Download 02_Classification and functions of simple and complex proteins

Biochemistry of Proteins: function
and classification
What are proteins?
• Proteins are necklaces of amino acids – long chains molecules.
• Proteins are the basis of how biology get this done. As
enzymes, they are the driving force behind all the biochemical
reactions which make biology work.
• As structural elements, they are main constituents of our
bones, muscles, hair, skin, and blood vessels.
• As antibodies, they recognize invading elements and allow the
immune system to get rid of the unwanted invaders.
• For these reasons, scientists have sequenced the human
genome – the blueprint for all of the proteins in biology.
General Characteristics of Proteins
• They are the most complex and most diverse in chemical
composition, conferring upon the different tissues.
• Protein molecule contains elements of C, H, O,N, S, and P
together with traces of Fe, Cu, I, Mn, and Zn.
• It has a molecular weight of 5,000 to 3,000,000
• They are the most important of the biologic substances
being the fundamental constituent of cell cytoplasm.
• They supply not only heat and energy but also material for
building and repair.
• Unlike carbohydrates and lipids, only small amounts of
protein is temporarily stored in the body, and which can be
quickly used up upon demand.
Classification of Proteins
Based on Axial Ratio:
Axial ratio is the ratio of the length to the breath.
• Globular proteins – with axial ratio less than 10 but
not below 3 or 4. They are compactly folded and
coiled.
Ex. Insulin, plasma albumin, globulin,
enzymes
• Fibrous proteins – with axial ratio greater than 10.
They are spiral and helical and are cross linked by
disulfide and hydrogen bonds.
Ex. Keratin, myosin, elastin, collagen
Globular and fibrous proteins
• On the basis of structural shape, proteins can be classified into
two major types: fibrous proteins and globular proteins.
• А fibrous protein is а protein that has а long, thin, fibrous
shape. Such proteins are made up of long rod-shaped or stringlike molecules that can intertwine with one another and form
strong fibers. They are water-insoluble and generally have
structural functions within the human body.
• А globular protein is а protein whose overall shape is roughly
spherical or globular. Globular proteins either dissolve in water
or form stable suspensions in water, which allows them to
travel through the blood and other body fluids to sites where
their activity is needed.
Simple and Conjugated Proteins
• Proteins are classified as either simple
proteins and conjugated proteins.
• А simple protein is made up entirely of
amino acid residues.
• А complex protein has other chemical
components in addition to amino acids.
These additional components, which may
be organic or inorganic, are called
prosthetic groups.
Globular Proteins
• Globular proteins have
their axial ratio less
than 10 but not below
3 or 4. They are
compactly folded and
coiled.
• Examples are insulin,
plasma albumin,
globulin, enzymes
Hemoglobin
Fibrous Proteins
• Fibrous proteins are
spiral and helical
and are cross linked
by disulfide and
hydrogen bonds
• Examples are
keratin, myosin,
elastin, collagen
The connective tissue protein
Collagen
Biologically Important Proteins
Protein
No. of
AA
Function
Insulin
51
Enzyme for sugar
metabolism
Cytochrome C
104
Enzyme for cell respiration
Growth hormone
191
Used as anti-aging treatment
Hemoglobin
574
Oxygen transport in blood
Hexokinase
730
Enzyme for glycolysis
Gamma globulin
1320
Myosin
6100
Part of immune system in
blood
Muscle action
Blood Proteins
Albumins
Immunoglobulins
Create osmotic pressure and
transport other molecules
Participate in immune system
Fibrinogens
Blood coagulation
Alpha-1-Antitrypsin Neutralize trypsin that has
leaked from the digestive
system
Regulatory proteins Regulation of gene
expression
Glycoproteins
Glycoproteins are proteins that contain
carbohydrate. Proteins destined for an
extracellular location are characteristically
glycoproteins. For example, fibronectin and
proteoglycans are important components of
the extracellular matrix that surrounds the
cells of most tissues in animals.
Immunoglobulin G molecules are the principal
antibody species found circulating free in
the blood plasma. Many membrane proteins
are glycosylated on their extracellular
segments.
Lipoproteins
Blood plasma lipoproteins are prominent
examples of the class of proteins conjugated
with lipid.
The plasma lipoproteins function primarily
in the transport of lipids to sites of active
membrane synthesis.
Serum levels of low density lipoproteins
(LDLs) are often used as a clinical index of
susceptibility to vascular disease.
Nucleoproteins
Nucleoprotein conjugates have many roles
in the storage and transmission of genetic
information.
Ribosomes are the sites of protein
synthesis. Virus particles and even
chromosomes are protein-nucleic acid
complexes.
Phosphoproteins
• These proteins have phosphate groups
esterified to the hydroxyls of serine,
threonine, or tyrosine residues.
• Casein, the major protein of milk, contains many
phosphates and serves to bring essential
phosphorus to the growing infant.
• Many key steps in metabolism are regulated
between states of activity or inactivity,
depending on the presence or absence of
phosphate groups on proteins.
• Glycogen phosphorylase a is one well-studied
example.
Metalloproteins
• Metalloproteins are either metal
storage forms, as in the case of
ferritin, or enzymes in which the metal
atom participates in a catalytically
important manner.
Hemoproteins
• These proteins are actually a subclass
of metalloproteins because their
prosthetic group is heme, the name
given to iron protoporphyrin IX.
• Because heme-containing proteins enjoy
so many prominent biological functions,
they are considered a class by
themselves.
Flavoproteins
Flavin is an essential substance for the
activity of a number of important
oxidoreductases.