Chapter 6
The Proteins and Amino Acids
Nutrition: Concepts & Controversies, 12e
Sizer/Whitney
The Structure of Proteins
 Difference from carbohydrates and fats
 Amino acids
 Carbon atom with amine group and acid
group
 Side chain
 Essential amino acids
 Conditionally essential
 Recycling
 Priority system
How Do Amino Acids Build
Proteins?
 Peptide bonds
 Link amino acids
 Strands of amino acids do not remain
straight
 Coils
 Folds
 Side chain electrical charge
 Activation
The Coiling and Folding of a
Protein Molecule
The Structure of Hemoglobin
Normal Red Blood Cells and
Sickle Cells
Protein Synthesis
Denaturation of Proteins
 Denaturing agents
 Digestion
 Stomach acid
 Dangers of
denaturation
Protein Digestion
 Stomach
 Denatures protein in food
 Uncoil protein’s strands
 Enzymes attack peptide bonds
 Small intestine
 Polypeptides
 Further break down
 Common misconceptions
A Dipeptide and Tripeptide
How Protein in Food Becomes
Amino Acids in the Body
Amino Acid Absorption
 Absorbed by cells of small intestine
 Larger molecules
 Hormones or allergens
 Separate sites for absorption
 Released into the bloodstream
 Carried to the liver
The Importance of Protein
 Amino acids must
be continually
available
 Building of new
proteins
 Amino acids are
needed each day
 Protein turnover
Roles of Body Proteins
 Regulation of gene expression
 Providing structure and movement
 Muscle tissue
 Other structural proteins
 Building enzymes, hormones, & other
compounds
 Building antibodies
Enzyme Action
Amino Acid Sequence of Human
Insulin
Roles of Body Proteins
 Transporting substances
 Hemoglobin and lipoproteins
 Maintaining fluid and electrolyte balance
 Edema
 Maintaining acid-base balance
 Blood clotting
 Providing energy and glucose
Proteins Transport Substances
Into and Out of Cells
Amino Acids to Glucose
 Protein can help maintain blood glucose
levels
 No storage compound for protein
 Dismantle tissue proteins
 Oversupply of amino acids
 Remove amine group
 Use of residues
Three Different Energy Sources
Amino Acids to Glucose
 Fate of an amino acid
 Cellular use
 Build protein
 Make a needed compound
 Dismantle amino acid for component parts
 Wasting of amino acids
 Preventing waste
People Most Likely to Be Harmed
by Amino Acid Supplements
How Much Protein Do People
Really Need?
 DRI
 Depends on body size
 Infants and growing children
 Recommended intake
 Vegetarians
 Minimum amount
 Upper limit
 Body’s health
 Quality
Nitrogen Balance
 Nitrogen excreted as compared to nitrogen
eaten
 Levels in healthy adults
 Variation in nitrogen balance
 Positive balance
 Examples
 Negative balance
 Examples
Which Foods Provide High Quality
Protein?
 High-quality proteins
 Enough of all essential amino acids
 Limiting amino acids
 Complementary proteins
 Mutual supplementation
 Protein digestibility
 Animal proteins
 Legumes
A Legume