Chapter 6: Proteins

Proteins

Nitrogen-containing macronutrients found in every body cell.

Essential amino acids

Nine amino acids that must come from food. (Histidine (His) lowercase aIsoleucine (Ile)Leucine (Leu)Lysine (Lys)Methionine (Met)Phenylalanine (Phe)Threonine (Thr)Tryptophan (Trp)Valine (Val))

Nonessential amino acids

Eleven amino acids the body can make. (Alanine (Ala)Arginine (Arg)Asparagine (Asn)Aspartic acid (Asp)Cysteine (Cys)Glutamic acid (Glu)Glutamine (Gln)Glycine (Gly)Proline (Pro)Serine (Ser)Tyrosine (Tyr))

Conditionally essential amino acids

Normally made by the body but may be needed from food during illness or special conditions.

Peptide bond formation

Condensation joins amino acids by removing water.

Peptide bond breakdown

Hydrolysis breaks peptide bonds by adding water.

Primary protein structure

The amino acid sequence of a protein.

Tertiary protein structure

The three-dimensional shape of a protein.

Quaternary protein structure

Multiple polypeptide chains joined together.

Protein denaturation

A change in protein shape and function that does not alter primary structure.

Stomach protein digestion

Hydrochloric acid denatures proteins; pepsin breaks them into smaller chains.

Small-intestine protein digestion

Pancreatic and brush-border enzymes continue and finish digestion.

Amino acid absorption

Amino acids enter the liver through the portal vein after absorption in the small intestine.

Protein turnover

The body continually breaks down and rebuilds proteins, exceeding 200 grams daily.

Transcription

DNA is used to produce messenger RNA.

Translation

Ribosomes read messenger RNA during protein synthesis.

Elongation

Transfer RNA delivers amino acids to build proteins.

Deamination

Removal of an amino group produces ammonia, which the liver converts to urea.

Transamination

Transfer of nitrogen to form new nonessential amino acids.

Protein's role in fluid balance

Protein helps maintain fluid balance.

Protein's immune function

Proteins support immunity by forming antibodies.

Energy from protein

4 kilocalories per gram.

Protein RDA for healthy adults

0.8 grams per kilogram of body weight daily.

Protein AMDR

10% to 35% of daily calories.

Protein needs of active individuals

1.2 to 2.4 grams per kilogram daily, depending on training level.

Positive nitrogen balance

Occurs during growth, pregnancy, and recovery.

Negative nitrogen balance

Can occur with illness, injury, or inadequate nutrition.

Complete proteins

Contain all nine essential amino acids.

Complementary proteins

Combining plant foods such as grains and legumes provides all essential amino acids.

Kwashiorkor

Severe protein deficiency associated with edema, growth failure, muscle loss, and increased infection risk.

Marasmus

Severe calorie deficiency associated with extreme weight loss, muscle wasting, and weakness.