Enzyme Flashcards
Extreme change in Ph causes:
Bonds in the enzymes to break
amino acid
Typically, the active site is formed by 3 to 12 amino acids.
Induce Fit Hypothesis
Koshland (1959) proposed this hypothesis/model
Naming and Classifying Enzymes
International Union of Biochemistry has developed a scheme for naming and
classifying enzymes. Enzymes are mostly named by adding the suffix -ase to the
name of their substrate. The rest of the name indicates the nature of the reaction.
For example, alcohol dehydrogenase - catalyzes the removal of hydrogen from
alcohol (ethanol).
Oxidoreductases
These are involved in oxidation and reduction (redox) reactions. In aerobic respiration, most of the cells ATP is generated by redox
reactions.
Transferases:
These catalyze the transfer of a chemical group from one compound another. Transfer of an amino group from an amino acid to another
organic acid in the process of transamination.
Hydrolases:
These catalyze hydrolyses (splitting by use of water) reactions. Most digestive enzymes are hydrolases.
Lyases:
These catalyze the breakdown of molecules by reactions that do not involved hydrolysis.
Isomerases:
These catalyze the transformation of one isomer into another, for instance the conversion of glucose 1,6 bisphosphate into fructose 1,6
bisphosphate.
Ligases:
These form bonds between compounds using ATP. For example, DNA ligase is involved in the synthesis of DNA.
Enzyme Inhibitors
An inhibitor is a chemical substance which can react (in place of substrate) with the
enzyme but is not transformed into product(s) and thus blocks the active site
temporarily or permanently (for example poisons, like cyanide, antibiotics,
antimetabolites and some drugs).
OR
Enzyme inhibitors are molecules that interact in some way with the enzyme to
prevent it from working in the normal manner.
Inhibitors may be nonspecific or specific. Specific inhibitors may be irreversible or
reversible. (Competitive and non-competitive)
Non-specific Inhibitors
A non-sspecific inhibition affects all enzymes in the same way. Non-specific methods
of inhibition include any physical or chemical changes which ultimately denature the
protein portion of the enzyme.
Two main types are:
• Temperature
Usually, the reaction rate increases with temperature, but with enzyme reactions,
a point is reached when the reaction rate decreases with increasing temperature.
At high temperatures the protein part of the enzyme begins to denature, thus
inhibiting the reaction.
• Acids and Bases
Enzyme activity is also controlled by pH. As the pH is decreased or increased the
nature of the various acid and amine groups on side chains is altered with
resulting changes in the shape or structure of the enzyme.
Specific Inhibitors
Specific inhibitors may be irreversible or reversible (competitive and
noncompetitive).
Irreversible Inhibitors
• These form strong covalent bonds with an enzyme.
• These inhibitors may act at near or remote from the active site.
• They may not be displaced by the addition of excess substrate.
• The basic structure of the enzyme is modified to the degree that it ceases to
work.
• Since many enzymes contain sulfhydral (– SH), alcohol, or acid groups as part
of their active sites, any chemical which can react with them acts as an
irreversible inhibitor. Heavy metals such as Ag+, Hg2+,Pb2+ have strong
affinities for –SH groups.
Reversible Inhibitors
They form weak linkages with the enzyme. Their effect can be neutralized
completely or partly by increase in the substrate concentration.
They are of two types which are competitive and non-competitive.
Competitive Inhibitors
They have structural similarity with the substrate and are selected by the binding
sites cannot activate the catalytic sites. As a result product(s) are not formed.
(a) Formation of enzyme-substrate complex resulting in the formation of product.
(b) Inhibitor malonic acid does not fit the active site, hence no product is formed.
Non-Competitive Inhibitors
They form enzyme inhibitor complex at a point other than the active site. They are
the enzyme structure in such a way that even if a substrate binds the active site
catalysis does not occur.
cofactor
There are three kinds of a cofactor:
(a) The detachable inorganic ion (metal ion) working as co-factor is known
as an activator e.g. Cu/Zn.
(b) The covalently bonded non-protein part of enzymes is known as
prosthetic group e.g., Lipids.
(c) If the non- protein portion is loosely attached to the protein part it is
known as coenzyme e.g. Vitamins
cofactor
There are three kinds of a cofactor:
(a) The detachable inorganic ion (metal ion) working as co-factor is known
as an activator e.g. Cu/Zn.
(b) The covalently bonded non-protein part of enzymes is known as
prosthetic group e.g., Lipids.
(c) If the non- protein portion is loosely attached to the protein part it is
known as coenzyme e.g. Vitamins
Apoenzyme
An enzyme with its coenzyme or prosthetic group removed
Holoenzyme.
An activated enzyme consisting of polypeptide chain and a cofactor.
Many enzymes are dissolved in the cytoplasm.
Others are bound to the subcellular
organelles.
For example:
(a) Enzymes for photosynthesis are present in the Chloroplasts.
(b) Enzymes for cellular respiration are present in the Mitochondria.
(c) Some enzymes of protein synthesis are present in Ribosomes
why pepsin is form in inactive form
Some enzymes are damaging if they become active in the wrong place. Pepsin
produced in inactive pepsinogen form. If it is produced in the active form .it
may cause cancer.
mechainism of enzymes formation (catalysis)
The binding site helps in identification/Recognition and binding of a proper
substrate: form E-S complex. This reaction activates the catalytic site. The
catalytic site catalyzes the transformation of substrate into product(s). The
enzyme after catalysis detaches from the products unchanged.
substrate concentration
If substrate concentration is unlimited then the rate of reaction depends on the amount of enzyme present at a specific time. If the amount of enzyme is doubled the reaction rate is also doubled.
Reason: The increase in enzyme number causes increase in active sites. More
active sites will convert more substrate into product(s), in a given time.
At low substrate concentration the reaction rate is directly proportional to the
substrate.
If the enzyme concentration is constant the rate of reaction increases with an
increase with substrate concentration.
optimum
temperature
The temperature at which activity of enzyme is maximum is called as optimum
temperature. The increase in temperature causes increase in reaction rate of
enzyme up to a certain limit. For enzymes of human body 37°C is the optimum
temperature.
Heat provides activation energy. Heat also supplies kinetic energy to the
molecules. At high temperature globular structure is lost and the enzyme is
denatured. Globular structure is necessary for enzyme activity,
optimum pH
The enzymes function at narrow pH range is called optimum pH. A slight
change in ‘pH can change the ionization of the amino acids at the active site and
the ionization of the substrates. Now enzyme activity is either retard or blocked
completely. A great change in pH causes the bonds in the enzyme to break. The
result is the denaturation of enzyme.
Enzyme saturation
A condition in which all of the active sites of enzymes are occupied by substrate
molecules is called Enzyme saturation
Enzyme-substrate (ES) complex
A complex consisting of an enzyme and its reactant (substrate) which is held
together by weak bonds is called Enzyme-substrate (ES) complex. The
formation of an ES is the first step in enzyme catalysis.
Feedback inhibition.
A type of metabolic pathway control that regulates the rate at which the cells
synthesize amino acids (or other monomers) and use them in building proteins
(or other polymers) is called Feedback inhibition.
Allosteric enzyme
Allosteric enzyme is an enzyme that undergoes reversible changes in shape and in catalytic activity.
Imp points (1)
- The catalytic activity of an enzyme is due to active site. It is a small portion of
enzyme consisting of few amino acids. - The enzyme and its substrate react with each other through active sites.
- The active site is a three dimensional cavity bearing a specific charge.
- Most of the enzymes have a non-protein part known as a co-factor.
- Cofactor is directly involved in chemical reaction for catalysis. Cofactor acts
as “bridge” between enzyme and its substrate. Sometimes the co-factor
provides energy to drive the reactions. - There are three kinds of a cofactor:
(a) The detachable inorganic ion (metal ion) working as co-factor is known
as an activator e.g. Cu/Zn.
(b) The covalently bonded non-protein part of enzymes is known as
prosthetic group e.g., Lipids.
(c) If the non- protein portion is loosely attached to the protein part it is
known as coenzyme e.g. Vitamins. - An enzyme with its coenzyme or prosthetic group removed is called Apoenzyme.
- An activated enzyme consisting of polypeptide chain and a cofactor is known a, Holo enzyme.
- The conditions under which enzymatic activity is destroyed by disrupting bonds between the atoms in an enzyme are: High temperature and extreme changes in pH.
- Enzymes are also produced in the cells near the site of function.
Imp point (2)
- Many enzymes are dissolved in the cytoplasm. Others are bound to the sub-
cellular organelles.
For example:
(a) Enzymes for photosynthesis are present in the Chloroplasts.
(b) Enzymes for cellular respiration are present in the Mitochondria.
(c) Some enzymes of protein synthesis are present in Ribosomes. - All metabolic activities occurring in the cells are carried out by specific
enzymes. - Enzymes are sensitive to a small change in pH, temperature and substrate
concentration. - Some enzymes are damaging if they become active in the wrong place. Pepsin
produced in inactive pepsinogen form. If it is produced in the active form .it
may cause cancer. - Mechanism of enzyme action is called catalysis.
- The active site of the enzyme is made up of binding site and catalytic site.
- The binding site helps in identification/Recognition and binding of a proper
substrate: form E-S complex. This reaction activates the catalytic site. The
catalytic site catalyzes the transformation of substrate into product(s). The
enzyme after catalysis detaches from the products unchanged. - An enzyme has specific function because its chemistry and configuration
(shape) is specific. Any factor that can change the chemistry and shape of an
enzyme can affect its rate of catalysis. - Some factors that can affect the rate of enzyme action are: enzyme
concentration, substrate concentration, temperature, and pH value. - If substrate concentration is unlimited then the rate of reaction depends on the
amount of enzyme present at a specific time. If the amount of enzyme is
doubled the reaction rate is also doubled
Imp points (3)
- Reason: The increase in enzyme number causes increase in active sites. More
active sites will convert more substrate into product(s), in a given time. - At low substrate concentration the reaction rate is directly proportional to the
substrate. - If the enzyme concentration is constant the rate of reaction increases with an
increase with substrate concentration. - The temperature at which activity of enzyme is maximum is called as optimum
temperature. The increase in temperature causes increase in reaction rate of
enzyme up to a certain limit. For enzymes of human body 37°C is the optimum
temperature. - Heat provides activation energy. Heat also supplies kinetic energy to the
molecules. At high temperature globular structure is lost and the enzyme is
denatured. Globular structure is necessary for enzyme activity, - The enzymes function at narrow pH range is called optimum pH. A slight
change in ‘pH can change the ionization of the amino acids at the active site and
the ionization of the substrates. Now enzyme activity is either retard or blocked
completely. A great change in pH causes the bonds in the enzyme to break. The
result is the denaturation of enzyme. - A condition in which all of the active sites of enzymes are occupied by substrate
molecules is called Enzyme saturation. - A complex consisting of an enzyme and its reactant (substrate) which is held
together by weak bonds is called Enzyme-substrate (ES) complex. The
formation of an ES is the first step in enzyme catalysis. - A type of metabolic pathway control that regulates the rate at which the cells
synthesize amino acids (or other monomers) and use them in building proteins
(or other polymers) is called Feedback inhibition. - An organic molecule that functions as a coenzyme is the Vitamin.
- Allosteric enzyme is an enzyme that undergoes reversible changes in shape and in catalytic activity.
