Chp. 19 Enzymes Flashcards
Exam 2
What are the six categories of enzymes based on the reactions they catalyze?
- Oxidoreductase
- Transferase
- Hydrolase
- Lyase
- Isomerase
- Ligase
These categories help in the classification of enzymes according to their specific functions.
What type of reactions do oxidoreductases catalyze?
Redox reactions
Includes reductases and oxidases.
What is the function of transferases?
Transfer a group from one molecule to another
Examples include transaminases, transmethylases, and kinases.
What do hydrolases do?
Cleavage of bonds by adding water
Examples include phosphatases, peptidases, lipases, and glycosidases.
What is the role of lyases?
Catalyze removal of groups to form double bonds or the reverse
Examples include decarboxylases and synthases.
What is the function of isomerases?
Catalyze intramolecular rearrangements
Examples include epimerases and mutases.
What do ligases catalyze?
Formation or breaking of C-C, C-S, C-O, or C-N bonds
Ligases are essential for joining two larger molecules.
What is the common suffix for enzyme names?
-ase
This suffix is typically used for enzymes, reflecting their function.
How does an enzyme affect the activation energy of a reaction?
It lowers the activation energy
This results in a faster reaction rate.
What are the two stages of enzyme-catalyzed reactions?
- Formation of enzyme-substrate complex
- Slow conversion of substrate into product
The rate is limited by enzyme availability.
What is the active site of an enzyme?
The part of the enzyme that combines with the substrate
Active sites have specific shapes complementary to their substrates.
What does the lock-and-key model of enzyme action suggest?
The enzyme and substrate fit exactly
This model does not account for conformational changes in proteins.
Describe the induced fit model of enzyme action.
The enzyme active site is a flexible pocket that changes to accommodate the substrate
This model explains enzyme specificity more accurately.
What is enzyme specificity?
The ability of an enzyme to bind only one or a very few substrates
Urease is an example of an enzyme with high specificity.
What are the four classes of enzyme specificity?
- Absolute
- Group
- Linkage
- Stereochemical
Each class describes how specific an enzyme is to its substrates.
What is a cofactor in enzyme activity?
A nonprotein prosthetic group required for enzyme function
bound to the enzyme for it to maintain the correct configuration of the active site (slide 27)
Includes organometallic compounds, metal ions, and organic compounds.
What is a coenzyme?
An organic molecule bound to an enzyme by weak interactions/hydrogen bonds
Coenzymes often carry electrons or small groups.
What effect does pH have on enzyme activity?
Extreme pH changes can denature the enzyme
low=acidic, high=basic
Each enzyme has a pH optimum for maximal function.
What is feedback inhibition?
A product of a reaction inhibits an earlier enzyme in the pathway
This is a common regulatory mechanism in metabolic pathways.
What are zymogens?
Inactive forms of enzymes that are activated when needed
Example: Pepsinogen is activated to pepsin in the stomach.
What distinguishes irreversible inhibitors from reversible inhibitors?
Irreversible inhibitors: bind tightly to enzymes, preventing E-S complex formation
Reversible Inhibitors: often structurally resemble the substrate and bind at the normal active site
(higher concentration wins)
Reversible inhibitors often resemble the substrate and compete for the active site.
What is the optimum temperature for enzyme function in humans?
37°C
This temperature is typically close to the physiological temperature of the human body.
What are irreversible inhibitors?
Substances that permanently inhibit enzyme activity, including:
* Arsenic
* Snake venom
* Nerve gas
Irreversible inhibitors bind to enzymes in a way that permanently disables their function.
What are reversible, competitive inhibitors also called?
Structural analogs
These inhibitors resemble the structure and charge distribution of natural substances for enzymes.
How do reversible, competitive inhibitors affect enzyme activity?
They occupy the enzyme active site, preventing the substrate from binding and inhibiting reaction.
This competition for the active site means that the degree of inhibition depends on the concentrations of both the enzyme and the inhibitor.
What is competitive inhibition?
The inhibitor and the substrate compete for binding to the active site
The outcome of this competition affects the rate of enzyme activity.
What do proteolytic enzymes do?
They cleave the peptide bond in proteins
This action breaks the peptide bonds that maintain the primary protein structure.
What determines the specificity of proteolytic enzymes?
A hydrophobic pocket
This pocket is formed by a cluster of hydrophobic amino acids in the 3-D structure of the protein.
What is the cleavage specificity of chymotrypsin?
Chymotrypsin cleaves at the carboxylic end of M=met, W=trp, F=tyr, Y=phe
Chymotrypsin is a type of proteolytic enzyme with specific targets.
What are pancreatic serine proteases?
A category of enzymes that hydrolyze peptide bonds and evolved divergently from a common ancestor
They share similar primary and tertiary structures but have different specificities.
What is the cleavage specificity of trypsin?
Trypsin cleaves on the carbonyl side of basic amino acids
K=lys, R=arg
This specificity is crucial for its function in protein digestion.
What is the cleavage specificity of elastase?
Elastase cleaves on the carbonyl side of G=Gly and A=Ala
Its specificity allows it to act on small, flexible amino acids.
What are some diagnostic uses of enzymes in medicine for acute myocardial infarction?
Biomarker levels altered include:
* Creatine kinase - MB
* Myoglobin
* Troponin I
These biomarkers help in diagnosing heart attacks.
What enzymes are used in the diagnosis of pancreatitis?
Amylase and Lipase
Elevated levels of these enzymes indicate pancreatic inflammation.
What is an analytical reagent in the context of enzyme use in medicine?
An enzyme used to measure another substance = urea being converted to NH3 via urease
This process is essential for measuring blood urea nitrogen (BUN).
Enzyme Specificity Classes: Absolute
enzyme reacts with only one substrate
This therapy helps manage a genetic disorder affecting lipid metabolism.
Enzyme Specificity Classes: Group
enzyme catalyzes reaction involving any molecules with the same functional group
Enzyme Specificity Classes: Linkage
enzyme catalyzes the formation or break up of only certain category or type of bond
Enzyme Specificity Classes: Stereochemical
Enzyme recognizes only one of the two enantiomers
Transition State
Features both a substrate and product & falls apart to yield product - dissociates from the enzyme
When the substrate interacts with the enzyme, its shape changes which is less energetically stable. (high energy = low stability)
First Possible Transition State
enzyme might put “stress” on a bond facilitating bond breakage (slide 22)
substrate + product = fall apart to yield product
Second Possible Transition State Change
the enzyme brings two reactants close to one another and in proper orientation
(slide 23)
-Removes possibility of side reactions
-Allows correct orientation=Correct Reaction
Third Possible Transition State Change
the enzyme might modify the pH of the microenvironment, donating or accepting a H+
How does an enzyme possibly decrease the activation energy of the reaction?
Binding Energy
Apoenzyme
Polypeptide portion of enzyme: No enzyme-substrate complex=no reaction (slide 27)
Holoenzyme
Active Enzyme
Methods Used to Regulate Enzyme Activity
- Produce the enzyme only when substrate is present
- Allosteric Enzymes
- Feedback Inhibition
- Zymogens
- Protein Modification
Methods Used to Regulate Enzyme Activity: Allosteric Enzymes
effector molecules change the activity of an enzyme by binding at a second site
4 General Stages in an Enzyme Catalyzed Reaction
- Enzyme + Substrate Binding
- Transition State
- Catalyzes
- Product Release
Allosteric Enzymes
-Positive Allosteric vs. Negative Allosteric
positive: effector binding converts the active site to an active configuration=higher activity of enzyme
negative: effector binding converts the active site to an inactive configuration=lower activity of enzyme
Methods Used to Regulate Enzyme Activity: Feedback Inhibition
Allosteric enzymes are the basis for feedback inhibition: product later in a series of enzyme-catalyzes reactions inhibits earlier allosteric enzymes in the series
Methods Used to Regulate Enzyme Activity: Zymogens and Proenzymes
enzyme made in an inactive form (zymogens), converted to an active form
- by hydrolysis of the enzyme (proteolysis), when needed at the active site in the cell = when needed the inactive form is removed
Why is it important for cells to regulate the levels of enzyme activity?
To Maintain Cellular Homeostasis
Methods Used to Regulate Enzyme Activity: Protein Modification
a chemical group is covalently after to or removed from the protein
ex. addition or removal of a phosphate group
Proteolytic Enzyme Specificities
*Chymotrypsin
*Trypsin
*Elastase
