Exercise Physiology - Proteins

About protein

• constructed from linked amino acids (contain Nitrogen)

• peptide bonds link amino acids together

• contain about 16% Nitrogen (fats and carbs have no nitrogen)

• dipeptide: two amino acids linked together

• tripeptide: three amino acids linked together

• polypeptide: 50 to more than 1000 amino acids joined together

What is the R group in an amino acid?

The R group is the side chain that is used to identify different amino acids

Protein categories (essential amino acids)

Body cannot synthesize so they must be consumed in foods (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine)

nonessential amino acids

synthesized in the body from other compounds at a rate to meet growth and tissue repair needs

complete proteins

Exist in foods that contain the essential amino acids in the quantity and correct ratio to maintain nitrogen balance

incomplete proteins

lack one or more essential amino acids

Protein’s role in the body

• constitutes up to 12-15% body mass

• 3 major sources of body protein (blood plasma, visceral (abdominal) tissue, muscle)

• major building blocks (help link everything together) for synthesizing tissue components like enzymes, hair, skin, nails

Protein Metabolism Dynamics

• nitrogen must be removed from amino acids prior to breakdown (catabolism)

• process of deamination (nitrogen removal) forms urea, which is eliminated as urine

• transamination occurs when an amine group from a donor amino acid transfers to an acceptor acid to form a new amino acid (removes nitrogen and donates it)

Nitrogen Balance - Postive

• nitrogen intake (from food) exceeds nitrogen excretion (urine, feces, sweat) to synthesize tissues from any additional protein - helps build muscle because the intake is greater than the removal

• occurs during: child growth, pregnancy, recovery from illness, protein synthesis with resistance - exercise training)

Nitrogen Balance - Negative

• Nitrogen intake less than nitrogen excretion

• protein increasingly becomes an energy fuel, which creates a negative protein or nitrogen balance and lean tissue loss

• can occur during: periods of tissue growth, high energy output and/or tissue synthesis requirements of intense training, diabetes, fever, burns, dieting, growth, steroid administration, semi starvation or starvation

Protein dynamics during physical activity

• as exercise progresses, plasma urea concentration increases along with a rise in sweat’s nitrogen excretion

• protein’s energy use reaches highest level during exercise in the glycogen depleted state

• illustrates carbohydrates important role as a protein-sparer

Alanine - Glucose cycle

• some proteins, like alanine, are directly broken down to create energy but can indirectly participate in energy metabolism

• alanine enters the blood where the liver converts it to glucose and urea

• increased alanine production helps to maintain blood glucose for nervous system and active muscle needs