Module 5 MCB: Microbial Metabolism - A coupling of energy – requiring and Energy is released when the terminal phosphate is • stressing the substrates and stabilizing the transition
energy releasing reactions, made possible split from ATP. state,
PPT 1: Metabolism through the molecule ATP. • providing a favorable microenvironment,
- Endergonic as it consume more energy Enzymes and Chemical Reactions • participating directly in the catalytic reaction.
Metabolism – refers to the sum of all chemical reactions
within a living organism. than they produce. Catalysts – are substances that can speed up a chemical 4. Substrates are converted into products.
- Examples: Formation of protein from reaction without being permanently altered themselves. 5. Products are released.
Metabolic pathways – a series of stepwise, interconnected amino acids, nuclei acids from nucleotides, 6. Active site is available for two new substrate mole.
chemical reactions where cellular processes such as the and polysaccharides from simple sugar; Enzymes – in living cells, serve as biological catalysts.
building or breaking down of complex molecules occur biosynthetic reactions generate the Enzyme Specificity and Efficiency
materials for cell growth. As catalysts, acts on a specific substance, called the
Exergonic Reactions – spontaneous and releases energy. enzyme’s substrate (or substrates, when there are two Enzymes have specificity for particular substrates.
Both types of pathways are required for maintaining or more reactants), and each catalyzes only one Each of the thousands of known enzymes have this
Endergonic Reactions – require energy to proceed. specificity because the three dimensional shape of the
the cell’s energy balance. reaction.
As catalysts, enzymes typically accelerate chemical specific amino acids of the active site fits the
Metabolic Pathways which are Beneficial rather than
In other words, catabolic and anabolic pathways are substrate somewhat as a lock fits with its key.
Pathogenic: reactions by lowering reactions by lowering their
linked by energy. Catabolic reactions provide the energy
activation energy. The unique configuration of each enzyme enables it
Nitrogen cycle` needed for anabolic reactions.
Example: Sucrose or Table Sugar – is the substrate of to “find” the correct substrate from among the diverse
Beverages and food The role of ATP in coupling anabolic and catabolic the enzyme sucrose, which catalyzes the hydrolysis molecules in a cell.
Sewage treatment of sucrose to glucose and fructose. However, the active site and substrate are flexible,
reactions. When complex molecules are split apart
Drugs (catabolism), some of the energy is transferred to and trapped An enzyme’s ability to accelerate a reaction without and they change shape somewhat as they meet to fit
the need for an increase in temperature is crucial to together more tightly.
in ATP, and the rest is given off as heat. When simple
Two Classes of Chemical Reactions:
molecules are combined to form complex molecules living systems because a significant temperature A certain compound can be a substrate for several
increase would destroy cellular proteins. different enzymes that catalyze different reactions, so
1. Catabolism – those that release energy. Catabolic (anabolism), ATP provides the energy for synthesis, and again
some energy is given off as heat. The crucial function of enzymes, therefore, is to the fate of a compound depends on the enzyme that
pathways generate energy by breaking down larger
speed up biochemical reactions at a temperature that acts on it.
molecules.
Adenosine Triphosphate (ATP) – stores energy is compatible with the normal functioning of the cell. At least four different enzymes can act on glucose 6-
- An enzyme regulated chemical reactions that
derived from catabolic reactions and releases it later to drive phosphate, a molecule important in cell metabolism,
release energy.
anabolic reactions and perform other cellular work. The General Sequence of Events in Enzyme Action is as and each reaction will yield a different product.
- It is the breakdown of complex organic
follows:
compounds into simpler ones. - Consists of an adenine, a ribose, and three Naming Enzymes
- Also called degradative reactions. phosphate groups. 1. The surface of the substrate contacts a specific region
- Releases energy by oxidation of molecules. - When the terminal phosphate group is split from of the surface of the enzyme molecule, called the The names of enzymes usually end in “ase”.
Catabolic pathways – break down macromolecules ATP, adenosine diphosphate (ADP) is formed, active site. All enzymes can be grouped into six classes,
into simple component parts, releasing energy in the and energy is released to drive anabolic 2. A temporary intermediate compound forms, called an according to the type of chemical reaction they
process. reactions. enzyme–substrate complex. The enzyme orients the catalyze.
Catabolic Reactions – generally, are hydrolytic substrate into a position that increases the probability Enzymes within each of the major classes are named
reactions or reactions which use water and in which PPT 2: Enzyme of reaction, which enables the collisions to be more according to the more specific types of reactions they
chemical bonds are broken. effective. assist.
Two key players in Metabolism:
-exergonic or it produce more energy than they 3. The substrate molecule is transformed by the Examples:
consume. 1. Enzymes – catalyze reactions for specific molecules rearrangement of existing atoms, the breakdown of 1. Oxidoreductases – involved with oxidation-
-Example: When cells break down sugars into called substrates. During enzymatic reactions, the substrate molecule, or in combination with reduction reactions.
carbon dioxide and water. substrates are transformed into new substances called another substrate molecule. 2. Dehydrogenases – Enzymes in the
2. Anabolism – those that require energy. Anabolic products. 4. The transformed substrate molecules—the products oxidoreductase class that remove hydrogen (H)
pathway require energy to synthesize larger - which are usually proteins, may need other of the reaction—are released from the enzyme from a substrate.
molecules. non-protein molecules called cofactors to molecule because they no longer fit in the active site 3. Oxidases – those that add electrons to molecular
- An enzyme-regulated energy-requiring reactions. work. Inorganic cofactors include metal ions. of the enzyme. oxygen (O2).
- The building of complex organic molecules from Organic cofactors, or coenzymes, include the 5. The unchanged enzyme is now free to react with
simpler ones. electron carriers FAD, NAD+, NADP+ other substrate molecules. Enzyme Classification Based on Type of Chemical
- Also called biosynthetic, reactions 2. ATP – Is a molecule that cells use to manage energy Reaction Catalyzed
- Often involve dehydration synthesis reactions or needs. The Catalytic Cycle of An enzyme
reactions that release water. 1. Oxidoreductase – oxidation – reduction in which
Without energy, certain reactions will never occur, 1. Substrates enter active site; enzyme changes shape so oxygen and hydrogen are gained or lost. Example:
- Uses energy to synthesize macromolecules that
even if enzymes are present. its active site embraces the substrates (induced fit). Cytochrome oxidase, lactate dehydrogenase.
make up the cell.
2. Substrates held in active site by weak interactions, 2. Transferase – transfer of functional groups, such as
Anabolic pathways – build up macromolecules, If a reaction results in excess energy, some can be such as hydrogen bonds and ionic bonds.
using energy in the process. an amino group, acetyl group, or phosphate group.
captured in the form of ATP’s bonds. A cell can then break 3. Active site (and R groups of its amino acids) can Example: Acetate kinase, alanine deaminase.
Catabolic Reactions – provide building blocks for
those same bonds and use the released energy to fuel other lower EA and speed up a reaction by 3. Hydrolase – hydrolysis (addition of water). Example:
anabolic reactions. reactions. • acting as a template for substrate orientation,
- furnish the energy needed to drive anabolic Lipase, sucrose.
reactions.
, 4. Lyase – removal of groups of atoms without a. Temperature - At any given time, many of the enzyme molecules to shutting down an assembly line by
hydrolysis. Example: Oxalate decarboxylase, The rate of most chemical reactions increases as the are inactive for lack of substrate; thus, the stopping the first worker).
isocitrate lyase. temperature increases. substrate concentration is likely to influence the - Because the enzyme is inhibited, the product
5. Isomerase – rearrangement of atoms within a Molecules move more slowly at lower temperatures rate of reaction. of the first enzymatic reaction in the
molecule. Example: Glucose-phosphate isomerase, than at higher temperatures and so may not have e. presence or absence of inhibitors. pathway is not synthesized.
alanine racemase. enough energy to cause a chemical reaction. An effective way to control the growth of bacteria is
6. Ligase – Joining of two molecules (using energy For enzymatic reactions, however, elevation beyond a to control, or inhibit their enzymes. Ribozymes - Prior to 1982, it was believed that only protein
usually derived from the breakdown of ATP). certain temperature (the optimal temperature) Certain poisons, such as cyanide, arsenic, and molecules had enzymatic activity.
drastically reduces the rate of reaction. mercury, combine with enzymes and prevent the - A unique type of RNA found in microbes.
Example: Acetyl-CoA synthetase, DNA ligase.
The optimal temperature for most disease producing bacteria from functioning. As a result, the cells stop - Like protein enzymes, ribozymes function as
Enzyme Components bacteria in the human body is between 35°C and functioning and die. catalysts, have active sites that bind to
40°C. substrates, and are not used up in a chemical
Although some enzymes consist entirely of proteins, most The rate of reaction declines beyond the optimal Enzyme inhibitors are classified as either: reaction.
consist of both a protein portion, called an apoenzyme, and a temperature because of the enzyme’s denaturation or 1. COMPETITIVE INHIBITORS - Cuts and splice RNA and are involved in
non-protein component, and called a cofactor. the loss of its characteristic three-dimensional An inhibitor which fills the active site of an protein synthesis at ribosomes.
structure (tertiary configuration). enzyme and compete with the normal
Examples of Cofactors: Ions of iron, zinc, magnesium, or b. Denaturation substrate for the active site. PPT 3: Energy Production
calcium Denaturation of a protein involves the breakage of A competitive inhibitor can do this because
hydrogen bonds and other noncovalent bonds that its shape and chemical structure are similar Nutrient molecules have energy associated with the
Coenzyme – If the cofactor is an organic molecule hold the active protein in its three-dimensional shape to those of the normal substrate. However, electrons that form bonds between their atoms. When
renders the denatured protein nonfunctional. unlike the substrate, it does not undergo any it’s spread throughout the molecule, this energy is
Apoezymes – are inactive by themselves; difficult for the cell to use.
Example: Transformation of uncooked egg white (a reaction to form products.
- Must be activated by cofactors. protein called albumin) to a hardened state by heat. Some competitive inhibitors bind Various reactions in catabolic pathways, however,
Denaturation of an enzyme changes the arrangement irreversibly to amino acids in the active site, concentrate the energy into the bonds of ATP.
- Apoenzyme and cofactor form a holoenzyme, or
of the amino acids in the active site, altering its shape preventing any further interactions with the ATP - Serves as a convenient energy carrier.
whole, active enzyme.
and causing the enzyme to lose its catalytic ability. substrate. - Generally referred to as having “high-energy” bonds.
- If the cofactor is removed, the apoenzyme will - Actually, a better term is probably unstable bonds
not function. In some cases, denaturation is partially or fully 2. NONCOMPETITIVE INHIBITORS
reversible. Do not compete with the substrate for the - The amount of energy in these bonds is not
- Cofactors may help catalyze a reaction by exceptionally large, but it can be released quickly and
However, if denaturation continues until the enzyme enzyme’s active site; instead, they interact
forming a bridge between an enzyme and its with another part of the enzyme. easily.
has lost its solubility and coagulates, the enzyme
substrate. Allosteric (“other space”) Inhibition - the inhibitor binds to a Oxidation-Reduction - Oxidation is the removal of electrons
cannot regain its original properties.
site on the enzyme other than the substrate’s binding site, (e−) from an atom or molecule, a reaction that often produces
Components of holoenzyme. Many enzymes require both an Enzymes can also be denatured by concentrated
called the ALLOSTERIC SITE. energy.
apoenzyme (protein portion) and a cofactor (non-protein acids, bases, heavy-metal ions (such as lead, arsenic,
This binding causes the active site to change - If molecule A has undergone oxidation, meaning that
portion) to become active. The cofactor can be a metal ion, or or mercury), alcohol, and ultraviolet radiation. it has lost one or more electrons, whereas if molecule
c. pH its shape, making it nonfunctional. As a
if it is an organic molecule, it is called a coenzyme. The result, the enzyme’s activity is reduced. B has undergone reduction, meaning that it has
apoenzyme and cofactor together make up the holoenzyme, or Typically, enzymes have an optimum pH at which gained one or more electrons.
they are most active. Above or below this pH value, This effect can be either reversible or
whole enzyme. The substrate is the reactant acted upon by the irreversible, depending on whether the Redox Reaction - A pairing reactions and reactions which are
enzyme activity, and therefore the reaction rate, always coupled.
enzyme. active site can return to its original shape.
decline. - Each time one substance is oxidized, another is
When the H+ concentration (pH) in the medium is In some cases, allosteric interactions can
Coenzymes - May assist the enzyme by accepting atoms simultaneously reduced.
changed drastically, the protein’s three-dimensional activate an enzyme rather than inhibit it.
removed from the substrate or by donating atoms required by Dehydrogenation reactions - involve the loss of hydrogen
structure is altered. Others bind reversibly, alternately
the substrate. atoms.
Extreme changes in pH can cause denaturation. occupying and leaving the active site; these
Acids (and bases) alter a protein’s three-dimensional slow the enzyme’s interaction with the
- Some act as electron carriers, removing electrons
substrate. Cells use biological oxidation-reduction reactions in
from the substrate and donating them to other structure because the H+ (and OH−) compete with catabolism to extract energy from nutrient molecules.
hydrogen and ionic bonds in an enzyme, resulting in Increasing the substrate concentration can
molecules in subsequent reactions.
overcome reversible competitive inhibition. Cells take nutrients, some of which serve as energy
- Many are derived from vitamins. the enzyme’s denaturation. sources, and degrade them from highly reduced
d. substrate concentration As active sites become available, more
compounds with many hydrogen atoms to highly
Two important coenzymes in cellular metabolism: 1. Under conditions of high substrate concentration: substrate molecules than competitive
oxidized compounds.
Nicotinamide adenine dinucleotide (NAD) 2. Nicotinamide - Enzyme is said to be in saturation; that is, its inhibitor molecules are available to attach to
Examples:
active site is always occupied by substrate or the active sites of enzymes.
adenine dinucleotide phosphate (NADP) When a cell oxidizes a molecule of glucose
product molecules, and it’s catalyzing a specific (C6H12O6) to CO2 and H2O, the energy in the
Enzymes are subject to various cellular controls. reaction at its maximum rate. Feedback Inhibition – or end-product inhibition.
glucose molecule is removed in a stepwise manner
- A noncompetitive, or allosteric inhibition.
Two primary types are the control of enzyme - This maximum rate can be attained only when and ultimately is trapped by ATP, which can then
the concentration of substrate(s) is extremely - A control mechanism which stops the cell
synthesis and the control of enzyme activity or how serve as an energy source for energy-requiring
high. from making more of a substance than it
much enzyme is present versus how active it is. reactions.
- In this condition, a further increase in substrate needs and thereby wasting chemical
resources. Compounds such as glucose that have many
concentration will not affect the reaction rate hydrogen atoms are highly reduced compounds,
because all active sites are already in use. - Feedback inhibition generally acts on the
first enzyme in a metabolic pathway (similar containing a large amount of potential energy. Thus,
The following are several factors that influence the activity of Under normal cellular conditions: glucose is a valuable nutrient for organisms.
an enzyme: - Enzymes are not saturated with substrate(s).
energy releasing reactions, made possible split from ATP. state,
PPT 1: Metabolism through the molecule ATP. • providing a favorable microenvironment,
- Endergonic as it consume more energy Enzymes and Chemical Reactions • participating directly in the catalytic reaction.
Metabolism – refers to the sum of all chemical reactions
within a living organism. than they produce. Catalysts – are substances that can speed up a chemical 4. Substrates are converted into products.
- Examples: Formation of protein from reaction without being permanently altered themselves. 5. Products are released.
Metabolic pathways – a series of stepwise, interconnected amino acids, nuclei acids from nucleotides, 6. Active site is available for two new substrate mole.
chemical reactions where cellular processes such as the and polysaccharides from simple sugar; Enzymes – in living cells, serve as biological catalysts.
building or breaking down of complex molecules occur biosynthetic reactions generate the Enzyme Specificity and Efficiency
materials for cell growth. As catalysts, acts on a specific substance, called the
Exergonic Reactions – spontaneous and releases energy. enzyme’s substrate (or substrates, when there are two Enzymes have specificity for particular substrates.
Both types of pathways are required for maintaining or more reactants), and each catalyzes only one Each of the thousands of known enzymes have this
Endergonic Reactions – require energy to proceed. specificity because the three dimensional shape of the
the cell’s energy balance. reaction.
As catalysts, enzymes typically accelerate chemical specific amino acids of the active site fits the
Metabolic Pathways which are Beneficial rather than
In other words, catabolic and anabolic pathways are substrate somewhat as a lock fits with its key.
Pathogenic: reactions by lowering reactions by lowering their
linked by energy. Catabolic reactions provide the energy
activation energy. The unique configuration of each enzyme enables it
Nitrogen cycle` needed for anabolic reactions.
Example: Sucrose or Table Sugar – is the substrate of to “find” the correct substrate from among the diverse
Beverages and food The role of ATP in coupling anabolic and catabolic the enzyme sucrose, which catalyzes the hydrolysis molecules in a cell.
Sewage treatment of sucrose to glucose and fructose. However, the active site and substrate are flexible,
reactions. When complex molecules are split apart
Drugs (catabolism), some of the energy is transferred to and trapped An enzyme’s ability to accelerate a reaction without and they change shape somewhat as they meet to fit
the need for an increase in temperature is crucial to together more tightly.
in ATP, and the rest is given off as heat. When simple
Two Classes of Chemical Reactions:
molecules are combined to form complex molecules living systems because a significant temperature A certain compound can be a substrate for several
increase would destroy cellular proteins. different enzymes that catalyze different reactions, so
1. Catabolism – those that release energy. Catabolic (anabolism), ATP provides the energy for synthesis, and again
some energy is given off as heat. The crucial function of enzymes, therefore, is to the fate of a compound depends on the enzyme that
pathways generate energy by breaking down larger
speed up biochemical reactions at a temperature that acts on it.
molecules.
Adenosine Triphosphate (ATP) – stores energy is compatible with the normal functioning of the cell. At least four different enzymes can act on glucose 6-
- An enzyme regulated chemical reactions that
derived from catabolic reactions and releases it later to drive phosphate, a molecule important in cell metabolism,
release energy.
anabolic reactions and perform other cellular work. The General Sequence of Events in Enzyme Action is as and each reaction will yield a different product.
- It is the breakdown of complex organic
follows:
compounds into simpler ones. - Consists of an adenine, a ribose, and three Naming Enzymes
- Also called degradative reactions. phosphate groups. 1. The surface of the substrate contacts a specific region
- Releases energy by oxidation of molecules. - When the terminal phosphate group is split from of the surface of the enzyme molecule, called the The names of enzymes usually end in “ase”.
Catabolic pathways – break down macromolecules ATP, adenosine diphosphate (ADP) is formed, active site. All enzymes can be grouped into six classes,
into simple component parts, releasing energy in the and energy is released to drive anabolic 2. A temporary intermediate compound forms, called an according to the type of chemical reaction they
process. reactions. enzyme–substrate complex. The enzyme orients the catalyze.
Catabolic Reactions – generally, are hydrolytic substrate into a position that increases the probability Enzymes within each of the major classes are named
reactions or reactions which use water and in which PPT 2: Enzyme of reaction, which enables the collisions to be more according to the more specific types of reactions they
chemical bonds are broken. effective. assist.
Two key players in Metabolism:
-exergonic or it produce more energy than they 3. The substrate molecule is transformed by the Examples:
consume. 1. Enzymes – catalyze reactions for specific molecules rearrangement of existing atoms, the breakdown of 1. Oxidoreductases – involved with oxidation-
-Example: When cells break down sugars into called substrates. During enzymatic reactions, the substrate molecule, or in combination with reduction reactions.
carbon dioxide and water. substrates are transformed into new substances called another substrate molecule. 2. Dehydrogenases – Enzymes in the
2. Anabolism – those that require energy. Anabolic products. 4. The transformed substrate molecules—the products oxidoreductase class that remove hydrogen (H)
pathway require energy to synthesize larger - which are usually proteins, may need other of the reaction—are released from the enzyme from a substrate.
molecules. non-protein molecules called cofactors to molecule because they no longer fit in the active site 3. Oxidases – those that add electrons to molecular
- An enzyme-regulated energy-requiring reactions. work. Inorganic cofactors include metal ions. of the enzyme. oxygen (O2).
- The building of complex organic molecules from Organic cofactors, or coenzymes, include the 5. The unchanged enzyme is now free to react with
simpler ones. electron carriers FAD, NAD+, NADP+ other substrate molecules. Enzyme Classification Based on Type of Chemical
- Also called biosynthetic, reactions 2. ATP – Is a molecule that cells use to manage energy Reaction Catalyzed
- Often involve dehydration synthesis reactions or needs. The Catalytic Cycle of An enzyme
reactions that release water. 1. Oxidoreductase – oxidation – reduction in which
Without energy, certain reactions will never occur, 1. Substrates enter active site; enzyme changes shape so oxygen and hydrogen are gained or lost. Example:
- Uses energy to synthesize macromolecules that
even if enzymes are present. its active site embraces the substrates (induced fit). Cytochrome oxidase, lactate dehydrogenase.
make up the cell.
2. Substrates held in active site by weak interactions, 2. Transferase – transfer of functional groups, such as
Anabolic pathways – build up macromolecules, If a reaction results in excess energy, some can be such as hydrogen bonds and ionic bonds.
using energy in the process. an amino group, acetyl group, or phosphate group.
captured in the form of ATP’s bonds. A cell can then break 3. Active site (and R groups of its amino acids) can Example: Acetate kinase, alanine deaminase.
Catabolic Reactions – provide building blocks for
those same bonds and use the released energy to fuel other lower EA and speed up a reaction by 3. Hydrolase – hydrolysis (addition of water). Example:
anabolic reactions. reactions. • acting as a template for substrate orientation,
- furnish the energy needed to drive anabolic Lipase, sucrose.
reactions.
, 4. Lyase – removal of groups of atoms without a. Temperature - At any given time, many of the enzyme molecules to shutting down an assembly line by
hydrolysis. Example: Oxalate decarboxylase, The rate of most chemical reactions increases as the are inactive for lack of substrate; thus, the stopping the first worker).
isocitrate lyase. temperature increases. substrate concentration is likely to influence the - Because the enzyme is inhibited, the product
5. Isomerase – rearrangement of atoms within a Molecules move more slowly at lower temperatures rate of reaction. of the first enzymatic reaction in the
molecule. Example: Glucose-phosphate isomerase, than at higher temperatures and so may not have e. presence or absence of inhibitors. pathway is not synthesized.
alanine racemase. enough energy to cause a chemical reaction. An effective way to control the growth of bacteria is
6. Ligase – Joining of two molecules (using energy For enzymatic reactions, however, elevation beyond a to control, or inhibit their enzymes. Ribozymes - Prior to 1982, it was believed that only protein
usually derived from the breakdown of ATP). certain temperature (the optimal temperature) Certain poisons, such as cyanide, arsenic, and molecules had enzymatic activity.
drastically reduces the rate of reaction. mercury, combine with enzymes and prevent the - A unique type of RNA found in microbes.
Example: Acetyl-CoA synthetase, DNA ligase.
The optimal temperature for most disease producing bacteria from functioning. As a result, the cells stop - Like protein enzymes, ribozymes function as
Enzyme Components bacteria in the human body is between 35°C and functioning and die. catalysts, have active sites that bind to
40°C. substrates, and are not used up in a chemical
Although some enzymes consist entirely of proteins, most The rate of reaction declines beyond the optimal Enzyme inhibitors are classified as either: reaction.
consist of both a protein portion, called an apoenzyme, and a temperature because of the enzyme’s denaturation or 1. COMPETITIVE INHIBITORS - Cuts and splice RNA and are involved in
non-protein component, and called a cofactor. the loss of its characteristic three-dimensional An inhibitor which fills the active site of an protein synthesis at ribosomes.
structure (tertiary configuration). enzyme and compete with the normal
Examples of Cofactors: Ions of iron, zinc, magnesium, or b. Denaturation substrate for the active site. PPT 3: Energy Production
calcium Denaturation of a protein involves the breakage of A competitive inhibitor can do this because
hydrogen bonds and other noncovalent bonds that its shape and chemical structure are similar Nutrient molecules have energy associated with the
Coenzyme – If the cofactor is an organic molecule hold the active protein in its three-dimensional shape to those of the normal substrate. However, electrons that form bonds between their atoms. When
renders the denatured protein nonfunctional. unlike the substrate, it does not undergo any it’s spread throughout the molecule, this energy is
Apoezymes – are inactive by themselves; difficult for the cell to use.
Example: Transformation of uncooked egg white (a reaction to form products.
- Must be activated by cofactors. protein called albumin) to a hardened state by heat. Some competitive inhibitors bind Various reactions in catabolic pathways, however,
Denaturation of an enzyme changes the arrangement irreversibly to amino acids in the active site, concentrate the energy into the bonds of ATP.
- Apoenzyme and cofactor form a holoenzyme, or
of the amino acids in the active site, altering its shape preventing any further interactions with the ATP - Serves as a convenient energy carrier.
whole, active enzyme.
and causing the enzyme to lose its catalytic ability. substrate. - Generally referred to as having “high-energy” bonds.
- If the cofactor is removed, the apoenzyme will - Actually, a better term is probably unstable bonds
not function. In some cases, denaturation is partially or fully 2. NONCOMPETITIVE INHIBITORS
reversible. Do not compete with the substrate for the - The amount of energy in these bonds is not
- Cofactors may help catalyze a reaction by exceptionally large, but it can be released quickly and
However, if denaturation continues until the enzyme enzyme’s active site; instead, they interact
forming a bridge between an enzyme and its with another part of the enzyme. easily.
has lost its solubility and coagulates, the enzyme
substrate. Allosteric (“other space”) Inhibition - the inhibitor binds to a Oxidation-Reduction - Oxidation is the removal of electrons
cannot regain its original properties.
site on the enzyme other than the substrate’s binding site, (e−) from an atom or molecule, a reaction that often produces
Components of holoenzyme. Many enzymes require both an Enzymes can also be denatured by concentrated
called the ALLOSTERIC SITE. energy.
apoenzyme (protein portion) and a cofactor (non-protein acids, bases, heavy-metal ions (such as lead, arsenic,
This binding causes the active site to change - If molecule A has undergone oxidation, meaning that
portion) to become active. The cofactor can be a metal ion, or or mercury), alcohol, and ultraviolet radiation. it has lost one or more electrons, whereas if molecule
c. pH its shape, making it nonfunctional. As a
if it is an organic molecule, it is called a coenzyme. The result, the enzyme’s activity is reduced. B has undergone reduction, meaning that it has
apoenzyme and cofactor together make up the holoenzyme, or Typically, enzymes have an optimum pH at which gained one or more electrons.
they are most active. Above or below this pH value, This effect can be either reversible or
whole enzyme. The substrate is the reactant acted upon by the irreversible, depending on whether the Redox Reaction - A pairing reactions and reactions which are
enzyme activity, and therefore the reaction rate, always coupled.
enzyme. active site can return to its original shape.
decline. - Each time one substance is oxidized, another is
When the H+ concentration (pH) in the medium is In some cases, allosteric interactions can
Coenzymes - May assist the enzyme by accepting atoms simultaneously reduced.
changed drastically, the protein’s three-dimensional activate an enzyme rather than inhibit it.
removed from the substrate or by donating atoms required by Dehydrogenation reactions - involve the loss of hydrogen
structure is altered. Others bind reversibly, alternately
the substrate. atoms.
Extreme changes in pH can cause denaturation. occupying and leaving the active site; these
Acids (and bases) alter a protein’s three-dimensional slow the enzyme’s interaction with the
- Some act as electron carriers, removing electrons
substrate. Cells use biological oxidation-reduction reactions in
from the substrate and donating them to other structure because the H+ (and OH−) compete with catabolism to extract energy from nutrient molecules.
hydrogen and ionic bonds in an enzyme, resulting in Increasing the substrate concentration can
molecules in subsequent reactions.
overcome reversible competitive inhibition. Cells take nutrients, some of which serve as energy
- Many are derived from vitamins. the enzyme’s denaturation. sources, and degrade them from highly reduced
d. substrate concentration As active sites become available, more
compounds with many hydrogen atoms to highly
Two important coenzymes in cellular metabolism: 1. Under conditions of high substrate concentration: substrate molecules than competitive
oxidized compounds.
Nicotinamide adenine dinucleotide (NAD) 2. Nicotinamide - Enzyme is said to be in saturation; that is, its inhibitor molecules are available to attach to
Examples:
active site is always occupied by substrate or the active sites of enzymes.
adenine dinucleotide phosphate (NADP) When a cell oxidizes a molecule of glucose
product molecules, and it’s catalyzing a specific (C6H12O6) to CO2 and H2O, the energy in the
Enzymes are subject to various cellular controls. reaction at its maximum rate. Feedback Inhibition – or end-product inhibition.
glucose molecule is removed in a stepwise manner
- A noncompetitive, or allosteric inhibition.
Two primary types are the control of enzyme - This maximum rate can be attained only when and ultimately is trapped by ATP, which can then
the concentration of substrate(s) is extremely - A control mechanism which stops the cell
synthesis and the control of enzyme activity or how serve as an energy source for energy-requiring
high. from making more of a substance than it
much enzyme is present versus how active it is. reactions.
- In this condition, a further increase in substrate needs and thereby wasting chemical
resources. Compounds such as glucose that have many
concentration will not affect the reaction rate hydrogen atoms are highly reduced compounds,
because all active sites are already in use. - Feedback inhibition generally acts on the
first enzyme in a metabolic pathway (similar containing a large amount of potential energy. Thus,
The following are several factors that influence the activity of Under normal cellular conditions: glucose is a valuable nutrient for organisms.
an enzyme: - Enzymes are not saturated with substrate(s).
