Regulation of Enzyme Activity Flashcards
Enzyme activity is often regulated by the
cell
Often the reason for this is to
conserve energy
If the cell runs out of chemical energy, it will die; therefore, many mechanisms exist to
conserve cellular energy
The simplest mechanism of enzyme regulation is to produce the enzyme only when
the substrate is present
This mechanism is used by ____ to regulate the enzymes needed to break down various sugars to yield ____ for cellular work.
bacteria
ATP
Thus, the bacteria save energy by producing the enzymes only when a specific sugar ___ is available.
substrate
Other mechanisms for regulating enzyme activity include use of
allosteric enzymes, feedback inhibition, production of proenzymes, and protein modification
(amazing friends please pray peace)
One type of enzyme regulation involves enzymes that have more than a single binding site. These enzymes, called
allosteric enzymes
These enzymes, called allosteric enzymes, have active sites that can be altered by the binding of small molecules called
effector molecules
the effector binding alters the shape of the ____ of the enzyme
active site
effector binding converts the active site to an inactive configuration
negative allosterism
effector binding converts the active site to an active configuration
positive allosterism
In either case, binding of the effector molecule regulates enzyme activity by determining whether it will be
active or inactive
The third reaction in glycolysis is the transfer of a phosphoryl group from an ATP molecule to a molecule of fructose-6-phosphate. This reaction, shown here, is catalyzed by an enzyme called
phosphofructokinase
Phosphofructokinase activity is sensitive to both
positive and negative allosterism
For instance, when ATP is present in abundance, it is a signal that the body has
sufficient energy
and the pathway should slow down
negative allosteric effector of phosphofructokinase, inhibiting the activity of the enzyme.
ATP
an abundance of AMP, which is a precursor of ___, is evidence that the body needs to make ___.
ATP
ATP
When AMP binds to an ____ binding site on phosphofructokinase, enzyme activity is ____, speeding up the reaction and the entire pathway. Thus, AMP is a ___________-of the enzyme.
effecotr
increased
positive allosteric effector
Allosteric enzymes are the basis for __________biochemical pathways
feedback inhibition
Feedback inhibition usually regulates pathways of enzymes involved in the synthesis of a
biological molecule
the cell uses feedback inhibition, in which the ___ can shut off the entire pathway for its own synthesis
product
Another means of regulating enzyme activity involves the production of the enzyme in an inactive form called a
proenzyme
The proenzyme is converted by _____________ to the active form when it has reached the site of its activity.
proteolysis (hydrolysis of the protein)
he cells that produce pepsin actually produce an inactive proenzyme, called
pepsinogen
Pepsinogen has an additional
42 amino acids
In the presence of stomach acid and previously activated pepsin, the extra forty-two amino acids are ______ and the _____ is transformed into the _____
cleaved off
proenzyme
acitve enzyme
Proelastase
activator
enzyme
trypsin
elastase
Trypsinogen
activator
enzyme
trypsin
trypsin
Chymotrypsinogen A
activator
enzyme
Trypsin + chymotrypsin
chymotrypsin
Pepsinogen
activator
enzyme
Acid pH + pepsin
pepsin
Procarboxypeptidases
activator
enzyme
Trypsin
Carboxypeptidase A, Carboxypeptidase B
is another mechanism that the cell can use to turn an enzyme on or off. This is a process in which a chemical group is covalently added to or removed from the protein. This covalent modification either activates the enzyme or turns it off.
protein modification
The most common type of protein modification is
phosphorylation or dephosphorylation of an enzyme.
typically, the phosphoryl group is added to (or removed from) the R group of
serine, tyrosine, or threonine in the protein chain of the enzyme.
Notice that these three amino acids have a free ─___in their R group, which serves as the site for the addition of the ____ group.
OH
phosphoryl
The covalent modification of an enzyme’s structure is catalyzed by other
enzymes
Protein ____ add phosphoryl groups to a target enzyme, while _____ remove them
kinases
phosphatases
in adipose tissue, phosphorylation activates the enzyme __________, an enzyme that breaks triglycerides down to fatty acids and glycerol
triacylglycerol lipase
an enzyme involved in the breakdown of glycogen, is also activated by the addition of a phosphoryl group.
Glycogen phosphorylase
However, for some enzymes, phosphorylation
inactivates the enzymes
This is true for________an enzyme involved in the synthesis of glycogen. When this enzyme is phosphorylated, it becomes inactive.
glycogen synthase
The convenient aspect of this type of regulation is the ______. An enzyme can quickly be turned on or off in response to environmental or physiological conditions.
reversibility
