Proteins

Proteins are polymers of amino acids. The shape and thus the function of a protein is determined by the sequence of its amino acids. Proteins must be broken down (hydrolyzed) to amino acids before they can be utilized. Once absorbed, amino acids are utilized to make proteins or are converted to energy. About 20% of the human body is made of protein.
Functions of Proteins include:

Sources of protein
Eggs        Milk        Legumes        Meat        Fishs

Amino Acid

Proteins are composed of amino acids

Contain an amino group ( -NH₂ ) and an acid group ( - COOH ).

There are twenty amino acids that are found in proteins.

Why do we need to eat protein?

Peptide Bond

A bond formed by the condensation of the amino group ( -NH₂ ) of one amino acid with the acid group (-COOH ) of another amino acid resulting in the loss of water.

These bonds are not easily broken. Cooking would not normally result in their breakage.

Condensation - Hydrolysis

Removal of water (H₂O) and formation of a bond is called condensation. This occurs in the formation of a number of polymers

The reversal of this is hydrolysis that involves the addition of water to a bond, with the result that the bond is broken.

You should know the difference.

Amino Acids

The body can make over half of the kinds of amino acids it uses to make proteins.

Those amino acids the body cannot make must be eaten.

These are known as essential amino acids.

You should know the essential amino acids for man.

Essential

Phenylalanine (PKU)

Tryptophan

Histidine (Essential for infants)

Valine

Leucine

Isoleucine

Lysine (Extra Nitrogen Very important to growing animals)

Threonine

Methionine( Contains sulfur - Often limiting in legumes)

Additional Needs

Some additional needs for nitrogen: Synthesis of: Purines, Pyrimidines, Porphyrin

For example:

Nucleic Acids

ATP

Hemoglobin

Cytochromes

Protein Deficiencies

• Kwashiorkor -Results from a protein deficient diet that contains sufficient calories. Symptoms: bloated belly and extreme apathy
• Marasmus - Results from a deficiency of both protein and calories. Symptoms: Very low body weight and muscle wasting.

Protein Quality

Does the kind of protein matter?

Yes, Protein Quality Matters

Describes nutritive value of a protein related to amino acid composition & digestibility

Ultimately related to ability of a protein to provide the amino acids necessary for body to synthesis new proteins

Protein Quality

Ideal protein would have all the essential amino acids in the correct proportions for optimum rates of growth & maintenance

Does such a food exist?

Limiting Amino Acid

When necessary amino acids are present, protein synthesis occurs

If even one necessary amino acid is missing, protein synthesis stops

= Specific amino acid present in the lowest quantity compared to need

Limiting Amino Acids: 
               "Keep off the Grass"

Amino Acid Requirements

Measuring Protein Quality

3 main indices

Protein Efficiency Ratio (PER)

Net Protein Utilization (NPU)

Biological Value (BV)

PER Values

Egg                                    3.90

Soy                                    2.32

Cotton seed meal                   2.35

Sesame seed                         1.77

Chick pea                            1.68

Peanuts                               1.65

Corn                                  1.41

Kidney beans                        0.88

Limiting Amino Acids

Cereals:  Corn, Rice, Wheat, Oats, Barley                             LYSINE

Legumes & Oilseeds: Black bean, Peanut, Chickpea,             METHIONINE

         Soy, Green bean, Potato, Milk

Complementary Relationships

By combining a protein deficient in a specific amino acid with a protein that has an excess of that amino acid, protein quality is increased!

Complementary Relationships

Food                                                   PER

Rice                                                   2.30

Black beans                                        nil

Rice (70%) + Black beans                   2.70

Rice (60%) + Black beans                   2.60

Rice (50%) + Black beans                   1.30

Corn                                                  1.41

Corn + Black beans                            2.05

Amino Acid Requirements

Prion Diseases

TSE

Kuru (1950Õs)

Scrappie (1750)

BSE (1986) "Mad Cow"

Chronic Wasting Disease (1960Õs)

Sporadic Fatal Insomnia - 6 known cases

Creutzfeldt-Jakob Disease (1920)

Variant Creutzfeldt-Jakob Disease (1994)

Slow Virus or Prion?

Thought to be  very slow growing virus

Incubation time = 40 years

No nucleic acid

Prion - infectious protein

Normal form plays a role in brain plasticity

Resistant to heating and hydrolysis

Prion Proteins

Kuru

South Fore on New Guinea (8000 total population)

Total of 1000 died in the 1960Õs

Women 8 times as likely 

Mortuary cannibalism

Scrapie

First detected in sheep in Great Briton 250 years ago

2 to 5 years for infection to show

From ewe via placenta

Cross species spread via inoculation in brain

Creutzfeldt-Jakob Disease

Usually between ages of 50 and 70

         Inherited - 5% of all cases

         Sporadic - unknown

         Infection -rare

Average = 63  one case per million

vCJD - Average age= 28 (156 as of 6/30/2006)

Tissue Infectivity

Category I: High Infectivity

Brain, spinal cord, (eye)

Category II: Medium Infectivity

Spleen, tonsil, lymph nodes, ileum, proximal colon, cerebrospinal fluid, pituitary gland, adrenal gland

Category III: Low Infectivity

Peripheral nerves, nasal mucosa, thymus, bone marrow, liver,lung, pancreas

Category IV: No Detectable Infectivity

Skeletal muscle, heart, mammary gland, serum, feces, kidney, thyroid, salivary gland, saliva, ovary, uterus, testis, seminal testis, (colostrum, bile, bone, cartilaginous tissue, connective tissue, hair, skin, urine).

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