Biology Chapter 6: Proteins and Nutrition

Proteins

• Critical molecules for metabolism, immunity, fluid balance, and nutrient transport
• Provide energy and are a form of nitrogen that the body uses
• Function: metabolism, immunity, fluid balance, and nutrient transport

Amino Acids

• Nitrogen-containing molecules that form proteins
• Essential amino acids: 9 out of 20, cannot be produced by the body, and must be obtained from food
• Nonessential amino acids: made by the body

Protein Synthesis

• 2 amino acids join to form a dipeptide through a peptide bond
• 10 or more amino acids bond together to form a polypeptide
• Proteins are made by combining multiple amino acids through transcription and translation
• Transcription: genetic information in DNA is copied to make RNA
• Translation: conversion of genetic information in RNA to assemble amino acids in the sequence to synthesize a protein on the ribosome

Protein Structure

• Primary structure: sequential order of amino acids
• Secondary structure: spiral shape due to chemical bonding between amino acids
• Tertiary and quaternary structure: folding into a unique 3-dimensional shape that may be globular or fibrous
• Denaturation: loss of protein shape due to heat, acids/bases, heavy metals, or alcohols, resulting in an irreversible loss in protein function

Protein Quality

• Incomplete protein: lacks essential amino acids in sufficient quantities, compromising growth and health
• Complete protein: contains sufficient amounts of all 9 essential amino acids, considered a "high-quality" protein
• Mutual supplementation: combining 2 incomplete proteins to make a complete protein
• Complementary proteins: 2 protein sources that together supply all 9 essential amino acids

Importance of Proteins

• Cell growth, repair, and maintenance
• Enzymes, hormones, and antibodies
• Fluid and electrolyte balance, PH balance, and energy source
• Transport and storage of nutrients

Protein Digestion and Absorption

• Stomach acids and enzymes break proteins into short polypeptides
• Digestion continues in the small intestine, where polypeptides are further broken down
• Pancreatic enzymes called proteases complete the digestion of proteins into single amino acids
• Protein digestibility affects protein quality

Protein Requirements

• Nitrogen balance: relationship between nitrogen consumption and excretion
• Recommended dietary allowance (RDA): 0.8 grams of protein per kilogram of body weight per day, 10-35% of total energy intake
• Certain groups require more protein: children, adolescents, pregnant or lactating women, athletes, and vegetarians

Protein Sources

• Animal protein sources (meat, dairy), soy products, and legumes are highly digestible
• Grains and veggie proteins are less digestible
• Legumes, nuts, and "new" foods (quorn, quinoa, amaranth, teff, millet, and sorghum) are alternative protein sources

Risks of Excessive Protein Intake

• High cholesterol and heart disease
• Kidney disease in people who are susceptible
• No evidence that high-protein diets lead to bone loss, except in people consuming inadequate calcium

Protein-Energy Malnutrition

• Disorder caused by inadequate intake of protein and energy
• Two most common forms: marasmus and kwashiorkor
• Marasmus: disease resulting from severely inadequate intakes of protein, energy, and other nutrients, characterized by extreme tissue wasting and stunted growth and development
• Kwashiorkor: disease resulting from extremely low protein intake, characterized by weight loss, muscle wasting, and edema, often seen in children in developing countries

Vegetarianism

• Restricting the diet to foods of plant origin
• Many versions and reasons to adopt a vegetarian diet, including health benefits, ecological, religious, ethical, and food safety concerns

Health Benefits of Vegetarianism

• Lower intake of fat and total energy
• Lower blood pressure
• Reduced risk of heart disease, certain types of cancer, and kidney disease
• Fewer digestive problems

Challenges of Vegetarianism

• Can be low in some vitamins and minerals (iron, calcium, zinc, vitamin D, and vitamin B12)
• Must plan a balanced and adequate diet
• Soy products are an excellent protein source
• Should include complementary proteins

Vitamins and Minerals

• Macronutrients: carbohydrates, fats, and protein, provide energy, require large amounts
• Micronutrients: vitamins and minerals, don't supply energy, small amounts, assist body functions, and may have low absorption rates
• Fat-soluble vitamins: A, D, E, and K, have large storage, toxicity, and deficiency symptoms may take months to develop
• Water-soluble vitamins: 9 vitamins, have minimal storage, toxicity is rare, and deficiency symptoms occur quickly
• Minerals: inorganic, can't be synthesized by plants/animals, 2 classifications based on need: major minerals (100mg/day required, 5g or higher in body) and trace minerals (less than 100mg/day required, body contains less than 5g)
• Absorption of micronutrients depends on factors: chemical form, food components, other nutrients, and supplementation
• Adequate intake of micronutrients has been associated with lowered disease risks

This quiz covers the basics of proteins, their functions, and importance in nutrition. Learn about amino acids, essential and nonessential ones, and how proteins are made.