Module 13: Proteins

Proteins - are high molecular weight organic compounds made up of amino acids joined together by peptide linkages in a sequential order.

Proteios – proteins came from what Greek word?

Johannes Mulder – Who came up with the name protein from a Greek word “proteios. STRUCTURAL PROTEINS – are important components of living structures that provide mechanical support to living bodies and provide them outer covering for protection. Collagen – makes up the fibrous connective tissues in bones and cartilages Elastin – makes up the elastic connective tissues in the skin, ligaments and blood vessels Keratin – serves like a laminating material in the hair, nails, feathers, hooves and skin of animals Sclerotin – makes up the exoskeletons of insects and other arthropods

STORAGE PROTEINS – also known as nutrient proteins
STORAGE PROTEINS - they serve as potential sources of biochemical energy and proteins, especially amino acids, for the maintenance of good health and for proper growth and living, especially infants or embryos
Ovalbumin – found in eggs
Casein – found in milk
Gliadin – found in wheat
Zein – found in corn
Ferritin – iron-containing protein found in lean meat
ENZYMES – organic or biological catalysts that enhance or stimulate particular chemical reactions involved in important metabolic processes
Cytochrome oxidase – responsible for the transport of electrons
Ribonucleases – used for the hydrolysis of RNA
Sucrase – used for the hydrolysis of sucrose
Alcohol dehydrogenase - used for the fermentation of ethanol
Trypsin – hydrolyzes the polypeptide chain from the carboxyl end of arginine and lysine
Chymotrypsin – hydrolyzes the polypeptide chain from the carboxyl end of phenylalanine and tyrosine

HORMONES – chemical transmitter substances secreted by endocrine glands that has specific regulatory effects as to stimulate or retard life processes
Insulin – regulates the entry of glucose molecules to red blood cells
Growth hormone – promotes growth of muscles and bones
ACTH (adenocorticotropic hormone) – regulates the synthesis of corticosteroids
(adenocorticotropic hormone) – ACTH means?
ADH (anti-diuretic hormone) / Vasopressin – promotes reabsorption of water from the kidneys, thus retards diuresis or urination
Vasopressin – other name for ADH
ADH (anti-diuretic hormone) – ADH means?

TRANSPORT PROTEINS – also known as carrier proteins,
Transport proteins - they deliver other important substances needed by a living body from a certain source to its proper site for storage or utilization in metabolic processes
Transcobalamin – transports vitamin B12 or cobalamin in the bloodstream
Transferrin – transports iron in the bloodstream
Ceruloplasmin – transports copper in the bloodstream
Lipoproteins – carrier molecules of lipids, primarily triglycerides and cholesterol
Hemoglobin – carries oxygen in the blood of vertebrates
Hemocyanin – carries oxygen in the blood of invertebrates
Myoglobin – transports oxygen in the muscle tissues
CONTRACTILE PROTEINS – proteins necessary for all forms of movement, voluntary or involuntary
Myosin – found in the thick and stationary filaments in the myofibril of skeletal muscles necessary for contraction
Actin – found in the thin and moving filaments in the myofibril of skeletal muscles necessary for contraction

Dynein – found in the locomotory appendages of microorganisms like the cilia and flagella

PROTECTIVE PROTEINS – they help the body to recover from injury like in the healing of wounds and to increase resistance or induce immunity from infectious diseases
Fibrinogen – precursor for fibrin threads necessary for blood clotting
Prothrombin – proenzyme of thrombin that converts fibrinogen into fibrin
Complement – set of proteins which aids in the formation of antigen – antibody (immune) complexes
Immunoglobulins – also known as antibodies
Immunoglobulins - produced by plasma cells used to protect the body from various types of infections

TOXINS – poisonous substances that can yield harmful effects to the body when taken such as intoxication or
paralysis of living cells
Ricin – toxic protein found in castor bean
Botulism toxin – bacterial toxin produced by Clostridium botulinum that causes food poisoning
Diphtheria toxin – bacterial toxin produced by Corynebacterium diphtheriae that causes diphtheria
Snake venom – neurotoxin that contains enzymes that hydrolyzes phosphoglycerides
Clostridium botulinum – Botulism toxin is produced by?
Corynebacterium diphtheriae – Diphteria toxin is produced by?
SIMPLE PROTEINS – true proteins found abundantly in both animals and plants that will yield amino acids only when hydrolyzed

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Albumins – soluble in water and neutral dilute salt solutions
Globulins – insoluble in water but soluble in neutral dilute salt solutions
Glutelins – soluble in dilute acids and alkalis but insoluble in neutral solvents
Prolamines – insoluble in ordinary solvents but soluble in 70% alcohol at about a neutral pointHistones – soluble in water, dilute acids and alkalis but not in dilute Ammonia
Protamines – soluble in water and dilute acids and alkalis and are not coagulated by heat
Scleroproteins – insoluble in water and neutral solvents
CONJUGATED PROTEINS – made up of simple protein molecules combined with non-protein groups (prosthetic group)

Nucleoproteins – combinations of histones and protamines with nucleic acid
Glycoproteins – proteins with a carbohydrate component utilized for lubricating purposes
Phosphoproteins – phosphate group joined to the protein molecule
Chromoproteins – protein compounds with hematin or other similar pigments
Lipoproteins – fatty substances combined with protein molecules
DERIVED PROTEINS – class of proteins formed from the hydrolysis of simple and conjugated proteins

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Primary Protein derivatives – also known as denatured proteins
Primary Protein derivatives – have undergone slight intramolecular rearrangement through the hydrolytic action of certain physical and chemical agents
Proteans – insoluble substances resulting from the preliminary action of water, dilute acids or enzymesMetaproteans (Infraproteans) – products of further hydrolysis that are soluble in weak acids and alkalis but insoluble in neutral salt solutions
Infraproteans – metaproteans is also called?
Coagulated proteins – insoluble products resulting from the action of heat, alcohol, ultraviolet radiation or even simple mechanical shaking
Secondary Protein derivatives – products of more extensive hydrolysis that are mixtures of original protein varying in composition and size

Primary proteoses – soluble in water and precipitated by concentrated HNO3 and half saturation with (NH4)2SO4 or ZnSO4; not coagulated by heat

Secondary proteoses – precipitated by complete saturation with (NH4)2SO4
Peptones – soluble in water and precipitated by saturation with certain alkaloidal reagents like phosphotungstic acid and tannic acid
Peptides – combinations of 2 or more amino acids, the carboxyl group of one being united with the amino group of the other
COMPLETE PROTEINS – are those that supply all the essential amino acids needed by the human body.
COMPLETE PROTEINS - They are capable of both maintaining life and providing normal growth when used as a sole protein food. Most are derived from animal sources.

PARTIALLY INCOMPLETE PROTEINS – are those that are capable of maintaining life but not supporting normal growth

INCOMPLETE PROTEINS – those that are deficient in one or more essential amino acids. They are incapable of maintaining life or supporting growth when fed as the sole protein source. Many proteins, especially those from vegetable sources, are incomplete.

COMPLETE PROTEINS – proteins made up of polypeptide chains arranged in a parallel fashion along a single axis, thus belong to the class of proteins that contain highly developed secondary structures.
COMPLETE PROTEINS - They are insoluble in water and in dilute salt solutions and are used mainly for structural purposes

GLOBULAR PROTEINS – proteins made up of polypeptide chains which are tightly folded into a compact spherical or globular shape, thus belong to a class of proteins that have a three-dimensional tertiary structure.

GLOBULAR PROTEINS - They are soluble in water and most biologically active proteins for non-structural purposes belong to this classification

MIXED PROTEINS – proteins that have the same conformation as fibrous proteins but have the same solubility property as globular

PRIMARY STRUCTURE – refers to the linear sequential arrangement of amino acids in the polypeptide chain including the location of the disulfide bonds. It results from the covalent bonding between amino acids in the chain.

Peptide bonds - are amide bonds formed between the alpha-carboxylate group of one amino acid and the alpha amino group of another.

SECONDARY STRUCTURE – refers to the folding of the primary structure of proteins that results from the hydrogen bonding between the amine hydrogens and carbonyl oxygens of the peptide bonds.

ALPHA – HELIX – is the coiled, helical conformation of the secondary structure of protein oriented like a normal screw.

BETA – PLEATED SHEET – is the accordion-like conformation of the secondary structure of protein.
Parallel -pleated sheet – the N termini are head to head

Anti-parallel -pleated sheet – the N terminus of one chain is aligned with the C terminus of the second chain (head to tail)

TERTIARY STRUCTURE – refers to the distinctive and characteristic conformation or shape of a protein molecule.
TERTIARY STRUCTURE - This overall three-dimensional structure results from the folding of the secondary structure that occurs spontaneously by a variety of interactions between amino acid side chains.
Van der Waals forces – between the R groups of non-polar amino acids that are hydrophobic
Hydrogen bonds – between the polar R groups of polar amino acids
Ionic bonds – between the R groups of oppositely charged amino acids
Covalent bonds – beween the thiol-containing amino acids

QUARTERNARY STRUCTURE – refers to the shape of the entire complex molecule and is determined by the way in which the subunits are held together by non-covalent bonds.
QUARTERNARY STRUCTURE - It is the aggregartion of more than one folded peptide chain to yield a functional complex protein. Non-protein components may also be present.

1. Millon's test: When illon's reagent (mercurous nit rate in HNO3) in added to a protein solution, the protein is pre cipitated as mercury salt. On heating. the precipitate turns flesh to red color, if proteins containing tyrosine are present. This reaction is due to the phenol group contained in tyrosine.
2. Biuret test:Alkaline solution of proteins treated with CuSO4 solution results in the production of a rose-pink to violet, then purple color. This is due to the presence of the peptide link age (-CONH2). All substances therefore containing this link age respond positively to this test. Biuret, having a similar linkage, gives a positive reaction,hence the name biuret test, Dipeptides do not give the biuret teat, but all other polypeptides do. This test serves as a good index for determining the extent of protein hydrolysis. When ammonium sulfate is used for the salting out process, an excess of alkali should be added.
3. Hopkins Cole reaction: When protein mixed with glyoxylic acid (CHOCOOH) is treated with concentrated H2SO4, a violet ring is produced at the point of contact of the two solutions. This is due to the presence of an indole nucleus in the trytophan component. The tryptophan condenses with the aldehyde to form the colored compound.
4. Xanthoproteic reactions Proteins when treated with concentrated HNO3 turn yellow and change to orange when neutralized with NaOH. This is due to the nitration of the benzene ring (C6H5) present in the structure of such amino acids as tyrosine, tryptophan and phenylalanine. (The yellow stain on the skin produced by HNO, in due to this reaction.)
5. Test for SH group: Solution of proteins containing cystine, cysteine or methionine, when heated with NaOH, splits up the sulfur to form Na2S. This when treated with lead acetate produces a black precipitate due to the formation of lead sulfide.
6. Lieberman's test:-When solid protein is boiled in concentrated HCl, and a few drops of sucrose solution are added, a violet color appears if tryptophan is present. This involves the same principle as that of the Hopkins Cole test; the aldehyde being liberated from the sugar through the action of HCI.
7. Molisch's test: If a protein solution is treated with Molisch's reagent and layered with H2SO4, a violet ring will develop if glyco-protein is present.
8. Ninhydrin reaction: When protein is boiled with nin hydrin (triketohydrindene hydrate) a blue color is produced. This is due to the presence of the a-amino group in the molecule. All proteins, peptides and amino acids except proline and hydroxyproline, give this typical reaction.
9. Sakaguchi reaction: In alkaline solution, protein containing arginine gives red color with a-naphthol and sodium hypochlorite.
   10. Nitroprusside test: Proteins containing cysteine give a red color with sodium nitroprusside in dilute ammoniacal solution.
   11. Follin's reaction: Amino acids in alkaline solution give a deep red color with sodium 1,2 naphtho quinone-4-sulfonate. This is used for rapid quantitative estimation of amino acids.
   12. Sullivan's teat: In the presence of strong reducing agent like Rodium hydrosulfite (Na2S2O2) cysteine in alkaline solution gives red color with sodium 1,2 naphtho quinone-4-sulfonate. This can be used for the quantitative estimation of cysteine and cystine after reduction.
   13. Pauly reaction: Histidine and tyrosine in alkaline no lution when made to react with diazotized sulfanilic acid gives a red color.

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