Protein: Amino Acids Chapter 6

The Chemist’s View of Proteins Atoms Carbon, hydrogen, oxygen, nitrogen Amino acids Carbon Hydrogen Amino group Acid group Side group or side chain

The Chemist’s View of Proteins

The Chemist’s View of Proteins More complex than carbohydrates or fats Twenty amino acids Different characteristics Essential amino acids Nonessential amino acids Conditionally essential

The Chemist’s View of Proteins

The Chemist’s View of Proteins Peptide bonds link amino acids Condensation reactions Amino acid sequencing Primary structure – chemical bonds Secondary structure – electrical attractions Tertiary structure – hydrophilic & hydrophobic Quaternary structure – two or more polypeptides

The Chemist’s View of Proteins

The Chemist’s View of Proteins Denaturation Disruption of stability Uncoil and lose shape Stomach acid

Protein Digestion Mouth Stomach Small intestine Hydrochloric acid denatures proteins Pepsinogen to pepsin Small intestine Hydrolysis reactions Peptidase enzymes

Protein Digestion

Protein Absorption Transport into intestinal cells Uses of amino acids by intestinal cells Unused amino acids transported to liver Enzyme digestion Predigested proteins

Protein Synthesis Uniqueness of each person Diet Amino acid sequences of proteins Genes – DNA Diet Adequate protein Essential amino acids

Protein Synthesis DNA template to make mRNA Transcription mRNA carries code to ribosome Ribosomes are protein factories mRNA specifies sequence of amino acids Translation tRNA Sequencing errors

Protein Synthesis

Protein Synthesis Gene expression and protein synthesis Capability of body cells Protein needs Dietary influence on gene expression Disease development

Roles of Proteins Growth and maintenance Enzymes Building blocks for most body structures Collagen Replacement of dead or damaged cells Enzymes Break down, build up, and transform substances Catalysts

Roles of Proteins

Roles of Proteins Hormones Regulators of fluid balance Messenger molecules Transported in blood to target tissues Regulators of fluid balance Edema Acid-base regulators Attract hydrogen ions Transporters – specificity

Roles of Proteins

Roles of Proteins Antibodies Energy and glucose Other roles Defend body against disease Specificity Immunity – memory Energy and glucose Starvation and insufficient carbohydrate intake Other roles

Preview of Protein Metabolism Protein turnover & amino acid pool Continual production and destruction Amino acid pool pattern is fairly constant Used for protein production Used for energy – if stripped of nitrogen Nitrogen balance Zero nitrogen balance or equilibrium Positive and negative nitrogen balance

Preview of Protein Metabolism Making other compounds Neurotransmitters Melanin Thyroxin Niacin Energy and glucose Wasting of lean body tissue Adequate intake of carbohydrates and fats

Preview of Protein Metabolism Making fat Energy and protein exceed needs Carbohydrate intake is adequate Can contribute to weight gain Deaminating amino acids Stripped of nitrogen-containing amino group Ammonia Keto acid

Preview of Protein Metabolism Make proteins & nonessential amino acids Breakdown of proteins Keto-acids Liver cells and nonessential amino acids Converting ammonia to urea Liver – ammonia and carbon dioxide Dietary protein

Preview of Protein Metabolism

Preview of Protein Metabolism

Preview of Protein Metabolism Excreting urea Liver releases urea into blood Kidneys filter urea out of blood Liver disease: blood ammonia will be high Kidney disease: blood urea will be high Protein intake and urea production Water consumption

Preview of Protein Metabolism

Protein Quality Two factors Digestibility Amino acid composition Other foods consumed Animal vs. plant proteins Amino acid composition Essential amino acid consumption Nitrogen-containing amino groups Limiting amino acid

Protein Quality Animal proteins (complete proteins) Reference protein Preschool-age children High-quality proteins Animal proteins (complete proteins) Plant proteins (incomplete proteins) Complementary proteins Low-quality proteins combined to provide adequate levels of essential amino acids

Protein Regulations for Food Labels Quantity of protein in grams Percent Daily Value Not mandatory Protein claims Consumption by children under 4 years old Quality of protein

Protein-Energy Malnutrition (PEM) Insufficient intake of protein, energy, or both Prevalent form of malnutrition worldwide Impact on children Poor growth Most common sign of malnutrition Impact on adults Conditions leading to PEM

Protein-Energy Malnutrition (PEM) Marasmus Chronic PEM Children 6 to 18 months Poverty Little old people – just “skin and bones” Impaired growth, wasting of muscles, impaired brain development, lower body temperature Digestion and absorption

Protein-Energy Malnutrition (PEM) Kwashiorkor Acute PEM Children 18 months to 2 years Develops rapidly Aflatoxins Edema, fatty liver, inflammation, infections, skin and hair changes, free-radical iron Marasmus-Kwashiorkor mix

Protein-Energy Malnutrition (PEM)

Protein-Energy Malnutrition (PEM) Infections Degradation of antibodies Dysentery Heart failure and death Rehabilitation Rehydration and nutrition intervention Add protein slowly

Health Effects of Protein High-protein diets Heart disease Animal-protein intake Homocysteine levels Arginine levels Cancer Protein-rich foods; not protein content of diet Kidney disease Acceleration of kidney deterioration

Health Effects of Protein High-protein diets Osteoporosis Calcium excretion increases Ideal ratio has not been determined Animal protein intake Weight control Satiety

Recommended Intakes of Protein Need for dietary protein Source of essential amino acids Practical source of nitrogen 10 to 35 percent of daily energy intake RDA Adults = 0.8 grams / kg of body weight / day Groups with higher recommended intakes Assumptions

Recommended Intakes of Protein Protein in abundance Intake in U.S. and Canada Dietary sources Serving sizes Key diet principle – moderation

Protein and Amino Acid Supplements Protein powders Muscle work vs. protein supplements Athletic performance Whey protein Impact on kidneys Amino acid supplements Potential risks associated with intake Lysine & tryptophan

Highlight 6 Nutritional Genomics

Nutritional Genomics New field Nutrigenomics Nutrigenetics Nutrients influence gene activity Nutrigenetics Genes influence activity of nutrients Human genome

Nutritional Genomics

A Genomics Primer DNA Gene expression Epigenetics 46 chromosomes Nucleotide bases Gene expression Genetic information to protein synthesis Gene presence vs. gene expression Epigenetics DNA methylation

A Genomics Primer

Genetic Variation and Disease Genome variation About 0.1 percent Goal of nutritional genomics Customize recommendations that fit individual needs Single-gene disorders Phenylketonuria (PKU)

Genetic Variation and Disease Multigene disorders Study expression and interaction of multiple genes Sensitive to environmental influences Example Heart disease Single nucleotide polymorphisms (SNPs)