Upload
jagadeesh-goli
View
222
Download
0
Embed Size (px)
Citation preview
8/8/2019 EAMCET QR Chemistry Sr Chem 15.Biomolecules PROTEINS
http://slidepdf.com/reader/full/eamcet-qr-chemistry-sr-chem-15biomolecules-proteins 1/7
1
• Amino acids contains both amine group (–NH2) and carboxylic acid group (–COOH).
• Amino acid molecules are linked by forming an amide bond
NH C
O
• Carboxylic acid of one molecule reacts with the amino group of another molecule to form amide
bond.
2H O2NH CH COOH H NH CH COOH
| |
R R
−− − + − − − ⎯⎯⎯→
2Amide bond(Peptide bond)
O H|| |H N CH C NH C COOH
| |RR
− − − − −
• Linkages between amino acids are known a peptide linkages or peptide bonds.
• The product obtained from two amino acid molecule through peptide bond is called dipeptide.
• Based on number of amino acid molecule in peptide they are called tri, tetra and polypeptides.
• Protein from a Greek word proteios mean prime importance.
• Proteins are naturally occurring, polypeptides containing 100 to 300 amino acid units.
• Silk, hair, skin, connective tissues most of the enzymes, hormone etc are examples for proteins.• In carboxylic acid chain based on the location of NH2 group on the carbon amino acids are
named as α, β, γ, δ.
H2N – CH2 – COOH α-amino acid
H2 – N – CH2 – CH2 – COOH β-amino acid
H2N – CH2 – CH2 – CH2 – COOH γ-amino acid
• Naturally occurring amino acids are more than 700 but important amino acids are 20.
• Protein forming amino acids are α-amino acid containing a primary amine group except protein a
secondary amine.
• Simplex amine acid is glycine Greek meaning sweet.• IUPAC name of glycine is 2-amino ethanoic acid.
• Amino acid containing equal number of –NH2 and –COOH groups are neutral.
• Amino acid contains more number of –NH2 group it is basic, if it containing more COOH groups it
is acedic.
• Amino acids that cannot be synthesized in the body must be supplied through diet are called
essential amino acids.
• Non-essential amino acid can be synthesized in the body.
• Amino acids are colourless crystalline solids.
• Amino acids are highly polar in aqueous solution.
• Proton transfers from acid group to amine group to give Zwitter ion or inner salt.
15. BIOMOLECULES
ii) PROTEINS
8/8/2019 EAMCET QR Chemistry Sr Chem 15.Biomolecules PROTEINS
http://slidepdf.com/reader/full/eamcet-qr-chemistry-sr-chem-15biomolecules-proteins 2/7
Biomolecules
2
• In Zwitter ion acedic nature is due to –NH3+
group and basic nature is due to COO−− group.
H2N CH COOH
R
H2O
H3N CH COO
ROH
H+
(Cation)H3N CH COOH
R
(Anion)H2N CH COO
R
• Zwitter ion in acid medium becomes positive ion and in basic medium becomes negative ion.
• Dipolar Zwitter ion act as a neutral ion and does not migrate towards anode or cathod at a
particular pH called isoelectric point of the aminoacid.
• Isoelectric point of the amino acid depends on the groups present in the amino acids.
• For neutral amino acids isoelectric point is in the range 5.5 to 6.3.
• Least solubility of amino acid at isoelectric point helps in the separation of different amino acids
obtained from the hydrolysis of protein.
• Due to asymmetric (chiral) α-carbon all amino acids are optically active except glycine.
• In fisher projection D-form of amino acid –NH2 group on the right and in L-form – NH2 group is on
the left – COOH group is on the top in both forms.
COOH
HH2N
RL - form
COOH
NH2H
RD - form
• Most of the naturally occurring amino acids are with L-configuration.
• In a polypeptides free amino group (NH2)
N-terminal residue to the left and acid group is to the right.
• Alanyl glycylalanine can be represented as
Ala - Gly - Ala
Alanyle glycyl alanine
NH2 CH C NH CH2 C NH CH COOH
CH3 CH3
OO
N-terminal C-terminal
• Shorter peptides are called oligopeptides longer peptides are polypeptides.
• Proteins are polypeptides containing many amino acids molecular mass is more than 10,000.
• Polypeptides are amphoteric.
• Most of the toxins which poisonous substances present in animal and plant venoms are proteins.
• Oligopeptides are effective hormones.
• Aspertame is a dipeptides which is 160 times sweeter than sucrose.
• Aspertame is aspartyl phenylalanine methyl ester.
8/8/2019 EAMCET QR Chemistry Sr Chem 15.Biomolecules PROTEINS
http://slidepdf.com/reader/full/eamcet-qr-chemistry-sr-chem-15biomolecules-proteins 3/7
Biomolecules
3
H2N CH CO NH CH COOCH3
CH COOH CH2C6H5
STRUCTURE OF PROTEINS :
• Proteins are biopolymers of large number of amino acid linked through peptide bonds or
disulphide bond.
• In disulphide linkage S S| |
H H
− = −
• Primary structure of amino acid gives specific sequence of amino acids in polypeptide.
• 100 amino acid units having 20 different amino acids can combine (20)100
different ways.
• Primary structure tells us about peptide linkages and sulphide linkages.• Primary structure is only due to covalent bond linkage.
• Secondary structure of protein or polypeptide explains shape and describes conformation of
segments.
• Peptide chain folds to limit the possible conformation, to minimise number of hydrogen bonds
and to avoid steric hindrance between R groups.
• Secondary structure is due to hydrogen bonds between N and O.
• The segment of the protein back bone fold either α-helix or β pleated sheet or coil conformation.
• Tertiary structure is three-dimensional arrangement of atoms in the protein.
• It explains extensive coiling or folding to produce a complex.
• Quaternary structure defines the structure resulting from the inhalations between the subunits of
polypeptide chains.
• The interactions between subunits to give quarlernary structure are
i) Hydrogen bonding
ii) Electrostatic attraction
iii) Hydrophobic interactions
• Sub units arrangement in space is given by quarlernary structure.
• Protein denaturation involves breaking of tertiary structure of protein.
• Proteins with weak interactive bonds can be easily denatured.
• Denaturation can be by
i) Changing pH to disrupts hydrogen bonds.
ii) By adding reagent like urea to form strong hydrogen bonds with urea.
iii) Adding detergents like sodium dodecyl sulphate.
iv) Organic solvents associates with non-polar groups to interfere with hydrophobic interactions.
v) Heating or agitation which causes disruption of attractive forces.
AMINO ACIDS DERIVED FROM PROTEINS :
A. Neutral Amino Acids :1. Glycine (Gly)
8/8/2019 EAMCET QR Chemistry Sr Chem 15.Biomolecules PROTEINS
http://slidepdf.com/reader/full/eamcet-qr-chemistry-sr-chem-15biomolecules-proteins 4/7
Biomolecules
4
(Aminoacetic acid)
C
H
NH2
COOHH
2. Alanine (Ala)
(α-Aminopropinoic acid)
C
H
NH2
COOHCH3
3. Valine (Val)
(α-Aminiosovaleric acid)
C
H
NH2
COOHCH3
CH3
H
C
4. Leucine (Leu) (α-Aminoisocaproic acid)
C
H
NH2
COOHCH3
CH3
H
C C
H
H
5. Isoleucine (Ileu) (α-Amino-β-methylvaleric)
C
H
NH2
COOHCH3
CH3
H
CCH2
6. Serine(Ser) (α-Amino-β-hydroxypropionic acid)
C
H
NH2
COOHHOC
H
H
7. Threonine (Thre) (α-Amino-β-hydroxybutyric acid)
CH3 C
H
OH
C
H
NH2
COOH
8. Phenylalanine (Phe) (α-Amino-β-phenylpropionic acid)
8/8/2019 EAMCET QR Chemistry Sr Chem 15.Biomolecules PROTEINS
http://slidepdf.com/reader/full/eamcet-qr-chemistry-sr-chem-15biomolecules-proteins 5/7
Biomolecules
5
C
H
H
C
H
NH2
COOH
9. Tyrosine (Tyr) (α-Amino-p-hydroxyhydrocinnamic acid)
C
H
H
HO C
H
NH2
COOH
10. Tryptophan (Try) (α-Amino-β-(3-indolyl) propionic acid)
N
H
C
H
H
C
H
NH2
COOH
11. Proline (Pro)1
(2-Pyrrolidine carboxylic acid)
CHCOOH
CH2H2C
H2C
N
H
12. Hydroxyproline (Hpro)1
(4-Hydroxy-2-pyrrolidine carboxylic acid)
CHCOOH
CH2CH
H2C
N
H
HO
1Proline and hydroxyproline are imino acids . The nitrogen atom, although joined to the α-carbon,is part of a ring. An imino nitrogen bears only one hydrogen atom but can still take part in theformation of proteins.
B. Basic Amino Acids: 13. Histidine (His)
(α-Amino-β-4-imidazolylpropionic acid)
C
H
NH2
COOH
NH
C
C
H
H CH2C
N
8/8/2019 EAMCET QR Chemistry Sr Chem 15.Biomolecules PROTEINS
http://slidepdf.com/reader/full/eamcet-qr-chemistry-sr-chem-15biomolecules-proteins 6/7
Biomolecules
6
14. Lysine (Lys) (α, ε-Diaminocaproic acid)
C
H
NH2
COOHCH2
NH2
CH2 CH2 CH2
15. Arginine (Arg) (α-Amino-δ-guanidinovaleric acid)
C
H
NH2
COOHH2N C N
HN
H
CH2CH2CH2
C. Acidic Amino Acids :
16. Aspartic acid (Asp) (Aminosuccinic acid)
H
NH2
COOHHOC
O
CH2 C
17. Glutamic (Glu)
(α-Aminoglutaric acid)
HOC
O
CH2 CH2
H
NH2
COOHC
D. Sulfur-Containing Amino Acids :
18. Methionine (Met) (α-Amino- γ-methylthiobutyric acid)
CH3 S CH2 CH2
H
NH2
COOHC
19. Cysteine (Cys) (α-Amino-β-mercaptopropionic acid)
CH2
H
NH2
COOHCHS
20. Cystine (Cys-Scy)
8/8/2019 EAMCET QR Chemistry Sr Chem 15.Biomolecules PROTEINS
http://slidepdf.com/reader/full/eamcet-qr-chemistry-sr-chem-15biomolecules-proteins 7/7
Biomolecules
7
•
CH2
H
NH2
COOHCS
CH2
H
NH2
COOHCS