Proteins

• Large molecules that supply amino acids and nitrogen

• aa-aa-aa - is a peptide (link)

• Each group of aa is a polypeptide

• One or more polypeptide chains is a protein

Amino Acids and Proteins• Amino acids are defined as any organic

compound containing both an amino and a carboxyl group.

Proteins• Amino acids are called the building blocks of

protein.• Proteins are essential to all living cells.• Protein functions include:

– Regulation of metabolism– Cell membrane construction-hair, skin, nails– Muscle fiber formation, contraction regulation– Tissue growth and repair

• Proteins also serve as enzymes, hormones, and antibodies.

Proteins are sometimes bound to other substances to form even more complex molecules. For example:

Proteins conjugated with carbohydrates are called glycoproteinsProteins conjugated with fats are called lipoproteins

Proteins/Amino Acids

• They are not stored in the body like fat and carbs. If not consumed in required levels, breakdown of protein in the viscera and skeletal muscle will occur. This breakdown in protein provides amino acids for energy. The breakdown of circulating and structural protein into glucose is called gluconeogenesis.

Recommended Requirements

• Protein requirements p. 298 table 9-5

Factors affecting protein requirement

• Protein quality

• Amino Acid Composition

• Digestibility

• Energy Density

• There are several tests that predict the quality of protein.

• * This information can be found in table 9 – 6 on page 299

• Net protein utilization (NPU): This compares the amino acids composition to a source known to be of a very high quality. Egg protein is typically used as the reference protein as it has been given a chemical score of 100.

• Amino acid score (AAS): This test measures the contribution a protein makes to all of the essential amino acids. This test is a modification of the chemical score test

• Protein efficiency ratio (PER): This is the simplest and most commonly used test. Weanling male rats or growing chicks are fed an adequate diet containing the test protein for 28 days and changes in weight are measured. PER is calculated by the amount of weight gained divided by the total grams of protein consumed.

• Biological Value: This is the percentage of absorbed protein retained in the body. It is a measure of the ability of the body to convert absorbed amino acids into body tissue. Nitrogen in the food is measured against the nitrogen in the feces and urine.

Protein Values

• High quality protein is especially needed during:– Periods of growth– Physical exertion– Pregnancy– Lactation– Repair of damaged tissues

Signs of Protein Deficiency

• Decrease of muscle mass

• Weight loss• Dull hair coat• Anorexia• Immunodeficiency• Generalized edema• Death

Felines

• Cats are specifically adapted for a high protein, low carb diet. They depend on gluconeogenesis as a major source of energy. Cat’s are limited in their ability to conserve protein due to continuous protein catabolism.

• Metabolism of excess amino acids increases liver and kidney overload.

Amino acids occur naturally in plant and animal tissue and are the chief constituents of protein. Amino acids are broken down into two groups, Essential Amino acids and Nonessential amino acids.

*

Page 297

Deficiencies of even one of the amino acids can have grave consequences.

For example:Arginine deficiency causes a build up of ammonia in the bloodstream, causing vomiting in dogs and death in cats.Methionine and Cysteine deficiencies cause weight loss and skin disordersTaurine deficiency in cats leads to blindness and heart failure.

This information is found on page 298

Specific Nutrient Related Diseases

• Hepatic Lipodosis

• Diabetes Melllitus

Cont. Felines

• Due to the dependency on gluconeogenesis, the feline has very little energy in reserve. If a cat becomes anorexic for any period of time, the body has little or no protein to breakdown for energy. Instead it breaks down fat. The fat accumulates in the liver causing acute liver failure, a condition called hepatic lipidosis (fatty liver disease).

Ketosis• Primarily occurs in animals with diabetes mellitus. A

deficiency of insulin prevents the animal from utilizing the glucose circulating in the blood stream. Insulin is

needed to get glucose to enter the body cells, consequently the animal breaks down fat for energy. Excessive amounts of acetyl-Coa (product A) starts to accumulate in the blood. Accumulated product A is

converted to Ketone Bodies, large amounts of ketone bodies cause a condition called ketoacidosis. Ketosis is life threatening because ketone bodies are acidic and

the body can not function when the blood drops below a pH of 7.35.

National Exam note:

• Normal Animal = blood pH 7.4

• If pH rises above 7.45 = alkalosis

• If pH goes below 7.35 = acidosis

• Normal range pH of blood: 7.35 – 7.45