Nutrition Ch. 6: Protein and Amino Acids

If Protein Shape is Altered, Function May Be Altered

Figure- Review

Protein Denaturation (Figure- Review)

Folded Protein Denaturation Denatured Protein

Amino Acids: Transamination

When a nonessential amino acid is not available from the diet, it can be made in the body by the process of transamination Alanine + @-Ketoglutarate <---> Pyruvate +Glutamate

Amino Acid Metabolism

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Amino Acid Pool Allows for Amino Acid Availability

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Essential Amino Acids

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

Nutrients Supplied by Plant and Animal Foods

-Animal products provide sources of protein, vitamin B and minerals such as iron, zinc , and calcium. -However, animal products are low in fiber and can be high in fat -Plant sources of protein are also a good source of B vitamins, iron, zinc, fiber, and calcium, but less in absorbance forms.

Protein Digestion and Food Allergies

-Food allergies are triggered when a protein from the diet is absorbed without being completely digested. -Proteins from milk, eggs, nuts, wheat, soy, fish, and shellfish, and peanuts are common causes of food allergies -A rapid, severe allergic reaction is called anaphylaxis -People with GI disease are prone to allergies because their damaged intestines allow for the absorption of whole proteins.

PEM

-Kwashiorkor is characterized by a swollen bellly -Maramus is characterized by depletion of fat stores and wasting of muscle.

Proteins that May Harm Certain Individuals: Monosodium Glutamate

-MSG consists of the amino acids glutamic acid (or glutamate) bound to sodium. -Ancedotal reactions include flushed face, tingling or burning sensations, headache, rapid heartbeat, chest pain, and general weakness. -MSG symptom complex, is commonly termed Chinese restaurant syndrome.

Proteins that May Harm Certain Individuals: Phenylketonuria

-PKU is an inherited condition attributed to a defective gene -Aspartame, a sugar substitute, contains phenylalanine

Protein Structure

-Peptide bonds are chemical bonds that link amino acids together -Peptide bonds are formed between the acid group of one amino acid and nitrogen group of the next amino acid. -Dipeptide bonds are formed between two amino acids -Polypeptides are formed between many amino acids -A protein is made of one or more polypeptide chains folded into a three dimensional shape.

Sources of Protein in the Diet

-Protein deficiency is rare in the US -In the US, about 2/3 of protein in diets come from meat, poultry, seafood, eggs, and dairy products. -Most of the world relies on plant proteins from grains and vegetables -As a country's economy improves, the proportion of animal foods in the diet increases.

Protein Deficiency

-Protein- energy malnutrition (PEM) is a term that covers a range of protein deficiency conditions that may include only protein deficiency or protein deficiency plus energy deficiency -Kwashiorkor is a pure protein deficiency -Marasmus is an energy and protein deficiency

Protein Shape Determines Function

-The final shape of a protein determines its function. -Connective tissue proteins and collagen are elongated -Hemoglobin has a spherical shape -If the shape of a protein is altered, its function may be disrupted

Limiting Amino Acids

-The proportion of amino acids in the amino acid pool depends on the amino acid composition of the diet. -A shortage of the amino acid represented by the orange spheres limits the ability to synthesize a protein that is high in this amino acid.

Protein Functions

-enzymes speed up metabolic reactions -transport proteins move substances in and out of the cells. -antibodies help the immune system in fighting off foreign bodies -contractile proteins help the muscles to move -hormones are chemical messengers, such as insulin and glucagon. -Proteins help to regulate fluid and acid-base balance.

Amino Acids

-the building blocks of protein -Each amino acids contains a central carbon atom bound to a hydrogen atom, an amino group, an acid group and a side chain (unique to each amino acid). -Essential amino acids cannot be synthesized by the human body in sufficient amounts to meet needs. -Essential amino acids must be included in the diet.

Protein Digestion and Absorption Figure

1. In the mouth, chewing begins the mechanical breakdown of protein. 2. In the stomach, hydrochloric acid and the enzyme pepsin begin the chemical digestion of protein. 3. In the small intestine, protein-digesting enzymes secreted from the pancreas, and those in the microvilli, break down polypeptides into amino acids, dipeptides, and tripeptides. 4. A variety of transport proteins move the products of protein digestion into the mucosal cell. Amino acids that share the same transport system, such as those shown here in blue and green, compete for absorption 5. Dipeptides and tripeptides can enter the mucosal cell. Once inside, they are broken down into single amino acids. 6. Amino acids pass from the mucosal cell into the blood and travel to the liver. 7. Little dietary protein is lost in the feces.

Protein Synthesis: Transcription and Translation

1. In the nucleus, the code for a protein is copied from the DNA into a molecule of messenger RNA (mRNA). 2. The mRNA takes the genetic information from the nucleus to ribosomes in the cytosol, where proteins are made. 3. At the ribosomes, transfer RNA (tRNA) reads the genetic code and delivers the needed amino acids to the ribosome to form a polypeptide chain.

Foods with sources of protein

Chicken Breast, Beef, Salmon, Cottage Cheese, Tofu, Kidney Beans, Eggs, Peanut Butter, and yogurt

Protein Excess

Elevated protein intakes over long periods of time can result in: a. hydration and kidney function issues b. bone health issues c. kidney stones d. increased risk of heart disease and cancer

Protein Structure Figure

Review

Nonessential Amino Acids

alanine, arginine*, asparagine, aspartic acid, cysteine*, glutamic acid, glutamine*, glycine*, proline*, serine, tyrosine* *Considered conditionally essential