Enzymes Flashcards
What enzymes are secreted in salivary glands?
Alpha-amylase
Lingual Lipase
What is the product of Amylose (a polysaccharide) digestion?
Disaccharide
What is the product of lipid digestion?
DAG, MAG, FFA, Glycerol
What enzymes are secreted in the stomach?
Pepsin (protease)
Gastric lipase
What is the product of protein digestion?
Peptides
What enzymes are secreted in the pancreas?
Pancreatic amylase
Trypsin (protease)
Chymotrypsin (protease)
Acid Lipases
What are the pancreatic enzymes that digest proteins into peptides?
Trypsin and Chymotrypsin
What are the pancreatic enzymes that digest lipids into DAG, MAG, FFA, glycerol?
Acid lipases
What are the pancreatic enzymes that digest polysaccharides into disaccharides?
Pancreatic amylase
What enzymes in the small intestine brush border digest disaccharides into monosaccharides?
Lactase, maltase, sucrase
What enzymes in small intestine brush border digest DNA and RNA into nucleotides and ribose?
Nucelotidases and nucleases
What enzymes in the small intestine brush border digest polypeptides into amino acids?
Peptidases
What plays the role of the key in the key and lock behavior of enzymes?
Ligand/substrate
What plays the role of the lock in the key and lock behavior of enzymes?
Protein
The ability of a protein to change shape, resulting in a change in binding affinity at a different binding site
Allostery
What enzymes have an active site as well as an additional allosteric site?
Allosteric enzymes
What enzymes degrade proteins for use of detergents?
Protease
What enzymes degrade cellulose for use of detergents?
Cellulase
What enzymes degrade lipids for use of detergents?
Lipase
What form does the substrate take before it becomes the product?
Transition state
What is the highest energy point of a reaction?
Transition state
What does stabilizing the transition state in an enzyme do?
It can greatly decrease the concentration of the reactive intermediate, accelerating the reaction.
What stabilizes the transition state?
Enzymes
What is the substrate and product of the enzyme pepsin?
Substrate - Protein
Product - Short polypeptides
What is the substrate and product of the enzyme rennin?
Substrate - Soluble casein (milk protein)
Product - Insoluble casein (curdled milk)
What class of enzymes catalyze reactions in which one molecule is oxidized while the other is reduced?
Oxidoreductases
What class of enzymes transfer carbon, nitrogen or phosphate groups?
Transferases
What class of enzymes catalyze a hydrolytic cleaveage reaction (uses water to break a chemical bond)?
Hydrolases
What class of enzymes catalyze the cleavage of C-C, C-S, and C-N bonds? (Often form a new double bond or ring structure)
Lyases
What class of enzymes catalyze the rearrangement of bonds within a single molecule, yielding isometric forms?
Isomerases
What class of enzymes join two molecules in an energy-dependent process?
Ligases
Which of the following requires ATP? Synthase or synthetase?
Synthetase requires ATP
Synthase does NOT require ATP
Hint to remember: Synthetase has T in it and synthase does not
What is the difference between phosphatase and phosphorylase?
Phosphatase removes phosphates
Phosphorylase ADDS phosphates
What enzyme catalyzes the incorporation of molecular O2 to a substrate?
Oxygenase
What enzyme is an O2 acceptor of electrons or hydrogen (the oxygen atoms are NOT incorporated into substrate)?
Oxidase
What enzyme catalyzes ox/redox reactions transferring hydrogen to NAD/NADPH?
Dehydrogenase
What does polymerase do?
It catalyzes polymerization reactions such as synthesis of DNA and RNA
What does Protease do?
Breaks down proteins by hydrolyzing bonds between amino acids
What do kinases do?
Catalyze the addition of phosphate groups to molecules
What do ATPases do?
Hydrolyze ATP
What do synthases do?
They synthesize molecules in anabolic reactions by condensing two smaller molecules together - WITHOUT ATP
What does phosphatase do?
Catalyzes the hydrolytic removal of a phosphate group from a molecule
TCA Cycle, Fatty acid oxidation and oxidation of pyruvate occur where in the cell?
Mitochondria
Where does glycolysis, PP pathway and fatty acid synthesis take place?
Cytosol
Where does DNA and RNA synthesis take place?
Nucleus
What happens in the lysosome?
Degradation of complex macromolecules
Km is equal to the substrate concentration at which the reaction velocity is…
1/2 Vmax
True or False
Km varies with the enzyme concentration
FALSE it does not vary
If an enzyme has high affinity, will the Km be low or high?
High affinity = low Km
If the velocity of a reaction is nearly proportional to the substrate concentration what order reaction would we have?
First order
If the velocity of the reaction is constant or equal to Vmax what order reaction would we have?
Zero order
If the rate of the reaction is independent of the substrate concentration what order reaction do we see?
Zero order
In what order reaction would adding substrate have no effect on the reaction?
Adding substrate to Zero Order would have no effect because all of the enzymes are already bound/saturated
What kind of curve is seen by the Michaelis-Menten Constant?
Hyperbolic curve
What kind of curve would be seen with Allosteric enzymes?
Singmoidal
What kind of curve would hemoglobin binding to O2 show?
Allosteric/Sigmoidal
Does Myoglobin show Michaelis-Menten or Sigmoidal?
Michaelis-Menten (Hyperbolic curve)
What has a higher affinity for oxygen, hemoglobin or myoglobin?
Myoglobin has a higher affinity for oxygen.
Why is it beneficial for hemoglobin to have a low affinity for oxygen?
Because it needs to be readily unbound from hemoglobin so that it can be delivered and released to other areas of the body.
What is the purpose of the Lineweaver-Burk plot?
To more accurately visualize Km and Vmax
What is the optimal temperature for most mammalian enzymes?
35-40C (95-104F)
What are the two forms of reversible inhibition?
Competitive and Non-competitive
What mode of inhibition is seen with covalent bonds?
Irreversible
What mode of inhibition is seen with non-covalent bonds?
Reversible
What kind of inhibitor would bind to the same site the substrate normally would bind?
Competitive Inhibitor
How is competitive inhibition reversed?
Increasing substrate
How does Competitive Inhibition effect Km and affinity?
It increases Km, reducing affinity because more substrate is needed to reach 1/2 Vmax
When looking at a Lineweaver-Burk Plot, if 1/Vmax is unchanged, but 1/Km is higher, what kind of inhibition is indicated?
Competitive Inhibition
What type of inhibitor binds at the allosteric site?
Noncompetitive Inhibitor
How do Non-Competitive Inhibitors cause inhibition?
They bind to the allosteric site, causing conformational changes in the enzyme or active site.
When looking at a Lineweaver Burk Plot, if 1/Vmax is increased, what type of inhibitor is present?
Non-Competitive inhibitor
If the Km is unchanged, what kind of inhibition is seen?
Non-competitive
Why does Km remain unchanged with Non-Competitive Inhibition?
Because the inhibitors do not interfere with the binding of substrate to enzyme since they are binding to an allosteric site.
How do B-Lactam antibiotics, such as penicillin and amoxicillin, help to treat infections?
They act by inhibiting enzymes that synthesize bacterial cell walls.
How do ACE inhibitors work?
They block the enzyme that cleaves angiotensin I into the potent vasoconstrictor antiotensin II, this causes vasodilation which lowers the BP
What irreversibly inhibits prostaglandin and thromboxane synthesis?
Aspirin
What type of inhibitor does Statin act as?
Competitive
Drug that acts to lower plasma cholesterol levels by preventing De Novo Synthesis, acts as an analog to the enzyme’s natural substance
Statin
The catalytic activity of many enzymes depends on the presence of these small, non-protein molecules, also called “helpers”
Cofactors
What are the two groups of cofactors?
Inorganic metals
Small organic molecules (coenzymes)
What are the tightly bound (covalently bonded) cozenzymes?
Prosthetic groups
Heme is an example of what type of coenzyme?
Prosthetic group (tightly bound)
What are the loosely bound coenzymes?
Co-substrates
Coenzymes are associated with the enzyme’s ______ _______ that assist with their catalytic function
Active Site
Why is biotin an important coenzyme?
Attaches to a distinct lysine residue in histones, affecting chromatin structure and mediating gene regulation (epigenetic modification)
What is the inactive precursor in an enzymatic reaction?
Zymogen/Proenzyme
What activates zymogen?
Proteolytic cleavage of peptide bonds
Where does proteolytic cleave generally take place in the body?
Golgi apparatus, when inside secretory vesicles, or at the site of action of the enzyme (i.e. digestive enzymes)
Why does the pancreas secrete zymogen?
To prevent enzymes from digesting proteins in the cells in which they are synthesized.
True or False
ATP is needed for proteolytic cleavage
FALSE
No ATP is needed
Is proteolytic cleavage reversible or irreversible?
Irreversible and occurs only once.
What is an example of accidental zymogen activation?
When the secretion duct in the pancreas is blocked by a gallstone, resulting in acute pancreatitis
True or False
Only proteins located inside cells can be activated by proteolytic cleavage
False - those located OUTside of the cells can be activated.
What are 4 zymogens synthesized in the pancreas?
Chymotrypsinogen
Trypsinogen
Procarboxypeptidase
Proelastase
What zymogen is synthesized in the stomach?
Pepsinogen
Where are pepsinogens converted into pepsins?
Gastric lumen
What are two steps that can regulate enzyme activation in the gastric glands?
Parietal cells secreting HCl
Chief cells secreting Pepsinogen (zymogen)
If the goal was to increase blood coagulation, would vitamin K or Warfarin be used and why?
Vitamin K because it is the coenzyme for synthesis of blood coagulation factors (II, VII, IX, X)
What drug reduces blood clot formation and competes irreversibly with the liver enzyme, epoxy reductase complex?
Warfarin
How is Warfarin related to Vitamin K?
It reduces the activation of vitamin K
What do the proteolytic enzymes, caspases, do?
Mediate apoptosis (programmed cell death)
What is the precursor (zymogen) form of caspase?
Procaspase
How is apoptosis different from necrosis?
Apoptosis does not cause cell inflammation and is highly regulated
What is the function of caspase?
To cause cell death in multicellular organisms, producing special cell fragments (apoptotic bodies) which are cleared by macrophages
What do executioner caspases do?
Kill the cell by degrading proteins indiscriminately
True or False
Once apoptosis has been started it can not be stopped
True
What are the pathways that can initiate apoptosis?
Intrinsic and Extrinsic
What are some other roles of zymogens in biology?
Developmental processes (i.e. metamorphosis of a tadpole into a frog)
Conversion of procollagenase into collagenase in the remodeling process (i.e. formation of hands/fingers)
What are three mechanisms for regulating enzyme activity and which are reversible vs irreversible?
Cofactors/Cosubstrates - Reversible
Zymogens/Proenzymes - Irreversible activation
Enzyme activation cascades - Irreversible once started
In allosteric activation, when does the active site become available to the substrate?
When a regulatory molecule binds to a different site on the enzyme
In allosteric deactivation, when does the active site become unavailable to the substrate?
When a regulatory molecule binds to a different site on the enzyme
Allosteric enzymes change their shape based on what?
The binding of an effector
Effectors bind ________ at a site other than the active site
Non-covalently
What will a positive effector do to enzyme activity?
It will increase enzyme activity
What will a negative effector do to enzyme activity?
It will decrease enzyme activity
True or False
Effectors have no influence on affinity of an enzyme for its substrate
False. Effectors CAN influence affinity
What is an example of a homotropic allosteric protein?
Hemoglobin
What is a homotropic effector?
When the substrate itself serves as an effector
What is an effector?
Modifier/regulator
What is a heterotropic effector?
When an effector is different from the substrate
Feedback inhibition of a metabolic pathway (end-product inhibition) is a classical example of what?
Heterotropic effector
Covalent modifications usually involve the addition or removal of what?
Phosphate groups from specific amino acids of enzymes (Ser, Try, Thr)
How are phosphorylation reactions catalyzed?
By kinases using ATP as a phosphate donor
True or False
Covalent modifications are irreversible
False - they are reversible
Induction or repression of protein synthesis are ______ compared with allosteric or covalent regulations
Slow (hours to days)
What regulator events occur immediately in enzyme regulation?
Substrate inhibition
Product inhibition
Allosteric regulation (control enzyme kinetics)
Covalent modification (turn enzyme on or off)
What regulator event results in changes to velocity (Vo)?
Substrate inhibition
What regulator event results in changes in Vmax and/or Km?
Product inhibition and Covalent modifications
What regulator event results in changes in Vmax and/or K(0.5)?
Allosteric control
What regulator event results in change in amount of enzyme?
Synthesis or degradation of enzyme
All of the following are characteristics of enzymes except
a) High degree of specificity
b) Mediators for almost all chemical reactions
c) Can bind to several substrates
d) Proteins can act as catalysts of reactions
C) Can bind to several substrates
–> No because they are highly specific
True or False
Allosteric enzymes have only an active site for substrate binding
False
They have an allosteric site for binding as well
Which of the following is NOT true of transition states:
a) Stabilized by enzymes
b) It is the form the substrate takes before it becomes a product
c) Highest energy point
d) Form enzyme must take to lower activation energy
D) Form enzyme must take to lower activation energy
—> No it is the form the SUBSTRATE must take to lower activation energy
What do proteases degrade?
a) Cellulose
b) Proteins
c) Lipids
d) All of the above
b) Proteins
True or False
The ligase class of enzymes do not require energy
FALSE- they DO require energy
Which classes of enzymes are responsible for adding phosphate groups? (There are two correct answers)
a) Polymerase
b) Phosphorylase
c)Hydrolase
d) Kinase
B, D
True or False
For first order reactions the velocity of the reaction is constant and equal to Vmax
False
True or False
Hemoglobin follows allosteric enzyme kinetics while myoglobin follows Michaelis-Menten?
True
True or False
Myoglobin has higher affinity for oxygen than hemoglobin because it has a lower Km value?
True
Why do allosteric enzymes display a sigmoidal curve?
Because binding of one substrate increases the enzymes affinity for more substrates
True or False
Vmax is lowered in non-competitive inhibition
True
Which of the following factors does NOT affect reaction velocity?
a) Temperature
b) Concentration of substrate
c) pH
d) Chemical bonds
e) All of them affect velocity
d) Chemical bonds
True or False
Adding more substrate will reverse the effects of noncompetitive inhibition
False
Which of the following are derived from vitamins?
a) Essential ions
b) Cofactor
c) Coenzyme
d) Zymogen
C) Coenzyme
Which of the following does NOT apply to Zymogens?
a) Cleavage requires ATP
b) Pancreas secretes zymogen granules
c) Activated by proteolytic cleavage
d) Inactive precursors for enzymes
a) Cleave requires ATP
–> it does NOT require ATP
True or False
Apoptosis is involved in development of fingers?
True
