Protein

PROTEINS
Proteins
 Derived from the Greek word : ‘PROTOS’
 Compounds composed of carbon, hydrogen, oxygen,

and nitrogen atoms.
 These nitrogen atoms gives the name amino

(nitrogen containing) to the amino acids – the links
the chains of proteins.
 Amino acids are also called building blocks or units

of structure of proteins.
Basic Structure of Amino acids
 The human body needs 20 different amino acids for tissue synthesis.
 Of these 20 amino acids:
 9 are Essential amino acids(EAA)
 Essential amino acids are called as indispensible amino acids because
the human body cannot synthesis it. These amino acids must be
supplied by the diet only.
 Histidine
 Isoleusine
 Leucine
 Lysine
 Methionine
 Phenylalanine
 Threonine
 Tryptophan
 Valine
 11 are Non-Essential Amino Acids {NEAA}
 Non-essential amino acids are also known as
Dispensable amino acids because they can be
synthesized in the body
 Despite the above labels, tissue protein synthesis

cannot take place in the absence of either Essential
or Non-essential amino acids.
 In other words, all 20 amino acids are required to
build tissue proteins.
 The human body is estimated to contain many
thousand different proteins.
 Bonds between amino acids are called “Peptide
Bonds” or “Peptide Linkages”
 The bonds that form between adjoining amino acids
are called peptide bonds.
 Proteins often contain from 35 to several hundred or
more amino acids.
 Protein fragments with 10 or more amino acids are
called polypeptides.
Amino Amino Amino

acid acid acid
 Proteins with 2 amino acids : Di- peptides.
 With 3 amino acids : Tri – peptides.
 With 10 or more amino acids : Poly – peptides.
 Where is Protein found in the body?
 Protein resides in our skin, hair, nails, muscles,
blood, tendons, ligaments.
 All hormones, enzymes, antibodies, red – blood
cells, are mainly Protein in nature.
 In fact, almost all body cells and all body fluids
contain Protein except ‘Bile’ and ‘Urine’.
Classification of Proteins
On the Basis of
On the basis of
Physical and On the basis
Nutritional
Chemical Physical Shape
properties
properties
On Physical & Chemical Properties
 i. Simple Proteins: On hydrolysis, give only amino-acids
 E.g. Albumin (Egg, Blood, Milk)
 Globulin (Milk, Blood, Potato)
 Gluten (Wheat)
 Collagen, Elastin, Keratin
 Legumin, Gliadin, Zein
 ii. Conjugated Proteins: Simple Proteins plus a non-protein
substance
 E.g. Lipoproteins, Phosphoproteins, Glycoproteins
 iii. Derived Proteins: Substances resulting from breakdown or re-
arrangement of molecules within simple or conjugated proteins
 E.g. Curdled Milk, Coagulated Egg Protein
On Physical Shape
 i. Fibrous Protein:
 Linear in shape
 Generally insoluble in body fluids
 Give strength to the tissues in which they appear.
 E.g. Keratin (Hair, nails)
 Collagen (Bones, Tendons)
 Elastin (Skin, Blood vessel walls)
 ii. Globular Protein:
 Round in shape
 Generally soluble in body fluids
 E.g. Hemoglobin, Insulin, Albumin
On Nutritional Properties
 Complete Proteins:
 Contain all the essential amino acids
 Capable of supporting growth as well as maintenance
 E.g. All Animal Proteins (Egg, Milk, Meat, etc.)
 Partially Complete Proteins:
 Lacking in 1 or 2 essential amino acids
 Cannot help in growth but will support the function of
maintenance
 E.g. Gliadin (wheat) and Legumin (legumes/peas)
 Incomplete Proteins:
 Lacking in more than 2 essential amino acids
 Incapable of replacing or building new tissues, so can neither
support growth nor maintenance.
 E.g. Zein (maize protein)
What are Reference Proteins?
1. Should be complete Proteins
 2. The sequence of amino acids in this protein should
be similar to or close to the sequence of amino acids
in the body proteins.
 Egg Protein is called as a “Reference Protein”.
 It has a ‘Net Protein Utilization’= 100.
 Used as a reference standard while judging the
quality of other Dietary Proteins.
 What are Limiting Amino Acids?
 All amino acids needed for the synthesis of a particular
protein must be present in sufficient amounts at the same
time.
 If any ‘essential amino acid’ is missing or present only in a

limited amount, a new protein cannot be synthesized.
 Essential Amino Acids that are missing or in short supply,

are known as “Limiting Amino Acids”.
 They are called so because they limit the construction and

utilization of a complete protein.
 Examples:
 Methionine and Cysteine are the major limiting amino acid in
Pulses.
 Lysine and Threonine are the main limiting amino acids in Cereals
 What is meant by “Mutual Supplementation of
Proteins”?
 When 2 or more incomplete proteins are eaten together,
they complement or supplement each other’s deficiency
of the limiting amino acids, thereby resulting in a
complete protein.
 This is known as ‘Mutual Supplementation of Proteins’
and is the basis for advising / prescribing mixed diets for
vegetarians.
 E.g. of Limiting AA:
 Legumes & Pulses:
 Methionine and Cysteine
 Cereals:
 Lysine and Threonine
 Examples of Mutual Supplementation:
 Rice / Chapati + Pulses / Beans / Tofu
 Corn + Peas / Beans OR Beans and Toast
 Legume / Peas / Beans soup + Bread / Chapati
 Idli / Dosa OR Bread + Peanut butter
RDA for Proteins
 Adults:
 1gm / kg body weight / day
 Infants (0-12months):
 2.3 to 1.8gm/kg body weight/day
 Children (1-18yrs):
 1.8gm to 1gm / kg body weight / day
Functions of Proteins
 1. Growth, Maintenance and Repair
 Formation of Enzymes, Blood Proteins, Hormones, other body
proteins.
 Growth during Infancy, Childhood, Adolescence and Pregnancy
 Continuous replacement of daily losses or damage (i.e.
Maintenance and Repair)
 2. Energy Giving
 1 gm on oxidation gives 4kcals
 However, using Protein for energy limits its other functions in the
body.
 So, the body uses Protein as a source of energy only as a last
resort.
 3. Regulation of Body Processes
 Proteins have specialized regulatory functions in

body processes. Some examples-
 -Catalytic Proteins: i.e. Enzymes
 -Hormonal Proteins: i.e. Hormones
 -Immune Proteins: i.e. Antibodies
 -Contractile Proteins: Actin / Myosin
 -Blood Proteins: Haemoglobin
 4. Maintenance of Fluid Balance
 Blood Proteins like Albumin and Globulin, play

an important role in regulating the water balance
inside the body.
 During protein deficit, decrease in the level of
blood proteins upsets this water balance within
the body.
 This leads to an accumulation of fluids in the
tissues, commonly referred to as “Edema”
 Edema or Swelling is one of the main
characteristics features of “Kwashiorkor”.
 5. Maintenance of Acid-Base Balance
 Normal body processes produce acids and bases

that can cause major problems, even death, if not
buffered or neutralized.
 Blood must remain neutral otherwise dangerous
conditions like ‘Acidosis’ and ‘Alkalosis’ can occur
leading to coma and eventually death.
 Some Blood proteins have the chemical ability to
acts as buffers and neutralize both acids and
bases.
Food Sources of Proteins
 Good Sources:
 Animal Foods like Meat,
Fish, Eggs.
 Plant Foods such as Pulses & Nuts.
Soyabean (40% Prot)
 Moderate Sources:
 Cereals and Millets
 Poor Sources:
 Roots, Tubers, Fruits, GLVs
Protein Metabolism
Amino Acid
De- amination
Trans - amination
PROTEIN SYNTHESIS
Removal of Amino Enzymes, Hormones
Group from the Amino ,Tissues, Blood Proteins,
Acid Antibodies, etc.
Part of the amino group Carbon Skeletons used

is used for synthesis of Production for-
Non-Essential amino- Free Ammonia •Gluconeogenesis
acids Converted to •Lipogenesis
UREA •Energy Production
Protein Deficit and Health
 Eating too little protein can:
 •Slow down the protein rebuilding and repairing process.
 •Weaken the immune system.
 Eating too little protein in many developing countries leads to
PEM.
 •Kwashiorkor
 •Marasmus
Protein Energy Malnutrition
 Marasmus:
 A type of PEM characterized by severe insufficiency of
calories and protein that accounts for the child’s gross
underweight and wasting away of muscles.
 Kwashiorkor:
 A type of PEM associated with children who are getting
inadequate amounts of protein and only marginal amounts
of calories.
Marasmus
• Infancy (less than 2 yr.)
• Severe deprivation, or impaired absorption,
of protein, energy, vitamins, and minerals
• Develops slowly; chronic PEM
• Severe weight loss
• Severe muscle wasting, with no body fat
• All “Skin & Bones” look. Frequently referred
to as the “Little Old Man Face appearance.
• Growth: <60% weight-for-age
• No detectable edema
• No fatty liver
• Anxiety, apathy
• Good appetite possible
• Hair is sparse, thin, and dry; easily pulled out
• Skin is dry, thin, and easily wrinkles
Kwashiorkor
• Older infants and young children (1 to 3 yr.)
• Inadequate protein intake or, more
commonly, infections
• Rapid onset; acute PEM
• Some weight loss
• Some muscle wasting, with
retention of some body fat
• Growth: 60 to 80% weight-for-age
• Edema
• “Swollen Belly” –enlarged liver due to
accumulation of fat
• Apathy, misery, irritability, sadness
• Loss of appetite
• Hair is dry and brittle; easily pulled out;
changes color; becomes straight
• Skin develops lesions
• Diarrhea and other infections are common
Can Eating Extra Protein Make Muscles
Grow Larger?
 NO.
 Exercise and hard work, not excess dietary protein,
is the trigger for the genes to build more muscle
tissue
 Exercise generates cellular messages that stimulate
the process of building up muscle fibers
 Eating too much protein has no benefits and may
result in:
 Excessive kcalories
 Excessive fat if you are eating too much high-fat
animal foods and increased cholesterol
 Calcium loss
 Extra load on kidneys
DENATURATION
 Under specific conditions, a protein's shape is
distorted, causing it to lose its ability to function. This
is called as Denaturation. It is irreversible beyond a
point.
 Denaturation is caused by-
 -High Temperatures
 -UV Radiation
 -Agitation or Whipping
 -High Salt Concentration
 -Acids / Bases
 Denaturation can make the protein insoluble due to
the intra-molecular re-arrangements and the protein
is said to have “denatured”.
 E.g. Denaturation of Egg Protein, Wheat Protein
COAGULATION
 As a result of any of the actions that cause denaturation, if the protein
gets separated as a precipitate, it is said to have undergone
“Coagulation”. E.g. Making of Curd / Paneer.
 All Proteins are first Denatured and then Coagulated.
 Coagulation is the change from a liquid to a thickened, curd-like,

insoluble state, not by evaporation, but by some kind of chemical
reaction.
 As, the spontaneous coagulation of freshly drawn blood; the

coagulation of milk by acid, and the coagulation of egg albumin by
heat.
 The casein in milk is coagulated (curdled) by the addition of acetic acid

or citric acid. The albumin in egg white is coagulated by heating.
 The clotting of blood is another example of coagulation. Coagulation

usually involves a chemical reaction.

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What are the different types of proteins?

What are the different types of proteins?

What are essential and non-essential amino acids?

What are essential and non-essential amino acids?

PROTEINS

 Compounds composed of carbon, hydrogen, oxygen,

 These nitrogen atoms gives the name amino

 Amino acids are also called building blocks or units

 Despite the above labels, tissue protein synthesis

Amino Amino Amino

 If any ‘essential amino acid’ is missing or present only in a

 Essential Amino Acids that are missing or in short supply,

 They are called so because they limit the construction and

 Proteins have specialized regulatory functions in

 Blood Proteins like Albumin and Globulin, play

 Normal body processes produce acids and bases

Part of the amino group Carbon Skeletons used

 All Proteins are first Denatured and then Coagulated.

 Coagulation is the change from a liquid to a thickened, curd-like,

 As, the spontaneous coagulation of freshly drawn blood; the

 The casein in milk is coagulated (curdled) by the addition of acetic acid

 The clotting of blood is another example of coagulation. Coagulation

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