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Proteins and Amino Acids

Department of Biochemistry and Molecular BiologyTarumanagara Univ. School of Medicine.

BIOCHEM Lecture

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Natural Proteins

Polymers consisting of widely varying numbers and

combinations of about 22 individual amino acids linked by

peptide bonds in various alignments and shapes.

Plants synthesize all 22 AAs. Animals synthesize

only 11-14. Rest (8-11) are dietary essentials.

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Peptide Bond

Bonds that couple the alpha carbonyl group of

one amino acid residue to the alpha amino group

of another residue.

Peptide bond

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Classification of Proteins

- Based on shapes and solubilities

I. Globular Proteins

Soluble in water, dilute acids or bases or

alcohol

II. Fibrous Proteins

Insoluble in water, resistant to digestive enzymes

III. Conjugated Proteins

Amino acids bound to some type of non-amino

group

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Proteins Differ Greatly in

QualityQuality of a protein is high if it contains all of the

essential amino acids in the proper ratios for a

specific animal.

Varies by: species, age, gender, productive

function

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Alpha Amino Acid

Acid =

Amino = NH2

General Structure

= Carboxyl

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A. Albumins; Egg and Serum

- Soluble in water

- Coagulated by heat

- Some contain carbohydrate (CHO)

-Therefore, are conjugated proteins also.

__________________

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B. Globulins, 80% of oilseed proteins

- Insoluble in water

- Soluble in salt solutions, NaCl

- Heat labile

- Examples: fibrinogen, myosinogen, legumin

of peas, glycinin in soybean, serum globulin(also a glycoprotein)

__________________

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C. Glutelins; corn, wheat, barley

- Insoluble in water, neutral saline

- Soluble in dilute acids or bases

__________________D. Prolamines

- Soluble in ethanol

- Examples:

Zein in cornHordein of barley

Gliadins of wheat, rye

_________________

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E. Histones

- Basic proteins

- Excess of basic amino acids- Often combined with nucleic acids;

DNA, RNA

- Examples: globin, part of hemoglobin

__________________

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A. Collagens; skeletal connective tissue

- Insoluble without treatment

- Changed into digestible gelatins by boiling- Large amounts of hydroxyproline

- No cystine, cysteine or tryptophan

__________________

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B. Elastins; tendons and arteries

- Similar to collagens

- Cannot be converted to gelatin- Poorly digested

- High in lysine

________________

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C. Keratins; feathers, hair, claws, beaks

- Very insoluble & indigestible, zero

- High cystine, 14-15%- Treatment with heat and pressure

Cystine to 5-6%

breaksS-S- bonds

Digestibility to 70-80%

__________________

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A. Nucleoproteins

- With nucleic acids

- Examples

ribonucleoprotein

deoxyribonucleoproteins

B. Mucoproteins- With mucopolysaccharides; i.e., glucosamine,

galactosamine

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C. Glycoproteins

- < 4% CHO, hexose

- Example: in egg albumin

D. Lipoproteins

- Water soluble proteins with:

lecithin

cephalin

cholesterol

other lipids or phospholipids

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E. Chromoproteins

- simple protein to a colored prosthetic group

- Examples:

hemoglobin

cytochromes

flavoproteins

visual purple of retina

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Protein - Functions

1. Organs and soft tissues, muscle myofibrilar contractile

2. Structural proteins

Collagen

Elastin

Keratin

3. Blood

Globulins

Albumin

Globin

Fibrinogen

Lipoproteins

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Protein - Functions

4. Body Metabolism

Enzymes

digestive (Table 4.3)

degradative (Table 9.5)

synthesis, rapid to slow (See Table 9.4)

Hormones

Examples? Page. 128PTH, _______, _______

Immune antibodies

Hereditary transmission

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Protein - Functions

5. Source of energy after deamination

(pp. 135-136 in Text)

alanine PA + NH3

Also, AA, BA, VA, IVA

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Amino Acids - Classification

(pp 121-122 in Text)

Neutral

AliphaticAromatic

Sulfur-containing

Acidic

Basic

Imino

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Neutral Amino Acids1) Aliphatic

Glycine

Alanine

Serine

Threonine

Valine

Leucine

IsoleucineAlanine

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Neutral Amino Acids

(2) Aromatic amino acids

(a) Phenylalanine (b) Tyrosine

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Neutral Amino Acids

(2) Aromatic amino acids

(c) Tryptophan

Indol

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Neutral Amino Acids3) Sulfur-containing: AA + Thiol(s)

Cysteine

Alanine + HS

Cystine

2 Cysteines with -S-S-

Methionine

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Neutral Amino Acids

(3) Sulfur-containing amino acids

(a) Cystine (b) Cysteine

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Neutral Amino Acids

(3) Sulfur-containing amino acids

(c) Methionine

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Acidic Amino Acids

2 Hydroxyl groups

Aspartic Acid4 Cs

Glutamic Acid

5 Cs

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Acidic Amino Acids

(1) Aspartic acid (2) Asparagine

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Acid Amino Acids

(3) Glutamic acid (4) Glutamine

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Basic Amino Acids

2 NH2s

Arginine

HistidineLysine

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Imino Amino Acids

NH2 not on alpha carbon

Rings, pyrolidine

Carboxylic acids

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Imino Acids

(1) Proline

2) Hydroxyproline

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L- and D-Amino Acids

Schematic

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Amino Acid Isomers

Biological ActivityAnimal TissuesAll 22 are L-isomers.

D- have no function.

DietAll must be L-isomers except:

D-Methionine, up to 50% of methionine requirement

D-Threonine, up to 25%.

D-Tryptophan, 60% for pig

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Amino Acid Isomers

Biological ActivitySynthetic AAs

Via recombinant DNA technology

Most sold as salts:

Lysine HCl = 78.8% L-Lysine

Lysine, Threonine, Tryptophan, Methionine

MHA, 80-100% relative activity

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Essential/Nonessential AAs

All 22 are required for protein synthesis/metabolism

Dietary essential/Indispensable = Those not synthesized in animal tissuesof most species in sufficient amounts to meet metabolic needs without

being added to diet.

Others are nonessential.

Varies by:

SpeciesStage of life cycle

Productive function

Maintenance vs milk

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Essential Amino Acids, Rats

Rose, 1948PVT TIM HALLA Arginine

H Histidine

I IsoleucineL Leucine

L Lysine

M Methionine

P Phenylalanine

T Threonine

T Tryptophan

V Valine

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Essential Amino Acids

A Arginine B

H Histidine B

I Isoleucine N

L Leucine NL Lysine B

M Methionine N-S

P Phenylalanine N-R

T Threonine NT Tryptophan N-R

V Valine N

E ti l A i A id

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Essential Amino Acids

A Argininefor maintenance

H Histidine

for maintenance

I Isoleucine

L Leucine

L Lysine

M Methionine/Cystine

P Phenylalanine/Tyrosine

T Threonine

T Tryptophan

V Valine

T TaurineCat

P Proline (-Amino sulfonic)

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