Proteins and Amino Acids Flashcards
Explain the role of proteins in the body
- Structural elements: fibrous & contractile proteins
- Building material: growth, continual repair and turnover
- Catalyze reactions: enzymes
- Communication: hormones, cytokines, catecholamines, receptors
- Immune function: immunoglobulins (antibodies)
- Transportation: albumin, transferrin, ceruloplasmin, lipoproteins
- Storage: ferritin
- Fluid balance: albumin
- Energy source: 4kcal/gram of protein
- Satiety
Define and list the essential and non-essential amino acids
Essential amino acids must be consumed within the diet because we cannot make them at a sufficient rate. There are 9 and include:
Phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, histidine, lysine, leucine.
Non-essential amino acids can be made within the body. There are 11 and include:
Alanine, arginine, asparagine, cysteine, glutamine, glycine, proline, serine, tyrosine, aspartate, glutamate.
Explain Nitrogen Balance
Protein N(in) = N(out) Protein is about 16% N
N balance = 0.16(g of protein ingested) - (urinary N + fecal N + skin N)
Urinary N = urea + urinary creatine + ammonia, uric acid
Fecal and skin N ~ 1g each/day
Explain when would see a positive N balance and a negative N balance
Positive N balance during times of growth, pregnancy and tissue repair.
Negative N balance burns, fevers, wasting disease and fasting
What effect does insulin and glucagon have on protein metabolism?
Insulin promotes protein synthesis and inhibits protein degradation.
Glucagon promotes protein degradation
and slows protein synthesis.
Give an overview of protein and amino acid metabolism.
Deamination, transamination, formation of ketone bodies
Deamination: removal of amino group. Carbon skeleton can be used to synthesize energy, glucose, ketone bodies, fatty acids or cholesterol. Amino group can be used to make another amino acid or excreted as urea by kidneys.
Transamination: transfer of an amino group from one amino acid to the carbon skeleton of another amino acid or alpha-keto group
Ketone body formation: accumulation of acetyl CoA, which is converted into ketone bodies in the liver which are then used as an energy source
Evaluate dietary protein quality
High quality or complete proteins contain all essential amino acids in the approximate amounts needed by humans and usually come from animal products (gelatin and soy also).
Low quality or incomplete proteins has a limiting essential amino acid:
Legumes low in methionine
Grains low in lysine
However grains are high in methionine and legumes are high in lysine so they are complementary proteins.
Protein quality is also based on protein digestibility - amount of amino acids absorbed following ingestion of a given protein Meat - 95% Dairy - 95% Eggs - 97% Tofu - 90% Split peas - 70%
Describe protein-energy malnutrition
Marasmus & kwashiorkor
Marasmus:
Deficient in proteins and calories
Begins before age of 2
Develops slowly
Extreme emaciation –> muscle & adipose tissue wasting
Serum protein levels normal or only slightly low
Increased appetite
Digestive enzyme production decreased and GI lining deteriorates
Kwashiorkor: Only deficient in proteins Begins in children 1-3yrs, after weaning May be due to infections Rapid onset Low serum protein levels Enlarged fatty liver Ascites --> loss of appetite - feel full because of build up of fluid in abdomen
Discuss protein digestion in the stomach
Gastric juices (stimulated by gastrin - pH of 1-2):
HCL
- secreted by parietal cells
- denatures proteins
- converts pepsinogen (secreted by chief cells) to pepsin
Pepsin
- functions at pH >3.5
- hydrolyzes pelted bound
- left with large polypeptides and some free a.a.
Discuss protein digestion in the small intestine
Secretin and cholecystokinin
- secreted from mucousal cells
- stimulate pancreas cells to release gastric juices containing:
- bicarbonate
- electrolytes
- water
- digestive enzymes
- mucous-rich secretions from Brunner’s glands
