HOMEWORK #4 - CHAPTER 6 - HUN 1201 - PROTEINS

Outline the health benefits and recommendations for protein.

Protein deficiency impairs the body's ability to grow and function optimally. Excesses of protein offer no advantage; in fact, overconsumption of protein-rich foods may incur health problems as well. The optimal diet is adequate in energy from carbs and fat and delivers 0.8 gram of protein per kilogram of healthy body weight each day. U.S. diets are typically more than adequate in this respect. Normal, healthy people do not need protein or amino acid supplements.

Explain the difference between high-quality protein and low-quality protein, and give important food sources of each. Define complementing proteins and give an example.

A diet that supplies all of the essential amino acids in adequate amounts ensures protein synthesis. The best guarantee of amino acid adequacy is to eat foods containing high-quality proteins or mixtures of food containing complementary proteins that can each supply the amino acids missing in the other. In addition to its amino acid content, the quality of protein is measured by its digestibility and its ability to support growth. Such measures are of great importance in dealing with malnutrition worldwide, but in countries where protein deficiency is not common, the protein quality of individual foods deserves very little emphasis.

Describe briefly how the body makes proteins and then uses them to perform various roles.

Cells synthesize proteins according to genetic information that dictates the sequence in which amino acids are grouped together. Each protein plays a specific role, specifically 8. (see Table 6-3 for more information). Proteins are constantly being synthesized and broken down as needed. The body's assimilation of amino acids into proteins and its release of amino acids via protein breakdown and excretion can be tracked by measuring nitrogen balance, which should be positive during growth and steady in adulthood. An energy deficit or an inadequate protein intake may force the body to use amino acids as fuel, creating a negative nitrogen balance. Protein eaten in excess of need may be deaminated and converted to glucose (and stored as glycogen) or ketone bodies (and stored as fat).

Explain the chemical structure of amino acids and proteins.

Chemically speaking, proteins are more complex than carbs or lipids; they are made of some 20 different amino acids, 9 of which the body cannot make (the essential amino acids). Each amino acid contains an amino group, an acid group, a hydrogen atom, a distinctive side group, and an R group, all attached to a central carbon atom. Peptide bonds link amino acids together in a series of condensation reactions to create proteins. The distinctive sequence of amino acids in each protein determines its unique shape its various functions.

Summarize protein digestion and absorption.

Digestion is facilitated mostly by the stomach's acid and enzymes, which first denatures dietary proteins, then cleave them into smaller polypeptides and some amino acids. Pancreatic and intestinal enzymes split these short polypeptides further, to tripeptides and dipeptides, and then split most of these to single amino acids. Then carriers in the membranes of intestinal cells transport the amino acids into the cells, where they are released into the bloodstream.