This document discusses proteins and amino acids. It defines proteins as large biomolecules composed of chains of amino acids that are essential to life processes. The 20 standard amino acids are the building blocks of proteins. They contain an amino group, a carboxyl group, a hydrogen atom, and a variable side chain that determines each amino acid's properties. Proteins have primary, secondary, tertiary, and quaternary structures that give them their final 3D shapes and functions in the body.

1. Dr. Ifat Ara Begum
Assistant Professor
Dept of Biochemistry
Dhaka Medical College

3.  Large molecules
 Made up of chains of amino acids
 Are found in every cell in the body
 Are involved in most of the body’s
functions and life processes
 The sequence of amino acids is
determined by DNA

4. Greek word, “PROTEIOS” , means,
“Holding the first place”. Swedish chemist
Berzelius suggested the name.
 Most abundant molecule of living system
& constitute about 50% of cellular dry
weight.

5. First protein to be sequenced: Insulin.
Frederick Sanger won noble prize for
this achievement in 1958

6. Figure
6.1

7. Amino group containing carboxylic acid.

8. Amino acid has a central carbon atom to which
4 diff groups of atoms are attached:
 An Amino group (NH2)
 A Carboxylic acid group (COOH)
 A Hydrogen atom (H)
 A Radical or R group: H, CH3, CH3-CH2 etc
which determines its properties and functions in
protein.

9.  The acidic and basic properties of NH2 &
COOH groups make the AA molecule
“Amphoteric”.
 Primary amino acid
 L- α type, i.e. the amino group is usually
attached with the α carbon and placed on
left side with respect to spatial
configuration.

11.  All AAs (except glycine) show optical
isomerism & optical activity as they have
at least 1 asymmetric carbon.

12. Nomenclature: By the first three
letters of their name. e.g. Serine (ser)
Exception:
Tryptophan (Trp), Isoleucine (Ile)
Asparagine (Asn) & Glutamine (Gln)

13.  Based on structure of side chain (R) &
their reaction in solution:
Acidic/ Mono amino di carboxylic Acid:
Asp, Glu.
Basic/ Di amino mono carboxylic Acid:
Lys, Arg, His.
Neutral/ Mono amino mono carboxylic
Acid: Rest 15 AAs. e.g. Ala, Tyr, Trp, Cys, Met,
etc.

14.  Based on polarity of side chain (R) :
 Polar Amino Acid: Have hydrophilic side
chain with/without charge. e.g. Acidic AA
(negative charge), Basic AA (positive
charge), Other AAs like Gly, Ser, Thr, Tyr,
Cys, Gln, Asn are of without charge.
 Non-polar Amino Acid: Have hydrophobic
side chain with no charge. e.g. Rest 8 AAs.

15.  Nutritional classification of Amino Acid:
 Essential/Indispensable AA: 8 in number.
e.g. Phe, Val, Trp, Thr, Ile, Met, Leu, Lys.
Semi essential AA: 2 in number. e.g. Arg, His.
Needed for children.
Non-essential/ Dispensable AA: Rest 10 AAs.
e.g. Asp, Glu, Cys, Ser, Gly, Ala, Asn, Gln, Tyr,
Pro.

17. Within the body, Tyrosine and Cystine
are synthesized from the EAA-Phenylalanine
& Methionine
respectively. So, Tyr & Cys may
become EAA if the dietary supply of
Phe & Met is reduced or absent.

18.  Metabolic Classification of Amino Acid
(Based on their catabolic fate):
Glucogenic/Glycogenic AA: AA having C
skeleton possessing metabolic potential to
produce glucose. e.g. Gly, Ala, Glu, Gln, Val
etc.
Ketogenic AA: AA having ……ketone
bodies. e.g. Leu, Lys.
Both glucogenic & ketogenic AA: Phe,
Tyr, Trp, Ile.

20.  Physical : Colorless, Crystalline, water soluble,
high melting point (>200 degree C),
stereoisomerism (D-L isomers, optical isomers)
& optical activity.
 Chemical :
 Act as ampholytes (COOH group acts as acidic
group by donating proton and NH2 group acts
as basic group by accepting proton).

21.  Acts as buffer and have definite iso-electric
PHH (( PH at which molecules carry
no net charge).
 Forms salts with acid or base by reacting
with NH2 or COOH group respectively.
 Forms esters with alcohol.
 Forms carbamino compounds with CO2.

22.  Gives color reaction with ninhydrine.
 Undergo acetylation & amidation
reaction due to NH2 group.

23.  1. Act as building block of peptides,
polypeptides & proteins.
[Arbitrarily peptide, polypeptide & protein
are made of 2-10 AAs, 10-100 AAs &
>100 AAs respectively.]

24.  2. Supports gluconeogenesis in fasting &
starvation.
 3. Participates in synthesis of specialized
products. e.g. neurotransmitters,
hormones, purine, pyrimidine, heme, etc.
 4. Source of S (Cys/Met) /Methyl group
(Met) in body.

25. Definition:
Macromolecular polymer of Amino Acids
linked together by peptide bond.
Minimum molecular weight: 5000-8000
Number of amino acid: >100
Elementary Composition of protein:
C, O, N, H, S in different percentages.

26. Covalent bond formed by joining the –
COOH group of one amino acid and
the –NH2 group of another amino
acid with removal of one molecule of
water.

28. Covalent bond, i.e. sharing of electron
pair.
Shows partial double bond character
Rigid, planer & do not rotate.
Not broken by denaturing agent
Broken by proteolytic enzymes.

29. Types of protein Function Example
Structural Protein Support framework of
cell
Collagen, Elastin, etc
Catalytic Protein Catalysis Enzymes
Transport Protein Transport of
substances
Albumin, Transferrin
Hormonal Protein Regulation of
functions
Insulin, Glucagon
Gene regulatory
Protein
Regulate genetic
functions
Histone, Protamine
Protective Protein Prevent infection Immunoglobulin
Receptor Protein Receptor function LDL receptor
Contractile Protein Muscle contraction Actin, Myosin

30. 1. Simple Protein: Contains only AAs without any
non-protein substances.
Fibrous protein/scleroprotein: Fibre like, animal
origin, possess high tensile strength, water insoluble
& highly resistant to proteolytic enzymes. Chief
component of tendon, ligaments, cartilage, hair,
nail, etc. Example: Collagen, Elastin, keratin, etc.
Globular protein: oval/spherical in shape, water
soluble, digestible. Example: Albumin, Globulin,
Histone, etc.

31. 2. Conjugated Protein: Composed of simple
protein along with non-protein prosthetic substances.
Example:
 Nucleoprotein: Nucleohistones (Nucleic acid)
 Lipoprotein: VLDL, HDL, etc (Lipid)
Glycoprotein: Mucin (Carbohydrates)
 Chromatoprotein: Hemoglobin, cytochrome (Heme)
Metalloprotein: Ceruloplasmin (Cu), Carbonic
anhydrase (Zn) etc.

32. 3. Derived Protein: Denatured/degraded
products of simple/conjugated proteins.
Protein → Protean → Metaprotein → Proteose
→Peptone → Peptides → Amino Acids.
[Protean, Metaprotein → Primary derived
protein as no/little change in peptide bond,
Rest are secondary derived proteins
produced by progressive hydrolytic cleavage of
peptide bonds. ]

33. Complete Proteins: Contains all EAAs
in proportion required for body. Example:
Egg albumin, Meat etc.
Incomplete Proteins: Lacks 1/more
EAAs. Example: Gelatin.
Partially incomplete Proteins:
Partially lacks 1/more EAAs.

34. Proteins are abundant in
◦Dairy foods
◦ Meats
◦Poultry
◦ Meat alternatives such as dried
beans, peanut butter, nuts, and soy

35.  A well-balanced diet can meet daily
protein needs
 Most people consume adequate protein
from their diet and do not need protein
supplements

36.  Isoelectric point of protein
 Colloidal properties
 Protein denaturation
 Protein precipitation
 Protein sedimentation
 Protein hydrolysis
 Color reaction
 UV light absorption

37. Isoelectric point, pI, is the pH
of an aqueous solution of an
amino acid (or protein) at which
the molecules on average have
no net charge. 。

39. Any alteration in the
structure or sequencing
changes the shape and
function of the protein

40. Primary structure: Exact sequence
of AAs held together by peptide
bonds in peptide chain. It is
determined genetically and this in
turns determines secondary, tertiary
& quaternary structures. Example:
Insulin.

42. Secondary structure: Helical or
pleated sheet like conformation
produced by a definite, periodic
folding, twisting or coiling of primary
structure. Hydrogen bond is present
here Example: fibrous protein
(collagen, elastin, keratin) .

43. α helix: Most common and stable
conformation for a PP chain
Spiral structure
Right handed
Stabilized by H-bond
Distance between AAs are 1.5 degree
A

44. (1) a-Helix

45. β pleated sheet: PP chains are
almost fully extended.
Distance between AAs are 3.5
degree A
Stabilized by H-bond
Major structural motif of protein.

47. Adjacent strands in a sheet can run in
the same direction with regard to the
amino and carboxyl ends of PP chain
or in opposite direction.

50.  Tertiary Protein: Three dimensional
globular form of protein produced by further
folding and twisting of secondary structure
about itself with the hydrophobic side chains
buried interiorly and hydrophilic groups
exposed outside. It is stabilized by hydrogen
bond, disulfide bond, ionic interaction and
hydrophobic interactions. Example:
albumin, globulin, antibody etc.

53. Quaternary Protein: consists of
2/more PP subunits/monomer.
Example: Hb.

55. 1. Hydrogen bond
2. Electrostatic interaction
3. Hydrophobic interaction
4. van der waals force
5. Disulfide bond

56. A.三级结构中的作用力
1. Disulfide bond 2. Electrostatic interaction
3. Hydrogen bond 4. Hydrophobic interaction

57. The unfolding and disorganization of
protein’s secondary, tertiary & quaternary
structures, which are accompanied by
hydrolysis of sulfide and hydrogen bond
but not accompanied by hydrolysis of
peptide bond.

58. Denaturing agents: Heat, Organic
solvents, Mechanical mixing, Strong
acid/base, Detergents, Ions of heavy
metals, e.g. lead, mercury etc.

59. Figure
6.5

60.  Formation of cytoskeleton (Flexible structural
framework for cell/tissues)
 Provides mechanical support (by structural
protein), defense against infection (by
antibody)
 Acts as vehicle for transport of diff molecules
 Provide COP
 Have function as receptors and maintains the
homeostasis of the body.

61.  Muscle contraction
 Source of energy
 Helps in coagulation
 Acts as buffer
 Promote catalytic function & hormonal
function
Genetic information-storage, expression &
transmission etc.

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