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Transcript of · Web viewSo all the reducing sugars will give Benedicts qualitative test and Fehling test...
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
The Chemist’s View of CarbohydratesCarbohydrates are made of carbon, hydrogen and oxygen atoms .
Carbohydrates (glycans) have the following basic composition:
At the molecular level, most carbohydrates are polyhydroxyaldehydes, polyhydroxyketones, or compounds that yield either of these after hydrolysis. Therefore, the chemistry of carbohydrates is essentially the chemistry of hydroxyl groups and carbonyl groups, and of the acetal
bonds formed between these two functional groups .
Classification of Carbohydrates .A- Number of carbohydrate units
1 -Monosaccharides (simple carbohydrates) : one carbohydrate unit .
.2 -Disaccharides (complex carbohydrates) : two carbohydrate units
.3 -Trisaccharides : three carbohydrate units
.4 -Polysaccharides : many carbohydrate units
B- Position of carbonyl group
at C1, carbonyl is an aldehyde : aldose .
at any other carbon, carbonyl is a ketone : ketose .
C- Number of carbons
three carbons : triose ‚
four carbons : tetrose ‚
five carbons : pentose ‚
six carbons : hexose‚
seven carbons : heptose ‚ etc .
D- Cyclic form
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Monosaccharides
Monosaccharrides : are single sugars (most are hexoses). 1- Glucose : serves as the essential energy source, and is commonly known as blood sugar or dextrose .
2 -Fructose : is the sweetest, occurs naturally in honey and fruits, and is added to many foods in the form of high-fructose corn syrup.
3 -Galactose : rarely occurs naturally as a single sugar.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Disaccharides
Disaccharides : are pairs of monosaccharides, one of which is always
glucose Condensation reactions link monosaccharides together.
Hydrolysis reactions split molecules and commonly occur during digestion.
Maltose : consists of two glucose units. It is produced during the
germination of seeds and fermentation.
Sucrose : is fructose and glucose combined. It is refined from sugarcane
and sugar beets, tastes sweet, and is readily available.
Lactose : is galactose and glucose combined. It is found in milk and milk
products .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
The Complex Carbohydrates
Few (oligosaccharides) or many (polysaccharides) glucose units bound /
linked together in straight or branched chains.
1 - Glycogen
Storage form of glucose in the body Provides a rapid release of energy
when needed . Starches Storage form of glucose in plants Found in grains,
tubers, and legumes . A glycogen molecule contains hundreds of glucose
units in highly branched chains. Each new glycogen molecule needs a
special protein for the attachment of the first glucose (shown here in red).
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Glycogen
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Dietary fibers provide structure in plants, are very diverse, and cannot be broken down by human enzymes . Soluble fibers are viscous and can be digested by intestinal bacteria ( this property is also known as fermentability ) . These fibers are found in fruits and vegetables. Insoluble fibers are nonviscous and are not digested by intestinal bacteria . These fibers are found in grains and vegetables.
Sugar Nomenclature
For sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group. Most naturally occurring sugars are D isomers . D & L sugars are mirror images of one
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
another. They have the same name, e.g., D-glucose & L-glucose. Other stereoisomers have unique names ,
e.g., glucose, mannose, galactose, etc. The number of stereoisomers is 2n, where n is the number of asymmetric centers. The 6 - C aldoses have 4 asymmetric centers. Thus there are 16 stereoisomers (8 D-sugars and 8 L-sugars) .
Furan Pyran
Cyclic Forms of Carbohydrates : Pyranose Forms.
Pentoses and hexoses can cyclize as the ketone or aldehyde reacts
with a distal OH . Glucose forms an intra - molecular hemiacetal , as the
C1 aldehyde & C5 OH react , to form a 6 - member pyranose ring , named
after pyran . These representations of the cyclic sugars are called Haworth
projections .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Fructose forms either a 6 - member pyranose ring, by reaction of the
C2 keto group with the OH on C6, or a 5-member furanose ring, by
reaction of the C2 keto group with the OH on C5 .
Cyclization of glucose produces a new asymmetric center at C1.
Haworth projections represent the cyclic sugars as having essentially planar
rings, with the OH at the anomeric C1:
a (OH below the ring)
b (OH above the ring).
Because of the tetrahedral nature of carbon bonds, pyranose sugars
actually assume a "chair" or "boat" configuration, depending on the sugar .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
The representation above reflects the chair configuration of the
glucopyranose ring more accurately than the Haworth projection.
Reactions of Monosaccharides and Properties
1-Action of acids:
Monosaccharides on treatment with strong concentrated sulphuric acid
undergoes dehydration to give furfural or furfural derivatives which on
condensation with α – naphthol yield a violet or purple colored complex.
Pentoses yield furfural whereas hexoses yield 5- hydroxyl furfural.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
+ 3H2O Conc. H2SO4+˃-------------
+Conc. H2SO4 ------˃ + 3H2O
2 -Mutarotation
Mutarotation is defined as the change in specific rotation of optically active
solution without any change in other properties . When glucose is dissolved
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
in water , the optical rotation of the solution gradually changes and attains
an equilibrium value . The change in optical rotation is called mutarotation
Mutarotation occurs due to the cyclization of open chain form of glucose
into α or β form with equal probability . This α and β cyclic form of
glucose have different optical rotations. They differ in configuration about
the anomeric carbon ( C1) but have the same configuration at C2, C3, C4,
and C5 asymmetric carbons. These cyclic forms are in equilibrium with
open chain structure in aqueous solution .such a change from a single form
to an equilibrium mixture that includes its other form is called
mutarotation .
3 -Reducing property
Monosaccharides by virtue free aldehydic or ketonic group in their
structure , i.e., presence of free anomeric carbon atom, reduces certain
heavy metallic cation, e.g., Cu+2 ions in alkaline solution at high
temperature .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
So all the reducing sugars will give Benedicts qualitative test and Fehling
test positive . The reaction is as follows:
CuSO4 ↔ Cu++ + SO4 --
Reducing sugars + Na2CO3 ----------------> Enediol form of reducing
sugar Cu+2 + Enediols + high temp.--------------> Cu+ + Mixture of
sugar acids Cu+ + OH- + Δ --------------> CuOH
2CuOH + Δ -------------------> Cu2O ( cuprous oxide ) + H2O
Benedict s qualitative reagent contains cupric sulphate , sodium carbonate ՚and sodium citrate whereas Fehling solution contains cupric sulphate ,
sodium hydroxide and sodium potassium tartrate ( Rochelle salt ) .
Benedict s qualitative reagent is preferred above Fehling solution because ՚it is stable .
4 -Osazone Formation
It involves two reactions . Firstly glucose with phenylhydrazine gives
glucosephenylhydrazone by elimination of a water molecule from the
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
functional group. The next step involves reaction of one mole of
glucosephenylhydrazone with two moles of phenylhydrazine (excess). First
phenylhydrazine is involved in oxidizing the alpha carbon to a carbonyl
group, and the second phenylhydrazine involves in removal of one water
molecule with the formyl group of that oxidized carbon and forming the
similar carbon nitrogen bond . The alpha carbon is attacked here because
its more reactive than the others . Osazones are highly coloured and
crystalline compounds and can be easily detected . Glucose gives
broomstick or needle shaped crystals with this whereas maltose gives
sunflower shaped crystals .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
5 -Action of dilute alkali
Monosaccharides on treatment with dilute alkali undergo a variety of molecular transformation through enediol formation.
The enediols of sugars are good reducing agents and form the basis of
reducing action of sugars in alkaline medium . When glucose is treated
with dilute alkali for several hours, the resulting mixture obtained
contains both fructose and mannose in addition to glucose . A similar
mixture of same sugars is optained with any of the other tow sugars .
Mannose
║
Enediol = fructose = glucose
mannose
║
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
6 -Oxidation
Aldoses are oxidized under variety of conditions to the following:
1 -Aldonic acid : Whereby the first carbon atom (C-1) is oxidized to
carboxyl group only . The rest of the molecule structure remains unaffected
.
2 -Uronic acid : Whereby the terminal carbon atom is oxidized to carboxyl
group only.
3 -Aldaric acid or saccharic acid : Whereby both the first carbon atom, i.e.,
aldehydic group and the terminal carbon atom , i.e., primary alcoholic
group are oxidized to carboxyl group.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
7 – Fermentation
Fermentation is the process of breakdown of complex organic substances
into smaller substances with the help of Glucose is fermented to ethyl
alcohol and carbon dioxide by yeast . Hence this process is called alcoholic
fermentation as alcohol is produced.
Lactobacilli
C6H12O6 --------------> 2CH2CH.OH.COOH
galactose Sterptococcoi lactic acid
8 -Ester formation
Monosaccharides interact with phosphoric acid to give phosphoric sugars,
and this plays an important role in the metabolic processes of
carbohydrates
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
9 -Glycoside or acetal formation
Glycosides are sugar derivatives in which hydrogen of the hydroxyl group
of hemiacetal or hemiketal form of the sugar is replaced by an organic
moiety. A molecule of water is eliminated when this reaction takes place .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Glycosides are not reducing sugars and do not show mutarotation . I f the
organic moiety is derived from another monosaccharide , the product
formed is disaccharide. If the organic moiety is a noncarbohydrate, then it
is called a glycone. A glycone: The noncarbohydrate portion of the
glycoside is called the a glycone or a glucone . Glycosides do not reduce
alkaline copper sulphate because sugar group is combined , i.e., aldehyde
group is converted to an acetal group .
Gcosides = Carbohydrate + Carbohydrate part or noncarbohydrate part (a
glycone).
D - glucose+
CH3OH
↓
Types of glycosidic bonds in carbohydrate
)1:4 - ( α - D - Glucosidic linkage in maltose.
)1:4 - ( β - D - Glucosidic linkage in lactose.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
α ( 1 ) → β ( 2 ) - D - Glucosidic linkage in sucrose.
α ( 1 → 6 ) - D - glycosidic linkage in isomaltose ( a disaccharide
is derived from the branch point of starch ).
α ( 1 , 4 ) and α ( 1 , 6 ) glycosidic linkages in starch.
β ( 1 , 4) glycosidic inkage in cellulose.
Α ( 1 , 4 ) and α ( 1 , 6 ) glycosidic linkage in glycogen.
β ( 1,4 ) and β ( 1,3 ) glycosidic linkage in hyaluronic acid.
α ( 1,4 ) glycosidic linkage in heparin.
Poly saccharides:
Polysaccharides have two important biological functions:
1- As storage form of fuel (i.e. glycogen of animal origin and starch of
plant origin ) .
2- As structural components.
Polysaccharides can be divided into two groups:
-Homopolysaccharides .
-Heteropolysaccharides.
Homopolysaccharides.
Starch
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Native starch is a mixture of two polysaccharides.
a- Amylose : is a linear unbranched molecule in which D-
glucose units are linked by a ( 1 → 4 ) glycosidic linkages . It is
water soluble and gives blue color with iodine.
b- Amylopectins : is a branched chain molecule in which D –
glucose units in addition to α- ( 1→4 ) linkages are branched by α- (
1→6 ) glycosidic linkages . This branching occurs on an average of
24 to 30 D- glucose units. It is water insoluble and gives violet color
with iodine . Starch is a non reducing polysaccharide, on hydrolysis
with dilute mineral acids, i.e. with hydrochloric acid gives glucose
only .
Starch
2 -Cellulose
Cellulose is a linear polymer of D – glucose units joined together by β
(1,4 ) glycosidic linkages. On partial hydrolysis, cellulose yields β – 1,4
disaccharide cellobiose instead of maltose.
Cellobiose is a disaccharide with the formula
[HOCH2CHO(CHOH)3]2O. is a reducing sugar, consists of two β-glucose
molecules linked by a β(1→4) bond. It can be hydrolyzed to glucose
enzymatically or with acid. Cellobiose has eight free alcohol (OH) groups, 21
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
one acetal linkage and one hemiacetal linkage, which give rise to strong
inter- and intra-molecular hydrogen bonds. It can be obtained by enzymatic
or acidic hydrolysis of cellulose and cellulose rich materials such as cotton,
or paper .
3 -Glycogen:
Glycogen is the carbohydrate reserve of the body . Glycogen is also called animal starch, because it serves as nutritional reservoir in animal tissues. Glycogen is a highly branched chain molecule in which glucose unit in addition to linear α (1,4) linkages are also linked by α (1,6) at the branched point . This branching repeats after every 8 -10 glucose units. Glycogen is water soluble and has no reducing property. It gives red color with iodine .
4 -Dextrins
They are the partial hydrolytic products of starch by α-amylase, β –amylase and acids. All dextrins have free sugar group and accordingly reduced alkaline copper sulphate solution .
b- Heteropolysaccharides
1 -Hyaluronic acid
2 -Heparin
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
heparin
3-Chondroitin sulphates.
4-Sialic Acids.
mesotartaric acid
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
D - glyceraldehyde
-glyceraldehyde(+)
l - glyceraldehyde
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
-glyceraldehyde(−)
ChemistryofLipids
Lipids(fats)
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Lipids : are one of the large biological molecules (Carbohydrates,
fats, proteins and nucleic acids) , substances such as a fat, oil or wax
that dissolves in alcohol , non polar solvents like ether, chloroform,
benzene, etc., but not in water . Associated with them are various fat
soluble , non - lipid substances which includes carotenoid pigments
(are organic pigments that are found in the chloroplasts and
chromoplasts of plants and some other photosynthetic organisms,
including some bacteria and some fungi. Carotenoids can be
produced from fats and other basic organic metabolic building blocks
by all these organisms), and certain vitamins, i.e., vitamins A, D, E
and K. Lipids contain carbon, hydrogen and oxygen atoms and they
are an important part of living cells which widely distributed
throughout both plant and animal kingdom and are essential
constituents of cell membrane. Fats are said to be protein sparing
because their availability in the diet reduces the need to burn proteins
for energy. Lipids consist about 5% of the organic materials used in
the structure of a living cell, and there are about 40-50 type of lipid
molecules in the cell. The brain cells and especially nerve tissues are
rich in complex lipid compounds. Some lipids contain ionic groups as
phosphates or cholines but the largest part of the lipid molecule is non
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
polar. The essential building units of lipids are mostly consist of fatty
acids, glycerol, sphingosine, and steroids .
Lipids biological functions
Lipids have several important biological functions:
1- They serve as the reservoir of energy because of their:
a- High energy content. The calorific value is 9 Kcal / gm as compared
to carbohydrates which have calorific value of 4 Kcal / gm.
b- Storage in concentrated form in water free state in the tissues as
compared to carbohydrates which are highly hydrated and cannot be
stored in such concentrated form .
2 -As structural components of cell membranes.
3 -As transport forms of various metabolic fuel.
4 -As protective coating on the surface of many organs such as kidney,
against injury .
5 -To facilitate the absorption of the fat soluble vitamins A, D, E and K.
Dietry fat can be divided into two types:
a- Visible fat or fat consumed as such, e.g. butter, oil, ghee.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
b- Invisible fat or fat present as part of other foods items, e.g. egg,
fish, meat, cereal, nuts, etc.
Classification of lipids
1 -Neutral lipids ( glycerides ) ( ester compounds for fatty acids
with glycerol ) .
2- Phosphoglycerides (phospholipids) :
) ester phosphate for glyceride compounds it may also contains
nitrogen compound .(
3 -Sphingolipids (sphingosine , fatty acid, phosphate group,
nitrogen compound).
4- Glycolipids (compounds contain fatty acid, alcohol, sugar).
5- Lipoproteins (compounds contain lipids and proteins).
6 -Waxes (ester compounds for fatty acids, mono hydroxyl
alcohols) .
7 -Steroids (derivatives of cyclic alcohol compounds).
8 -Terpens (derivatives for polymers contain condensed isoprene
units .
Fatty acids
a- Fatty acids in nature as such are not very abundant but are present as ester.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
b- Fatty acids are derivatives of lipid because they interfere in the formation of various types of lipids.
c- Fatty acids are represented as general formula R— COOH.
General points about fatty acids:
1 -They are monocarboxylic acids.
2 -Number of carbon atoms are even, though odd number fatty acids
exist but are very rare.
3- They may be saturated or may be unsaturated.
If unsaturated they can be monounsaturated acid or polyunsaturated
acid. Mammals and plants contain both mono saturated and poly
unsaturated fatty acids whereas all the fatty acids containing double
bonds that are present in bacteria are monounsaturated.
Plant and fish fats contain more polyunsaturated fatty acids than
animal fats. The double bonds in a polyunsaturated fatty acid are
neither adjacent nor conjugated since this would make the structure
to easily oxidisable when exposed to environment oxygen.
1- The most common among the saturated fatty acids are palmitic
acid (C16), stearic acid (C18) and among the unsaturated fatty acid,
oleic acid (C18) .
2 -Unsaturated fatty acids have lower melting point than saturated
fatty acids of same chain length.
3- Fatty acids with odd number of carbon atoms occur in trace
amounts in terrestrial and marine animals .29
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
4 -Fatty acids with one to eight carbons are liquids at room
temperature while those with more carbon atoms are solids.
5- The presence of double bond in the molecule gives rise to
geometric isomerism. All naturally occurring unsaturated long chain
fatty acids are found in cis isomer.
6- Most plant fats are liquid since they contain a large proportions
of unsaturated fatty acids with melting points.
7- Animal fats, on the other hand, contain a high proportion of
palmitic and stearic acids, and are solid or semi – solid at room
temperature. Milk fat is unusual in containing a high proportion of
shorter chain (C4 – C14) fatty acids .
The most common fatty acids in neutral fats are:
FormulaNo. of atoms
CH3 — (CH2)2 — COOH
CH3 — (CH2)4 — COOH
CH3 — (CH2)10 — COOH
CH3 — (CH2)14 — COOH
CH3 — (CH2)16 — COOH
CH3 — (CH2)7 —CH═CH—
4
6
12
16
18
18
Butyric acid
Caproic acid
Lauric acid
Palmitic
Stearic acid
Oleic acid
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Naturally occurring straight chain saturated fatty acid
Systematic nameType of
chain
Common nameNo. of
C
atoms
n- Ethanoic acid
n- Propanoic acid
n- Butanoic acid
n- Octanoic acid
n- Decanoic acid
n- Dodecanoic acid
n- Tetradecanoic acid
n- Hexadecanoic acid
n- Octadecanoic acid
n- Eicosanoic acid
Short chain
Short chain
Short chain
Medium chain
Medium chain
Long chain
Long chain
Long chain
Long chain
Long chain
Acetic acid
Propionic acid
Butyric acid
Caprylic acid
Capric acid
Lauric acid
Myristic acid
Palmitic acid
Stearic acid
Arachidic acid
2
3
4
8
10
12
14
16
18
20
Structures
The first three fatty acids are known as the volatile fatty acids VFA's
Acetic Acid (C 2:0) :
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Propionic Acid (C 3:0):
Butyric Acid (C 4:0):
Caproic Acid (C 6:0):
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Caprylic Acid (C 8:0):
Capric Acid (C 10:0):
Lauric Acid (C 12:0):
Myristic Acid (C 14:0):
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Palmitic Acid (C 16:0):
Stearic Acid (C 18:0):
Oleic Acid (C 18:1)
Linoleic Acid (C 18:2):
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Arachidonic acid
Essential Fatty Acids
They are also called polyunsaturated fatty acids. They are not
synthesized in the body and hence, have to be provided in the diet .
They deficiency of essential fatty acids in humans gives rise to dry,
scaly skin, hair loss, poor wound healing, failure of growth and
increase in metabolic rate, These essential fatty acids requirement is
about 1% of the caloric intake be in the form of essential fatty acids.
Two of the essential fatty acids, linoleic and linolenic acids are not
synthesized in the mammal but are synthesized by plants. Essential
fatty acids are necessary in the biosynthesis of prostaglandins.
Prostaglandins are hormone like compounds which in small
amounts have profound effect .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Essential fatty acids are:
Dietary source
Position of double bonds from carboxyl end
No. of double bonds
No. of carbon atoms
Fatty acid
Vegetable oil
Vegetable oil
Vegetable oil
Fish oil
9,12
9,12,15
5,8,11,14
5,8,11,14,17
2
3
4
5
18
18
20
20
1 -Linoleic acid
2 -Linolenic acid
3 -Arachidonic acid
4 -Timnodonic acid
Important fatty acids in mammalian tissues
Position of double bonds
Double bondsNo. of carbon atoms
Common name
-
-
-
9
-
9
9,12
9,12,15
5,8,11,14
0
0
0
1
0
1
2
3
4
2
12
14
16
18
18
18
18
20
Acetic acid
Lauric acid
Myristic acid
Palmitic acid
Stearic acid
Oleic acid
Linoleic acid
Linolenic acid
Arachidonic acid
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Prostaglandins:
1 -Prostaglandins are the derivatives of prostanoic acid which are
the cyclic derivatives of unsaturated fatty acids having twenty
carbon atoms .
2 -Prostaglandins are synthesized from essential fatty acids such as
linoleic acid, linolenic acid and arachidonic acid.
3 -Five type of rings are found in the naturally occurring
Prostaglandins.
4 -The Prostaglandins which are widely distributed in the body are:
PGE1, PGE2, PGE3, PGF1α, PGF2α and PGF3α.
5 -Linolenic acid is the precursor to PGE3 and PGF1α, Arachidonic
acid is the precursor to PGE2 and PGF2α.
6 -Prostaglandins are synthesized and released by all mammalian
cells and tissues except RBC.
7 -All Prostaglandins are not stored in cells but are synthesized and
released immediately.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Biological function of prostaglandins:
1 -They lower blood pressure.
2 -They are used in the induction of labor, termination of pregnancy
and prevention of conception (PGE2).
3 -They are used in treatment of gastric ulcer (PGE).
4 -They are used to prevent inflammation.
5 -They are used in asthma.
6 -They are used in congenital heart disease.
7 -They inhibit platelet aggregation and promote clotting process.
1 -Neutral lipids:
Neutral lipids considered as simplest type of lipids, which are
compounds of glycerol and fatty acids ester, they also called
triacylglycerols or triglycerides when the three OH groups in
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
glycerol esterifies with three fatty acids. If the fatty acids from
stearic acid, the fat called tristearin while from palmitic acid it
called tripalmitin .
grease and oil
Neutral lipids include grease (fat) and oil, stored in adipose tissue,
mostly, the fats are solid in room temperature (25cᵒ), because of
containing large amount of saturated fatty acids. While oils are
liquid because of containing large amount of unsaturated fatty acids.
Important reactions of neutral lipids
1 -Acrolein formation:
When glycerol is heated with potassium bisulphate or concentrated
H2SO4, dehydration occurs and aldehyde Acrolein formed which
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
has characteristic unpleasant odor. This test responds to glycerol
free or linked as an ester.
2 -Hydrogenation
Unsaturated fats can be hydrogenated by the addition of hydrogen
across the double bonds of the fatty acids in the presence of nickel
as catalyst to give fully saturated fats. The above process is called
Hardening of oils whereby vegetable oils are hydrogenated to
produce commercial cooking fats.
3 -Saponification:
Hydrolysis of a fat by alkali is called Saponification. The products
of hydrolysis are glycerol and alkali salts of fatty acids, which are
called soaps. Soaps are polarized molecules which formed groups
in the water called micelles.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
CH2OCOR—CHOCOR—CH2OCOR +3NaOH→ CH2OH—CHOH—CH2OH+3RCOONa
Fat Glycerol soaps
4 -Rancidity (Peroxidation):
1 -Rancidity is a chemical change resulting in unpleasant odor and
taste on storage when fats are exposed to light, heat, air and
moisture.
2 -Rancidity is more rapid at high temperature.
3 -Rancidity may be due to hydrolytic or oxidative change taking
place at the double bonds of the unsaturated fatty acids resulting in
short chain aldehydes or ketones which have unpleasant odor .
4 -The addition of certain substances, called antioxidants such as
ascorbic acid and vitamin E prevents rancidity whereas addition of
peroxidants like copper, lead and nickel quickens rancidity.
5 -The oxidation of unsaturated bonds in fatty acids when are
exposed to oxygen in the environment is referred to as either auto
oxidation or peroxidation.
6 -Rancid fats are those that contain an appreciable amount of
peroxidized fatty acid .
7 -Antioxidants are generally added to many food fats to improve
their storage quantities.
2-Compound lipids
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
1 -Phosphoglycerides (phospholipids):
They are also known as phosphatides. Phospholipids act as a
detergent and increase the solubility of other lipids. They are
present in all cells as well as in the plasma. Phospholipids include
the following groups:
a- Phosphatidyl cholines (Lecithins):
1 -When choline or trimethyl ethanol amine esterified with
phosphoric acid side of phosphatidic acid, the phosphatidyl cholines
produces also called lecithins .
2 -Lecithin contains saturated fatty acid residue at the α– position
and unsaturated fatty acid residue at the β– position of the glycerol.
3- Lecithins on hydrolysis give glycerol, fatty acid, phosphoric acid
and choline .
4 -Lecithin compounds play an essential role in reducing the surface
tension of the cells in the lung alveoli, without it, shortness of breath
process happens .
b – Phosphatidyl ethanolamine (Cephalins)
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Cephalins differ from lecithins with respect to base attached to
phosphoric acid.
1 -If the base is ethanol amine then it is called phosphatidyl
ethanolamine or ethanolamine cephalin.
2 -If the base is amino acid serine then it is called phosphatidyl
serine which is also called serine cephalin.
Cephalins on hydrolysis yield glycerol, fatty acids, phosphoric
acids, ethanol amine or serine.
2 -Cerebrosides or glycolipids:
Glycolipids are carbohydrate - glyceride derivatives containing
sugar, sphingosine and a fatty acid. These compounds do not
contain phosphoric acid. If the sugar component is galactose, the
lipid is termed galactolipid. The term cerebroside is used because it
is found in large quantities in brain tissues particularly in white
matter. On hydrolysis cerebrosides give sphingosine, a fatty acid
and galactose. Cerebrosides are differentiated on the basis of fatty
acid present.
3 -Gangliosides:
They are found in nerve tissues. They contain carbohydrates, N-
acetyl galactosamine and N-acetyl neuraminic acid.
4 -Sulfatides (Sulpholipids):
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
They are cerebrosides having a sulphate group attached to the
galactosyl residue.
Derived lipid :
Lecithins are hydrolyzed by certain enzymes, phospholipases or
lecithinases. The nature of hydrolysis depends upon the type of
phospholipase used.
1 -Phospholipase A: present in snake venom (cobra) hydrolyzes
fatty acid in α or 1- position of glycerol in the lecithin to form
lysolecithins .
2 -Phospholipase B: hydrolyzes the remaining fatty acid of
lysolecithin present at β or 2- position to form glyceryl phosphoryl
choline.
3 -Phospholipase C: hydrolyzes phosphorylcholine from lecithins to
form diglycerides.
4 -Phospholipase D: hydrolyzes choline from phosphatidyl
ethanolamine (cephalin) form phosphatidyl serines.
These are two classes of non saponifiable lipids :
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
1 -Terpenes: They are linear or cyclic compounds formed by
condensation of two or more isoprene units.
Isoprene
Other important terpenoid compounds are:
a- Tocopherol (vitamin E)
b- Coenzyme Q (also called ubiquinone)
c- Vitamin K (naphthoquinone)
2 -Steroids:
1 -Steroids are the derivatives of cyclopentano-perhydro-
phenanthrene ring (consists of four fused rings).
2 -Steroids are steroidal alcohol. The most important member of the
group is cholesterol.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Some of the biologically important steroids are:
1 -Ergosterol: UV radiation causes rupture of ring B to produce
vitamin D .
2 -Bile acids: In lipid metabolism.
3 -Adrenal cortex steroids: Corticosterone and cortisol.
4 -Female hormones: Progesterone and estrogen.
5 -Male sex hormones: Testosterone and androsterone.
Mammalian cell membrane composition:
1 -The cell membrane (also known as the plasma membrane or
cytoplasmic membrane) is a biological membrane that separates the
interior of all cells from the outside environment .
2 -The cell membrane is selectively permeable to ions and organic
molecules and controls the movement of substances in and out of
cells .
3 -The basic function of the cell membrane is to protect the cell
from its surroundings. It consists of the phospholipids bilayer with
embedded proteins .
4 -Cell membranes are involved in a variety of cellular processes
such as :
a- cell adhesion ,
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
b- ion conductivity and cell signaling,
c- serve as the attachment surface for several extracellular
structures, including the cell wall, glycocalyx, and intracellular
cytoskeleton .
Glycocalyx: A thin layer of material that covers the surface of
many (especially the free surfaces), or all cells. It contains
polysaccharide mucous acid. It can be responsible for the selective
permeability of the cell wall.
d- Cell membranes can be artificially reassembled
Composition
1 -Cell membranes contain a variety of biological molecules,
notably lipids and proteins.
2 -Material is incorporated into the membrane, or deleted from it, by
a variety of mechanisms:
a- Fusion of intracellular vesicles with the membrane (exocytosis)
not only excretes the contents of the vesicle but also incorporates
the vesicle membrane's components into the cell membrane .
b- The membrane may form blebs around extracellular material that
pinch off to become vesicles (endocytosis).
c- If a membrane is continuous with a tubular structure made of
membrane material, then material from the tube can be drawn into
the membrane continuously.47
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
3 -Although the concentration of membrane components in the
aqueous phase is low (stable membrane components have low
solubility in water), there is an exchange of molecules between the
lipid and aqueous phases .
Lipids:
Examples of the major membrane phospholipids and glycolipids :
1 -phosphatidylcholine (PtdCho),
2 -phosphatidylethanolamine (PtdEtn),
3 -phosphatidylinositol (PtdIns) ,
4 -phosphatidylserine (PtdSer).
The cell membrane consists of three classes of amphipathic
lipids:
1- phospholipids,
2 -glycolipids, and
3- sterols .
The amount of each depends upon the type of cell, but in the
majority of cases phospholipids are the most abundant. In RBC
studies, 30% of the plasma membrane is lipid .
The fatty chains in phospholipids and glycolipids usually contain an
even number of carbon atoms, typically between 16 and 20. The 16-
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
and 18-carbon fatty acids are the most common. Fatty acids may be
saturated or unsaturated, with the configuration of the double bonds
nearly always "cis". The length and the degree of unsaturation of
fatty acid chains have a profound effect on membrane fluidity as
unsaturated lipids create a kink, preventing the fatty acids from
packing together as tightly, thus decreasing the melting temperature
(increasing the fluidity) of the membrane. Under physiological
conditions phospholipid molecules in the cell membrane are in the
liquid crystalline state. It means the lipid molecules are free to
diffuse and exhibit rapid lateral diffusion along the layer in which
they are present. However, the exchange of phospholipid molecules
between intracellular and extracellular leaflets of the bilayer is a
very slow process. A fraction of the lipid in direct contact with
integral membrane proteins, which is tightly bound to the protein
surface is called annular lipid shell; it behaves as a part of protein
complex .
In animal cells cholesterol is normally found dispersed in varying
degrees throughout cell membranes, in the irregular spaces between
the hydrophobic tails of the membrane lipids, where it confers a
stiffening and strengthening effect on the membrane .
Carbohydrates
Plasma membranes also contain carbohydrates, predominantly
glycoproteins, but with some glycolipids (cerebrosides and
gangliosides). For the most part, no glycosylation occurs on 49
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
membranes within the cell; rather generally glycosylation occurs on
the extracellular surface of the plasma membrane. The glycocalyx is
an important feature in all cells, especially epithelia with microvilli.
Recent data suggest the glycocalyx participates in cell adhesion,
lymphocyte homing, and many others. The penultimate sugar is
galactose and the terminal sugar is sialic acid, as the sugar backbone
is modified in the Golgi apparatus. Sialic acid carries a negative
charge, providing an external barrier to charged particles .
Proteins:
The cell membrane has large content of proteins, typically around
50% of membrane volume. These proteins are important for cell
because they are responsible for various biological activities .
The cell membrane, being exposed to the outside environment, is an
important site of cell–cell communication. As such, a large variety
of protein receptors and identification proteins, such as antigens, are
present on the surface of the membrane.
Functions of membrane proteins can also include :
1 -cell–cell contact ,
2 -surface recognition,
3 -cytoskeleton contact ,50
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
4 -signaling,
5 -enzymatic activity, or transporting substances across the
membrane.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Chemistry of amino acids and proteins
Chemistry of amino acids:
Amino acid, any of a group of organic molecules that consist of a
basic amino group (−NH2), an acidic carboxyl group (−COOH),
and an organic R group (or side chain) that is unique to each amino
acid. The term amino acid is short for “α-amino [alpha-amino]
carboxylic acid.” Each molecule contains a central carbon (C) atom,
termed the α-carbon, to which both an amino and a carboxyl group
are attached. The remaining two bonds of the α-carbon atom are
generally satisfied by a hydrogen (H) atom and the R group. The
formula of a general amino acid is :
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Structure of amino acids: The structures of the most important amino
acids are:
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Physical properties of amino acids: 1 -Solubility: Amino acids are soluble in water, acids, alkalies, but
sparingly soluble in organic solvents and insoluble in ether.55
الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
2 -Color: Amino acids are colorless, white and solids.
3 -State: Amino acids are solid crystalline compounds (crystals).
4- Optical activity: All amino acids ( except glycine) are optically active.
5- Melting points: Amino acids have high melting points.
6- Amphoteric (react as acidic and basic), (NH2 and COOH group).
Due to presence of basic and acidic groups in the same molecule,
they may be regarded as salts and hence, most of them either
possess higher melting point or melt with decomposition.
Chemical properties of amino acids:2 reactive groups
A – COOH Reactions: 1- Ester with alcohol
Amino acids react with alcohol to form ester. Esterification of the
carboxylic acid is usually conducted under acidic conditions.
COO COOH COOR
| HCl | ROH |
NH3 — C — H —————> ClNH3 — C — H ————> ClNH3 — C — H + H2O
| | |
R R R
2- With NH3 (Amidation).
Aspartic acid ————> Aspargine
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Aspartic acid
↓
Aspargine
3 -Reduction by LiAlH4
Lithium aluminium hydride , commonly abbreviated to LAH, is an
inorganic compound with the chemical formula LiAlH4. This
compound is used as a reducing agent in organic synthesis,
especially for the reduction of esters, carboxylic acids, and amides. LiAlH4 R— CH — (NH2) —
COOH —————> R— CH — (NH2) CH2 OH
Amino alcohol
4 -Decarboxylation
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
B – NH2 Reaction: 1- Salt formation with acids H H
| HCl |
R — C — COOH —————> R — C — COOH
| |
NH2 NHCl
2- Acylation: Reaction with strong acids
)Acid anhydride + NaOH(
In order to convert the amine function of an amino acid into an amide,
the pH of the solution must be raised to 10 or higher so that free amine
nucleophiles are present in the reaction system. Carboxylic acids are all
converted to carboxylate anions at such a high pH, and do not interfere
with amine acylation reactions .
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
3 -Methylation and benzoylation: important, detoxification
process.
4- Reaction with Sanger s reagent FDNB (1-floro-2,4-di nitro ՚benzene).
FDNB
Amino acid + FDNB ————> Di nitro phenyl amino acid
Is a test for free amino acid.
5- With nitrous acids HNO2
α- amino acids are deaminated to the corresponding α- hydroxy acids with
nitrous acid. Each amino group yields one molecule of nitrogen which can
be measured accurately.
H H
| |
R — C — COOH + HNO2————> R — C — COOH + N2 + H2O
| |
NH2 OH
N2= measure of free NH2 group in amino acids, peptides and proteins.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
6- Oxidative deamination (Removal of NH2) ——> Oxo acid.
H | R— C — COOH————> R— C— COOH———> R— C — COOH + NH3 | || || NH2 NH O
Oxo acid (keto acid)
7 -Ninhydrin Reaction
In addition to these common reactions of amines and carboxylic
acids, common alpha - amino acids, except proline, undergo a
unique reaction with the tri ketohydrindene hydrate known as
ninhydrin. (Quantitative measurement of free - amino group)α.
Ninhydrin Hydrindentin
Proteins:
Proteins are defined as compounds of high molecular weight
made up of - amino acids linked to one another by peptideα
linkages. Proteins contain 20 amino acids present in
characteristic proportions and linked in a specific sequence in
each protein. Proteins are linear polymers consisting of L- -αamino acids. The amino acids are joined together by peptide
bonds. The peptide bond is formed by the anion of carboxyl
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group of one amino acids with amino group of other amino acid
with an elimination of water molecule.
The polymeric Nature of Protein
1 -Peptides: A short chain of residues with a defined sequence.
-No max number of residues in a peptide.
-Its physical properties are those expected from the sum of its
amino acid resides.
-No fixed 3D conformation.
2 -Polypeptide: A longer chain with a defined sequence and
Length.
3 -Polyamino acids: Nonspecific polymerization of one or a few
amino acids
4- Protein:
– Polypeptides that occur naturally
– Have a definite 3D structure under physiological conditions
Peptide bonding
A covalent bond that links amino acids together in protein.
(α- amino group of amino acid with α- COO group of another amino acid) .
Polypeptide: many repeated peptide bonds. Biological active protein
contain 1 or more polypeptide chains.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
Protein FunctionMake up about 15% of the cell and have many functions in it:
1 -Catalysis: enzymes.
2 -Structure: muscle proteins. ( Structural proteins form the basis
of the cells, which come together to form organs, muscle tissue,
bones, skin, hair and nails. They help organize the cells into
separate tissues and they can protect the body as well; for example,
specialized proteins tightly connect one skin cell to another to create
a cohesive barrier against the outside environment. When tissues
become damaged due to injury or illness, structural proteins repair
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wounds and can generate new cellular components.
3- Movement: myosin, actin. (The bulk of the muscle tissue is
made of protein, which provides not only structural integrity but
also the ability to move. Muscle fibers consist of the proteins actin
and myosin, organized in a manner that allows them to slide back
and forth to shorten or lengthen a muscle, leading to movement. The
proteins involved in nerve impulses are also part of stimulating
muscle contraction) .
4 -Defense: antibody. (Immunity: The immune system is rich in
proteins. The white blood cells synthesize several immune
molecules, including antibodies and chemokines, to help protect the
body against infection and inflammation. In concert with biological
messengers, which can warn of foreign invaders or injury, the
immune system has the ability to rapidly ramp up production of
immune proteins to respond to this type of physiological threat to
the well - being .
5 -Communication and regulation: enzymes, hormones.
)Proteins serve as messengers in many ways. Enzymes are
biological catalysts, molecules that speed up a reaction without
themselves becoming involved, and they can orchestrate
physiological functions ranging from energy production to new
protein synthesis to activating another protein, depending on your
body’s needs. Hormones are molecules that can influence the
behavior of cells or tissues; for instance, insulin stimulates glucose
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uptake. Receptor proteins can also stimulate the activity of other
cellular components by binding molecules and eliciting a change
within a cell .(
6 -Transport and storage: globins, Mb, ferritin.( Protein can
function as both transport and storage molecules. For instance,
hemoglobin is a protein that carries oxygen to the tissues throughout
the body, and specialized transporter proteins allow the cells of the
small intestine to absorb digested nutrients from the gut into the
blood stream. Myoglobin stores small amounts of oxygen in the
muscles, while, in the liver, the protein ferritin binds iron as a
backup source of this mineral .
7 -Energy: Although not the body’s preferred fuel source, protein
can provide energy to the cells. Each gram you eat can supply 5.5
calories to help power your physiological functions.
8- Stress Response: hormones .
Classification of protein structureProteins exhibit four levels of organization.
1 -Primary structure: Refers to amino acid sequence.
2 -Secondary structure: Refers to folding of polypeptide chain into
specific coiled structure which is repetitive in one direction.
3 -Tertiary structure: Refers to arrangement and interrelationship of
twisted chain into a three dimensional structure.
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الطبية الكيمياء نوال محاضرات الدكتورةمرتضى عبدالله
4 -Quaternary structure: Refers to the association of different
monomeric subunit into a composite polymeric protein.
Chemistry of nucleic acid
65