1.7 Enzymes Flashcards
Enzyme definition
A biological catalyst, usually a protein, that speeds up a chemical reaction
The enzyme lipase speeds up the _________ of the lipid triglycerides.
hydrolysis
Sucrase speeds up the hydrolysis of
sucrose into _______ and ________.
glucose; fructose
Another term that is used to describe an enzyme is _______.
catalyst
Catalyst definition
A catalyst is a substance that speeds up a reaction without being consumed by the reaction.
For a chemical reaction to move forward, it must overcome an ________ _______
energy barrier
Enzymes bind a specific reactant called a _________; in doing so, they _____ the energy barrier so that the reaction proceeds at a ______ rate than it would without the enzymes
substrate; lower; faster
Substrate definition
A substance that is recognized by and binds to an enzyme
Each type of enzyme __________ the reaction of only one type of molecule or one
group of closely related molecules.
catalyzes
Active site definition
A pocket or groove in an enzyme that binds its substrate
The substrate interacts with only a very small _______ of the enzyme called the active site.
The active site is usually a pocket or groove that forms when the newly synthesized enzyme ____ into its correct 3D shape (________ structure).
region; folds; tertiary
Induced-fit model definition
A model of enzyme activity that describes how an enzyme changes shape to better accommodate
a substrate
What are the steps in the enzyme cycle?
1) An enzyme binds to one or more substrates,
forming an enzyme-substrate complex.
2) The enzyme then converts the substrate(s)
into one or more products.
3) Since enzymes remain unchanged after a
reaction, enzyme molecules can rapidly bind to
other substrate molecules, catalyzing the same
reaction repeatedly.
The rate at which enzymes catalyze reactions varies depending on the ________ and ________ involved
enzyme; substrates
Cofactor definition
A non-protein group that binds to an enzyme and is essential for catalytic activity
Coenzyme definition
An organic molecule that acts as a cofactor of an enzyme
True or false
Cofactor are often non-metals.
False
Cofactors are often METALS, such as iron, copper, zinc, and manganese.
Many coenzymes ________ molecules from one enzyme to another.
shuttle
Several control mechanisms modify enzyme activity and adjust _______ rates to meet a cell’s
requirements for chemical __________.
reaction; products
The _____________ of both the enzyme and the substrate will influence the rate of a ________ reaction.
concentration; catalysis
If there is excess substrate present, then the rate of reaction is _____________ to the enzyme concentration. This occurs because the amount
of enzyme _______ the rate of reaction.
proportional; limits
If, however, the amount of enzyme is at a _______
intermediate concentration, then increasing the substrate concentration will increase the rate of reaction up to a point, called the _________ ______
constant; saturation level
The rate of the reaction ________ as collisions become more _______.
increases; frequent
However, as the enzyme molecules approach the _________ rate at which they combine with the substrate, increasing the substrate concentration has a _______ effect.
Eventually, the rate of reaction levels off. At this point, the enzyme molecules are ________ with substrate.
maximum; reduced; saturated
Enzyme inhibitor definition
Enzyme inhibitors lower the rate at which an enzyme catalyzes a reaction.
Inhibitor definition
Inhibitors are molecules that bind to an enzyme and decrease its activity.
Competitive inhibition definition
A situation in which a competitor substance binds to a normal substrate binding site to block
enzyme activity
Noncompetitive inhibition
A situation in which molecules bind to an enzyme
at a site that is not the active site, thus blocking enzyme activity
Reversible inhibition
In reversible inhibition, the binding of the inhibitor to the enzyme is weak and readily reversible.
Enzyme activity returns to normal following the release of the inhibitor.
Irreversible inhibition
In irreversible inhibition, some inhibitors
bind so strongly to the enzyme through the formation of covalent bonds that they completely disable the enzyme.
Many irreversible inhibitors that act on critical enzymes are highly ______ to the cell.
toxic
Allosteric site definition
A binding site on an enzyme that binds regulatory molecules.
Allosteric regulation definition
The regulation of one site of a protein by binding to another site on the same protein. It may either inhibit or stimulate enzyme activity.
Binding of an allosteric activator molecule ______ the enzyme in a shape that causes its active site to have a high ________ for its substrate.
In this state, the enzyme ____ its substrate.
stabilizes; affinity; binds
Binding of an allosteric inhibitor stabilizes an _________ form of the enzyme.
The inhibitor molecule changes the ______ of the enzyme in such a way that the substrate is _________ from the active site.
inactive; shape; released
Allosteric regulators are important molecules, functioning to control chemical _________ in a cell.
activity
An allosteric inhibitor is a ________ of the biochemical pathway that it regulates.
product
Feedback inhibition definition
The regulation of a pathway by one of the products of this pathway.
Feedback inhibition prevents cellular resources from being _______ in the _________ of molecules at intermediate steps in the pathway.
wasted; synthesis
Enzymes usually reach _________ activity within a narrow range of temperatures and pH values.
At levels outside this range, enzyme activity _____ off.
This usually produces a _______ curve when enzyme activity is plotted, with the peak where temperature and pH produce maximal activity.
maximal; drops; peaked
As the pH either increases or decreases away from its optimal value, the rate of the catalyzed reaction __________
decreases
The more the pH value deviates from the _________ value, the more _________ the effects on the structure and function of the active site of the enzyme become, until the rate of the reaction falls to _____.
optimal; extreme; zero
Temperature has a general effect on all kinds of chemical reactions. As the temperature ____, the rate of a chemical reaction usually increases.
This effect reflects increases in the ______ motion of the molecules.
As the temperature rises, there are more frequent and stronger ________.
rises; kinetic; collisions
Temperature has an effect on all proteins, including enzymes.
As the temperature rises, the kinetic motions of the amino acid chains of an enzyme _________.
At the same time, the strength and frequency of the ________ between the enzyme molecules and any surrounding molecules also ________.
increase; collisions; increases
In the range of 0 to about 40°C, the reaction rate _______ for every 10°C _______ in temperature
doubles; increase
Above 40°C, the increasing kinetic motion begins to unravel, or _______, an enzyme.
The hydrogen bonds and other forces that hold together the enzyme’s 3D structure ______.
As this happens, the enzyme loses its ability to __________.
denature; break; function
The denaturation process reduces the rate of _________ in enzyme activity.
increase
The rate of an enzyme-catalyzed reaction _____ at a temperature at which kinetic motion is the _________ but no significant _________ of the enzyme has occurred.
peaks; greatest; unfolding
Explain how lactose intolerance relates to enzymes.
Lactose intolerance is the inability to properly break down lactose, the primary disaccharide in milk.
To absorb the lactose, the digestive cells need to secrete an enzyme called lactase.
Lactase catalyzes the efficient breakdown of lactose in the monosaccharides glucose and galactose.
People with lactose intolerance do not produce enough lactase, and therefore lactose is not digested or absorbed properly.
The lactose is then consumed by bacteria living in the gut.
Effects of enzymes on animal feed
degradation of the components of feed to improve nutrient digestion and uses of the feed
Effects of enzymes on brewing
faster maturation of beer; removal of carbohydrates in light beer
Effects of enzymes on dairy
cheese making; removal or conversion of lactose in milk
Effects of enzymes on detergent
breakdown of starch and fatty acid stains as an active biological component of powder and liquid detergents; colour brightening and softening
Effects of enzymes on starch
production of glucose, dextrose, fructose
Effects of enzymes on wine and juice
degradation of the protein pectin for clarification and increase in juice yield
What is a substrate? What is an active site? How are they related?
A substrate is a substance that is recognized and binds to an enzyme.
An active site is the location on an enzyme where a substrate binds and is the location of the enzymatic reaction.
Why is an enzyme considered a biological catalyst?
Enzymes are considered biological catalysts because they can be used repeatedly and are not wasted after they catalyze a reaction.
Describe the induced-fit hypothesis of an enzyme-substrate interaction.
In the induced-fit hypothesis, the conformation of the enzyme changes slightly to allow for a more precise binding of the substrate.
What is the functional role of a coenzyme or a cofactor in an enzyme-induced reaction? Give an example of an enzyme that requires a cofactor or a coenzyme.
Coenzymes and cofactors are required for an enzyme to properly catalyze a reaction.
Pyruvate dehydrogenase requires the cofactor magnesium.
How does the rate of a reaction change as a result of each of the following factors?
(a) enzyme concentration
As the concentration of enzyme increases, so does the rate of the reaction.
How does the rate of a reaction change as a result of each of the following factors?
(b) substrate concentration
The rate of a reaction will increase with increasing substrate concentration until the enzyme reaches its saturation level.
At this point there is no change in the rate of the reaction.
How does the rate of a reaction change as a result of each of the following factors?
(c) temperature
Temperature above the optimal point will slowly cause decrease of enzymatic activity and ultimately stop it at the point of denaturation; lower temperature will decrease the activity due to a decrease of available energy.
How does the rate of a reaction change as a result of each of the following factors?
(d) pH
Significant deviation from the optimal pH will cause enzyme denaturation.
Describe noncompetitive enzyme inhibition. Provide an example to support your answer.
A noncompetitive inhibitor binds to the enzyme at a site other than the active site.
It changes the conformation of the enzyme so that it no longer binds its normal substrate.
Alanine non-competitively inhibits pyruvate kinase forming a feedback loop preventing more alanine production.
Describe the different effects of an activator and an inhibitor on an allosterically regulated enzyme.
The activator binds in such a way that it stabilizes the active conformation of the enzyme, and it is then able to better bind the substrate.
An inhibitor stabilizes the inactive conformation of the enzyme, so it cannot bind to its normal substrate.
Describe how feedback inhibition reduces the waste of cellular resources.
The products of a reaction pathway inhibit the production of more products.
Therefore, if there is too much product in the cell, the pathway is inhibited, and the resources needed for the intermediate steps in the pathway are not wasted.
Why is it important for the human body to maintain a proper temperature and a proper pH at all times?
Maintenance of proper temperature and pH is important in providing optimal conditions for the body’s enzymes to perform their activity.
You are making a gelatin dessert, but the directions tell you not to use fresh pineapple because the gelatin will not solidify. Gelatin is a structural protein made from collagen. Pineapple contains an enzyme, bromelain, which is a protease.
(a) What effect does a protease have on a protein like collagen?
A protease is an enzyme that begins protein catabolism by breaking the peptide bonds that link the amino acids in the polypeptide chain.
This disrupts the gelatin and stops it from setting.
Humans produce enzymes in the mouth, stomach, and small intestine that aid in the process of digestion. As we age, we tend to produce less of these enzymes. What effect could this have on digestion and nutrition?
As we age, it becomes harder to utilize the nutrients in our food due to loss of function of digestive enzymes.
This can lead to malnutrition and/or digestive problems
Digestion cannot take place unless water is present. Explain this statement.
Carbohydrates and proteins are broken down by hydrolysis into smaller subunits by the addition of water molecules.
Without water, hydrolysis cannot happen, therefore, digestion cannot take place.
What are enzymes?
-a biological catalyst
Speeds up chemical reactions
Helps to break down/build molecules
REUSABLE
Have very specific shapes and only react with specific substances
substrate
the substance that reacts with
an enzyme
true or false:
substrates and enzymes bond together
true
active site
a pocket/groove in an enzyme that
binds to the substrate
induced fit hypothesis
describes how enzymes
change shape to better attach to a substrate
Enzyme-Substrate Complex
term used to describe
enzymes bonded to substrate(s)
cofactor and examples
non-protein
group that binds to
enzymes and helps them
function
Often metals such as
copper, iron, zinc etc.
coenzyme
Coenzyme – an organic
molecule that acts as a
cofactor of an enzyme
may be derived from
vitamins
how does concentration affect enzyme activity?
the concentration of both enzyme and substrate will influence the rate of reaction
Rate of reaction is proportional to enzyme concentration (enzymes limit reaction speed)
enzyme inhibitors
Lower enzyme reaction rate
Bind to enzymes to inhibit activity
competitive inhibitor
binds to active site to prevent
substrate from binding
Non-competitive Inhibitor
binds to enzyme and changes the
shape, indirectly prevents substrate from binding
irreversible inhibitors
often highly toxic to cells as they
prevent enzymes from functioning
(Ex. Cyanide binds to
cytochrome oxidase and interferes with cellular respiration)
allosteric regulation
regulation of enzyme function using other molecules that bind to the enzyme
allosteric site
a binding site on an enzyme where allosteric molecules attach
allosteric inhibition
stabilizes enzyme into an inactive form
allosteric activation
stabilizes enzyme into an active form
what is feedback inhibition and how does it affect enzyme activity?
the regulation of a pathway by one of the products of the pathway
-essentially once enough product is produced then the pathway shuts down until more product is needed
process of feedback inhibition
A series of different enzymes
break down a large molecule
into several smaller molecules
The small molecules (the
finished product) can bind to
the first enzyme and inhibit it
The pathway shuts down until
the smaller molecules become
scarce; then the enzymes
become reactivated
Temperature and pH can both affect _____________
Enzymes will often only ________ optimally within a specific range of temperatures and pH levels
enzyme activity; function
how is treating lactose intolerance an application of enzymes?
taking lactase pills to help break down lactose in dairy products
how is making cheese an application of enzymes?
enzymes used to solidify milk into cheese
how is breaking down starch an application of enzymes?
enzymes used to break down plant starches into sugars
how is stain removal an application of enzymes?
used to break apart certain types of staining molecules without heating (cold water detergents)
