Chp. six Flashcards
____ tells if a reaction can thermodynamically happen, but it doesn’t say that it will happen. Rate of reaction is a function of specialized enzymes.
delta G
Molecules that should react with one another often _____ because they lack sufficient energy.
do not
___ is the minimum amount of energy that 2 molecules must have in order to react.
activation energy Ea
For a reaction to occur you must have a ______ and
favorable delta G and enough energy to reach Ea
The rate of enzymatic reaction is proportional to _____ that have an evergy content >=
fraction of molecules
Under most biologically normal conditions, the Ea is ___ that few molecules have that much energy.
so high
The rates of uncatalyzed reaction in cells are ____
very slow.
non-reacting molecules are ____ unstable but ____ stable in a metastable state.
thermodynamically, kinetically
life depends on the high Ea to ____ cellular reactions from happening at appreciable rates ____ in the presence of a suitable catalyst.
prevent, except
Providing a reactive surface is the task of a_____`
catalyst
Protein catalysts are called
enzymes
RNA catalyst are called
ribozymes
3 basic properties of catalysts
- All catalysts increase the rate of a reaction by lowering the Ea requirement.
- All catalysts act by forming transient intermediate complexes with the substrate molecules and thus position them in a manner that facilitates their interaction.
- All catalysts change only the rate at which equilibrium is reached; no effect on the position of the equilibrium.
Every enzyme contains, somewhere within its 3 prime structure, a characteristic cluster of ______ forming an _____.
amino acids, active site
What is the location of domain on the enzyme’s structure where the actual catalytic action occurs
active site
what is usually a groove or pocket with chemical or structuaral properties that accommodate the intended substrate with high specificity
active site
Active site involves only about ____ of the surface area of the enzyme.
5%
Amino acids most commonly found at an active site
cysteine, histidine, serine, aspartate, glutamate, lysine
The amino acids that make up the active site of an enzyme are not usually contiguous along the ___ sequence of a polypeptide. Instead, they are brought into the right conformation by the specific ____ folding of the polypeptide chain and by additional conformational change when the substrate binds.
1 prime, 3-D
The reaction seen in peroxisomes is _____ favorable… yet hydrogen peroxide exists in nature in a _____ state.
thermodynamically, metastable
When ferric ions are added to the solution it increases the reaction rate about
30,000X
fe+3 reacts with O2 to form iron oxides and drive the break down of
H2O2
If ____ is present the reaction occurs about 1x10^9 X faster than if uncatalyzed
catalase
if a catalase is present the reaction occurs about ____ faster than if uncatalyzed.
1x10^9 X
ion groups that are integral parts of enzyme structure
prosthetic groups
Prosthetic groups can be ___ organic molecules or ___ ions or combination of ____
small, metal
Prosthetic groups function as ____ acceptors since none of the a.a. are good _____ acceptors.
electron, electron
Prosthetic groups are usually associated with the ____ and are indispensable for ____.
active site, catalytic activity
Not all enzymes have prosthetic groups; ones that do RedOx reaction ____
require one
While all of the vitamins may have been discovered, new catalytic cofactors and prosthetic groups are ______.
still being found. They are too numerous to mention.
The coenzyme ____ is a hydrogen carrier that replaces ____ in certain bacterial alcohol dehydrogenases.
PQQ, NAD
____ is a cofactor for amino oxidases found in bacterial, plan, and human tissues. It is a prosthetic group that is formed by oxidation of a specific tyrosine in the active site.
Topaquinone
Topaquinone functions together with a nearby ___ ion which binds the ___ substrate. The same copper center and ___are apparently involved in ____ synthesis of the prosthetic group.
copper, O2, O2
Formation of topaquinone is only one case of many, in which _____ groups are self-assembled using components of the ___ that carries the group.
prosthetic, protein
A recently discovered example of formation is ______, from glycine and serine units of protein. The prosthetic group is involved in a previously hard-to-explain isomerization of histidine and phenylalanine.
4-methylidene-imidazole-5-one
Enzyme must bind the substrate then ____ the reaction.
catalyze
A consequence of the structure of the active site is that the enzymes display a high degree of substrate specificity.
Enzyme specificity
Enzyme specificity can discriminate between very _____ molecules.
similar
Enzyme specificity has a difference between an ____ catalyst vs. an ____ one
inorganic, organic
Are all enzymes specific as others?
no
Some enzymes accept a ____ of ____ related substrates.
number, closely
Which enzymes tend to accept entire groups of substrates as long as they posses some common structural feature.
enzymes involved in synthesis or degradation of polymers.
How many major classes are based on function, with subgroups used to define their function more precisely.
6
maintains a narrow range of cellular temps
homeotherms
Within this narrow range, the rate of an enzyme-catalyzed reaction increases with temp Why?
increases the kinetic energy of the molecules and their reactivity.
Outside of this temp range the enzyme begins to fall apart or _____.
denature
The temp range over which an denatures varies _____ from enzyme to enzyme and especially from organism to organism.
greatly
organisms that live in an environment with a higher than average temperature for biotic life such as bacteria that thrive in environments that average 70 degrees C.
thermophiles
They have essentially the same genes as other bacteria, however, the alleles for their proteins encode heat tolerate varieties of enzyme.
thermophiles
Thermophiles enzymes operate at _____ teps and are critical to bio-technology.
high
______ is an ex. DNA polymerase (replicates DNA) from Thermus aquaticus is the driving force of PCR and DNA sequencing.
thermophiles
Most enzymes are active within a range of only _____pH units.
3-4
The pH dependence is usually due to the need for one or more charged _______ at the active site.
amino acids.
_____ dependence usually reflects the environment in which an enzyme is normally active
pH
The active site of ______ involves the caroxyl groups from each of 2 glutamates (positions 72, 270)
carboxypeptidase A
reaction type: oxidation-reduction reactions
class: oxidoreductases
Reaction type: Transfer of functional groups from one molecule to another.
transferases
Reaction type: Hydrolytic cleavage of one molecule into two molecules
classes: hydolase
Reaction type: Removal of a group from, or addition of a group to , a molecule with rearrangement of electrons.
Classes: lyases
Reaction type: Movement of a functional group within a molecule
classes: isomerases
Reaction type: Joining of two molecules to form a single molecule
classes: Ligases
List the six enzyme classes.
oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases
Enzyme name: alcohol dehydrogenase
oxidoreductases
Enzyme name: Glycerokinase
transferases
Enzyme name: Carboxypeptidase A
hydrolases
Enzyme name: Pyruvate decarboxylase
lyases
Enzyme name: Maleate isomerase
Isomerases
Enzyme name: Pyruvate carboxylase
Ligases
