proteins Flashcards
peptide bone
The –COOH group of one amino acid can be
joined to
O the –NH2 group of another by a covalent
bond called as peptide bond.
O In the process of formation of a peptide
bond a molecule of water is eliminated
dipeptide and tripeptide
When two amino acids are joined together
by one peptide bond, such a structure is
called as dipeptide.
third amino acid can form a second peptide
bond through its free –COOH end and is
called tripeptide
toxic peptides
O Some peptides act as toxin.
O Alpha amanitin is a bicyclic octapeptide
present in many mushrooms and is extremly
toxic to human being.
O They immadietly cause pain in GIT, Nausea,
vomiting, diarrheoa.
O Death may occur within a week due to
impairment of liver and kidney functions.
cyclic petides
O Cyclic peptides differ from normal peptide due
to their ring structure.
O Gramicidin S is a cyclodecapeptide,constructed
as two identical pentapeptides joined head to
tail, formally written as cyclo(-Val-Orn-Leu-D-
Phe-Pro-)2
. That is to say, it forms a ring
structure composed of five different amino
acids, each one used twice within the
structure.
important peptides
Glutathione: This is a tripeptide consisting of
glutamic acid, cysteine and glycine. By virtue
of easy dehydrogenation it gets converted to
disulphide form and function in oxidation-
reduction systems.
O Bradykinin: Bradykinin (9 amino acids) or
Kallidin I and Kallidin II (10 amino acids)
have relaxant effects on smooth muscle.
Antibiotics: Penicillin, gramicidin, polymyxins,
bacitracins, actinomycin, chloramphenicol
are all peptides which act as antibiotics.
O Gastrin, Secretin and Pancreozymin: Are
gastrointestinal peptides which act as
hormones which stimulate secretion of bile
and other enzymes of digestive juices.
Angiotensins: The enzyme Renin is released
from kidneys and acts on globulin fraction of
plasma to release a peptide Angiotensin I (10
amino acids) which has only a slight effect on
blood pressure, Angiotensin I is then converted
to Angiotensin II by splitting off two amino acids
which has eight amino acid, has greater effect
on BP.
Removal of one residue aspartic acid from
Angiotensin II results in formation of Angiotensin
III (7 amino acids) which plays role in pathology
of hypertension.
proteins
Proteins are most complex biological
molecule composed of a large number of
amino acids residue arranged in one or
more polypepetide chain.
classification based on shape
- fibrous proteins
- Globular proteins
fiborous protein
When the polypeptide chains are extended
along one axis, it is called a fibrous protein.
Examples: α-keratin and b- keratin from
hair, collagen and elastin from bones.
globular proteins
Polypeptide chains of these proteins are
folded into compact globular (Spherical
shape).
O For example: Myoglobin, haemoglobin,
ribonuclease, chymotrypsin.
classification on basis of functional properites
The second way of classifying proteins
makes use of their functional properties.
defense proteins
- Defence proteins: Immunoglobulins
involved in defence mechanism. Other
example gamma globulin.
contractile proteins
- Contractile proteins: Proteins of skeletal
muscle involved in muscle contraction and
relaxation.
Example: Actin and myosin
repiratory protein
- Respiratory proteins: Involved in the
function of respiration, like haemoglobin,
myoglobin, cytochromes.
structural proteins
- Structural proteins: Involved to the
structure of tissue like Proteins of skin,
cartilage, nail.
regulatory proteins
- Regulatory Proteins:
Act as hormones like insulin , growth hormone
