Module 1.3 (Enzymes) Flashcards
_____ are key to life.
no ____ no life
enzymes
globular protein which functions as a biological catalyst, speeding up reaction rate by lowering activation energy without being affected by the reaction it catalyze
enzymes
- are protein in nature (globular protein)
- are composed of long chains of amino acids that have folded into a very specific three-dimensional shape which contains an active site.
enzymes
are RNA molecule with enzymatic activity
Ribozymes
Catalytic behaviour of any enzyme depends upon its _________________ (4)
primary, secondary, tertiary or quaternary structure
Enzymes of digestive tract and those found in blood are present in inactive form called ______or _______
zymogen or proenzymes.
is a region on the surface of an enzyme to which substrates will bind and catalyzes a chemical reaction.
active site
Enzymes are _________ for the type of the reaction they catalyze and for their substrate.
highly specific
Type of specificity recognized: (4)
- Absolute specificity
- group specificity
- reaction specificity
- stereospecificity
Enzymes with highest specificity and accuracy are involved in __________. These enzymes have proof reading function e.g. _________
copying and expression of genome;
DNA polymerase
Some enzyme require non protein molecule for their activity. So enzymes are conjugated proteins known as ________
holoenzyme
holoenzyme = _______ + _______
apoenzyme + cofactor/coenzyme
Enzyme without non protein part is inactive and called ______
apoenzyme
true or false
cofactors are inorganic compouns.
false
cofactors can be either inorganic or organic compounds.
The polymerization of deoxyribonucleotides into a DNA strand is catalyzed by_________, a holoenzyme. The catalytic activity of this enzyme is catalyzed by the ____________
DNA polymerase
magnesium ion
The enzymatic reactions takes place by binding of the substrate with the active site of the enzyme molecule by several ____ bonds
weak bonds
is the first step in the enzyme catalyzed reaction
Formation of ES complex (enzyme-substrate complex)
then ES complex is subsequently converted to _____ and _______
product
free enzyme
(E + S ‹——–› ES ——–› E + P)
Two models of enzymes?
lock and key / template model
induced-fit model
a model where the enzymes changes shape so its active site embraces the substrates
induced-fit model
According to the IUBMB system of enzyme nomenclature enzymes are grouped into 6 major classe
EC 1 OXIDOREDUCTASES
EC 2 TRANSFERASES
EC 3 HYDROLASES
EC 4 LYASES
EC 5 ISOMERASES
EC 6 LIGASES
Factors affecting reaction velocity of enzymes (8)
Temperature - dp, opt
Hydrogen ion concentration (pH) - dp, opt
Substrate concentration - dp
Enzyme concentration- dp
Products of the reaction- inhibit
Presence of activator/inhibitor
Allosteric effects
Time
Rate of the reaction or velocity is _____ proportional to the Enzyme Concentration when sufficient substrate is present.
directly
Accumulation of Product in a reaction causes _______ of enzyme activity.
inhibition
Study of reaction rate and how they changes in response to change in experimental parameter is known as
kinetics
Amount of _______ present is one of the key factor affecting the rate of reaction catalyzed by an enzyme in vitro
substrate
The model involves one substrate molecule:
E + S ‹——-k1, k-1 ——› ES ——k2—— › E + P
K1 , k-1 and k2 are the rate constants
Michaelis- Menten Kinetics
The mathematical equation that defines the quantitative relationship between the rate of an enzyme reaction and the substrate concentration is the
Michaelis-Menten equation:
V₀ = Vmax [S] / Km + [S]
V₀ is the observed velocity at the given [S]
Km is the Michaelis-Menten constant
Km = (K-1 + K2) / K1
Vmax is the maximum velocity at saturating [S]
conc.
A linear representation is more accurate and convenient for determining Vmax and Km.
is obtained by taking reciprocal of both the side of Michelis-Menton equation.
Lineweaver-Burk (double reciprocal) plot
- Any substance that can diminish the velocity of an enzyme catalyzed
- These include drugs, antibiotics, poisons, and anti-metabolites.
- Useful in understanding the sequence of enzyme catalyzed reactions, metabolic regulation, studying the mechanism of cell toxicity produced by toxicants.
- Forms the basis of drug designing.
Enzyme Inhibiton
Types of Enzyme Inhibiton (2)
- Reversible inhibitors
- Irreversible inhibitors
Reversible inhibitors can be classified into : (3)
- Competitive
- Non-competitive
- Un-competitive
Binds only to the enzyme-substrate
complex.
Does not have the capacity to bind to the free enzyme.
Not overcome by increasing substrate concentration.
Both the Km and Vmax are reduced.
Un-competitive Inhibiton
