amino acids amino acids are the building units of proteins. proteins are polymers of amino acids...
TRANSCRIPT
![Page 1: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/1.jpg)
Amino Acids
Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see latter).
There are about 300 amino acids occur in nature. Only 20 of them occur in proteins.
Structure of amino acids:
Each amino acid has 4 different groups attached to α- carbon ( which is C-atom next to COOH). These 4 groups are : α-amino group, COOH group, Hydrogen
atom and side Chain (R)
R
![Page 2: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/2.jpg)
Classification of amino acids
1- Chemical classification: According to number of COOH and NH2 groups i.e. according to net charge on amino acid and
A- Monobasic, monocarboxylic amino acids i.e. neutral or uncharged:
R
![Page 3: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/3.jpg)
According to chemical structure of R group, neutral amino acids are subclassified into:
I- Aliphatic, neutral amino acids: (6 amino acids)
1- Glycine (Gly): R= H
2- Alanine (Ala) R= CH3
3, 4, 5-Branched chain amino acids: valine, leucine and isoleucine R is branched Valine (Val): R= isopropyl group
![Page 4: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/4.jpg)
Leucine (Leu): R= isobutyl gp
Isoleucine (Ile) R = is isobutyl
R is isobutyl in both leucine and isoleucine but branching is different: in leucine → branching occurs on γ carbon
in isoleucine→ branching occurs on β- carbon
6- Proline: In proline, amino group enters in the ring formation being α-imino group so proline is an α-imino acid rather than α-amino acid
![Page 5: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/5.jpg)
Valine
Leucine
Isoleucine
![Page 6: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/6.jpg)
II- Neutral Sulfur containing amino acids: 2 amino acids
1- Cysteine (Cys): R= CH2SH
What is cystine?
2- Methionine (Met):
III- Neutral, hydroxy amino acids: 2 amino acids 1- Serine (Ser): R= CH2OH
2- Threonine (Thr):
![Page 7: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/7.jpg)
Formation of cystine
The bond S-S in cystine is called: disulfide bond
![Page 8: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/8.jpg)
Serine
Threonine
![Page 9: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/9.jpg)
Cysteine
Methionine
![Page 10: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/10.jpg)
VI- Neutral aromatic amino acids: includes 3 amino acids
1- Phenyl alanine (Phe) :
It’s alanine in which one hydrogen of CH3 is substituted with phenyl group. So it’s called phenyl alanine.
2- Tyrosine (Tyr): - it is P- hydroxy phenyl alanine
- it is classified as phenolic amino acid
![Page 11: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/11.jpg)
3- Tryptophan: contains indol ring
![Page 12: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/12.jpg)
Phenylalanine
Tyrosine
Tryptophan
![Page 13: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/13.jpg)
VI- Neutral amino acids with amide group in R (2):
1- Aspargine (Asn):
2- Glutamine (Gln):
![Page 14: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/14.jpg)
• At physiological PH (7.4), in neutral amino acids, -COOH
group is dissociated forming a negatively charged
carboxylate ion (COO-) and amino group is protonated
forming positively charged ion (NH3+) forming Zwitterion
![Page 15: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/15.jpg)
B- Basic amino acids: contain two or more NH2 groups or nitrogen atoms that act as base i.e. can bind proton. At physiological pH, basic amino acids will be positively charged.
a- Lysine( Lys)
b- Arginine(Arg): contains guanido group:
c- Histidine (His): contains imidazole ring.
guanido
![Page 16: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/16.jpg)
C- Acidic Amino acids:
e.g. a- Aspartic acid (Asp) (aspartate),
b- Glutamic acid (Glu) (glutamate)
at physiological pH, acidic amino acids will carry negative charge .
![Page 17: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/17.jpg)
![Page 18: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/18.jpg)
Summary:
A- Neutral amino acids (15 amino acids)
Classified according to R into
- Aliphatic amino acids including glycine, alanine, valine, leucine,
isoleucine and proline
- Sulfur containing amino acids including: cysteine and methionine
- Hydroxy amino acids including serine and threonine
- Aromatic amino acids including phenylalanine, tyrosine and
tryptophan
- Amino acids containing amide group including aspargine and
glutamine
![Page 19: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/19.jpg)
Lysine
Arginine
Histidine
Basic amino acids (3)
![Page 20: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/20.jpg)
Aspartic acid
Glutamic acid
Acidic amino acids (2)
![Page 21: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/21.jpg)
-At physiologic pH, neutral amino acids are present as Zwitterion
(carry equal positive and negative charges) so it is neutral (not
charged).
- At physiological pH, basic amino acids will be positively charged.
While acidic amino acids are negatively charged
So, Basic and acidic amino acids are called charged amino acids
![Page 22: Amino Acids Amino Acids are the building units of proteins. Proteins are polymers of amino acids linked together by what is called “ Peptide bond” (see](https://reader030.vdocuments.net/reader030/viewer/2022032806/56649efd5503460f94c11ee2/html5/thumbnails/22.jpg)