chapter 6: proteins. overview of protein body is made up of thousands of protein substances contains...
TRANSCRIPT
Chapter 6: Proteins
Overview of Protein
• Body is made up of thousands of protein substances
• Contains nitrogen
• Regulates and maintains body functions
Amino Acid
R group Acid group
Amine group
NH2 O
R C C OH
H
Tyrosine
Serine
ProlineValine
GlycineTryptophan
GlutamineThreonine
Glutamic acidPhenylalanine
CysteineMethionine
Aspartic AcidLysine
AsparagineLeucine
ArginineIsoleucine
AlanineHistidine
Nonessential AAEssential AA
Dietary Protein
• High-quality– complete
• Low-quality– incomplete
• All-or-none principle in protein synthesis
• Limiting amino acid
• Complementary protein
Limiting Amino Acid
CCCCC
AAAAAAAA CAR CAR CAR
RRRRRR CAR CAR
R
A A A
C is the limiting amino acid in this example
Complementary Protein
Food 1 Food 2
CC CCCC
AAAA AA CAR CAR CAR
RRR RRR CAR CAR CAR
Complementary ProteinBeans (legumes)
Grains Nuts/seeds
Vegetables
Protein Synthesis
• DNA contains coded instructions
• Copies of codes are transferred to the cytoplasm (via mRNA)
• Amino acids added one at a time with aid of tRNA
Protein Synthesis
Protein Turnover
• Protein undergo breakdown and synthesis
• Responds to change
• Amino acid can be recycled
Protein Organization
• Peptide bond• Dipeptide• Tripeptide• Oligopeptide
SH SH
CH2 CH2
H O CH H2O H O CH
H N C OH H N C OH H N C N C OH
CH H O CH H O
CH3 H2O CH3
Denaturation of Proteins
Heat/acid/alkaline/enzymes
Results in alteration of the protein’s three
dimensional structure
Protein in Foods
Plant Protein
• Provide protein, minerals, and dietary fiber
• Contain no cholesterol
• Limited saturated fats
• Allow a few weeks for the GI tract to adjust to the higher fiber
• Availability of Beno®
Digestion of Protein in the Stomach
• Proteins are denatured by cooking and acid in the stomach
• Gastrin stimulates the release of acid and pepsin• Pepsin is activated and breaks down proteins into
peptones
Digestion of Protein in the Small Intestine
• Stimulates the release of CCK• Pancreas release the protein splitting
enzymes: trypsin, chymotrypsin, and carboxypeptidase into the duodenum
• The enzymes will break peptones into smaller peptides and amino acids
• Peptides and amino acids are ready for absorption
Protein Absorption• Active absorption• Whole proteins are broken down at the
microvilli surface and within the absorptive cells• Whole proteins are eventually broken down to
amino acids • Many different amino acid transport
mechanisms • Amino acids are sent to the liver via portal
circulation
Functions of Proteins
• Building blocks of body components
• Maintain fluid balance
• Contribute to acid/base balance
• Building blocks for hormones and enzymes
• Immune function
• Gluconeogenesis
• Energy yielding
RDA for Protein
• Promotes equilibrium• 0.8 gm of protein / kg of healthy body weight
154 lb. = 70 kg
2.2 kg/lb.
70 kg x 0.8 g protein = 56 g protein
kg healthy body wt
RDA for Protein
• Increased by ~10-15 gm /day for pregnancy• Endurance athletes may need 1.5 - 2 gm/kg
healthy weight• About 8-10% of total kcals• Most of us eat more than the RDA for
protein• Excess protein cannot be stored as protein• New DRI for protein coming
Is a High-Protein Diet Harmful?
• Low in plant foods (fiber), vitamins, phytochemicals
• Intake of animal protein increases risk for heart disease (high in saturated fat)
• Excessive intake of red meat is linked with colon cancer
• Burden on the kidney• Increase calcium loss• National Academy of Sciences recommend no more
than 2 x RDA for protein
Individual Amino Acid Supplement
• Supplement may cause imbalances and toxicities
• Body is designed to handle whole proteins
• Supplement can overwhelm the absorptive mechanism
• Excess of one AA can hamper absorption of other AAs
Malnutrition
• Protein-Energy Malnutrition
• Marasmus– Seen in hospitalized patients
• Kwashiorkor
Kwashiorkor• Low protein density
diet• Energy needs are
marginally met• Signs and symptoms:
– Apathy, listlessness, failure to grow, poor weight gain, change in hair color, nutrient deficiency, flaky skin, fatty infiltration in the liver, massive edema in the abdomen and legs
Marasmus
• Starving to death• Insufficient protein,
energy, nutrients• “skin and bones”
appearance• Little or no
subcutaneous fat• Reduce brain growth
Soy
• Soy protein is similar to animal protein (used in school lunches)
• High in linoleic acid and some linolenic acid
• Calcium source and bone health• Isoflavones• Heart disease• Cancer
Vegetarian Diets
• Why become a vegetarian?
• Vegans
• Fruitarians
• Lactovegetarians
• Lactoovovegetarians
The Vegetarian Diet Pyramid