PROTEIN

General: ~100,000 different proteins in the body. Protein is present in every cell. Body is ~80% protein on a dry fat-free basis. Primary function of CHO & lipid is energy, BUT protein is different.

Function:

1. Structural (skeletal muscle, connective tissue, protective protein)

2. Specialized functions (enzymes, hormones, blood proteins)

3. Energy - AA converted to Krebs cycle intermediates

Hogs - starving - use protein for energy (glucose can be made from some aa)

 Composition: C,H, O, N some have S, and (or) P, [ALL have N]

Range 14-20% N for proteins, AVG. = 16% (100/16 = 6.25)

Kjeldahl N= allows us to measure N content Þ %N X 6.25 = %Crude Protein

True protein is comprised up of Amino Acids. Polymer (many units) of amino acids.

We eat protein because our body needs AA

Dietary AA ® AA in intestinal lumen ® AA in blood ® Tissue Protein

Amino Acids

There are about 20 AA we are concerned with for this class.

All ~100,000 different proteins are comprised of several combinations of these proteins.

General Structure:

a -carbon is the most reactive

R-group = what gives the AA individuality to the 20 different AA

Properties: Serve in two capcities

Carboxyl group = has acid properties Þ donates H in solution

Amino group = has base properties Þ accepts H in solution

Dissolve AA in neutral solution (pH = 7.0), can act as an acid or a base ("Zwitter ion")

Classification

Chemical (R-group) Method = based on properties of R group

1) Neutral = R group is uncharged (monoamino, monocarboxyl)

2) Acidic = R group contains more carboxyl than amino (neg. charge)

3) Basic = R group contains more amino than carboxyl (pos. charge)

4) Sulfur = R group is/contains S

5) Aromatic = R group has a ring structure

l

Dietary Requirement Method

1) Essential = Any AA that can not be synthesized by the body at a rate that can meet the bodies requirement Þ required in the diet (essential to consume). There are ~10 essential AA.

MATT HILL V.P. or PVT. TIM HALL

P = Phenylalanine

V = Valine

T = Threonine

T = Tryptophan

I = Isoleucine

M = Methionine

H = Histidine

A = Arginine

L = Leucine

L = Lysine

2) Non-Essential = can be synthesized by the body (at an appreciable rate)

1930's: Dr. Rose of Univ. Illinois was first to classify essential vs. non-essential AA. His model was the growing rat.

Exceptions:

Arginine = Adult mammals do not require (growth only)

Glycine = chickens require, feathers and uric acid production

Taurine = essential for the cat