Protein: Amino Protein: Amino AcidsAcids

Chapter 6Chapter 6

The ChemistThe Chemist’’s View of Proteinss View of Proteins

• Atoms• Carbon, hydrogen, oxygen, nitrogen

• Amino acids• Carbon• Hydrogen• Amino group• Acid group• Side group or side chain

The ChemistThe Chemist’’s View of Proteinss View of Proteins

• More complex than carbohydrates or fats• Twenty amino acids

• Different characteristics• Essential amino acids• Nonessential amino acids

• Conditionally essential

Amino AcidsAmino Acids

Examples of Amino AcidsExamples of Amino Acids

The ChemistThe Chemist’’s View of Proteinss View of Proteins

• 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

Amino Acid Sequence of Amino Acid Sequence of Human InsulinHuman Insulin

The Structure of HemoglobinThe Structure of Hemoglobin

The ChemistThe Chemist’’s View of Proteinss View of Proteins

• Protein• Denaturation

• Disruption of stability

• Uncoil and lose shape

• Stomach acid

Protein DigestionProtein Digestion

• Mouth • Stomach

• Hydrochloric acid denatures proteins• Pepsinogen to pepsin

• Small intestine• Hydrolysis reactions • Peptidase enzymes

Protein Digestion in the GI Protein Digestion in the GI TractTract

Protein AbsorptionProtein Absorption

• Transport into intestinal cells• Uses of amino acids by intestinal cells

• Unused amino acids transported to liver• Enzyme digestion• Predigested proteins

Protein SynthesisProtein Synthesis

• Uniqueness of each person• Amino acid sequences of proteins

• Genes – DNA

• Diet• Adequate protein

• Essential amino acids

Protein SynthesisProtein 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

Sickle Cell Compared with Sickle Cell Compared with Normal Red Blood CellNormal Red Blood Cell

Protein SynthesisProtein Synthesis

• Gene expression and protein synthesis• Capability of body cells• Protein needs

• Dietary influence on gene expression• Disease development

Roles of ProteinsRoles of Proteins

• Structural materials• Building blocks for most body structures

• Collagen

• Replacement of dead or damaged cells

• Enzymes• Break down, build up, and transform

substances • Catalysts

Stepped Art

Enzyme Enzyme Enzyme

AB

BA

BANew compound

The separate compounds, A and B, are attracted to the enzyme’s active site, making a reaction likely.

The enzyme forms a complex with A and B.

The enzyme is unchanged, but A and B have formed a new compound, AB.

Figure 6-9 p175

Roles of ProteinsRoles of Proteins

• Hormones• Messenger molecules• Transported in blood to target tissues

• Regulators of fluid balance• Edema

• Acid-base regulators• Attract hydrogen ions

• Transporters – specificity

Examples of Hormones and Examples of Hormones and Their ActionsTheir Actions

An Example of Transport An Example of Transport ProteinProtein

Roles of ProteinsRoles of Proteins

• Antibodies• Defend body against disease• Specificity

• Immunity – memory

• Energy and glucose• Starvation and insufficient carbohydrate

intake

• Other roles

Preview of Protein MetabolismPreview 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• Positive and negative nitrogen balance

Preview of Protein MetabolismPreview 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 MetabolismPreview 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 MetabolismPreview 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

Transamination and Synthesis Transamination and Synthesis of a Nonessential Amino Acidof a Nonessential Amino Acid

Urea SynthesisUrea Synthesis

Preview of Protein MetabolismPreview of Protein Metabolism

• Excreting urea• Liver releases urea into blood

• Kidneys filter urea out of blood

• Liver disease• Kidney disease• Protein intake and urea production

• Water consumption

Urea ExcretionUrea Excretion

Protein Functions in the BodyProtein Functions in the Body

Protein QualityProtein Quality

• Two factors• Digestibility

• Other foods consumed

• Animal versus plant proteins

• Amino acid composition• Essential amino acid consumption

• Nitrogen-containing amino groups

• Limiting amino acid

Protein QualityProtein Quality

• Reference protein• Preschool-age children

• High-quality proteins• Animal proteins• Plant proteins

• Complementary proteins• Low-quality proteins combined to provide

adequate levels of essential amino acids

Complementary ProteinsComplementary Proteins

Health Effects of ProteinHealth Effects of Protein

• Protein deficiency• Consequences • Protein-energy malnutrition• Marasmus and kwashiorkor

• Heart disease• Animal-protein intake• Homocysteine levels• Arginine levels

Health Effects of ProteinHealth Effects of Protein

• Cancer• Protein-rich foods; not protein content of diet

• Osteoporosis• Increase in calcium excretion• Animal proteins

• Weight control• Kidney disease

• Acceleration of kidney deterioration

Recommended Intakes of Recommended Intakes of ProteinProtein

• 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

• Adequate energy

From Guidelines to GroceriesFrom Guidelines to Groceries

• Protein foods• One ounce equals 7 grams of protein• USDA Food Patterns• Recommended sources

• Milk and milk products

• Fruits, vegetables, and grains

• Read food labels• Current US and Canada intakes• Moderation

Protein and Amino Acid Protein and Amino Acid SupplementsSupplements

• Protein powders• Muscle work vs. protein supplements

• Athletic performance

• Whey protein• Impact on kidneys

• Amino acid supplements• Potential risks associated with intake• Lysine & tryptophan