Enzymes (General Properties) Flashcards
Enzyme classifications
Oxidoreductase - Adds or removes H+
Transferase - Transfers a functional group from one molecule to another molecule (ex. P from ATP to substrate)
Lyase - Adds or removes double bonds using H2O, ammonia, or CO2
Isomerase - converts substrate into isomer or epimer
Hydrolase - Adds water across a bond via hydrolyzation (splitting of water)
Ligase - Use ATP to create bonds
Substrate
Substrate vs. ligand
Anything that binds to an enzyme (proteins, drugs, steroids)
They could be used interchangeably, but ligand may be referring to a substrate that is released more endogenously
Enzyme vs. inorganic catalysts
Enzymes are specific and physically bring substrates together in proper orientation & location at active site
Inorganic catalysts (metal catalysts e.g.) are not specific
Enzyme activity affected by:
pH - every enzyme has an optimal pH (stomach enzymes, for example, may be lower than vascular enzymes)
temperature - higher temp = more activity to a point (think asymptote & drop-off). more activity occurs because enzyme loosens up, opening more active sites
[E] - [E] doubles -> rate doubles
[S] - [S] increase will incr enzymatic activity until all active sites are saturated. At this point, enzyme activity reaches a Vmax
cofactors - presence of cofactors incr activity
Cofactor
Are coenzymes a form of enzyme?
Non-protein structure that binds to protein (usu enzyme) that helps it undergo necessary biological changes. Two classifications:
Loosely bound - “coenzymes”
Tightly bound - “prosthetic groups”
NO.
Specificity
Generally:
Specifically:
Enzyme specificity (what binds to the enzyme) is determined generally by the properties of the active site
More specifically:
Size of the active site may determine what aa R groups bind to it
Hydrophobicity/Polarity could determine aa R-group binding
Charge of AS pocket affects amino acid R-group
Activation Energy
Enzymatic role?
Energy that must be overcome for a reaction to occur.
Enzymes lower the Ea of a reaction.
Enzyme effects on:
Ea
Keq
rate
Enzymes lower Ea. In so doing, they increase the rate of the reaction, while not affecting the equilibrium constant.
Molecular interactions for substrate binding (3)
Hydrophobicity
Electrostatic attraction
Size/orientation
Enzyme assay
How does it work?
Two types?
Analysis of the rate of an enzymatic reaction.
Observe the enzymatic reaction by the amount of substrate vs product. [S] will increase and [P] will decrease over time
Continuous enzyme assay: [S] vs [P] over the course of time
Discontinuous assay: [S] & [P] pair have different properties than other pairs (ex. absorption of light)
Clinical applications of enzymes
Destruction of tissues by disease = release of tissue-specific enzymes into serum (in serum, you can detect occurrence of this disease)
Diseases–>produce defective enzymes (ex. PKU: phenylketo in urine–>mental retardation, seizures)
Drugs & toxins affect 1+ enzyme activity (ex. tylenol or alcohol)
Deficiency in tyrosinase: albinism because it cannot polymerize to tyrosine to make melanin
Isoenzymes
Role in diagnostic medicine
2 enzymes that catalyze the same reaction but are made of different proteins (and so may have different aa sequences and different properties-pH optima, isoelectric activity)
Diagnostically - each tissue will produce at least 1 isozyme. finding an isozyme in the wrong location can help you determine what tissue might be damaged
Ex. Isozymes of LDH (lactase dehydrogenase) can be found in myocardium and liver and can be traced to either to determine whether the tissue damaged was myocardial or hepatic tissue (heart attack vs liver cirrhosis)
