Enzymes Flashcards
enzymes
- specialized, catalytically active biological macromolecules.
- act as specific, efficient, and active catalysts of chemical reactions in aqueous solutions.
- most enzymes are; globular proteins and ribosomal RNA.
how are enzymes named and classified
- by adding the suffix ‘-ase- to the name of their substrate or a word or phrase describing their catalytic action.
International classification of enzymes
naming of enzyme
-enzymes are assigned a ‘four-part classification and a ‘systematic name’ which identifies the reaction it catalyzes.
example for hexokinase:
formal name: ATP:glucose phosphotransferase
enzyme commission number is 2.7.1.1
2 = the class name (transferase)
7 = the subclass (phosphotransferase)
1 = phosphotransferase with a hydroxyl group as an acceptor
1 = D-glucose as the phosphoryl group acceptor.
key structure function features of enzymes.
- proteins
- globular shape and complex 3-D structure
- have an ‘active site’, its unique shape and chemical environment determine which substrate(s) will bind.
-some enzymes require additional non-protein chemical components called cofactors in order to function properly. cofactors act as non-protein helper molecules. these may be metal ions or organic / metallo - organic molecules.
metal ion cofactors
small inorganic ions - Mg++, k+, Ca++, Zn++, Cu++, Co, Fe
maybe free (e.g. Na+, K+) or held in coordination complexes with the enzyme protein (e.g. Zn++, Ca++)
-these assist with enzyme catalysts.
organic/metallo-organic factors
coenzymes - organic cofactors that are loosely bound and easily released from the enzymes. these usually act as cosubstrates or as transient carriers or specific functional groups.
prosthetic groups - organic factors that are tightly bound to the enzymes.
most are derived from vitamins - organic nutrients that are required in small amounts in the diet. examples include; NAD (niacin; b3), FAD (riboflavin; B2), Coenzyme A
enzyme and cofactors
complete, catalytically active enzyme together with its bound coenzyme and/or metal ion is called haloenzyme.
the protein part of this enzyme is called apoenzyme or apoprotein.
why are enzymes important?
catalyze biochemical reactions in the body.
biochemical and physiological reactions in the body proceed very slowly so enzymes speed these chemical reactions of life. without enzymes, chemical reactions of life would be slow to nonexistent that life may not exist.
what are the ‘chemical reactions of life’ which are catalyzed by enzymes?
- catalyze cellular metabolic reactions/metabolism
- metabolism is the sum of the chemical reaction that takes place in an organism.
-the two types of metabolism or metabolic actions are known as anabolism/anabolic reactions or catabolism/catabolic reactions.
the two types of metabolism/metabolic reaction
anabolism or anabolic reactions: involves the formation of bonds between molecules. these are catalyzed by anabolic enzymes.
catabolism or catabolic reactions: involve the breaking of bonds between molecules. these are catalysed by catabolic enzymes
the two types of metabolism/metabolic reaction
anabolism or anabolic reactions: involves the formation of bonds between molecules. these are catalyzed by anabolic enzymes.
catabolism or catabolic reactions: involve the breaking of bonds between molecules. these are catalysed by catabolic enzymes
anabolism or anabolic reactions
they are biosynthetic, meaning the building of complex molecules from simpler ones.
- involves the formation of bonds between molecules.
- energy-utilizing processes/reactions
- involves dehydration synthesis reactions (reactions that release water) for example, carbohydrate/protein synthesis.
they are endergonic - they consume more energy than they produce.
catabolism/catabolic reactions
degradative- breakdown of complex molecules into simpler ones
- involves the breaking of bonds between molecules.
-energy-releasing processes/ reactions
- involves hydrolytic reactions (use water to break chemical bonds) e.g. digestion of carbs
-exergonic - they produce more energy than they consume.
why do cellular metabolic reactions require energy?
chemical/metabolic reactions require activation energy in order to proceed. this is to increase collisions between reactant molecules and to shift the reactant molecules into a transition state where existing bonds ca be broken and new ones can be formed.
activation energy is usually too high for metabolic reactions to proceed at the surrounding temperature therefore enzymes act as catalysts to help lower activation energy. this lets metabolic reaction proceed at a faster rate.
how do enzymes work?
- enzymes bind their substrates with high specificity which is governed by 3D arrangements of atoms.
LOCK AND KEY MODEL:
- a simplistic model of enzyme action.
-substrate fits into 3D structure of enzyme active site - weak chemical bonds formed between substrate and enzyme.
INDUCED FIT MODEL
- more accurate model of enzyme action
- substrate-binding causes the enzyme to change shape ‘conformational change’ leading to a tighter fit. this brings chemical groups in position to catalyse reactions.
effect of enzyme concentration
higher enzyme concentration, the higher the reaction rate.
then, reaction rates level off with a further increase in enzyme concentration. then, substrate concentration becomes the limiting factor. however, not all enzymes may be able to find substrates.
effect of substrate concentration
substrate concentration increases so does the reaction rate.
reaction rate levels off with a further increase in substrate concentration. all enzyme active sites become engaged (saturated). the maximum rate of reaction has been reached.
effect of PH
add or removing H+ gives small changes in the charges on the enzyme and substrate molecules (altered critical ionization states)
- optimum PH - peak effect on the enzyme-catalyzed reaction. optimum pH is usually 6-8 for most human enzymes, this depends on localized conditions.
- extreme PH levels cause enzymes to denature as it disrupts attraction between charged amino acids. disrupts bonds and enzyme 3D shape. the active site is distorted which means loss of substrate fit.
‘saturation effect’ Michaelis-Menten kinetics
all enzymes show a ‘saturation effect’ with their substrate.
low substrate concentration [S], reaction rate or velocity [V] is proportional to [s]
as [s] is increased, reaction rate falls off, no longer proportional to [S]
on further increase in [S], the reaction rate or velocity becomes constant and independent of [S].
at this stage, the enzyme is saturated with substrate.
a plot of initial reaction velocity [v] against substrate concentration [S] gives a rectangular hyperbola.
A michaelis-Menten equation or kinetics model was developed to explain or account for this ‘saturation effect’.
michaelis-menten kinetics | equation mechanism
michaelis-menten kinetics
