Download Proteins - TC Online

Protein: Amino Acids
Chapter 6
Major points in chapter 6







What is a protein
Factors affecting the shape of a protein
Digestion and absorption
Roles of proteins in the body
Protein quality
Protein recommendations
Health effects
What is a protein?





Greek—”to come first”
Contains nitrogen
Used primarily for regulation and
maintenance of the body
Can supply energy—4 kcal/g
Made of amino acids (at least 100)
Amino Acids

Body proteins made of 20 different
amino acids linked together by
condensation reactions and cleaved by
hydrolysis




Amino acids differ in side chain
9 are essential (see p. 174)
11 are nonessential—can be synthesized
by transamination
Conditionally essential
Levels of protein structure



The shape of a protein eventually dictates its
function
This shape is dependant on the amino acid
sequence (primary structure), the kinking and
twisting of the chain (secondary structure),
the folding of the chain (tertiary structure),
and interaction with other proteins
(quaternary structure)
Hemoglobin example
denaturation



Changing the shape of a protein
It can no longer perform its usual
function
Example cooking a egg
Digestion and absorption of
protein


Enzymes and HCl in stomach begin process
(pepsin)
In small intestine




Pancreatic enzymes (proteases) polys into 1,2, &
3 amino acid units
Intestinal enzymes on villi (peptidases) convert
to single amino acids
Amino acids are absorbed from the villi into
the blood stream
Travel to the liver
Making proteins


We use the amino
acids from dietary
proteins as building
blocks for our own
proteins
DNA provides the
template for the
formation of body
proteins
Roles of protein in the body








Vital body constituents
Fluid balance
Acid/base balance
Hormones and enzymes
Immune function
Transporters
Gluconeogenesis
energy
Nitrogen balance



Protein turnover
Positive
Negative
Protein in food



Complete proteins provide all of the
essential amino acids
Animal sources usually complete, plant most
have a limiting amino acid except soy
Protein quality—ability of a food protein to
support growth and maintenance based on
digestibility and amino acid content



Biological value, PER, chemical score, PDCAAS
All based on comparisons to albumin (reference
protein)
Complementary proteins
Protein recommendations

10-35% total kcals


50-175g/day for adults
0.8g/kg of healthy body weight
Health effects: too little
protein

PEM


Kwashiorkor
Marasmus
Health Effects: too much
protein


Osteoporosis—calcium loss in urine
Colon cancer?




Red meat
Processed foods
Kidney disease
Heart disease?


Animal proteins
Homocysteine