Proteins and

Amino Acids

Blithe

Topic:

Content:

1. Proteins:a) Etymologyb) Classification by:

Biological functions, andNutritional Basis.

c) Sourcesd) Importance

2. Amino Acidsa) Nature of Amino Acids

General Formula of Amino AcidsThe 20 Amino Acids, and Classification Peptide Formation

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Proteins: -the most abundant organic molecule of the living system , and constitute about 50% of the cellular weight.-It’s name was derived from the Greek word “Proteios” which means “Primary” or “Holding the First Place”.-A protein is a biological molecule that consists of one or more polypeptides, whichare chains of polymerized amino acids.

Protein Compositio

n - basically, all proteins contain carbon, hydrogen, oxygen, and nitrogen.

Carbon: 48.2%Hydrogen: 7.8%Oxygen: 24%Nitrogen: 16%Sulfur: 4%

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Structure of sperm whale myoglobin determined by

S. E. V. Phillips.

Classification of Proteins: Class Biological

FunctionSample Proteins

1. Contractile Protein

Provide Motion or movement of Muscle.

Actin and Myosin

2. Defense Protein Protection against foreign bodies.

Antibodies and Toxic Proteins

3. Enzymes Catalysis and inhibitor of almost all the reaction of living cell.

Digestive enzymes

4. Regulatory Protein

Control of cell processes.

Hormones like Insulin and Oxytocin.

5. Storage Protein Store nutrients for organism.

Casein , Albumin, and Ferritin.

6. Structural Protein

Mechanical support for organism’s structure.

Fibrin, collagen, elastin, and keratin.

7. Transport Protein Facilitates transport of chemicals in body.

Hemoglobin and Lipoproteins.

Classification of Proteins on a nutritional Basis

a. Complete Protein- supplies all the essential amino acids.

b. Incomplete Proteins- deficient in one or more essential amino acids.

Continuation…

Sources of Proteins…

-Dairy Products.-meat-Vegetables-Fruits-eggs, and other protein rich foods.

Sources of Proteins…

Biochemical connection of Proteins…

On a farm in Wyoming, USA, goats are being milked for their spider web

Amino

Acids14

Nature of Amino Acids

an amino acid is a small molecule containing 4 different groups attached to α- carbon.

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R |H2N – C – COOH | H

Side Chain

Carboxyl Group

Hydrogen GroupAmino group

The Structural Formula of Amino Acids

The 20 Amino Acids

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cont…

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Naming Amino Acids19

Properties of Amino Acids1. Amino acids contain acidic (COOH) and basic

(NH2) groups.

Therefore, amino acids have amphoteric properties: –In acidic medium ; the amino acid is

positively charged, so it behaves as a base (proton acceptor).

–In alkaline medium ; the amino acid is negatively charged, so it behaves as an acid (proton donor).

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cont… 21

2. Chirality handedness (from the Greek word “cheir, “hand”),

which results from the asymmetry of the alpha carbon. Amino acids, except for Glycine, have at least one chiral

center.

H |H2N – C – COOH | H

Structural Formula of Glycine

3. Solubility The solubilities of

amino acids in water are highly variable. extremely soluble

like Alanine, and some are significantly less soluble such as cystine and tyrosine.

Soluble in water, acids, alkalis but insoluble in organic solvents.

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Classification of Amino Acids

Amino acids can be classified in 2 ways:1. Based on the side chain

characters2. Based on nutritional

requirements

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Classification based on side chain characters

1. Amino Acids with a Non-polar side-chain:Has nonpolar side chains that interact very weakly or not at all with water.

e.g.: Alanine, Valine, Leucine, Isoleucine, Phenylalanine, Tryptophan, Proline

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2. The Polar Amino Acids

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can interact with water because they contain hydrogen- bonding groups.

e.g. Serine, Threonine, Tyrosine, Cysteine, Asparagine and Glutamine.

3. Acidic Amino Acids

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An amino acids which contain carboxyl groups in their side chains in addition to the one present in all amino acids.

e.g. Glutamic acid and Aspartic acid.

4. Basic Amino Acids27

An amino acids which contain amino groups in their side chains in addition to the one present in all amino acids.

e.g. Lysine, Arginine and Histidine

Classification Based on Nutritional Requirements

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I. Essential amino acids:These amino acids cannot be synthesized in the body and have to be present essentially in the diet. Examples:

Valine, Isoleucine, Leucine, Lysine, Methionine, Threonine, Tryptophan and Phenylalanine.

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II.Semi-essential amino acids:

These amino acids can be synthesized in the body but the rate of synthesis is lesser than the requirement(e.g. during growth, repair or pregnancy)

Examples: Arginine and Histidine.

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III.Non-essential amino acids:These amino acids are synthesized in the body, thus their absence in the diet does not adversely affect the growth.

Examples: Glycine, Alanine, and the other remaining amino acids.

Peptide Formation31

When two amino acids are linked or joined together it forms peptides.This happen when the carboxyl group of one amino acid made contact with the amine group of another amino acid.

H R O | | ||H-N – C – C-OH | H

H R O | | ||H-N – C – C-OH | H

Cite of dehydration process

H R O | | ||-N – C – C-OH | H

H R O | | ||H-N – C – C- | H

-H2O

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H R O | | ||H-N – C – C- | H

H R O | | || -N – C – C-OH | H

Amino acids in the peptide is called Amino Acid Residues (the yellow shaded part).Peptide Bond – the bond that joined the two amino acidsFunctional Grouped: Carbonyl Group and Amide Group (the blue-green shaded part) . Peptide can be classified into dipeptides, tripeptides, tetrapeptides, Oligopeptides, and Polypeptides.

Extra Scoop of Knowledge about Proteins/ Amino

Acids.

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“Weird” Facts about Proteins…

Proteins can have a bizarre names: For example: The protein “Pikachurin” is a retinal protein that was named after Pokemon character Pikachu.Without a proteins called Albumin, the entire body would swell.Cataracts are caused by the denaturation of proteins in the lenses of the eyes.

Insects are more nutritious than many other common forms of proteins. For example: 100 grams of top sirloin beef contain 29 grams of proteins and 21 grams of fats. While in 100 grams of grasshopper contains 20 grams of proteins and just 6 grams of fat.

A protein in semen acts on the female brain to prompt ovulation.

A typical human male ejaculation contains about 150mg of proteins.

Having too much intake of proteins can be dangerous to the body.

Without protein, life is impossible to exist!

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