Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st year (First Year) Biochemistry ppt lectures Topic 85 Structures Of Amino Acids Notes. - biochemistry notes pdf, biochemistry mbbs 1st year notes pdf, biochemistry mbbs notes pdf, biochemistry lecture notes, paramedical biochemistry notes, medical biochemistry pdf, biochemistry lecture notes 2022 ppt, biochemistry pdf.
Structure of Amino Acids
Specific learning objectives
? Diverse functions of Proteins.
? Amino acids classification based on position of amino group and composition of
R-group and nutritional requirement.
? Properties of Amino Acids.
Introduction
? Proteins are made up of hundreds of smaller units called amino acids that are
attached to one another by peptide bonds, forming a long chain.
? Protein as a string of beads where each bead is an amino acid.
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Diverse Functions of Proteins
? Enzymes: Serve as biological catalysts.
? Defense: Immunoglobulins and Interferon are proteins that protect the human
against bacterial and viral infections.
? Signaling: Provide recognition/markers on surface of cells or organelles and can
illicit intracellular responses.
? Movement: Motor proteins provide contractile movement/energy transformation.
Cont---
? Structural related proteins: Make up the structural-architecture of
the cell or tissues.
? Storage related proteins: provide amino acids storage for growth and
reproduction.
? Transport proteins: move molecules through membranes.
Amino-Acids Classification Based on Standard and Non-
Standard Amino Acids
? Standard amino-acids
? Non-Standard amino-acids
General Structure of Common Amino Acids
? All proteins are composed of the 20 "standard "amino acids.
? Common central alpha ()-carbon atom bound to a carboxylic acid group, an
amino group and a hydrogen atom are covalently bonded.
? They have a primary amino group and a carboxylic acid group substituent on the
same carbon atom, with the exception of proline, (has a secondary amino
group).
Fig.4.1. Biochemistry. 4th edition by Donald Voet and Judith G. Voet
Cont---
? Proline classified as an imino acid, its -amine is a secondary amine with its a
nitrogen having two covalent bonds to carbon (to the -carbon and side chain
carbon), rather than primary amine.
? Incorporation of the amino nitrogen into a five membered ring constrains the
rotational freedom around the ?N -C
-bond in proline to specific rotational angle,
reduces the structural flexibility of polypeptide regions containing proline.
Cont---
? Ionized form of a common amino acid in solution at
physiological pH.
? Ionization state of an amino acid varies with pH.
? -Amino group is protonated and in its ammonium
ion form
? Carboxylic acid group is in its deprotonated or
Fig.4.2. Biochemistry. 4th edition by Donald Voet and Judith G. Voet
carboxylate ion form.
Selenocysteine, the 21st Protein L--Amino Acids
? Selenocysteine are non-standard amino-acid.
? Selenium atom replaces the sulfur of its elemental analog, cysteine.
? Selenocysteine is not the product of a posttranslational modification, but is
inserted directly into a growing polypeptide during translation.
? Incorporation of selenocysteine is specified by a large and complex genetic
element for the unusual tRNA called tRNA Sec which utilizes the UGA anticodon
that normally signals STOP.
L--Amino Acids Serve Additional Role
? L- amino acids and their derivatives participate in cellular functions (nerve
transmission and biosynthesis of porphyrins, purines, pyrimidines, and urea).
? Thyroid hormones are formed from tyrosine; glutamate serves as a
neurotransmitter as well as the precursor of g-aminobutyric acid (GABA).
? Ornithine and citrulline are intermediates in urea biosynthesis.
Cont--
? Homocysteine, homoserine, and glutamate--semialdehyde participate in the
intermediary metabolism of the protein amino acids.
? The protein amino acids phenylalanine and tyrosine serve as precursors of
epinephrine, norepinephrine, and DOPA (dihydroxyphenylalanine).
Amino Acids Classified on the Basis of Nutritional
Requirement
? Essential proteinogenic amino acids.
? Non-essential proteinogenic amino acids.
Amino-Acid Requirements of Humans
Table 28.1. Harper's Il ustrated Biochemistry 26th edition
Amino-Acids Classification Based on Side Chain Groups
? Based on the type of functional group (R group) present amino acids are
classified as: Aliphatic, aromatic, acidic, basic, acid amide, sulfur and cyclic amino
acids.
? Based on the characteristic of the functional group amino acids are classified as:
polar and non-polar amino acids.
? Based on the site of attachment of the functional group. They are also classified
as: alpha, beta, gamma and delta amino acids.
Amino Acids Classification
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Cont--
Nonpolar/Hydrophobic
Methyl R group
Isopropyl R group
Branching in isobutyl side chain on carbon of amino
acid
Branching in isobutyl side chain on carbon of amino
acid
Table 3.1. Harper's Il ustrated Biochemistry 30 edition
Cont--
Polar, uncharged-R group
Hydroxymethyl R group
Polar, uncharged-R group
Secondary Alcohol structure
Mentioned in amino acids with aromatic rings section
Polar, uncharged-R group
Thiolmethyl/Sulfhydryl R group
Nonpolar
Methyl ethyl thiol ether R group
Cont--
Negatively charged R group
-COOH R group
Polar, Uncharged-R group
Negatively charged R group
-COOH R group
Polar, Uncharged-R group
Cont--
Positively charged R groups
Guanidinium R group
-NH+3 R group
Imidazolium R group
Cont--
Mentioned in amino acids with basic groups section
Benzene ring R group
Phenol R group
Heterocyclic structure, indole R group
Imino group belongs to a five-member ring
Fig. 2.4. Textbook of Biochemistry with Clinical Correlations, 4th edition by Thomas M Devlin
Fig. 2.5. Textbook of Biochemistry with Clinical Correlations, 4th edition by Thomas M Devlin
Fig. 2.6. Textbook of Biochemistry with Clinical Correlations, 4th edition by Thomas M Devlin
Properties of Amino Acids
Genetic Code Specifies 20 L--Amino Acids
? Proteins are synthesized from the set of 20 L--amino acids encoded by
nucleotide triplets called codons.
? Common amino acids are those for which at least one specific codon exists in
the DNA genetic code.
? Sequences of peptides and proteins represent by using one- and three letter
abbreviations for each amino acid.
Cont---
Genetic information is transcribed from a DNA sequence into mRNA
and then translated to the amino acid sequence of a protein
Fig. 2.1. Textbook of Biochemistry with Clinical Correlations, 4th edition by Thomas M Devlin
Summary
? Functions of Proteins: transport, defense, movement, storage, signaling etc.
? Both -amino acids and non--amino acids occur in nature, but proteins are
synthesized using only L--amino acids.
? The R groups of amino acids determine their unique biochemical functions.
? Amino acids are classified as basic, acidic, aromatic, aliphatic, or sulfur-containing
based on the composition and properties of their R groups.
Interaction with students
? Distributed subtopics of class to students to participate in group
discussion in next class.
Reference Books
1) Harper 's Il ustrated Biochemistry-30th edition
2) Textbook of Biochemistry with Clinical Correlations. 4th edition. Thomas M.
Devlin.
3) Biochemistry. 4th edition. Donald Voet and Judith G. Voet.
4) Biochemistry 7th edition by Jeremy M. Berg, John L. Tymoczko and Lubert Stryer
5) Lehninger Principles of Biochemistry
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This post was last modified on 05 April 2022