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BIOCHEMISTRY: ENZYMES AND VITAMINS
GENERAL CHARACTERISTICS OF ENZYMES
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ENZYMES are usually protein that act as biological catalysts
Each cell in the human body contains thousands of different enzymes
Enzymes cause cellular reactions to occur millions of times faster that corresponding
uncatalyzed reactions
An enzyme speeds a reaction by lowering the activation energy, changing the reaction
pathway that provides a lower energy rout for conversion of substrate to product
As catalysts enzymes are not consumed in the reactions
A few enzymes are now known to be ribonucleic acids (RNA)
ENZYME STRUCTURE
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Most enzymes are globular proteins
Two general structural classes:
SIMPLE ENZYME
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CONJUGATED ENZYME
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Composed only of protein (amino acid chains)
o
It is the 3˚ structure of the simple enzymes that
makes it biologically active
Has a non-protein part in addition to a protein part
1.
Apoenzyme – the protein part of a conjugated
enzyme
2.
Cofactor – the nonprotein part of a conjugated
enzyme (bound to the enzyme for it is to maintain
the correct configuration at the active site
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The substrate is the substance upon which the enzyme “acts”
E.g. in the fermentation process sugar is converted to alcohol, therefore in this reaction
sugar is the substrate
THREE IMPORTANT ASPECTS OF THE NAMING PROCESS
1. Suffix –ase identifies it as an enzyme
→ E.g. urease, sucrose, and lipase are all enzyme designations
→ Exception: the suffix –in is still found in the names of some digestive enzymes,
e.g., trypsin, chymotrypsin, and pepsin
2. Type of reaction catalyzed by an enzyme is often used as a prefix
→ E.g. oxidase – catalyzes an oxidation reaction
→ E.g. hydrolase – catalyzes a hydrolysis reaction
3. Identity of substrate is often used in addition to the type of reaction
→ E.g. glucose oxidase, pyruvate carboxylase, and succinate dehydrogenase
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SIX MAJOR CLASSES
o Enzymes are grouped into six major classes based on the types of reaction they
catalyze
CLASSES
OXIDOREDUCTASES
TRANSFERASES
3.
4.
Holoenzyme – the biochemically active conjugated
enzyme produced from an apoenzyme and a
cofactor
Coenzyme – a small organic molecule that serves as
a cofactor in a conjugated enzyme
NOMENCLATURE AND CLASSIFICATION OF ENZYMES
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Most commonly named with reference to their function
o Type of reaction catalyzed
o Identity of the substrate
A substrate is the reactant in an enzyme-catalyzed reaction:
HYDROLASES
SELECTED SUBCLASSES & TYPE
OF REATION CATALYZED
 Oxidases
→ Oxidation of a substrate
 Reductases
→ Reduction of a substrate
 Dehydrogenases
→ Introduction of double
bond (oxidation) by
formal removal of two H
atoms from substrate,
the H being accepted by
a coenzyme
 Transminases
→ Transfer of an amino acid
group between substrate
 Kinases
→ Transfer of a phosphate
group between
substrates
REACTION
CATALYZED
an enzyme that
catalyzes an
oxidation–
reduction reaction
 Lipases
→ Hydrolysis of ester
linkages in lipids
 Proteases
→ Hydrolysis of amide
linkages in proteins
 Nucleases
→ Hydrolysis of sugarphosphate ester bonds in
nucleic acids
 Carbohydrases
→ Hydrolysis of glycosidic
bonds in carbohydrates
an enzyme that
catalyzes a
hydrolysis reaction
in which the
addition of a water
molecule to a
bond causes the
bond to break
an enzyme that
catalyzes the
transfer of a
functional group
from one molecule
to another
LYASES
 Phosphatases
→ Hydrolysis of phosphateester bonds
 Dehydratases
→ Removal of H2O from a
substrate
 Hydratases
→ Addition of H2O to a
substrate
 Decarboxylases
→ Removal of CO2 from a
substrate
 Deaminases
→ Removal of NH3 from a
substrate
ISOMERASE
 Racemases
→ Conversion of D isomer
to L isomer or vice versa
 Mutases
→ Transfer of a functional
group from one position
to another in the same
molecule
LIGASES
 Synthetases
→ Formation of new bond
between two substrates,
with participation of ATP
 Carboxylases
→ Formation of new bond
between a substrate and
CO2, with a participation
of ATP
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an enzyme that
catalyzes the
addition of a
group to a double
bond or the
removal of a
group to form a
double bond in a
manner that does
not involve
hydrolysis or
oxidation
ENZYME-SUBSTRATE COMPLEX: the intermediate reaction species that is formed when a
substrate binds to the active site of an enzyme
o Intermediate reaction species formed when substrate binds with the active site
o Needed for the activity of enzyme
o Orientation and proximity is favorable and reaction is fast
TWO MODELS FOR SUBSTRATE BINDING TO ENZYME
o Lock-and-Key Model:
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Active site in the enzyme has a fixed, rigid geometrical conformation
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Only substrate of specific shape can bind with the active site; a substrate
whose shape and chemical nature are complementary to those of the active
site can interact with the enzyme
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Fails to take into account protein’s conformational changes to accommodate
a substrate molecule
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There are weak binding forces (R group interactions) between parts
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an enzyme that
catalyzes the
isomerization
(rearrangement of
atoms) of a
substrate in a
reaction,
converting it into a
molecule isomeric
with itself
an enzyme that
catalyzes the
bonding together
of two molecules
into one with the
participation of
ATP
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Induced Fit Model:
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Substrate contact with enzyme will change the shape of the active site
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Allows small change in space to accommodate substrate
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The enzyme active site, although not exactly complementary in shape to that
of the substrate, is flexible enough that it can adapt to the shape of the
substrate
MODELS OF ENZYME ACTION
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Explanations of how enzymes function as catalysts
in biochemical systems are based on the concepts
of an enzyme active site and enzyme-substrate
complex
ACTIVE SITE: relatively small part of the enzyme’s
structure that is actually involved in catalysis
o Where substrate binds to enzyme
o Formed due to folding and bending of the
enzyme
o Usually a “crevice like” location in the
enzyme
o Some enzymes have more than one active site
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FORCES THAT DETERMINE SUBSTRATE BINDING
o H-bonding
o Hydrophobic interaction
o Electrostatic interactions
TEMPERATURE
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Higher temperature results in higher kinetic
energy which causes an increase in number
reactant collisions, therefore there is higher
activity
Optimum temperature: temperature at which
the rate of enzyme-catalyzed reaction is
maximum
Optimum temperature for human enzymes is
37˚C
Increased temperature (high fever) leads to
decreased enzyme activity
In high-temperature, high-pressure vessels
called autoclaves, super-heated steam is used
to produce a temperature sufficient to
denature bacterial enzymes
ENZYME SPECIFICITY
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ENZYME SPECIFICITY: the extent to which an enzyme’s activity is restricted to a specific
substrate, a specific group of substrates, a specific type of chemical bond, or a specific type
of chemical reaction
TYPES OF ENZYME SPECIFICITY
o Absolute Specificity
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An enzyme will catalyze a particular reaction for only one substrate
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This is most restrictive of all specificities (not common)
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E.g. Catalase is an enzyme with absolute specificity for hydrogen peroxide
(H2O2); Urease absolute specificity for urea
o Stereochemical Specificity
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An enzyme can distinguish between stereoisomers
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Chirality is inherent in an active site (amino acids are chiral compounds)
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L-amino acid oxidase – catalyzes reactions of L-amino acids but not D-amino
acids
o Group Specificity
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Involves structurally similar compounds that have the same functional groups
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E.g. Carboxypeptidase: cleaves amino acids one at a time from the carboxyl
end of the peptide chain
o Linkage Specificity
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Involves a particular type of bond irrespective of the structural features in the
vicinity of the bond
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Considered most general of enzyme specificities
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E.g. Phosphatases: hydrolyze phosphate – ester bonds in all types of
phosphate esters
FACTORS THAT AFFECT ENZYME ACTIVITY
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ENZYME ACTIVITY - a measure of the rate at which an enzyme converts substrate to products
in a biochemical reaction
FOUR FACTORS AFFECT ENZYME ACTIVITY
pH
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Substrate concentration
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Drastic changes in pH can result in
denaturation of proteins
Optimum pH: pH at which enzyme has
maximum activity
Most enzymes have optimal activity in the pH
range of 7.0-7.5
Exception: digestive enzymes
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Pepsin: optimum pH =2.0
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Trypsin: optimum pH = 8.0
At constant enzyme concentration, the
enzyme activity increases with increased
substrate concentration
Enzyme saturation: the concentration at which
it reaches its maximum rate and all of the
active sites are full
Turnover number: number of substrate
molecules converted to product per second
per enzyme molecule under conditions of
optimum temperature and pH
Enzyme concentration
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Enzymes are not consumed in the reactions
they catalyze
At a constant substrate concentration, enzyme
activity increases with increase in enzyme
concentration
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The greater the enzyme concentration, the
greater the reaction rate
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Noncompetitive inhibitors: do not compete with the substrate for the same
active site
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Binds to the enzyme at a location other than active site
REVERSIBLE COMPETITIVE
INHIBITION
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REVERSIBLE
NONCOMPETITIVE INHIBITION
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EXTREMOZYMES
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EXTREMOZYME –
o a microorganism that thrives in extreme environments, environments in which
humans and most other forms of life could not survive
o high interest for industrial chemists
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enzymes are heavily used in industrial processes
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industrial processes require extremes of temp., pressure, and pH
EXTREMOPHILE - a microorganism that thrives in extreme environments, environments in
which humans and most other forms of life could not survive.
o TYPES OF EXTREMOPHILES
ACIDOPHILES
ALKALIPHILES
HALOPHILES
HYPOTHERMOPHILES
PIEZOPHILES
CRYOPHILES
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IRREVERSIBLE INHIBITION
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A competitive enzyme inhibitor decreases enzyme activity by binding
to the same active site as the substrate
Binds reversibly to an enzyme active site and the inhibitor remains
unchanged (no reaction occurs)
The enzyme – inhibitor complex formation via weak interactions
(hydrogen bonds, etc.)
Competitive inhibition can be reduced by simply increasing the
concentration of the substrate
A noncompetitive enzyme inhibitor decreases enzyme activity by
binding to a site on an enzyme other than the active site
Causes change in the structure of the enzyme and prevents enzyme
activity
Increasing the concentration of substrate does not completely
overcome inhibition
Ex. Heavy metal ions: Pb2+ , Ag+ , and Hg2+
An irreversible enzyme inhibitor inactivates enzymes by forming a
strong covalent bon with the enzyme’s active site
o
The structure is not similar to enzyme’s normal substrate
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The inhibitor bonds strongly and increasing substrate
concentration does not reverse the inhibition process
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Enzyme is permanently inactivated
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E.g. chemical warfare agents (nerve gases) and
organophosphate insecticides
Optimal growth at pH levels of 3.0 or below
Optimal growth at pH levels of 9.0 or above
Salinity that exceeds 0..2 M NaCl needed for growth
A temperature between 80˚C and 122˚C needed to thrive
A high hydrostatic pressure needed for growth
A temperature of 15˚C or lower needed for growth
Extremozyme Application
o Biotechnology industry – production of enzymes for industrial applications
o Petroleum industry – oil well drilling operations
o Environmental scavenging and removal of heavy metals
o Environmental clean-up using genetically engineered extremophiles
o Laundry detergents used in cold wash cycles
ENZYME INHIBITION
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ENZYME INHIBITOR: a substance that slows down or stops the normal catalytic function of
an enzyme by binding to it
Two types of enzyme inhibitors:
o Competitive inhibitors: compete with the substrate for the same active site
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Will have similar charge and shape
REGULATION OF ENZYME ACTIVITY
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Enzyme activity is often regulated by the cell to conserve energy. If the cell rus out of
chemical energy, it will die
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Cellular processes continually produces large amounts of an enzyme and plentiful amounts
of products if the processes are not regulated
General mechanisms involved in regulation:
FEEDBACK CONTROL
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PROTEOLYTIC ENZYMES AND ZYMOGENS
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COVALENT MODIFICATION OF ENZYMES
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A process in which activation or inhibition of
the first reaction in a reaction sequence is
controlled by a product of the reaction
sequence
Regulators of a particular allosteric enzyme
may be:
→ Products of entirely different
pathways of reaction within the cell
→ Compounds produced outside the cell
(hormones)
Mechanism of regulation by production of
enzymes in an inactive forms (zymogens)
ZYMOGEN (pro-enzyme) – are “turned on”
at the appropriate time and place
→ Example: (proteolytic enzymes)
hydrolyze bonds in proteins
A process in which enzyme activity is
altered by covalently modifying the
structure of the enzyme
→ Involves adding or removing group
from an enzyme
Most common covalent modification –
addition and removal of phosphate group:
→ Phosphate group is often derived from
an ATP molecule
→ Addition of the phosphate
(phosphorylation) catalyzed by a
kinase enzyme
→ Removal of the phosphate group
(dephosphorylation) catalyzed by a
phosphatase enzyme
→ Phosphate group is added to (or
removed from) the R group of serine,
tyrosine, or threonine amino acid
residue in the enzyme regulated
Allosteric Enzymes
o Enzymes responsible for regulating cellular processes
o Characteristics:
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All allosteric enzymes have quaternary structure
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Have two kinds of binding sites: for substrate (active site) and regulator
(allosteric site)
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Active site – where the substrate binds lock-and-key
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Allosteric site “another site” – where the regulator binds;
distorts active site
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Some regulators of allosteric enzyme function are inhibitors
(negative regulators/allosterism), and some increase enzyme
activity (positive regulators/allosterism).
PRESCRIPTION DRUGS THAT INHIBIT ENZYME ACTIVITY
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Many common prescription drugs exert their mode of action by inhibiting enzymes
Antibiotic: a substance that kills bacteria or inhibits its growth
ANGIOTENSIN CONVERTING ENZYME (ACE
Inhibitor)
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SULFA DRUGS
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Angiotensin II – is an octapeptide hormone that
increases blood pressure via constriction of blood
vessels
ACE converts Angiotensin I to Angiotensin II in the
blood
ACE inhibitors block ACE reaction and thus reduce
blood pressure
→ Lisinopril is an example of a ACE inhibitor
Derivatives of sulfanilamide
Sulfa drugs exhibit antimetabolite activities
→ Sulfanilamide is structurally similar to
PABA (𝞺-aminobenzoic acid) which
→
→
→
bacteria need to produce coenzyme folic
acid
Sulfanilamide is a competitive inhibitor of
enzymes responsible for converting PABA
to folic acid in bacteria
Folic acid deficiency retards bacterial
growth and that eventually kills them
Sulfa drugs don’t affect humans because
we get folic acid pre-formed from food
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PENICILLIN
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Bacteria have one structural feature not found in
animal cells – a cell wall
The bacterial cell wall precursor is a polymer of a
repeating disaccharide unit with attached
polypeptide side chains that end with a D-alanylD-alanine unit
Transpeptidase catalyzed the formation of
peptide cross links between polysaccharide
strands in bacterial cell walls
Penicillin acts by complexing with the enzyme
transpeptidase that is responsible for cell wall
synthesis
Selective inhibits transpeptidase by covalent
modification of serine residue
The structural similarity between the penicillins
and D-alanyl-D-alanine allows the antibiotic to act
as inhibitory substrates for the transpeptidase
enzyme
Since animal cells do not have cell walls, there are
no such enzymes to be affected and penicillin has
no effect on animal cells
MEDICAL USES OF ENZYMES
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Enzymes can be used to diagnose certain diseases
o The appearance of these enzymes in the blood often indicates that there is tissue
damage in an organ and that cellular contents are spilling out (leaking) into the
bloodstream
o Assays of abnormal enzyme activity in blood serum can be used to diagnose
many disease states, some of which are listed in Table 21.3
o
Enzymes can also be used in the treatment of diseases
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A recent advance in treating heart attacks is the use of tissue
plasminogen activator (TPA), which activates the enzyme plasminogen
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When so activated, this enzyme dissolves blood clots in the heart and
often provides immediate relief
Medical use for enzymes is in clinical laboratory chemical analysis
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For example, no simple direct test for the measurement of urea in the
blood is available.
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However, if the urea in the blood is converted to ammonia via
the enzyme urease, the ammonia produced, which is easily
measured, becomes an indicator of urea.
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This blood urea nitrogen (BUN) test is a common clinical
laboratory procedure. High urea levels in the blood indicate
kidney malfunction
WATER-SOLUBLE VITAMINS: VITAMIN C
GENERAL CHARACTERISTICS OF VITAMINS
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VITAMIN : an organic compound, essential in small amounts for the proper functioning of
the human body, that must be obtained from dietary sources because the body cannot
synthesize it.
Must be obtained from dietary sources because human body can’t synthesize them in
enough amounts
Needed in micro and milligram quantities
o 1 gram vitamin B is sufficient for 500,00 people
Enough vitamin can be obtained from balanced diet
Supplemental vitamins may be needed after illness
Many enzymes contain vitamins as part of their structures – conjugated enzymes
Two classes of vitamins
o Water-soluble and fat-soluble
Synthetic and natural vitamins have the same function
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Vitamin C, which has the simplest structure of the 13 vitamins, exists in two active forms in
the human body: an oxidized form and a reduced form
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Humans, monkeys, apes, and guinea pigs need dietary vitamins
Co-substrate in the formation of structural protein collagen
o Collagen also contains hydroxylysine and hydroxylproline (important in binding
collagen fibers together)
o Hydroxylation of lysine and proline in collagen formation are catalyzed by
enzymes that require ascorbic acid (Vit. C) and iron
o In Vitamin C deficiency, hydroxylation is impaired, and the triple helix of the
collagen is not assembled properly
o
Persons deprived from Vit. C develops scurvy, a disease whose symptoms include
skin lesions, fragile blood vessels, loose teeth, and bleeding gums
Functions as a general antioxidant for water-soluble substances in the blood and other
body fluids.
o Because of its antioxidant properties, vitamin C is often added to foods as a
preservative
o Beneficial for several other vitamins: active form of vitamin E is regenerated by
vitamin C, and it also helps keep the active form of folate (a B vitamin) in its
reduced state
Involved in metabolism of certain amino acids
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Why is Vitamin C called ascorbic acid when there is no carboxyl group (acid group) present
in its structure?
o
Vitamin C is a cyclic ester in which the carbon 1 carboxyl group has reacted with a
carbon 4 hydroxyl group, forming the ring structure
Riboflavin (Vitamin B2)
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WATER SOLUBLE VITAMINS: THE B VITAMINS
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MAJOR FUNCTION: B Vitamins are components of many coenzymes
Serves as temporary carriers of atoms or functional groups in redox and group
transfer reactions associated with metabolism
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Niacin (Vitamin B3)
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Pantothenic acid (Vitamin B5)
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Thiamin (Vitamin B1)
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“Free” thiamin’s structure consists of a central carbon
atom to which is attached a six-membered heterocyclic
amine and a five-membered thiazole (sulfur-nitrogen)
ring system
The name thiamin comes from “thio,” which means
“sulfur” and “amine” which refers to the numerous
amine groups present
The coenzyme form of thiamin is called thiamin
pyrophosphate (TPP), a molecule in which a
diphosphate group has been attached to the side chain
The coenzyme TPP functions in the decarboxylation of
a-keto acids
Vitamin B6 (Pyridoxine, Pyridoxal, and
Pyridoxamine)
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Biotin (Vitamin B7)
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Riboflavin’s structure involves three fused sixmembered rings (two of which contain nitrogen) with
the monosaccharide ribose attached to the middle ring
Riboflavin was once called the “yellow vitamin”
because of its color
Its name comes from its color (flavin means “yellow”
in Latin) and its ribose component.
Two important riboflavin-based coenzymes exist:
→ flavin adenine dinucleotide (FAD)
→ flavin mononucleotide (FMN).
Both coenzymes are involved with oxidation-reduction
reactions in which hydrogen atoms are transferred
from one molecule to another.
Niacin occurs in food in two different, but similar,
forms: nicotinic acid and nicotinamide
It was prepared by oxidizing nicotine using nitric acid;
hence the name nicotinic acid
When the biological significance of nicotinic acid was
realized, the name niacin was coined to disassociate
this vitamin from the name nicotine and to avoid the
perception that niacin-rich foods contain nicotine or
that cigarettes contain vitamins
The name niacin is derived in the following manner
The name pantothenic acid is based on the Greek word
“pantothen,” which means “from everywhere.”
This vitamin is found in almost every plant and animal
tissue.
Pantothenic acid-containing coenzyme
o
Coenzyme A (CoA)
→ one of the most used of all vitamin B
coenzymes, contains pantothenic acid as part
of its structure
→ required in the metabolism of carbohydrates,
lipids, and proteins, where it is involved in the
transfer of acetyl groups between molecules
o
Acyl Carrier Protein (ACP)
→ a “giant coenzyme A molecule.”
→ important in the biosynthesis of fatty acids
Collective term for three related compounds:
o
pyridoxine (found in foods of plant origin)
o
pyridoxal and pyridoxamine (found in foods of
animal origin)
Contain an added phosphate group, are related to
each other in the same manner that the “free” forms
are related to each other
Coenzymes participate in reactions where amino
groups are transferred between molecules. Such
transfer occurs repeatedly when protein molecules are
metabolized
Unique among the B vitamins in that it can be obtained
both from dietary intake and also via biotin-producing
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Folate (Vitamin B9)
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Vitamin B12 (Cobalamin)
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bacteria (microbiota, hence the name biotin) present in
the human large intestine
Fused two-ring system with one ring containing sulfur
and the other ring containing nitrogen
o
Attached to the sulfur-containing ring is a
pentanoic acid residue
“Free” biotin is biologically active
The coenzyme form of biotin is formed by the carboxyl
group of biotin’s pentanoic acid attachment forming
an amide linkage with a residue of the amino acid
lysine present at the enzyme’s active site
As a coenzyme, biotin is a carrier for CO2; it has a
specific site (a nitrogen atom) where a CO2 molecule
can become attached.
Several forms of folate are found in foods. All of them
have structures that consist of three parts:
1.
a nitrogen-containing double-ring system
(pteridine)
2.
para-aminobenzoic acid (PABA)
3. one or more residues of the amino acid
glutamate.
Folic acid – folate when only one glutamate residue is
present
Polyglutamates – folate molecules that have three or
more glutamate residues
Tetrahydrofolate (THF)
o
Active coenzyme form of folate
o
Only one glutamate and four hydrogen atoms
have been added to the double-ring nitrogen
system
o
Needed in methylation reaction (one or more
methyl groups are transferred from one
molecule to another)
Folate
o
comes from the Latin word “folium,” which
means “leaf”
o
Dark green leafy vegetables are the best natural
source for folate
COBALAMIN
o
comes from the fact that an atom of the metal
cobalt and numerous amine groups are present
in the structure of vitamin B12, which is by far the
most complex of all vitamin structures
unique in that it is the only vitamin that contains a
metal atom
“free” vitamin B12 and coenzyme vitamin B12
difference
o
Cyanocobalamin – free form
o
Methylcobalamin – coenzyme form
only microorganisms can produce it; it cannot be
made by plants, animals, birds, or humans.
FAT-SOLUBLE VITAMINS

VITAMIN A, D, E, K
o Involved in plasma membrane processes
o More hydrocarbon like with fewer functional groups
o Occur in the lipid fractions of their sources
o Their molecules have double bonds or phenol rings, so oxidizing agents readily
attack them
o Destroyed by prolonged exposures to air or to the organic peroxides that
develop in fats and oils turning rancid
o Because the fat-soluble vitamins are easily oxidized, they destroy oxidizing
agents (which are involved in the development of coronary heart disease, genetic
mutations, and cancer)
 VITAMIN A
o Primary alcohol of molecular formula C20H30O; occur only in the animal world,
where the best sources are cod-liver oil and other fish-liver oils, animal liver and
dairy
products
o
Provitamin A – is found in the plant world in the form of carotenes. Provitamins
have no vitamin activity; however, after ingestion in the diet, β-carotene is
cleaved at the central carbon-carbon double bond to give 2 molecules of Vitamin
A
o
VISION: in the eye- vitamin A combines with opsin protein to form the visual
pigment rhodopsin which further converts light energy into nerve impulses that
are not sent to the brain
REGULATING CELL DIFFERENCE: a process in which immature cells change to
specialized cells with function

Ex: differentiation of bone marrow cells white blood cells and red blood
cells
MAINTENANCE of the health of epithelial tissues via epithelial tissue
differentiation

Lack of vitamin A causes skin surface to become drier and harder than
normal
REPRODUCTION AND GROWTH: in men, Vitamin A participates in sperm
development. In Women, normal fetal development during pregnancy require
vitamin A.
o
o
o
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o
VITAMIN D – SUNSHINE VITAMIN
o The antirachitic vitamin
o Necessary for the normal calification of bone tissue
o It controls correct ration of Ca and P for bone mineralization
o Two forms active in the body: Vitamin D2 (ergocalciferol) and D3 (cholecalciferol)
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o
o
o
VITAMIN K – ANTIHEMORRHAGIC VITAMIN
Pigment in the skin, 7-dehydrocholesterol, is a provitamin D; when irradiated by
the sun becomes converted to Vitamin D3
Humans exposed to sunlight year-round do not require dietary Vit. D
Vitamin D3 (cholecalciferol) is sometimes called the “sunshine vitamin” because
of its synthesis in the skin by sunlight irradiation
o
o
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A most important location in the human body where vitamin E exerts its
antioxidant effect is the lungs, where exposure of cells to oxygen (and air
pollutants) is greatest.
VITAMIN E – ANTISTERILITY VITAMIN
o Alpha-tocopherol – is the most active biological active form of Vitamin E
o Tocopherol came from the greek word meaning, promoter of childbirth
o Functions in the body as an antioxidant in that it inhibits the oxidation of
unsaturated fatty acids by O2
o Primary function: Antioxidant – protects against oxidation of another compounds
o There are four forms of vitamin E: alpha-, beta-, delta-, and gamma-tocopherol.
These forms differ from each other structurally according to which substituents
(9CH3 or 9H) are present at two positions on an aromatic ring.
o The tocopherol form with the greatest biochemical activity is alpha-tocopherol,
the vitamin E form in which methyl groups are present at both the R and R9
positions on the aromatic ring. Gamma-tocopherol is the main form of vitamin E
in vitamin-E rich foods.
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Vitamin K1 also called as phylloquinone,

has a side chain that is predominantly saturated;

only one carbon–carbon double bond is present (found in plants)
Vitamin K2 also called as menaquinones,

with the various forms differing in the length of the side chain (found in
animals and huans and can be synthesized by bacteria)
Synthesized by bacteria that grow in colon
Active in the formation of proteins involved in regulating blood clotting
Deficiency may occur during the first few days after birth, because newborns lack
the intestinal bacteria that produce Vitamin K and because they have no store of
Vitamin K(it does not cross the placenta)
Deficiency may also occur following antibiotic therapy that sterilizes the gut
ENZYME KINETICS