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Amino Acids and Proteins
Part: 1
Dr. Ifat Ara Begum
Associate Professor
Department of Biochemistry
Dhaka Medical College, Dhaka
8/17/2021 1
Dr Ifat, Dept of Biochemistry, DMC
Learning Objectives
 Mention some introductory facts about protein
 Define amino acid
 Describe the structure of an amino acid
 Understand the properties of amino acid
 List the functions of amino acid
 Define protein
 Define peptide bond
8/17/2021 2
Dr Ifat, Dept of Biochemistry, DMC
Introduction to Protein
 Large biomolecules
 Macromolecules that are made up of
one or more chain (s) of amino acids
 The sequence of amino acids is
determined by DNA
 Are found in every cell in the body
 Are involved in most of the body’s
functions and life processes
A representation of the 3-D
structure of the protein myoglobin
8/17/2021 3
Dr Ifat, Dept of Biochemistry, DMC
Biomolecule, also called biological molecule, any of numerous
substances that are produced by cells and living organisms.
The four major types of biomolecules
are carbohydrates, lipids, nucleic acids, and proteins
8/17/2021 4
Dr Ifat, Dept of Biochemistry, DMC
• Greek word, “PROTEIOS” , means “Primary” or
“Holding the first place”.
• Swedish chemist Berzelius suggested the name.
• The first protein to be sequenced was Insulin by
Frederick Sanger in 1949
He won the noble prize for this achievement in 1958
8/17/2021 5
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 6
Dr Ifat, Dept of Biochemistry, DMC
Definition & Structure of Amino Acid
 Amino group containing carboxylic acid
 Each amino acid has a central carbon atom
(Asymmetric α carbon)
to which four (04) diff groups or atoms are
attached:
 A basic amino ( -NH2 ) group
 An acidic carboxyl ( -COOH) group
 A hydrogen (H) atom
 A “R” group or side chain that is unique to each
amino acid
8/17/2021 7
Dr Ifat, Dept of Biochemistry, DMC
Amino (NH2 )
group
- Basic
- Has a pKa between 9 and 10
-At body pH (7.4), it exist as protonated form (NH3
+) by accepting proton
- It is metabolized to proton (H+)
Carboxyl
(COOH) group
- Acidic
- Has a pKa that is usually close to 2
-At body pH (7.4), it exist as deprotonated form (COO-) by donating proton
- It is metabolized to HCO3
- ion
Hydrogen (H)
atom
-
R group or side
chain
-Amino acids differ from each other with respect to this side chain
- Its nature determines the properties and functions in protein.
- Example: H, CH3, CH3-CH2 etc
- It may be polar / non polar, acidic / basic
8/17/2021 8
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 9
Dr Ifat, Dept of Biochemistry, DMC
The pKa of a group is the pH value at which the concentration of the
protonated group equals that of the unprotonated group.
In total, there are 20 amino acids in human body from where all body
proteins are constructed. So they are called “Primary Amino Acid” or
“Standard Amino Acid”
8/17/2021 10
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 11
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 12
Dr Ifat, Dept of Biochemistry, DMC
Remember:
The acidic properties of COOH group
&
the basic properties NH2 group
make the amino acid molecule “Amphoteric”
The carboxyl group is able to
donate proton
and
the amino group is able to accept
proton
8/17/2021 13
Dr Ifat, Dept of Biochemistry, DMC
 A carbon atom that is attached to four
different types of atoms or groups of atoms.
 Amino acids have the chiral carbon atom
adjacent to the carboxyl group (COO-).
Exception: Glycine
Asymmetric Carbon / Chiral carbon
Glycine: The smallest amino acid, which has
symmetric α carbon atom. Here, R is replaced by
another H atom
8/17/2021 14
Dr Ifat, Dept of Biochemistry, DMC
 As all body amino acids (except
glycine) have asymmetric α
carbon,
they can produce optical stereo
isomers (space isomer) with
optical activity
8/17/2021 15
Dr Ifat, Dept of Biochemistry, DMC
α Carbon: Carbon atom next to
carboxyl group
 Mirror image pairs of amino acids
are designated as L (levo) & D
(dextro)
L- α amino acids: Amino group is attached directly with the
α carbon and placed on left side with respect to spatial
configuration
 Body proteins are assembled from
L- α amino acids
8/17/2021 16
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 17
Dr Ifat, Dept of Biochemistry, DMC
 Conventionally, by the first three
letters of their name.
e.g. Alanine (Ala)
Nomenclature of Amino Acids
Exception:
Glutamine (Gln)
Asparagine (Asn)
Isoleucine (Ile)
Tryptophan (Trp)
Remember: “GAIT”
8/17/2021 18
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 19
Dr Ifat, Dept of Biochemistry, DMC
A) Based on structure of side chain (R) & their reaction in
solution
Three types of Amino Acids
Acidic AA Basic AA Neutral AA
Aliphatic AA Aromatic AA Imino AA
8/17/2021 20
Dr Ifat, Dept of Biochemistry, DMC
Types Synonym No. of
Amino group
No. of
carboxyl group
Charge at
normal body
pH
Example
Acidic
amino Acid
Mono amino
di - carboxylic
acid
01 02 Negatively
charged
Aspartic acid (Asp)
Glutamic acid (Glu)
Basic amino
Acid
Di - amino
mono
carboxylic acid
02 01 Positively
charged
Histidine (His),
Arginine (Arg),
Lysine (Lys)
Neutral
amino Acid
Mono amino
mono
carboxylic acid
01 01 No net charge Rest 15 amino acids
grouped under three
types again
(e.g. Ala, Tyr, Trp,
Cys, Met etc)
8/17/2021 21
Dr Ifat, Dept of Biochemistry, DMC
Neutral
amino acid
Aliphatic amino acid Aromatic amino acid Imino acid
Sulphur containing: Cysteine,
Methionine Example:
Phenyl alanine,
Tyrosine
Tryptophan
- It contains Imino group
(-NH) ,
not amino group (NH2 )
- Example: Proline
Branched chain: Valine,
Leucine, Isoleucine
Hydroxyl group containing:
Serine, Threonine
Amide group containing:
Asparagine, Glutamine
Simple structure: Glycine,
Alanine
8/17/2021 22
Dr Ifat, Dept of Biochemistry, DMC
B) Based on polarity of side chain (R)
Two types of Amino Acids
Polar AA /
Hydrophilic AA
Non polar AA /
Hydrophobic AA
8/17/2021 23
Dr Ifat, Dept of Biochemistry, DMC
Polar / Hydrophilic AA:
 They have hydrophilic side
chain (R)
 Example:
- Acidic AA
- Basic AA
- Some of the neutral AA like
Gly, Ser, Thr, Tyr, Cys, Gln,
Asn
Total 12 in numbers
Non polar / Hydrophobic AA:
 They have hydrophobic side
chain (R)
 Example:
Rest of the neutral AA like
Met, Val, Leu, Ile, Ala, Trp,
Pro, Phe
Total 08 in numbers
8/17/2021 24
Dr Ifat, Dept of Biochemistry, DMC
C) Nutritional Classification of Amino Acids
Three types of Amino Acids
Essential AA /
Indispensable
AA
Semi
essential
AA
Non essential AA /
Dispensable AA
8/17/2021 25
Dr Ifat, Dept of Biochemistry, DMC
Points Essential AA /
Indispensable AA
Semi essential AA Non essential AA /
Dispensable AA
Definition Amino acids which are not
produced in body ,
therefore essentially be
supplied in diet
Amino acids which are produced in body
in a limited rate , therefore essentially be
supplied in diet when their requirement
in body is high (like during growth in
children, not essential for adult)
Amino acids which are
produced in body in
sufficient amount , so, not
essential in diet.
Source Mainly from animal
protein- meat, fish, egg,
milk etc
- -
Total no. 08 02 -
Example Met, Trp, Thr, Val, Phe,
Ile, Leu, Lys
(Remember, MTV PILL)
Arg, His Asp, Glu, Cys, Ser, Gly,
Ala, Asn, Gln, Tyr, Pro
8/17/2021 26
Dr Ifat, Dept of Biochemistry, DMC
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.
8/17/2021 27
Dr Ifat, Dept of Biochemistry, DMC
D) Metabolic Classification of Amino Acids
Three types of Amino Acids
Absolute
Glucogenic AA
/ Glycogenic
AA
Absolute
Ketogenic AA
Both Glucogenic
& Ketogenic AA
8/17/2021 28
Dr Ifat, Dept of Biochemistry, DMC
Points Absolute Glucogenic AA /
Glycogenic AA
Absolute Ketogenic AA Both Glucogenic &
Ketogenic AA
Definition Amino acids having carbon
skeleton that possess metabolic
potential to produce glucose
Amino acids having carbon
skeleton that possess metabolic
potential to produce ketone bodies
Amino acids having carbon
skeleton that possess
metabolic potential to
produce both glucose &
ketone bodies
What
happens
really?
They initially produce
precursors of glucose (e.g.
pyruvate or intermediates of
TCA cycle)
from which later on, glucose is
produced
They initially produce precursors
of ketone bodies (acetyl CoA or
aceto acetyl CoA)
from which later on, ketone body
is produced
They initially produce acetyl
CoA or aceto acetyl CoA
along with pyruvate or TCA
cycle intermediates
and then produce ketone
body or glucose
Example Gly, Ala, Glu, Gln, Val etc Leu, Lys Phe, Tyr, Trp, Ile
8/17/2021 29
Dr Ifat, Dept of Biochemistry, DMC
E) Combined Nutritional & Metabolic Classification
Metabolic Type Nutritional type
Essential Non essential
Absolute Glucogenic His, Met, Thr, Val, Arg Ala, Asp, Asn, Cys, Glu, Gln,
Gly, Pro, Ser
Both Glucogenic &
Ketogenic
Phe, Trp, Ile Tyr
Absolute Ketogenic Leu, Lys -
8/17/2021 30
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 31
Dr Ifat, Dept of Biochemistry, DMC
Physical Properties
 Colorless
 Crystalline
 Water soluble
 High melting point (>200
degree C)
 Stereoisomerism (D-L
isomers, optical isomers)
 Optical activity
Chemical Properties
 Act as ampholytes (i.e. behave both as acid &
base)
 Acts as buffer and have definite iso-electric pH
 Undergo decarboxylation to form corresponding
amines
 Purple colour reaction with ninhydrine
 Forms
 Salts with acid or base
 Esters with alcohol.
 Carbamino compounds with CO2
8/17/2021 32
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 33
Dr Ifat, Dept of Biochemistry, DMC
1. Act as building blocks of
- Peptides (2-10 AAs )
- Polypeptides (10 - 100 AAs )
&
- Proteins (>100 AAs )
2. Supports gluconeogenesis in fasting &
starvation.
3. Synthesis of specialized products. e.g.
neurotransmitters, hormones, purine,
pyrimidine, heme, etc.
4. Directly acts as neurotransmitter (Gly, Glu,
Asp)
5. Detoxification of toxic substances in liver by
Gly, Cys etc
6. Acts as metabolic fuel meeting up 10% of body energy need
8/17/2021 34
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 35
Dr Ifat, Dept of Biochemistry, DMC
Definition of protein
 Macromolecular polymer of amino acids
linked together by peptide bond.
 Minimum molecular weight: 5000-8000
 Number of amino acid: >100
 Elementary Composition: C, O, N, H, S in different
percentages
8/17/2021 36
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 37
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 38
Dr Ifat, Dept of Biochemistry, DMC
Definition
 It is a covalent bond
that connects adjacent amino acids
to form
peptide, polypeptide & protein
 It is formed by joining
the – COOH group of one amino
acid
&
the –NH2 group of another amino
acid
with
removal of one molecule of water
Formation
8/17/2021 39
Dr Ifat, Dept of Biochemistry, DMC
Characteristics of peptide bond
 Covalent bond, i.e. sharing of electron pair.
 Shows partial double bond character
 Rigid, planer & do not rotate.
 It is not broken by denaturing agents
but
is broken by proteolytic enzymes
8/17/2021 40
Dr Ifat, Dept of Biochemistry, DMC
8/17/2021 41
Dr Ifat, Dept of Biochemistry, DMC

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Chemistry of protein, part 1 (Aug'21)

  • 1. Amino Acids and Proteins Part: 1 Dr. Ifat Ara Begum Associate Professor Department of Biochemistry Dhaka Medical College, Dhaka 8/17/2021 1 Dr Ifat, Dept of Biochemistry, DMC
  • 2. Learning Objectives  Mention some introductory facts about protein  Define amino acid  Describe the structure of an amino acid  Understand the properties of amino acid  List the functions of amino acid  Define protein  Define peptide bond 8/17/2021 2 Dr Ifat, Dept of Biochemistry, DMC
  • 3. Introduction to Protein  Large biomolecules  Macromolecules that are made up of one or more chain (s) of amino acids  The sequence of amino acids is determined by DNA  Are found in every cell in the body  Are involved in most of the body’s functions and life processes A representation of the 3-D structure of the protein myoglobin 8/17/2021 3 Dr Ifat, Dept of Biochemistry, DMC
  • 4. Biomolecule, also called biological molecule, any of numerous substances that are produced by cells and living organisms. The four major types of biomolecules are carbohydrates, lipids, nucleic acids, and proteins 8/17/2021 4 Dr Ifat, Dept of Biochemistry, DMC
  • 5. • Greek word, “PROTEIOS” , means “Primary” or “Holding the first place”. • Swedish chemist Berzelius suggested the name. • The first protein to be sequenced was Insulin by Frederick Sanger in 1949 He won the noble prize for this achievement in 1958 8/17/2021 5 Dr Ifat, Dept of Biochemistry, DMC
  • 6. 8/17/2021 6 Dr Ifat, Dept of Biochemistry, DMC
  • 7. Definition & Structure of Amino Acid  Amino group containing carboxylic acid  Each amino acid has a central carbon atom (Asymmetric α carbon) to which four (04) diff groups or atoms are attached:  A basic amino ( -NH2 ) group  An acidic carboxyl ( -COOH) group  A hydrogen (H) atom  A “R” group or side chain that is unique to each amino acid 8/17/2021 7 Dr Ifat, Dept of Biochemistry, DMC
  • 8. Amino (NH2 ) group - Basic - Has a pKa between 9 and 10 -At body pH (7.4), it exist as protonated form (NH3 +) by accepting proton - It is metabolized to proton (H+) Carboxyl (COOH) group - Acidic - Has a pKa that is usually close to 2 -At body pH (7.4), it exist as deprotonated form (COO-) by donating proton - It is metabolized to HCO3 - ion Hydrogen (H) atom - R group or side chain -Amino acids differ from each other with respect to this side chain - Its nature determines the properties and functions in protein. - Example: H, CH3, CH3-CH2 etc - It may be polar / non polar, acidic / basic 8/17/2021 8 Dr Ifat, Dept of Biochemistry, DMC
  • 9. 8/17/2021 9 Dr Ifat, Dept of Biochemistry, DMC The pKa of a group is the pH value at which the concentration of the protonated group equals that of the unprotonated group. In total, there are 20 amino acids in human body from where all body proteins are constructed. So they are called “Primary Amino Acid” or “Standard Amino Acid”
  • 10. 8/17/2021 10 Dr Ifat, Dept of Biochemistry, DMC
  • 11. 8/17/2021 11 Dr Ifat, Dept of Biochemistry, DMC
  • 12. 8/17/2021 12 Dr Ifat, Dept of Biochemistry, DMC
  • 13. Remember: The acidic properties of COOH group & the basic properties NH2 group make the amino acid molecule “Amphoteric” The carboxyl group is able to donate proton and the amino group is able to accept proton 8/17/2021 13 Dr Ifat, Dept of Biochemistry, DMC
  • 14.  A carbon atom that is attached to four different types of atoms or groups of atoms.  Amino acids have the chiral carbon atom adjacent to the carboxyl group (COO-). Exception: Glycine Asymmetric Carbon / Chiral carbon Glycine: The smallest amino acid, which has symmetric α carbon atom. Here, R is replaced by another H atom 8/17/2021 14 Dr Ifat, Dept of Biochemistry, DMC
  • 15.  As all body amino acids (except glycine) have asymmetric α carbon, they can produce optical stereo isomers (space isomer) with optical activity 8/17/2021 15 Dr Ifat, Dept of Biochemistry, DMC α Carbon: Carbon atom next to carboxyl group
  • 16.  Mirror image pairs of amino acids are designated as L (levo) & D (dextro) L- α amino acids: Amino group is attached directly with the α carbon and placed on left side with respect to spatial configuration  Body proteins are assembled from L- α amino acids 8/17/2021 16 Dr Ifat, Dept of Biochemistry, DMC
  • 17. 8/17/2021 17 Dr Ifat, Dept of Biochemistry, DMC
  • 18.  Conventionally, by the first three letters of their name. e.g. Alanine (Ala) Nomenclature of Amino Acids Exception: Glutamine (Gln) Asparagine (Asn) Isoleucine (Ile) Tryptophan (Trp) Remember: “GAIT” 8/17/2021 18 Dr Ifat, Dept of Biochemistry, DMC
  • 19. 8/17/2021 19 Dr Ifat, Dept of Biochemistry, DMC
  • 20. A) Based on structure of side chain (R) & their reaction in solution Three types of Amino Acids Acidic AA Basic AA Neutral AA Aliphatic AA Aromatic AA Imino AA 8/17/2021 20 Dr Ifat, Dept of Biochemistry, DMC
  • 21. Types Synonym No. of Amino group No. of carboxyl group Charge at normal body pH Example Acidic amino Acid Mono amino di - carboxylic acid 01 02 Negatively charged Aspartic acid (Asp) Glutamic acid (Glu) Basic amino Acid Di - amino mono carboxylic acid 02 01 Positively charged Histidine (His), Arginine (Arg), Lysine (Lys) Neutral amino Acid Mono amino mono carboxylic acid 01 01 No net charge Rest 15 amino acids grouped under three types again (e.g. Ala, Tyr, Trp, Cys, Met etc) 8/17/2021 21 Dr Ifat, Dept of Biochemistry, DMC
  • 22. Neutral amino acid Aliphatic amino acid Aromatic amino acid Imino acid Sulphur containing: Cysteine, Methionine Example: Phenyl alanine, Tyrosine Tryptophan - It contains Imino group (-NH) , not amino group (NH2 ) - Example: Proline Branched chain: Valine, Leucine, Isoleucine Hydroxyl group containing: Serine, Threonine Amide group containing: Asparagine, Glutamine Simple structure: Glycine, Alanine 8/17/2021 22 Dr Ifat, Dept of Biochemistry, DMC
  • 23. B) Based on polarity of side chain (R) Two types of Amino Acids Polar AA / Hydrophilic AA Non polar AA / Hydrophobic AA 8/17/2021 23 Dr Ifat, Dept of Biochemistry, DMC
  • 24. Polar / Hydrophilic AA:  They have hydrophilic side chain (R)  Example: - Acidic AA - Basic AA - Some of the neutral AA like Gly, Ser, Thr, Tyr, Cys, Gln, Asn Total 12 in numbers Non polar / Hydrophobic AA:  They have hydrophobic side chain (R)  Example: Rest of the neutral AA like Met, Val, Leu, Ile, Ala, Trp, Pro, Phe Total 08 in numbers 8/17/2021 24 Dr Ifat, Dept of Biochemistry, DMC
  • 25. C) Nutritional Classification of Amino Acids Three types of Amino Acids Essential AA / Indispensable AA Semi essential AA Non essential AA / Dispensable AA 8/17/2021 25 Dr Ifat, Dept of Biochemistry, DMC
  • 26. Points Essential AA / Indispensable AA Semi essential AA Non essential AA / Dispensable AA Definition Amino acids which are not produced in body , therefore essentially be supplied in diet Amino acids which are produced in body in a limited rate , therefore essentially be supplied in diet when their requirement in body is high (like during growth in children, not essential for adult) Amino acids which are produced in body in sufficient amount , so, not essential in diet. Source Mainly from animal protein- meat, fish, egg, milk etc - - Total no. 08 02 - Example Met, Trp, Thr, Val, Phe, Ile, Leu, Lys (Remember, MTV PILL) Arg, His Asp, Glu, Cys, Ser, Gly, Ala, Asn, Gln, Tyr, Pro 8/17/2021 26 Dr Ifat, Dept of Biochemistry, DMC
  • 27. 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. 8/17/2021 27 Dr Ifat, Dept of Biochemistry, DMC
  • 28. D) Metabolic Classification of Amino Acids Three types of Amino Acids Absolute Glucogenic AA / Glycogenic AA Absolute Ketogenic AA Both Glucogenic & Ketogenic AA 8/17/2021 28 Dr Ifat, Dept of Biochemistry, DMC
  • 29. Points Absolute Glucogenic AA / Glycogenic AA Absolute Ketogenic AA Both Glucogenic & Ketogenic AA Definition Amino acids having carbon skeleton that possess metabolic potential to produce glucose Amino acids having carbon skeleton that possess metabolic potential to produce ketone bodies Amino acids having carbon skeleton that possess metabolic potential to produce both glucose & ketone bodies What happens really? They initially produce precursors of glucose (e.g. pyruvate or intermediates of TCA cycle) from which later on, glucose is produced They initially produce precursors of ketone bodies (acetyl CoA or aceto acetyl CoA) from which later on, ketone body is produced They initially produce acetyl CoA or aceto acetyl CoA along with pyruvate or TCA cycle intermediates and then produce ketone body or glucose Example Gly, Ala, Glu, Gln, Val etc Leu, Lys Phe, Tyr, Trp, Ile 8/17/2021 29 Dr Ifat, Dept of Biochemistry, DMC
  • 30. E) Combined Nutritional & Metabolic Classification Metabolic Type Nutritional type Essential Non essential Absolute Glucogenic His, Met, Thr, Val, Arg Ala, Asp, Asn, Cys, Glu, Gln, Gly, Pro, Ser Both Glucogenic & Ketogenic Phe, Trp, Ile Tyr Absolute Ketogenic Leu, Lys - 8/17/2021 30 Dr Ifat, Dept of Biochemistry, DMC
  • 31. 8/17/2021 31 Dr Ifat, Dept of Biochemistry, DMC
  • 32. Physical Properties  Colorless  Crystalline  Water soluble  High melting point (>200 degree C)  Stereoisomerism (D-L isomers, optical isomers)  Optical activity Chemical Properties  Act as ampholytes (i.e. behave both as acid & base)  Acts as buffer and have definite iso-electric pH  Undergo decarboxylation to form corresponding amines  Purple colour reaction with ninhydrine  Forms  Salts with acid or base  Esters with alcohol.  Carbamino compounds with CO2 8/17/2021 32 Dr Ifat, Dept of Biochemistry, DMC
  • 33. 8/17/2021 33 Dr Ifat, Dept of Biochemistry, DMC
  • 34. 1. Act as building blocks of - Peptides (2-10 AAs ) - Polypeptides (10 - 100 AAs ) & - Proteins (>100 AAs ) 2. Supports gluconeogenesis in fasting & starvation. 3. Synthesis of specialized products. e.g. neurotransmitters, hormones, purine, pyrimidine, heme, etc. 4. Directly acts as neurotransmitter (Gly, Glu, Asp) 5. Detoxification of toxic substances in liver by Gly, Cys etc 6. Acts as metabolic fuel meeting up 10% of body energy need 8/17/2021 34 Dr Ifat, Dept of Biochemistry, DMC
  • 35. 8/17/2021 35 Dr Ifat, Dept of Biochemistry, DMC
  • 36. Definition of protein  Macromolecular polymer of amino acids linked together by peptide bond.  Minimum molecular weight: 5000-8000  Number of amino acid: >100  Elementary Composition: C, O, N, H, S in different percentages 8/17/2021 36 Dr Ifat, Dept of Biochemistry, DMC
  • 37. 8/17/2021 37 Dr Ifat, Dept of Biochemistry, DMC
  • 38. 8/17/2021 38 Dr Ifat, Dept of Biochemistry, DMC
  • 39. Definition  It is a covalent bond that connects adjacent amino acids to form peptide, polypeptide & protein  It is formed by joining the – COOH group of one amino acid & the –NH2 group of another amino acid with removal of one molecule of water Formation 8/17/2021 39 Dr Ifat, Dept of Biochemistry, DMC
  • 40. Characteristics of peptide bond  Covalent bond, i.e. sharing of electron pair.  Shows partial double bond character  Rigid, planer & do not rotate.  It is not broken by denaturing agents but is broken by proteolytic enzymes 8/17/2021 40 Dr Ifat, Dept of Biochemistry, DMC
  • 41. 8/17/2021 41 Dr Ifat, Dept of Biochemistry, DMC