2- Protein Chemistry

8/6/2019 2- Protein Chemistry

1/52

PROTEIN CHEMISTRY


2/52


3/52

Proteins

Proteins are complex organicnitrogenous compounds of highmolecular weight

Proteins are the most complexmaterials produced in nature

They are consisting largely orentirely of -amino acids linkedtogether by peptide linkages


4/52

Proteins The name protein is derived from the

Greekwordproteios of prime importance this is because proteins are the basis ofthe cytoplasm of cells and are present in all

living organisms Without proteins life would NOT bepossible

Proteins are the most abundantmacromolecules in living cells andconstitute 50 % or more of their dry

weight


5/52

Proteins Proteins are polymers of-Amino Acids.

Proteins are synthesized from only 20 aminoacids, known asthe common amino acids

Amino acids are formed mainly of carbon,

hydrogen, oxygen and nitrogen

Nitrogen is a characteristic component of

proteins forming about 16% of their weight i.e.100 g of protein contains 16 g of nitrogen

Proteins perform many essential functions


6/52

BIOLOGICAL IMPORTANCEOF PROTEINS

1- Plasma membrane proteins (channel,carrier, pump proteins) regulate thetransfer of various substances across

the cell membrane 2- All receptorsare protein in nature

3- All enzymes are proteins in nature 4- All antibodies (Immunogobulins) are

proteins in nature


7/52

BIOLOGICAL IMPORTANCE

OF PROTEINS

5- Some hormones are proteins in nature e.g.

Insulin, Glucagon, Growth hormone, FSH,LH. 6- Some proteins are protective e.g. Keratins

(skin, hair, nails) make the skin resistant tochemicals 7- Some proteins have supportive functions

e.g. Collagen; the most abundant protein in

animals. 8- Hemoglobin is a protein carries O2 in the

blood


8/52

BIOLOGICAL IMPORTANCEOF PROTEINS

9- Actin and Myosin are contractileproteins found in muscle cells and areresponsible for muscular contraction

10- Amino acids are converted to othernitrogenous substances of great

physiologic importance e.g. Creatine,Histamine, Serotonin, Heme, Purines,Pyrimidines.


9/52

AMINO ACIDS

- Amino acids are the building unitsof proteins.

Each - amino acid consists of an

amino group (-NH2), a carboxylic acidgroup ( -COOH ), a hydrogen atom

(-H ) and a side chain group (-R), allconnected to a carbon atom called -carbon atom.


10/52

AMINO ACIDS

The -carbon is the first carbonadjacent to the COOH group.

The side chain group ( R ) is specific

and unique for each amino acid. The R may be a hydrogen, a straight

or branched- chain aliphatic group, anaromatic ring or a heterocyclic ring.


11/52

AMINO ACID

Representation of Amino Acid

NH2

H

R C

carboxylicgroup

amino group

side chainradicle

- carbonatom

COOH

Hydrogen atom


12/52

Basic Amino Acid Structure -Carbon is chiralin all amino acids

except for glycine.

At pH 7.0 aminoacids have both

+ve and-ve chargesso called dipolar ionor zwitterions

Amino acids havea tetrahedralstructure (3Dshape).


13/52

Natural Amino Acid are inthe L-configuration

L and D forms are called Optical isomers (=Stereoisomers = Enantiomers)

Biological system in all organisms synthesize and use

only L-amino-acids


14/52

The R group determines the amino acid

Basic (+ve)

Charged polar

Lysine-CH2CH2CH2CH2NH2

Acidic (-ve)

Charged polar

Aspartic acid- CH2COOH

Uncharged polarCysteine- CH2SH

Uncharged polarSerine- CH2OH

Non-polarAlanine- CH3

Non-polarGlycine- H

Side chainAmino acidR group


15/52

VValValineIIleIsoleucine

YTyrTyrosineHHisHistidine

WTrpTryptophanEGluGlutamic acid

TThrThreonineQGlnGlutamine

SSerSerineGGlyGlycine

PProProlineCCysCysteine

FPhePhenylalanineDAspAspartic acid

MMetMethionineNAsnAsparagine

KLysLysineRArgArginine

LLeuLeucineAAlaAlanine

One letterThree

letter

One letterThree

letter

AbbreviationAmino AcidAbbreviationAmino Acid

Table: Abbreviations for the 20 Amino Acids


16/52

CHEMICAL CLASSIFICATION

The 20 amino acids are classified according to thechemical structure of the side chain ( R ) into:

1. Aliphatic

2. Hydroxy3. Sulfur containing

4. Aromatic

5. Acidic

6. Basic

7. Imino acids


17/52

All aliphatic AA are nonpolar (Hydrophobic)

Valine, Leucine and Isoleucine are branched-chain AA


18/52

Hydroxy Amino Acids

Hydroxy AA (Serine and Threonine) are Polar(Hydrophilic)

They Can form hydrogen bonds with their OH groups


19/52

Sulfur Containing Amino Acids

Cysteine: Important in disulfide linkages

polar, Can form hydrogen bonds

Methionine: Methyl donor

Non-polar (hydrophobic)


20/52

Aromatic Amino Acids

Phenylalanine and Tryptophan are nonpolar(hydrophobic)

Tyrosine is polar (hydrophilic): H-Bonding with its

(OH).


21/52

Aspartate and glutamate are polar and negativelycharged (-ve) at physiologic pH

Asparagine and glutamine are polar but non charged

Acidic Amino Acids and their

amides


22/52

Basic Amino Acids

Arginine, Lysine and Histidine are polar andpositively charged (+ve) at physiologic pH


23/52


24/52

Imino Acids

Proline is imino acid because it contains imino group

(-NH) not amino group (-NH2)

Proline is heterocyclic and non-polar AA.


25/52


26/52


27/52

NUTRITIONALCLASSIFICATION of AA

(B)- NON-ESSENTIAL AMINO ACIDS: Can be synthesized inside the body, so they must

not be taken in the diet. They include the other

10 amino acids N.B. The essential amino acids are not more

important to our body than the non-essential

amino acids. Both (all 20 AA) are equally needed and equally

essential for the normal growth and good health


28/52

Table: Nutritionally Essential and

non-Essential Amino Acids

10- Tyrosine10- Valine

9- Serine9- Tryptophan

8- Proline8- Threonine

7- Glycine7- Phenylalanine

6- Glutamic acid6- Methionine

5- Glutamine5- Lysine

4- Cysteine4- Leucine

3- Aspartic acid3- Isoleucine

2- Asparagine2- Histidine

1- Alanine1- Arginine

Non-Essential Amino AcidsEssential Amino Acids


29/52

Amino Acid deficiency in Selected

Vegetables and Grains

Low in MethionineSoy

Lysine, TryptophanAlmonds, Walnuts

MethioninePeas

Methionine, TryptophanBeans

Lysine, TryptophanCornLysineWheat, Rice, Oats

NoneEggs, Milk, Meat, Fish, Poultry

Amino Acid MissingFood Source


30/52

PROPERTIES OF AMINOACIDS

All amino acids are optically activeexcept Glycine, this is because all

AA contain asymmetric carbonatom but in Glycinethe R group isa hydrogen atom so it has noasymmetric carbon atom


31/52

Amino acids are linked together by condensationreaction between carboxylic and amino groupsfrom two different amino acids (with eliminationof water). The amide bond formed is called

peptide bond The product is called a peptide, and namedaccording to the number of amino acids involved:e.g. dipeptide (2), tripeptide (3), decapeptide

(10)

Big peptides (> 50 amino acids) are calledpolypeptides

Linking of amino acids: Peptide

Bond Formation


32/52


33/52


34/52

PROTEIN

STRUCTURE


35/52

PROTEIN STRUCTURE

A protein molecule may consist of one or

more polypeptide chains, which are usuallyfolded in regular manner that gives themolecule a specific shape

A polypeptide chain is formed of L--amino acids linked together by peptidebonds

At one end of the polypeptide chain thereis a free -amino group, the N-terminalamino acid residue


36/52

PROTEIN STRUCTURE

At the other end there is a free -

carboxyl group, the C- terminal amino acidresidue

The peptide structure are written with

the N-terminal residue at the left andwith the C-terminal residue at the right


37/52


38/52

Protein structure:

conformation and assembly

Primary Structure: The order of aminoacids: Amino acid sequence

Secondary Structure: H-bonding between

amino acids: twisting and folding Tertiary Structure Ionic-covalent- bonds:

Overall folding: spherical OR fibrous shape Quaternary Structure Organization ofmultiple protein units together


39/52


40/52

Secondary StructuresSecondary StructuresAAsAAs areare arranged to minimize collision and to form Harranged to minimize collision and to form H--bondsbonds

Alpha Helix


41/52

Alpha Helix

Pleated Sheets


42/52

Pleated Sheets


43/52


44/52

Intermolecular Forces in ProteinsIntermolecular Forces in ProteinsIntermolecular Forces in ProteinsIntermolecular Forces in Proteins


45/52

Intermolecular Forces in ProteinsIntermolecular Forces in ProteinsIntermolecular Forces in ProteinsIntermolecular Forces in Proteins

Hydrogen bonding

Ionic bonds

Disulfide linkages Dispersion forces

Q SQ t St t


46/52

rganization of multiple proteins (units) together

Quaternary StructuresQuaternary Structures

Example: hemoglobin: 2 units - 2 units.


47/52

DENATURATION OF PROTEINS


48/52


It is the destruction of the

organization (internal structure) ofthe protein molecule (2ry, 3ry and 4rystructures) but the primary structure

remains intact So the polypeptide chains become

unfolded and irregularly arranged


49/52


CAUSES:

a- Physical agents: Heat, UV rays, X-ray, ultrasound

wave, high pressure or excessiveshaking

b- Chemical Agents:

acids, alkalis or urea


50/52

Effects of Denaturation

Denaturation destroys the biologicactivity of a protein, there is loss ofhormonal, enzymatic and antibody

activity. The biologic activity of a protein

depends on their native conformation.

Denaturation destroys the nativeconformation of protein.


51/52

Applications of protein denaturing


52/52

Applications of protein denaturing

1- Boiling eggs: Change in albumin shape andsolubility.

2- Cooking meat: Easily chewable,digestible.

3- swabbing skin with alcohol (disinfectant):

Denatures/kills bacteria and viruses.

4- HCl in our stomach: denatures proteins,

making it easily digestible by enzymesSo, eating cooked eggs, meat and liver is more useful tohumans than eating them raw

Date post:	07-Apr-2018
Category:	Documents
Upload:	nhartono
View:	218 times
Download:	0 times

2- Protein Chemistry

Documents