8/8/2019 2 Protein 11

1/5

PROTEIN: Properties (11)

1) Macromolecule complex,

thousands to tens of thousands

of atoms. Molecular weight

from 20,000 to several million.2) CHON (sometimes S & P)

3) Condensation between

amino acid and amino acid =

polypeptide chain - protein.

4) amino acid = amino(base) +

side chain + carboxyl(acid).

5)Not dissolved yet =

amphoteric

( contains 1 group with basic

and another group with acidic

properties). After dissolving = zwitterion.

(bipolar ion with positive and

negative charges.)

6) 20 natural amino acids. 4

types of R = 4 groups.

A) Polar (R ends with OH)

Serine, Asparagine (Asn),Glutamine (Gln), Tyrosine,Cysteine, Threonine. Protein

molecule properties = partiallycharged, does not accept ordonate electrons. Increasessolubility of protein, allows H-bonds between polypeptidechains.

B) Non-polar (Ends with CH)

Glycine, Alanine, Valine,Leusine, Tryptophan (Trp),Proline, Methionine,Phenylalanine, Isoleusine (Ile)

Insoluble, non-reactive,structural proteins, e.g. collagen

C) Acidic ( negatively charged)

R ends with COOH)

Aspartic acid, Glutamic acid,

D) Basic (+ve charges)

Ends with NH2

Lysine, Arginine, Histidine

8/8/2019 2 Protein 11

2/5

PROTEIN ( 12 )

Acidic & Basic = producescharged ions, strong hydrophilicreaction, Dissolved, globuleproteins 3-D shape, partlymaintained by electrostaticbonds between charged Rgroups.

BUFFER e.g. amphoteric

compounds. Occurs in theblood. Function = prevents pHchanges, maintains neutral pH.

Amino acid solution = naturalbuffer in organisms. Otherbuffers = protein, phosphateions, bicarbonates.

How ? Amino acid is easilychanged into anion or cationreversibly, removing effects ofH+ or OH- added to a solution.

PEPTIDE BOND - 2 AMINOACIDS = dipeptide, 3 = tri-, 50

to thousands = poly.

3 differences a) the number of

amino acids b) relativequantity of each type of aminoacid c) the sequenceof amino acids in a polypeptideframe.

PROTEIN STRUCTURE :

Primary, secondary, Tertiary,Quaternary.

PRIMARY STRUCTURE : linearsequence of amino acids on thepolypeptide chain, sequencedetermined by genetic code inDNA molecule in the nucleus,

This sequence is the same, andfixed for a type of protein,unique to that type of proteinonly.

SECONDARY STRUCTURE :Twisted polypeptide chain a)

simple alpha helix b) double helix.

8/8/2019 2 Protein 11

3/5

PROTEIN ( 13 )

C) beta-pleated sheets.

ALPHA HELIX : Can lengthen

like a spring/telephone wire.Strengthened by hydrogenbonds.

Double orTriple helix : 2 or3 chains of closely twistedpolypeptides, forming a fibre.Double helix e.g. keratin in

hair, horn, nails, beak,feather, outermost skin layerof dead cells.

Triple helix e.g. collagen =protein that gives strength &flexibility to cartilage &tendon.

Beta-pleated sheets =hydrogen bonds formedbetween several polypeptidechains maximally extendedand placed anti-parallel.Resistance to extension,

strong but flexible, e.g.fibroin in silk.

TERTIARY STRUCTURE :

The way how an alpha-helixfolds in 3-D to give rise tocompact globular proteinmolecule. Stabilized by ionic,disulphide(e.g. methionine),hydrophobic, Van der Waalsand hydrogen bonds. Enzymes,protein hormones, plasmaproteins & antibodies.

QUATERNARY STRUCTURE : More than 1 polypeptide chain,

large molecules, likehemoglobin

CLASSIFICATION OFPROTEINS. I) Based onstructure = 1)globular 2)

fibrous. II) Based on composition =

1) simple 2) conjugated

FIBROUS : building of bodystructure, Mostly secondary,insoluble in water, e.g.collagen, myosin, fibrin,keratin.

8/8/2019 2 Protein 11

4/5

PROTEIN (14)

GLOBULAR PROTEINS :

Tertiary & quaternary structures.

Polypeptide chains twistedstrongly to become spheres,Soluble forming colloids.Examples = enzymes, antibody,hormone, globulin (in bloodserum)

SIMPLE PROTEINS : pureprotein, does not contain othermaterials, e.g. fibrous & globularproteins.

CONJUGATED PROTEINS :Bound to non-protein portion(prosthetic group)

Type of prosthetic group(TPG)=1) Lipid, Type of conjugatedprotein (TCP)= Lipoprotein,Found in the site (S) = cellmembrane.2) TPG=Polysaccharide, TCP =Glycoprotein, S = blood cells &

serum,

3)TPG = Pigment Molecule (e.g.hem group), TCP =chromoprotein, S = myoglobin &hemoglobin

4) TPG = metal ions [like Fe2+ inhem group], TCP =metaloprotein, S = Hb &myoglobin, cytochrome(carrierof electrons in photosynthesis.)DNA, RNA. TCP =

nucleoprotein, S = chromosome& ribosome.

PROPERTIES OF PROTEIN :1) Globular proteins not verysoluble in water because largemolecules, forming colloidalsuspension

2) Globular proteins have thesame properties as aminoacids, i.e. a) amphoteric, withcharacteristics of both acid &base, as polypeptide chainshave NH2 on 1 end, & --COOHat the other end.

8/8/2019 2 Protein 11

5/5

PROTEIN (15)

3) Denaturation process :e.g.Coagulation of egg whitebeing cooked, Hair perm.

Above 40o

C begins to destroyprotein cross network broken protein molecule opens,straightens folds, & becomesrandom conformation.=irreversible process.Caused by i) heat ii)chemicals with extreme pH,e.g. detergents, heavymetals, organic solvents.

FUNCTIONSOF PROTEIN

As an enzyme, hormone,building of bodily structures,broken down into amino

acids for cell respiration. In physiological activities :

1) Nutrition (e.g. amylase)

2) respiration & transport(e.g. Hb)

3) Growth (e.g. thyroxine)

4) Excretion (arginase)

5) Support and movement (osein)

6) Sensitivity & coordination (e.g.vasopressin /ADH reduces urineon a hot day)

7) reproduction (chromatin)

TESTS :1) Millon (mercuric nitrate+ nitrous acid) + protein whenheated produces brick red/pinkprecipitate

2) Biuret ( calcium hydroxide +copper sulphate + protein) =purple precipitate

Nucleic acids :

Complex, contains CHONP = longpolymer nucleotide chain =polynucleotide.

Structure of a nucleotide =phosphate group + pentose sugar+ nitrogenous base.

Phosphate group originatesfrom phosphoric acid, givingthe nucleic acid an acidicproperty.

Nitrogenous base = 2 groups Purine, with double rings =

adenine (A), Guanine (G)