This document provides information about proteins in 3 paragraphs: 1) It defines proteins as organic compounds made of amino acid chains that form complex 3D shapes and serve essential functions in living organisms. They are the most abundant organic compounds in cells. 2) It describes the 4 levels of protein structure from primary to quaternary, where the amino acid sequence determines the overall 3D shape through coiling and folding. 3) It briefly mentions the 20 common amino acids that make up proteins and the formation of peptide bonds between amino acid units.

1. Assignment
ON
Proteins
Submitted To:
Mam Saima Khubaib
Submitted By:
Muhammad Hannan
Date / Day:
30-11-2018 / Friday.
B.Sc. (Hons.) Agriculture (Water Management)
Semester 1st
Introduction

2. Any of Class of nitrogenous organic compounds that consists of large molecules composed
of one or more large long chains of amino acids and proteins are an essential part of living
organisms.
In fact, the name comes from the Greek word Proteios, meaning “Primary” or “first place”.
Proteins are made up of smaller building blocks called amino acids, joined together in
chains. There are 20 different amino acids. Some proteins are just a few amino acids long,
while others are made up of several thousands. These chains of amino acids fold up in
complex ways, giving each protein a unique 3D shape. Some, like keratin, the hair protein,
form long fibres. Others, like haemoglobin, the protein that carries oxygen around your
body, are roughly spherical.
Proteins are the most abundant organic compounds to be found in cell and comprise over
50% of their total dry weight. They are present in all type of cells in all parts of the cell.
Proteins are the "workhorse" molecules of life, taking part in essentially every structure and
activity of life. They are building materials for living cells, appearing in the structures inside
the cell and within the cell membrane. They carry oxygen, they build tissue, they copy DNA
for the next generation - they do all the work in any organism.
The human body probably contain at least 10,000 different types of amino acids. They
present in muscles, skin, hair, tissues, ligaments and tendons. So we use protein for growth.
One gram of protein contains four kilo calories of energy. Dietary source of proteins are
meat, eggs, grains and milk. Proteins can be converted in to carbohydrates.
Our bodies cannot use proteins directly. The proteins are broken down in to their amino
acid constituents in stomach by enzymes. The formula of amino acid is given as:
Discovery
Proteins were first noticed due to their ability to coagulate ( the ability to solidify usually
after being exposed to heat in Eighteen century i.e 1700 to 1899. However, Their first

3. description was presented by a Dutch scientist Gerardus Johannes Mulder. But they were
named by a Swedish chemist Jons Jacob Berzelius in 1838. Molder carried out analysis and
found that the proteins are actually large molecules. Molder went to study on protein
degradation and found out the molecular weight of 131 Da ( whereas 1 Da = 1.6605e-21 mg
or 1.6605e-24, Da is an abbreviation of Dalton ) for the amino acid leucine. The first protein
to be sequenced was insulin by Fredrick Sanger in 1949.
In the 1950’s, Linus Pauling became known as the founder of molecular biology due to his
discovery of the spiral structure of proteins (Taton, 1964). In 1922, Pauling studied a
technique known as X-ray crystallography “which makes it possible to determine the
arrangement of atoms in a crystal” (Taton, 1964, p.298). Although X-ray crystallography was
discovered by scientist W.H. Bragg, Pauling quickly deduced rules of interpreting X-ray
diffraction, allowing him to figure out the shape of proteins and provoking the discovery of
the DNA double helix.
In 1948, Pauling was stricken with an illness that confined him to bed. During this time, he
was able to ponder on Astbury’s idea that “globular proteins are made up of polypeptide
chains that are folded to make balls”, (Gribbin, 2002, p. 561). Pauling used his knowledge of
X-ray crystallography and his understanding of chemistry rules to determine how amino
acids fit together to make proteins (Gribbin, 2002). After using prape to make models and
working with jigsaw puzzles, he eventually figured out the structure of the alpha helix of
globular proteins.
Classification
According to the structure, proteins are classified as follows:
1. Fibrous Proteins:-
They consist of molecule having one or more than one polypeptide
chains in the form of fibrils. They are insoluble in aqueous media. They are non-crystalline
and are elastic in nature. They perform structural rolesin cells and organisms.
Examples are silk fiber( from silk worm and spider web), myosin( in muscle cells ), fibrin(
blood clot ) and keratin ( nails & hairs ).
2. Globular Proteins:-
They are spherical due to multiple folding of polypeptide chains. They
are soluble in aqueous media such as salt solutions and solutions of acidic and bases. They
can be crystallized. They disorganic with changes in the physical and phsiobgical
environment.

4. Examples are enzymes, antibodies, hormones and hemoglobin.
Classification of proteins on basis of composition and solubility:
1. Simple or Holo Proteins:-
These are globular type except for proteins which are fibrous in nature.
This group includes proteins containing only amino acids as structural components. With
acids, these liberate the constituent amino acids.
These are further classified mainly on their solubility basis which are protamines and
histoes, albumines, globulains, glutelines, prolamines and scleraproteins.
2. Comple/Conjugate or Hetro Proteins:-
These are also globular type except for the pigments in chicken feathers
which is probably of fibrus nature. These are the proteins linkes with a separable non
protein potion called prosthetic group.
These are further classified based on the nature of the prosthetic group present which are
metalloproteins, chromoproteins, glycoproteins, phospoproteins, lipoproteins and
nucleoproteins.
3. Derived Proteins:-
These are derivatives of proteins resulting from the action of heat,
enzymes or chemicals reagents. This group also includes the artificially produced
polypeptides.
These have further divisions which are Primary derived proteins ( Metaproteins &
Coagylated proteins ) and Secondary derived proteins ( Peptones & Polypeptides ).
Composition
Proteins are made up of hundreds or thousands of smaller units called amino acids, which
are attached to one another in long chains

5. About 2000 different proteins exist in nature and about 170 amino acids are occur in cells
and tissues. About 25 amino acids are constituents of proteins. Most of proteins are made
of 20 or more than 20 amino acids.
Amino acids can be divided into three groups.:
Essential Amino Acids:
These amino acids cannot be synthesized by the body and must be provided through the
food.There are nine essential amino acids.
Non-essential Amino Acids:
These amino acids are formed by the body either from the breakdown of proteins or from
the essential amino acids.
Conditional Amino Acids:
These amino acids are essential only during stress or sickness.
Essential amino acids Conditionally essential amino acids Nonessential amino acids
• Histidine
• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Valine
• Arginine
• Cysteine
• Glutamine
• Tyrosine
• Alanine
• Asparagine
• Aspartic acid
• Glutamic acid
• Proline
• Serine
In the formation of proteins, the amino group of one amino acid react with acid group of
another, liberating a molecule of water and forming the peptide link.
When only two amino acids link together through a peptide bond, the resultant product is
called dipeptide . When three are linked a tripeptide is formed and when several amino acid
join together, a polypeptide is produced. The characteristics of the proteins depend upon
the number and types of amino acids present in them.

6. Amino acids have the general structural molecular formula –NH2CHRCOOH. They have two
important functional groups:
Carboxylic acid Group
-COOH
Amine Group
-NH2
When an acid is added,
The –NH group combines with H+ ions from the acid to form NH3+NH2CHRCOOH (aq) +
H+(aq)->NH3+CHRCOOH (aq) (H+is frequently used as shorthand for H3O+)
When an alkali is added,
The –COOH group combines with OH-ions from the alkali by loss of H+to form –
COONH2CHRCOOH (aq) + OH-(aq) NH2CHRCOO-(aq) + H2O
In both cases, the concentration of H+ ions in solution does not change greatly and so the
pH remains about the same.
Peptide Bond Formation:
The amino acid units in a protein molecule are held together by peptide bonds, and form
chains called polypeptide chains.
Two amino acids can undergo a condensation reaction to form a dipeptide. Further
condensation reactions result in a polypeptide. The amino acid units are linked by peptide
bonds (sometimes called peptide links).
R1-COOH + R2-NH2R1-CO-NH-R2+ H2O

7. Figure : The relationship between amino acid side chains and protein conformation.
The defining feature of an amino acid is its side chain (at top, blue circle; below, all colored circles).
When connected together by a series of peptide bonds, amino acids form a polypeptide, another word
for protein. The polypeptide will then fold into a specific conformation depending on the interactions
(dashed lines) between its amino acid side chains.

8. Structure
Each protein has specific properties which are determined by the:
i ) Number and specific sequence of amino acids in a molecule .
ii) Shape which the molecule.
iii) Chain folds in to its final, compact form.
There are four levels organization which are described below:
1 ) Primary Structure:
The primary structure comprises the number and sequences of amino acids in a protein
molecule. They have linear polymer of amino acids. They held together with peptide bonds.
2 ) Secondary Structure:
The polypeptide chain in a protein molecule usually do not lie flat. They usually coil in to a
helix or in to some other regular configuration. a-helix, ß-sheet, held together with H-bonds
between backbone atoms. They have standard 3-D patterns.
For Example: a-helix ( A common secondary structure ).
3 ) Tertiary Structure:
Usually a polypeptide chain bends and folds upon itself forming a globular shape. This is the
proteins tertiary conformation. They have detailed 3-D conformation. It is maintained by 3
types of bonds namely ionic, hydrogen and disulfide ( -S-S- ).
4 ) Quaternary Structure:
In many highly complex proteins, polypeptide tertiary chains are aggregated and held
together by hydrophobic interactions, hydrogen & ionic bond. The specific arrangement is
called Quaternary Structure.
For Example: Insulin and Haemoglobin.

9. Figure: A diagram of protein structures

10. Functions
Proteins do most of their work in the cell and perform various jobs. Here are some
important functions of protein in your body.
1. Growth and Maintenance:
Protein is required for the growth and maintenance of tissues. Your body’s protein
needs are dependent upon your health and activity level.
2. Causes Biochemical Reactions:
Enzymes are proteins that allow key chemical reactions to take place within your
body.
3. Acts as a Messenger:
Amino acid chains of various lengths form protein and peptides, which make up
several of your body’s hormones and transmit information between your cells, tissues
and organs.
4. Provides Structure:
A class of proteins known as fibrous proteins provide various parts of your body with
structure, strength and elasticity.
5. Maintains Proper pH:
Proteins act as a buffer system, helping your body maintain proper pH values of the blood
and other bodily fluids.
6. Balance Fluids:
Proteins in your blood maintain the fluid balance between your blood and the surrounding
tissues.
7. Bolsters Immune Health:
Proteins form antibodies to protect your body from foreign invaders, such as disease-
causing bacteria and viruses.
8. Transports and Stores Nutrients:
Some proteins transport nutrients throughout your entire body, while others store them.

11. 9. Provide Energy:
Protein can serve as a valuable energy source but only in situations of fasting, exhaustive
exercise or inadequate calorie intake.
10. Antibody:
Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the
body.
Sources
Protein is an important nutrient for your body.
Good sources of protein include meat, fish, chicken, eggs, dairy, beans, soy foods, nuts ,
almonds, oats, cottage cheese, yogert, milk, seeds etc.
Cereals and their products also provide some proteins, which are of lower quality then
animals proteins. Vegetables and fruits are generally poor in protein content.
Foods Proteins Foods Proteins Foods Proteins
Almond 17.0 Chick Pea 12.4 Milk 4.1
Beef 16.6 Eggs Raw 11.8 Pistachio 21.5
Bread 8.3 Fish 21.2 Potato 1.8
Butter 0.9 Goat Meat 18.1 Rice 6.7
Carrots 0.9 Guava 1.0 Wheat 10.9
Chapatti 8.8 Mango 0.8 Tomato 1.3
Chicken Meat 20.1 Peanut 24.6 Sugar 0
Table : Proteins content of some foods. ( g/100g )

12. Proteins as Nutrient in Human Body
Proteins are needed in the body for building and maintenance of tissues and incase of
shortage of fats and carbohydrates to supply energy. One gram mole of protein yields 17kj (
4kcal ) of energy when oxidized in the body. Some proteins such are enzymes hormones and
antibodies have special rules in living organisms. Enzymes are biological catalyst without
which the control and execution of most body functions would be impossible. Similarly
hormones are essential to regulate the functions of different organs in the body. Antibodies
are also protein in nature and help fight against infections.
Children needs more protein on a body weight basis then adults because they are growing
and building body tissues.
Group Age g/kg in body weight
Infants 0 – 6 months 2.2
6 – 12 months 2.0
Children 1 – 3 years 1.8
4 - 6 years 1.5
7 – 10 years 1.2
Adolescents 11 – 18 years 0.9
Adults 19 + years 0.8
Table: Recommended daily intake of proteins.

13. Advantages & Disadvantages
Protein is a macronutrient necessary for the proper growth and function of the
human body. Our bodies need proteins and amino acids to produce important
molecules in our body like enzymes, hormones, neurotransmitters, and
antibodies – without an adequate protein intake, our bodies can’t function well
at all.
The recommended daily intake of protein is between 46-56 grams for most
adults, with pregnant and lactating women needing up to 72 grams of protein
per day. Athletes or other people looking to build muscle mass may also want
to consume more protein.
1. During digestion, the body breaks down the protein we eat into individual amino
acids, which contribute to the plasma pool of amino acids. This pool is a storage
reserve of amino acids that circulate in the blood.
2. Protein helps replace worn out cells, transports various substances throughout the
body.
3. Protein can also increase levels of the hormone glucagon, and glucagon can help
to control body fat.
4. Proteins also help to liberate free fatty acids from adipose tissue.
Too much protein can be damaging to your body. Eating a little extra protein every
now and then will not likely produce any symptoms.
1. When you intake high constantly proteins can hurt your kidneys and make it
harder for your body to obtain other important nutrients.
2. If you overeat protein, this extra protein can be converted into sugar or fat in the
body.
3. Keep in mind that eating too little protein can be just as dangerous as eating too
much protein. Your body needs protein -- if it cannot get protein from your diet, it will
take it from your muscle stores. As a result, insufficient protein intake can cause your
muscles to week.