Proteins and Amino Acids

Chapter

6

Amino Acids Are the Building Blocks of Protein

• Proteins are sequences of amino acids

• Types of amino acids• Indispensable• Dispensable• Conditionally

indispensable

Amino Acids Are theBuilding Blocks of Proteins

• Amino acids are identified by their side groups

Amino Acids Are theBuilding Blocks of Proteins

• Protein Structure: Unique Three-Dimensional Shapes and Functions• Amino-Acid

Sequence• Protein Shape

Amino Acids Are theBuilding Blocks of Proteins

• Protein Denaturation: Destabilizing a Protein’s Shape

Functions of Body Protein

Functions of Body Protein

• Structural and Mechanical Functions• Enzymes

Functions of Body Proteins

• Hormones• Immune Function• Fluid Balance• Acid–Base Balance

Functions of Body Proteins

• Transport Functions• Sources of Energy and Glucose

Courtesy of the USDA

Protein Digestion and Absorption

• Stomach• Proteins are denatured by hydrochloric acid• Pepsin begins digestion

• Small intestine• Pancreatic and intestinal proteases and

peptidases complete digestion• Amino acids are absorbed into the

bloodstream• Undigested Protein

Protein Digestion and Absorption

• Amino Acid and Peptide Absorption

Proteins in the Body

• Protein synthesis• Directed by cellular

DNA• Amino acid pool and

protein turnover • Synthesis of

nonprotein molecules

Proteins in the Body

• Protein and nitrogen excretion• Deamination of amino acids• Amino groups converted to urea for excretion

• Nitrogen balance• Nitrogen intake vs. nitrogen output

Proteins in the Diet

• Recommended protein intake• Adult RDA = 0.8 grams/kilogram body

weight• Infant RDA = ~1.5 grams/kilogram body

weight• Physical stress = can increase needs

• Protein consumption

Proteins in the Diet

• Protein quality• Complete proteins

• Supply all essential amino acids• Animal proteins, soy proteins

• Incomplete proteins• Low in one or more essential amino acids• Most plant proteins

• Complementary proteins• Two incomplete proteins = complete protein

© Photodisc

Proteins in the Diet

• Evaluating protein quality• Chemical or Amino Acid Scoring• Protein-Efficiency Ratio• Net Protein Utilization• Biological Value• Protein Digestibility Corrected Amino Acid

Score

Proteins in the Diet

• Estimating your protein intake• Proteins and amino acids as additives

and supplements

Vegetarian Diets

• Why people become vegetarians• Types of vegetarians

• Lacto-ovo-vegetarian• Semi-vegetarian• Vegan

• Health benefits vs. health risks• Less fat, saturated fat, and cholesterol• Restrictive diets may lack nutrients• Careful planning needed for children, pregnant

women

Vegetarian Diets

• Dietary Recommendations for Vegetarians• Choose a variety of foods• Choose whole, unrefined foods often• Choose a variety of fruits and vegetables• Choose lower fat dairy products, if used• Use a regular source of vitamin B12

The Health Effects of Too Little Protein

• Protein-energy malnutrition (PEM)• Kwashiorkor• Marasmus• Nutritional Rehabilitation

The Health Effects of Too Much Protein

The Health Effects of Too Much Protein

• Excess Dietary Protein• Kidney Function• Mineral Losses• Obesity• Heart Disease• Cancer• Gout

Denaturation

• Heat, pH, oxidation, and mechanical agitation are some of the forces that can denature a protein, causing it to unfold and lose its functional shape.

Structural Proteins

• Proteins provide structure to all cells, including hair, skin, nails, and bone. As part of muscle, they transform energy into mechanical movement.

Hormones

• Hormones are formed in one part of the body and carried in the blood to a different location where they signal cells to alter activities.

Proteins and the Immune System

• Protein antibodies are a crucial line of defense against invading bacteria and viruses.

Proteins in the Blood

• Blood proteins attract fluid into capillaries.

• This counteracts the force of the heart beating, which pushes fluid out of capillaries.

Proteins Act as Carriers

• Lipoproteins have embedded proteins that help them transport fat and cholesterol in the blood.

Protein and Gout

• A recent study sought to explore whether or not the risk of gout is independently increased by consumption of (1) a protein-rich diet, (2) a diet high in meat, and (3) a diet high in seafood.

• The results showed that a protein-rich diet was not associated with an increased risk of gout. However, the risk of gout increased 21 percent per additional portion of meat per day and 7 percent per additional portion of seafood per week. The study also found that consumption of dairy protein (especially in low-fat dairy products) reduced risk of gout.

Position on Vegetarian Eating

• It is the position of the Academy of Nutrition and Dietetics and Dietitians of Canada that appropriately planned vegetarian diets are healthful, nutritionally adequate, and provide health benefits in the prevention and treatment of certain diseases.

Protein (Nitrogen) Balance

• A pregnant woman adds protein so she has a positive nitrogen balance.

• A healthy person who is neither gaining nor losing nitrogen is in nitrogen equilibrium.

• A person who is severely ill and losing protein has a negative nitrogen balance.

Proteins in the Diet

• Meat, eggs, milk, legumes, grains, and vegetables are all sources of protein.

• Fruits contain minimal amounts and, along with fats, are not considered protein sources. © Photodisc