzed reaction.
negative regulator
allosteric enzyme
Enzyme activity can be regulated by allosteric enzymes, feedback control, and
covalent modifications
In feedback control, when the end product level is high
the end product of a series of reactions acts as a negative regulator and binds to the allosteric site.
the substrate cannot bind to the active site, and production of all of the intermediate compounds in the subsequent reaction sequence stops
when the level of end product is low
the regulator dissociates from the allosteric site on the enzyme, unblocking the active site.
the initial substrate is allowed to bind to the active site again.
Enzyme activity is modified by covalent bonds to a group on the polypeptide chain that are formed or broken.
Covalent modification is reversible.
Zymogens, or proenzymes, are produced in their inactive form and can be activated at a later time when they are needed
Once a zymogen is formed, it is
transported to where the active form is needed.
converted to its active form by a covalent modification.
different forms of an enzyme that catalyze the same reaction in different cells or tissues of the body.
have quaternary structures with slight variations in the amino acids in the polypeptide subunits
Isoenzymes
are molecules that cause a loss of catalytic activity.
prevent substrates from fitting into the active sites
Inhibitors
can be classified as either reversible inhibitors or irreversible inhibitors.
cause a loss of enzyme activity that can be restored.
can act in different ways but do not form covalent bonds with the enzyme
Reversible inhibitors
Reversible inhibition can be competitive or noncompetitive.
Competitive inhibitors compete for the active site.
Noncompetitive inhibitors act on another site that is not the active site.
chemical structure and polarity similar to the substrate
competitive inhibitor
competes with the substrate for the active site.
has its effect reversed by increasing substrate concentration
has a structure that is much different from that of the substrate.
does not compete for the active site.
distorts the shape of the enzyme, which prevents the catalyzing of the substrate at the active site.
cannot have its effect reversed by adding more substrate
noncompetitive inhibitor
the inhibitor covalently bonds with R groups of an amino acid that may be near the active site
the inhibitor changes the shape of the enzyme, which prevents the substrate from entering the active site
irreversible inhibition
an active enzyme that consists only of protein
simple enzyme
Many enzymes are active only when they combine with __ such as metal ions or small molecules
cofactors
A ___ is a cofactor that is a small organic molecule such as a vitamin
coenzyme
organic molecules that are essential for normal health and growth.
are required in trace amounts.
need to be obtained from the diet
Vitamins
Water-soluble vitamins
are soluble in aqueous solutions and cannot be stored in the body.
are cofactors for many enzymes.
are excreted in urine each day.
are easily destroyed by heat, oxygen, and ultraviolet light, so care must be taken in food preparation
B1 - thiamine
beriberi, fatigue, poor appetite, weight loss
B2 - riboflavin
dermatitis, dry skin, sore tongue, cataracts
b3 - niacin
pellagra, muscle fatigue, loss of appetite, diarrhea, mouth sores
b5 pantothenic acid
fatigue, retarded growth, muscle cramps, anemia
b6 pyridoxine
demratitis, fatigue, anemia, retarded growth
b9 folic acid
abnormal RBCs, anema, GI issues, loss of hair, growth impairment, depression
b12 cobalamin
pernicious anemia, malformed RBCs, nerve damage
Vit C ascorbic acid
scurvy, bleeding gums, weakened connective tissues, slowe healing wounds, anemia
Biotin H
dermatitis, loss of hair, fatigue, depression
Retinol Vit A
necessary to avoid blindness, immune system repression, slowed growth
Cholecalciferol - VIt D
necessary to avoid weakened bones
Vit E tocopherol
necessary to avoid hemolysis, anemia
Vit k menaquinone
necessary to avoid prolnged bleeding time & bruising
catalyzes the oxidation of a substrate
oxidase
oxidoreductase
catalyzes removal or addition of two H atomss and utilizes a coenzyme
dehydrogenase
oxidoreductase
transfer of an amino acid from one substrate to another
transaminase
transferase
transfer of phosphate gruops from one substrate to another
kinase
transferase
hydrolysis of peptide bond in proteins
proteases
hydrolase
hydrolysis of ester bonds in lipids
lipases
hydrolase
hydrolysis of phosphate ester bonds in nucleic acids
nucleases
hydrolase
removal of CO2 from a substrate
decarboxylase
lyase
removal of NH3 from a substrate
deaminases
lyase
removal of H20 from a substrate
dehydratases
lyase
catalyze the addition of H20 to a substrate
hydratases
lyase
rearrangment of carbohydrates
epimerases
type of isomerase
formation of a bond between two substrates utilizing ATP
synthestases
ligases
formaiton of a bond between CO2 and a substrate using ATP
carboxylases
ligase
