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 (AA)

• 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

Condensation of Two Amino Condensation of Two Amino Acids to Form a DipeptideAcids to Form a Dipeptide

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

• Protein in food ≠ muscle in body • Must be broken down and built back up

Protein (long polypeptides)

Short polypeptides

Tripeptides and dipeptides

Amino acids

Protein DigestionProtein Digestion

• Mouth• Mostly mechanical

• 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

Know these by name and function

Be able to recognize these names, don’t need to know exact mechanism of action

Protein AbsorptionProtein Absorption

• Specific carriers transport into intestinal cells• Some amino acids used by intestinal cells

• Unused amino acids transported to liver• Through bloodstream to liver

• Reminder: enzymes are digested when they are inactive – different pH levels are optimal

• Myth: predigested proteins are easier for the body to handle (i.e. better for you)

Protein SynthesisProtein Synthesis

• Uniqueness of each person determined by differences in proteins• Uniqueness found in amino acid sequences

• Determined by genes – DNA

• Diet is key to protein synthesis• Adequate protein

• Essential amino acids

Protein SynthesisProtein Synthesis

• DNA transcription RNA translation protein• 2 Steps:

1. Transcription: DNA template makes mRNA• mRNA carries code across nuclear

membrane to attach to ribosome

• Ribosomes are protein factories

2. Translation: mRNA specifies AA sequence• tRNA carry AA to ribosomes

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

Protein SynthesisProtein Synthesis

• Gene expression and protein synthesis• Cells differentiate based on protein needs

• Pancreas – insulin

• RBC – hemoglobin

• Dietary influence on gene expression• Protein and amino acids available to body• Disease development

Roles of ProteinsRoles of Proteins

1. Structural materials• Building blocks for most body structures

• Collagen: teeth, ligaments/tendons, arteries

• Replacement of dead or damaged cells

2. Enzymes• Break down (digestion), build up (bone), and

transform substances (gluconeogenesis)• Catalysts: remain unchanged, reusable

Enzyme ActionEnzyme Action

Roles of ProteinsRoles of Proteins

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

4. Regulators of fluid balance• Edema

5. Acid-base regulators• Attract hydrogen ions

6. 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

7. Antibodies• Defend body against disease• Specificity

• Immunity – memory

8. Energy and glucose• Starvation or insufficient carbohydrate intake

9. Other roles • Vision, blood clotting

Preview of Protein MetabolismPreview of Protein Metabolism

• Protein turnover & amino acid pool• Constant production/destruction in each cell• 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 (not just protein)• 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 amino group (N-containing)

• Ammonia

• Keto acid

Deamination and Synthesis of Deamination and Synthesis of a Nonessential Amino Acida Nonessential Amino Acid

Preview of Protein MetabolismPreview of Protein Metabolism

• Make proteins & nonessential amino acids• Essential: breakdown of proteins• Nonessential: keto-acids• Liver makes nonessential

• Converting ammonia to urea• Liver – ammonia and carbon dioxide Dietary protein ammonia production

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 ( blood ammonia)• Kidney disease ( blood urea)• Protein intake and urea production

• Water consumption

Urea ExcretionUrea Excretion

Protein Functions in the BodyProtein Functions in the Body

Proteins in Food: Proteins in Food: Protein QualityProtein Quality

• Two factors1. Digestibility

• Animal proteins (>90%)

• Plant proteins (70-90%; soy, legumes >90%)

2. 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

• AMDR: 10-35% of daily kcalorie• RDA: adults = 0.8g / kg of body weight

• 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• Whey protein

• Amino acid supplements• Potential risks associated with intake• Branched-chain amino acids (BCAA) • Lysine & tryptophan