Enzymes Flashcards
What is induced fit?
Selectivity of the enzymes for their substrates.
What are coenzymes & Cofactors?
What is the difference between them?
Non protein components essential to enzyme activity. Coenzymes are organic molecules that bind loosly to the active site. Cofactors do not bind the enzyme.
What is Km ?
Concentration of substrate when the enzyme rate is half of Vmax.
Describes the affinity of the enzyme for the substrate.
What do Oxidases do
Oxidases oxidize substrates
Means take away an H+
The substrate is thus oxidized and the enzyme, reduced.
OIL; RIG
What do esterases do ?
Cleave ester bonds by adding water.
Sub-class of hydrolases
What do dehydrogenases do?
Take away hydrogen
E.g pyruvate dehydrogenase
Type of oxidoreductase
Role of oxido-reductases?
Transfer hydrogen or electrons, or use molecular oxygen.
Dehydrogenases, peroxidases, oxygenases, electron carriers NADH & FADH2
Hydroxylases are the most common mono-oxygenases.
What do hydrolases do?
Cleave bonds by addition of water.
Esterases, peptidases, proteases, glycosidases, lipases, phospholipases
What do transferases do ?
Transfer a group (other than hydrogen or oxygen) from one molecule to another.
Kinases are transferases.
What do isomerases do?
Change positions of isomers i.e. switch groups around.
What do lyases do?
Cleave a group off a molecule, leaving a double bond i.e. molecular bonds are made without involving hydrolysis. Formation of double bonds by removal of water.
Dehydratases, enolases and aldolases are lyases.
What do ligases do?
Form covalent bonds between molecules, hydrolyzing a high-energy bond in the process.
What is the difference between apoenzyme & holoenzyme?
Apoenzyme : non-functional enzyme when not bound to its cofactor.
Holoenzyme is the functional version when the cofactor is present.
Cofactors that are tightly bound to the enzyme are called ?
Prosthetic groups.
Cofactors that are complexe organic molecules are called ?
Coenzymes.
What are isoenzymes?
Different versions of the same enzyme that catalyse the same rx, but differ in their structure or composition.
What are zymogens and give 2 examples.
An inactive precuror of an enzyme. It is activated when cleaved, to release the active site.
Trypsin, chemotrypsin.
What is covalent catalysis and give an exemple.
A covalent intermediate forms between the enzyme and the substrate.
For instance serine proteases and the catalytic triad.
Catalytic triad : serine, histidine and glutamic acid
Active site of the protease contains an AA serine whose side chain hydroxyl gr form covalent bond with carbonyl carbon of peptide bond, causing its hydrolysis. For serine to catalyze this reaction, it requires the help of his and glutamic acid.
Trypsin, chemotrypsin and elases are serine proteases that use triads
Lead affects which enzyme involved in the synthesis of heme ?
ALA-dehydratase.
When the reaction rate is independent of substrate concentration, this is known as ?
zero order rate.
What is first orde rate?
At low substrate concentrations, every substrate molecule is bound to enzyme molecule and thus the reaction rate is proportional to the substrate concentration.
What are coupled (redox) reactions ?
The product of one reaction becomes the substrate for another.
E.g. glycolysis.
The Y intercept on a Lineweaver & Burk curve represents ?
1/ Vmax
The X intercept on a Lineweaver & Burk curve represents?
-1/Km
