Protein: Amino Acids

Objectives• After reading Chapter 5, class

discussion and activities you will be able to:– Describe the role of proteins– Distinguish between complete and

incomplete proteins– Identify sources of quality protein – Calculate calories from protein

Objectives• Describe protein digestion/absorption• Identify RDA for protein• Discuss health related effects of

protein

Protein• Essential part of all living cells• Found in animals and plants;

Particularly rich in animal foods – meats, poultry, eggs, etc.

• Protein is in your skin, hair, nails, muscles, etc.

• Made of amino acids – amino acids contain nitrogen, which is necessary for life.

Amino Acids

p. 163Fig 5-1

Amino Acids• Nonessential amino acids

– Body can synthesize– Over half of the 20 AA

• Essential amino acids– Body cannot synthesize– Nine (9)

• Conditionally essential amino acids– PhenylalanineTyrosine; New Borns

Proteins• Peptide bond

– Dipeptide– Tripeptide– Polypeptide

Proteins• Dipeptide

Proteins• Polypeptide (Example: Insulin)

• Protein shape and function

• Amino Acid Sequences

Proteins• Protein denaturation

– Uncoiling & loss of shape– Therefore, loss of function– Caused by heat, acid, mechanical– Examples: cooked egg, egg whites,

curdling of milk, separation of foods with milk or egg (syneresis)

p. 176

Protein Digestion• Mouth

– Mixing, moisturizing• Stomach

– HCl– Pepsinogen pepsin

•ProenzymeEnzyme

Protein Digestion• Small intestine

– Proteases•Intestinal and pancreatic

– Peptidases

Protein Absorption• Carriers

– Transport AA into intestinal cells– Used for synthesis and energy

• Capillaries– Carried to liver

• Absorption misconceptions– Enzyme/amino acid supplements

Protein Synthesis• Delivering the instructions

– DNA•mRNA- attaches to ribosome

–Protein-making machine

Protein Synthesis• Sequencing errors

Roles of Proteins• Building material: Building blocks

of muscles, blood, skin, bones, teeth; protein matrix=collagen – Growth– Maintenance

p. 164-168

Roles of Proteins• Enzymes=catalysts

p. 165 Fig 5-6

Roles of Proteins

• Hormones– Switching Machines

Roles of Proteins• Regulation of fluid balance

– Edema

• Acid-base regulation– Acidosis– Alkalosis

• Transport proteins

Roles of Proteins• Immunity: Molecular Memory

– Antibodies: Giant protein molecules designed to combat

– Antigens: Invading foreign proteins (virus)

Roles of Proteins• Source of energy

– Gluconeogenesis– No storage source=muscle wasting– “Amino acid pool”

• Other roles– Fibrinblood clotting– Opsin—light-sensitive pigment

Protein Metabolism• Using amino acids to make

proteins=CONDENSATION

• Using amino acids to make nonessential amino acids

Protein Metabolism• Using amino acids to make other

compounds– Neurotransmitters

• Using amino acids for energy and glucose

• Deamination: AA stripped of N– Ammonia produced

Protein Metabolism• Protein turnover

– Amino acid pool: supply of AA from food/body; collect in cells & blood; ready for use

• Nitrogen balance– Positive nitrogen balance– Negative nitrogen balance

Protein Quality• High-quality proteins

– All essential AA– Animal proteins=complete– Plant proteins=incomplete

• Amino acid composition– Limiting amino acid

• Digestibility– Animal vs. vegetable

Protein Quality• PDCAAS

– Protein digestibility-corrected amino acid score

• Reference Protein

Protein Quality• Complementary proteins

– Two protein foods make up for the lack of certain amino acids in each other when eaten together

Food Labels• Quantity of protein

• Daily Value– 50 g protein

•10% of a 2000 kcal diet

Nitrogen Balance• Determine adequacy of protein intake• N2 In - N2 Out = Nitrogen Balance

– N2 In = Protein Intake as Nitrogen– N2 Out = 24 Hour Urine Collection for N2

+ Stool, Insensible Losses• Positive Nitrogen Balance

– Body excretes less protein than is taken in (Anabolism)

• Negative Nitrogen Balance– Body excretes more protein than is taken in (Catabolism)

Protein-Energy Malnutrition (PEM)

• Marasmus– Slow developing, chronic PEM– Muscle wasting; no body fat– Pluckable hair; dry skin

• Kwashiorkor ??????

• Marasmus-kwashiorkor mix

p. 171

Protein-Energy Malnutrition (PEM)

• Infections not protein intake– Dysentery

• C-Reactive Protein

Health Effects• Conditions Associated with Other

Nutrients:– Osteoporosis – Calcium– Heart Disease – Fat– Obesity – Fat/CHO– Cancer - Fat

Health Effects• Genetic Associated Diseases

– Phenylketonuria– Sickle Cell Anemia

• Celiac Disease; Sprue• Liver Disease• Kidney Disease

Recommended Intakes

• RDA– 0.8 g/kg/day– 10% - 35% of energy intake

Objectives• After reading Chapter 5, class

discussion and activities you will be able to:– Describe the role of proteins– Distinguish between complete and

incomplete proteins– Identify sources of quality protein – Calculate calories from protein

Objectives• Describe protein digestion/absorption• Identify RDA for protein• Discuss health related effects of

protein