Proteins Flashcards
Protein
Accounts for 20% of adult weight
Involved in most of the body’s functions and life processes
Make up of chains of amino acids
- sequence of amino acids is determined by DNA
Amino acid
Basic building blocks of protein
Composed of carbon, hydrogen, oxygen and nitrogen atoms
Twenty common amino acids
- 9 essential
- 11 essential
Functions of protein
◦ Major structural and functional component of every living cell
◦ Body structure and framework
◦ Enzymes
◦ Other body secretions and fluids
◦ Acid–base balance
◦ Transport molecules
Essential amino acids
Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine
Nonessential amino acids
Alanine Arginine Asparagine Aspartic acid Cystine (cysteine) Glutamic acid Glutamine Glycine Proline Serine Tyrosine
Structure of the protein
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
Denaturing
Alteration of the protein’s shape and this functions through the use of:
- Heat
- Acids
- Bases
- Salts
- Mechanical agitation
Digestion of proteins
Hydrochloric acid denatures protein and activates pepsinogen form the active enzyme pepsin
Pepsin breaks the polypeptide chain into smaller polypeptides
Enzymes from pancreases continue to break down peptide bonds resulting in dipeptides, tripeptides and single amino acids
Tripeptides and dipeptidases on the surface of the small intestinal cells finish digestion to yield single amino acids
Absorption of proteins
Amino acids, and sometimes a few dipeptides or larger peptides, are absorbed through the mucosa of the small intestine
These are transported to the liver vita portal vein
Liver metabolism
Retains amino acids to make liver cells, nonessential amino acids and plasma proteins such as heparin, prothrombin and albumin
Regulates the release of amino acids into the bloodstream
Removes the nitrogen from amino acids
Converts protein to fatty acids which form triglycerides
Forms urea from nitrogenous wastes of protein
Gluconeogenesis
Amino acids can be used to make glucose when glucose is limited
Energy production
Amino acids can be used for energy when the diet is deficient in kilocalories
Fat cells
Amino acids can be converted to fatty acids and stored as a triglyceride in adipose tissue when kilocalorie intake is sufficient
Protein turnover
Proteins are constantly made and broken down, releasing their amino acids into the amino acid pool or are used for protein synthesis
Metabolic pool
Contains a supply of each amino acid
Consists of recycled amino acids from body proteins that have broken down and also amino acids from food
In a constant state of flux
Nitrogen balance
Reflects the state of balance between protein breakdown and protein synthesis
Determined by comparing the amount of nitrogen intake with the nitrogen output.
Healthy adults are in neural nitrogen balance
Positive nitrogen balance
Protein synthesis exceeds protein breakdown
- Pregnant
- Growing children and adolescents
- Athletes
Negative nitrogen
An undesirable state that occurs when protein breakdown exceeds protein synthesis
- Experiencing a medical trauma
- Not eating a health diet
Mary is a 25 year old woman who was admitted to the hospital with multiple fractures and traumatic injuries from a car accident. A nutritional intake study indicated a 24-hours protein of 64 g. A 24-hour urinary urea nitrogen (UUN) collection result 19,8g. Calculate nitrogen balance
Determine nitrogen intake by dividing protein intake by 6.25
- 64 g / 6,25 = 10.24 g of nitrogen
Determine total nitrogen output by adding a coefficient of 4 of the UUN
- 19.8 g / 4 = 23.8g of nitrogen
Calculate nitrogen balance by subtracting nitrogen output from nitrogen output from nitrogen intake
- 10.24 g - 23.8g = -13.56g in 24 hours
Interpret the results
- A negative number indicates that protein breakdown is exceeding protein synthesis. Mary is in a catabolic state.
Complete proteins
High biologic value
Provide adequate amounts and proportions of all essential amino acids needed for protein synthesis necessary to support tissue growth and repair
Animal proteins and soy protein are complete proteins
Incomplete proteins
Lack of adequate amounts of one or more essential amino acids
Except for soy protein, all plants are sources of incomplete proteins
Gelatin is also an incomplete protein
Complementary proteins
Two proteins that when combined provide adequate amounts and proportions of all essential amino acids needed to support protein synthesis
Recommended Dietary Allowance (RDA)
Healthy adults is 0.8 g/kg
Acceptable Macronutrient Distribution Range for protein
10% to 35%
Kwashiorkor
Severe protein deficiency
Aggressive nutritional support is used to restore metabolic balance as quickly as possible
Marasmus
Results from a severe deficiency in kilocalories
Occurs secondary to chronic diseases
Nutritional therapy is started slowly and advanced gradually
Too little protein
◦ Cells lining the GI tract are not sufficiently replaced as they slough off
◦ Digestive function is inhibited
◦ Absorption of food is reduced
◦ Intestinal bacteria gets into the blood and causes septicemia
◦ Immune system is compromised due to malnutrition and cannot fight infection
Too little protein
◦ Cells lining the GI tract are not sufficiently replaced as they slough off
◦ Digestive function is inhibited
◦ Absorption of food is reduced
◦ Intestinal bacteria gets into the blood and causes septicemia
◦ Immune system is compromised due to malnutrition and cannot fight infection
Symptoms of Kwashiorkor
◦ Edema in legs, feet, and stomach
◦ Muscle tone and strength diminish
◦ Hair is brittle and easy to pull out
◦ Appear pale, sad, and apathetic
◦ Prone to infection, rapid heart rate, excess fluid in lungs, pneumonia, septicemia, and water and
electrolyte imbalances
Symptoms of Marasmus
◦ Frail, emaciated appearance
◦ Weakened and appear apathetic
◦ Many cannot stand without support
◦ Look old
◦ Hair is thin, dry, and lacks sheen
◦ Body temperature and blood pressure are low
◦ Prone to dehydration, infections, and unnecessary blood clotting
Symptoms of Marasmic Kwashiorkor
Chronic deficiency in kilocalories and protein
◦ Have edema in legs and arms
◦ Have a “skin and bones” appearance
◦ With treatment the edema subsides and appearance becomes more like someone with marasmus
Best sources of protein
Proteins are abundant in ◦ Dairy foods ◦ Meats ◦ Poultry ◦ Meat alternatives such as dried beans, peanut butter, nuts, and soy
3 oz serving of cooked meat, poultry, or fish provide
◦ Provides 21–25 grams of protein
◦ About 7 g/oz
◦ About the size of a deck of cards
◦ Adequate amount for one meal
