enzymes Flashcards
what are enzymes
Crucial for life.
Accelerate chemical reactions under physiological conditions (body temperature, normally aqueous solution at neutral pH) without being used up.
Catalyst is never used up
Catalysts are reused
Catalyst helps reaction proceed faster
almost all enzymes structures are what type of protein
globular proteins
what are the 2 classes of enzyme globular protein structure
Simple - only protein. Amino acid side chains carrying out catalysis.
Conjugated – also need small non-protein components to function.
(Conjugated means something attached to something else)
enzyme protein takes shape due to what
amino acid side chains
what are the 2 types of conjugate enzymes
Apoenzyme – the protein component
Cofactors - non protein component
(Cofactor are non organic, so no carbons in structure)
Organic means they have carbon
describe cofactor enzymes
May be one or more inorganic ions such as Zn2+, Mg2+, Mn2+, Fe2+, Ni2+ or a complex organic molecule such as NAD called a coenzyme.
eg. Ni2+ is the cofactor in the enzyme urease.
eg. NAD is the coenzyme in the enzyme lactate dehydrogenase
Most vitamins act as coenzymes in the human body.
When a cofactor/coenzyme is bound to the enzyme it is also referred to as a “prosthetic group”.
what are the rules for naming enzymes
‘Common’ given suffix “ase” or “in” e.g. DNA polymerase; Pepsin
Systematic names e.g. Hexokinase has the systematic name: ATP: glucosephosphotransferase
Enzyme Commission numbering system based on
the reactions they catalyse e.g. EC3.4.11.4 are the
“Tripeptide aminopeptidases”
name the main groups of enzymes
Oxidoreductases (EC1)
Transferase (EC2)
Hydrolases (EC3)
Lyases (EC4)
Isomerases (EC5)
Ligases (EC6)
describe the enzyme group Oxidoreductases (EC1)
Act on many chemical groupings to add or remove hydrogen ions eg. oxidases, reductases, dehydrogenases
eg. dehydrogenase catalyses the detoxification of alcohol in the body.
describe the enzyme group Transferase (EC2)
Transfer functional groups between donor and acceptor molecules.
eg. transaminase transfer amino groups, kinases transfer phosphate groups
describe the enzyme group Hydrolases (EC3)
Hydrolysis of substrates with addition of water across the bond.
eg. lipases hydrolyse fats, proteinases and peptidases hydrolyse proteins
(This happens when we digest our food
when we ingest proteins)
describe the enzyme group Lyases (EC4)
Add water, ammonia or CO2 across double bonds, or remove these groups to produce double bonds.
eg. decarboxylases remove carboxyl groups as CO2
describe the enzyme group Isomerases (EC5)
Carry out many different types of isomerization reactions
eg. racemases interchange between D and L amino acids
(2 mirror images – isomers )
describe the enzyme group Ligases (EC6)
Catalyse reactions in which two chemical groups are joined (ligated) using energy from ATP eg. synthetases, carboxylases.
enzymes provide an environment which is what
is energetically favourable for a reaction to take place.
for a reaction to occur what might have to happen to substrate molecules
Substrate molecules may have to be brought close together and be orientated correctly in space in relation to each other.
why is energy needed for a reaction to occur
Energy is needed to overcome forces of repulsion between reacting molecules and to weaken existing chemical bonds.
what is the activation energy
i.e. work is required – activation energy must be put into the system, even for ‘spontaneous’ reactions to occur.
what the affect of an enzyme on activation energy
But less activation energy is required when an enzyme is involved.
how does an enzyme reaction achieve a lower activation energy
A catalyst, eg. an enzyme, provides an alternative route for the reaction with a lower activation energy
how doe enzymes impact equilibrium
As with chemical catalysts, enzymes cannot alter the equilibrium of reversible reaction.
Enzymes however can still speed up the reversible reaction
what does the active site provide
specific, high-affinity binding of substrate(s) and an environment that favours catalysis
in most enzymes how many active sites participate in the interaction with substrates.
1
explain how the crevice-like active site id formed
formed by R-groups from different parts of the protein chain(s) - brought together by folding and bending of the protein (3o level structure).
(Shape the active site takes depends on the R group attached )
(There are also other sites on an enzyme )