Protiens and structure of protein
Proteins
Proteins are the most abundant organic
+ H compounds of the cell. They play most important role in cellular functions. They contain elements carbon, hydrogen, oxygen and nitrogen. Some R-group proteins also contain sulphur. Proteinsmacromolecules (polymers) formed of units Structure of Amino Acid(monomers) called amino acids. A large number of amino acids are known. Of these, only twenty different types of amino acids combine in different number and different sequence forming hundreds and thousands of different different types of protein molecules.
Structure of Amino Acids
Amino acids are carboxylic acids having amino groups. Each amino acid has a centralcarbon atom called alpha carbon. There are four different groups attached to the alphacarbon. These are amino group, carboxyl group, hydrogen of alpha carbon and Rgroup. The former three groups attached to the alpha carbon are constant members and Rare(variant)COO are present in all amino acids while the fourth one i.e. R-group is variable. It is eitherhydrogen or alkyl group. Due to this variable the amino acids are different from one another Nonpolar, aliphatic It groups
Aromatie Roupe
coo соо
Coo
сою
HN-C-H HN-C-R HN-CH
HN-C-H H.N-C- HN-C-H
н
CH, CH
CH,
CH
CH,
CH, CH
©CH
Glycine
NH
Сою
Alanine
Valine
OH
COO
Сою
HN-E-
HN-C-H
CH,
CH
CH, CH
COO
H.N-C-H
H-CCH..
CH,
CH,
$
CH,
Methionine
Leucine
Isoleucine
CHA
Phenylalanine
Tyrosine
Tryptophan
funcional
Positively charged R sroups
quod
COO
COO
сою
HN-C-H HN-C- HN-C-
сн.
сн.
CH,
CH,
CH
CH
CH
CH
CH,
1 -
NA
NH
CNH
NH
Lysine Arginine Histidine
соо
Polar, uneharged R groups
000
000
H.N-C-H HN-C-11 H.N-C-H
CH,OH H-C-OH CH,
SH
Sering
Threonine
Cysteine
000
Negatively charged Rgroups
C00
соо
LH
COO
COO
HN-C-H HN-C-H
H.N CH
HN-C-H H.N-C-H
CH
не
CH,
CH2
CH
HN
coo
CH
HN
Proline
Asparagine
Glutamine
coo
Aspartate Glutamate
Ala Alanine
Leu L Leucine
Arg R arginine
Lys K likesine (lysine)
Asn N asparagile
Met M Methionine
Asp D asparDic acid (asparitc) Phe F Fenylalanine (phenylalanine)
Cys C cystein
Pro P Proline
Glu E glutamic acid (giutamic) Ser S Serine
Gln Q Quetamine (glutamine)
Thr T Threonine
Gly G Glycine
Tip W Wyptophan (tryptophan)
His H Histidine
Tyr Y Tyrosine
Val V Valine
Tle 1 Isoleucine
tynesH
H
H
+
OH
R
H
OM
R
Reaction
A bond called peptide bond
links amino acids in a protein molecule
Peptide Bond to each other. The peptide bond is formed between an amino group of
one amino acid and carboxyl group of
another amino acid.
This is dehydration or condensation reaction
Dehydration in which one water molecule is
HO formed.A chain containing three amino
acids and two peptide bonds is known
as dipeptide chain. A chain with four
amino acids and three peptide bonds is
Peptide group called tripeptide and a chain with many amino acids and many peptide Peptide bond between two amino
bonds is called polypeptide. Most protein molecules are usually formed of two or
many polypeptide chains e.g. Haemoglobin and Insulin.Heme molecule with iron atom
[ chains
H
H
O
N
H
Amino
terminus
R.
Н
R
OH
Carboxy
terminus
chains
Hem molecule
with iron atom
Structure of Haemoglobin
Haemoglobin is an oxygen carrying protein in the red blood cells which
consists of four polypeptide chains while an insulin molecule is consists of two
polypeptide chains. The number and sequence of amino acids in a protein
molecule is highly specific for its normal function.
Hu
H
Amino
terminus
OH
R
H
R
Carboxy terminus I chains Hem molecule
with iron atom
Structure of Haemoglobin
Haemoglobin is an oxygen carrying protein in the red blood cells which
consists of four polypeptide chains while an insulin molecule is consists of two
polypeptide chains. The number and sequence of amino acids in a protein
molecule is highly specific for its normal function.Bat uitee structure
Solublº N 10 egg white place
globular proteins are hemoglobin, albumen of egg white, enzymes, antibodies and
the proteins of cell membranes. quanted
glubolin structure fail to perform its function. For example if one out of 574 amino acids in a If an amino acid is not occupying its specific position in a protein molecule it will haemoglobin molecule is not present in its specific position then haemoglobin changes its normal globular shape and becomes, sickle-shaped. As a result the molecule glutamic acid is replaced by valine. Such type of haemoglobin cannot
disc-shaped red blood cells also become sickle-shaped. In sickle cell haemoglobin
perform its function and the person with sickle cell haemoglobin dies. The size of
protein molecule depends upon the number and kinds of total amino acids presen
For your information Sickle cell anemia is a blood disorder that affects
hemoglobin.Sickle cell anemia occurs when a person inherits two abnormal genes (one from each parent) that cause their RBCs to change shape. Instead of being flexible and disc-shaped, these cells are more stiff and curved in the shape of the old farm tool known as a sickle that's where the disease gets its name. The shape is similar to a crescent moon. Red blood cells
Normal red with normal hemoglobin (hemoglobin A, or HbA) move blood cell
Sickle Cell easily through the bloodstream, delivering oxygen to all of the cells of the body. Normal RBCs are shaped like discs or doughnuts with the centers partially "scooped out" and are soft and flexible. They can easily "squeeze" through even very
small blood vessel.
Shape of Proteins
As regards the shape, proteins are classified into two types; fibrous
proteins and globular proteins
a. Fibrous proteins
The molecules of fibrous proteins are composed of one or more
polypeptide chains, which are linearly arranged in the form of fibers. They are
water insoluble. Some of these may form sheet-like structures. Examples of
fibrous proteins are keratin found in hairs, nails, fur, outer skin, myosin present in
muscle cells, collagen whickis
is the most abundant protein in higher vertebrates
found in skin, ligaments, tendons, bones and in the cornea of the eyes.
Globular proteins
as the name indicates are globulor or spherical in shape due to folding of polypeptide de chains. They are usually water-soluble. Examples of
b. Globular Proteins Levels of Structure (organization)
There are four levels of organization of protein molecules. This is because
each type of polypeptide chain bends, folds and twists in particular way within a
protein molecule. This gives protein molecule a characteristic structure that
classifies protein into four different types. The primary structure is the sequence
of the amino acids joined together by peptide bonds. Sanger in 1951 was the first
person who determined the sequence of amino acids in insulin molecule.
A polypeptide chain having a linear sequence of amino acids is called
primary structure. When a polypeptide chain of amino acids become spirally
coiled, the structure is called a secondary structure of protein. When the
secondary structure of protein is arranged into a three dimensional structure, it is
called a tertiary structure. When two or more polypeptide chains are arranged into
a large sized molecule, it is called a quaternary structure e.g. haemoglobin.
Functions of Proteins
Proteins perform the most important functions in the life of living organisms.
Proteins are the structural and building materials of cellular membranes called
lipo-protein membranes. All enzymes are proteins. They speed up biochemical
reactions inside the body of living organisms. The digestive enzymes are
important for the process of digestion. Without their presence food cannot be
digested. Some hormones such as insulin are proteins which regulate biochemical
processes. Myosin and actin fibers play an important role in the contraction of
muscles and movements. Haemoglobin is oxygen-carrying protein of red blood
cells. In animals' proteins form most structures such as skin, nails, hairs, claws,
hooves etc. In plants proteins are stored in most seeds for the future need of the
embryos e.g. bean, pulses, pea etc.
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