Unit 4 - Enzymes Flashcards
4 properties of enzymes
- Catalysts - increase the speed of a chemical reaction
- Not consumed during the reaction
- highly specific
- normally found only inside the cells (diseased/damaged cells let enzymes spill out, we in the lab can measure the enzyme activity in the blood)
Free energy change
- delta G
- the energy released or used in a chemical reaction represents the difference between the energy contents of the products and the reactants.
delta G = free energy of product - free energy of reactants
Exergonic vs. endergonic reactions
Exergonic reaction = energy is released; There is less energy in product. Delta G is negative.
Endergonic reaction = energy is used; There is more energy in product. Delta G is positive.
Collision frequency
- velocity of a chemical reaction depends on the frequency of collision between reaction molecules
- collision frequency is influenced by the concentration of reactant molecules and how fast they move (their kinetic energy)
Transition state
- an unstable, halfway transient phase in which bond and orientation are distorted as reactants are turned into products.
- it possess a certain minimum energy.
On an energy diagram, be familiar with:
- reactants come together
- activation energy
- transition state
- product
- delta G
Two ways to increase the rate of a reaction
- Raise the temperature
2. Lower the energy of activation
Velocity vs. Substrate concentration Plot
First order = area of linearity
Zero order = plateau
Linearity due to:
- increasing concentrations of substrate when at low levels of concentration which increases velocity
Plateau due to:
- high concentration of substrate reaches maximum velocity
Lock and Key Analogy
- enzyme specificity
- enzymes are specific (lock) for a certain substrate (key)
- only the correct substrate that fits into the enzymes active site will react
- creates enzyme-substrate complex (ES)
Active site
- part of the enzyme responsible for its catalytic activity
- a tiny segment, usually a crevice as a result of secondary and tertiary structures, on the enzyme that substrate binds to
Apoenzyme
- the protein component of a conjugated enzyme
- doesn’t exhibit biological activity alone
Cofactor
- the nonprotein component of a conjugated enzyme
- doesn’t exhibit biological activity alone
- many are inorganic ions
Conjugated enzymes
- a subdivision of enzymes
- have both a protein and nonprotein component
Simple enzymes
- a subdivision of enzymes
- consist only of protein
Coenzyme
- a small organic molecule that is a cofactor
- many vitamins function as coenzymes
(ex. TTP = coenzyme from Vit B)
Substrate
- the substance that is acted upon by the enzyme
Activation Energy
- the minimum amount of energy needed before collision between molecules results in a reaction
- after the reaction begins, enough energy is release to keep reaction going
V
= velocity
the rate of the enzyme-catalyzed reaction
Vmax
- the maximum velocity at a finite amount of enzyme and saturated with substrate
Km
- Michaelis constant
- based on the affinity of substrate to enzyme complex.
Michaelis-Menten equation
- the relationship btwn the rate and the substrate concentration expressed mathematically
V = Vmax * ( [S] / ([S] + Km) )
Lineweaver-Burke plot
- rearrange Michaelis-Menten equation to simplify evaluation of Km and Vmax
- uses inverses to obtain a straight line.
1/v = Km/Vmax * 1/[S] + 1/Vmax
Note: y = mx + b
Five reasons for determining Km
- establishes approximate value for intracellular levels of substrate
- a means of comparing enzymes from different organisms or tissues from the same organism
- regulate activity of an enzyme by analyzing ligand-induced change via value of Km
- determine V max to measure total enzyme concentration by setting [S] > Km
- the substrate with the lowest Km has the highest affinity for the enzyme
6 categories of Enzymes
HOT LIL
- Hydrolase
- Oxidoreductase
- Transferase
- Lyase
- Isomerase
- Ligase / Synthase
Hydrolase
- catalyze hydrolysis reactions ( a reaction where a water molecule breaks apart into 2 different products)
Oxidoreductase
- catalyze oxidation -reduction reactions
- includes: catalase, dehydrogenase, hydroxylase, oxidase, oxygenase, peroxidase, and reductases.
Transferase
- catalyze the transfer of a functional group between 2 substrates
- includes: kinase (transfer of phosphate group) and aminotransferase (transfer of amino group)
Lyase
- catalyze the removal of certain groups without hydrolysis (usually by double bond formation)
- ex: decarboxylase
Isomerase
- catalyze the conversion of a compound into another which is isomeric (same molecular formula different structural formula)
Ligase / Synthase
- catalyze the formation of new bonds from carbon to a nitrogen, oxygen, sulfur, or another carbon atom
Temperature on the rate of an enzymatic reaction
- the higher the temperature, the faster the reaction
- BUT if the temperature is raised too high the enzyme will denature
- optimum temperature = 37 degrees Celsius
pH on the rate of an enzymatic reaction
- each enzyme has its own optimum pH (because enzymes have acidic and basic groups)
- Maximum activity = narrow range of pH
- lower/higher pH values can cause denaturation
Competitive inhibition
- inhibitor binds to active site on enzyme
- reversible
- competes against substrate for binding site
Ex: Methanol - oxidized to formaldehyde by ADH enzyme = toxic. Intravenous infusions of ethanol keeps ADH enzyme occupied by oxidizing ethanol instead
Noncompetitive inhibition
- inhibitor binds to an allosteric site on the enzyme which changes the enzymes structure = alters active site
- reversible
Ex: Heavy metal poisoning - Silver, mercury, and lead have a high affinity for sulfhydryl groups, when bound the protein’s structure changes and the enzyme can’t function.
Irreversible inhibiton
- formation of a covalent bond between inhibitor and enzyme at the active site.
- blocks active site = enzyme is deactivated
Ex: Sarin - a nerve gas that forms covalent bonds with serine residue on acetylcholinesterase enzyme which is important in transmission of nerve impulses => paralysis of respiratory system => death
Cytochrome p450
- absorb UV light at 450 nm
- detoxification of xenobiotics via biotransformation
- important in the metabolism of endogenous and exogenous substrates - make lipophilic / non-polar substances more soluble
- found in highest concentrations in liver and GI tract
Phase I Biotransformation
- the addition of oxygen (typically in form of -OH) to make the compound more water soluble
Phase II Biotransformation
- if phase I was not enough for elimination, other water soluble groups are attached
- ex: sulfates, glucuronic acid, and glutathione
Consequences of Phase I and Phase II reactions on exogenous compounds
- Inactivation of compound
- Activation of compound
- Formation of toxic metabolite
Acetaminophen
- an example where the consequence of phase I/II reaction leads to the formation of toxic metabolite
- 2/3 major routes of its metabolism includes phase II reactions
- metabolism by CYP450 = NAPQI which can cause liver damage if too much is made at one time
- antidote = N-acetylcysteine which blocks acetaminophen uptake by liver
Clinical Importance of alkaline phosphatase
- Liver diseases: Obstructive liver disease***
- Bone disease
Clinical Importance of Creatine Kinase
- assesses cardiac damage
- but is not very specific (many different tissue sources)
Clinical Importance of Lactate dehydrogenase
`- AMI
- megaloblastic anemia
- liver disase
- malignant disease
Clinical Importance of Gamma Glutamyltransferase (GGT)
- sensitive indicator of chronic alcoholism
- most sensitive of the liver enzymes for gallbladder inflammation
- elevated in most hepatobilliary disorders
Clinical Importance of Amylase
- elevated in pancreatic dysfunction
- acute pancreatitis = amylase elevates within 12 hours of onset and returns to normal in 48-72 hours
- chronic pancreatitis = amylase remains elevated
Clinical Importance of Lipase
- used in differential diagnosis of pancreatitis, specifically for acute pancreatitis
Enzyme activity
- IU = one international unit of any enzyme it that amount which will catalyze the transformation of one micromole of substrate per minute under specific conditions
Isoenzyme
- multiple molecular forms of an enzyme
Isoform
- multiple molecular forms of isoenzymes that result from enzyme modification of the parent form after its release from tissue
