NTD411 - Proteins

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there are __ essential, ___ truly essential (name them), ___ non-essential, and ___ conditionally essential amino acids

9, 3 (histidine, lysine, threonine), 11, 6

the old definition of an essential amino acid vs. what makes the essential ones totally indispensable now

one that cannot be made from scratch in the human body vs. 3 amino acids whose carbon skeletons don't exist in our body, so transamination cannot form them endogenously


phenylketoniuria, a condition in which the body lacks the enzyme to transaminate phenylalanine into tyrosine, rendering tyrosine conditionally essential

why must patients with PKU avoid nutrasweet/aspartame?

this sweetener is made with 2 amino acids, phenylalanine included, so the body can't break it down properly

endogenous proteins

proteins made by the body in the digestive tract

complete vs. incomplete proteins

protein sources with adequate and balanced amounts of all essential amino acids. vs. protein sources that do not have that

limiting amino acids

the amino acid in an incomplete protein that is found in the lowest amount in relation to its amount in the reference protein

protein complementation

the consumption of a variety of incomplete protein sources in a way that the limiting amino acids of one food are made up for by those contained in anther

protein quality

a complex set of factors including whether the protein is complete, how well your body can digest/absorb them, that determine how good of a source of protein a particular food is

nitrogen balance

an evaluation of dietary nitrogen intake and the measurement and summation of nitrogen losses from the body

protein is approximately ___% nitrogen, so to calculate grames of nitrogen per grams of protein you ____

16, multiple grams of protein by .16

chemical score

involves determination of the amino acid composition of a test protein to be compared to the amino acid pattern of an egg; the lowest score in relation to the reference protein becomes the first limiting acid of the protein


protein digestibility corrected amino acid score: mg limiting amino acid in 1g test protein / mg amino acid in 1g reference protein x true digestibility as a %

protein efficiency ratio

represents body weight gained on a test protein divided by the grams of protein consumed

biological value

a measure of how much nitrogen is retained in the body for maintenance and growth; high BVs indicate a food that provides the amino aicds in amounts consistent with body amino acid needs

information on food labels

quantity of protein in grams is required; %DV is required for foods intended for kids below age 4 or if a health claim is made; PDCAAS is required to get the %DV

which amino acid has the highest RDA? Lowest?

leucine, tryptophan


no, but high protein diets increase risk of dehydration (urea excretion), kidney and bone damage (high acid load)

DV for protein


you need to consume dietary protein for ___ major reasons:

2: supple adequate amounts of essential amino aicds; additional nitrogen needed to make the nonessential amino acids and other non-protein, N-containing compounds

protein requirements increase during

pregnancy, lactation, growth, recovery

protein energy malnutrition

PEM, a way of referring to protein deficiency based on the fact that diets lacking protein are almost always lacking in energy too; a condition of overall malnutrition


protein malnutrition in which people receive enough energy; water diffuses out of blood to cause edema, mostly among children


protein malnutrition characterized by extreme emaciation with wasted muscle mass and adipose tissue, prominent bones, drooping skin

functional categories of proteins

enzymes, hormones, structural elements, immunoproteins, transporters, buffers, fluid balancers, source of glucose/ATP

what do each of these transport proteins carry? albumin, prealbumin, transferrin, lipoprotein

Ca/Zn/B6, retinol/VitA, iron, lipids

how can protein be a source of glucose/ATP?

the body can disassemble proteins and convert their glucogenic amino acids to glucose via deamination of the N-containing amino group

what happens to excess amino acids?

they are converted to fat

describe protein digestion

1. mouth: physical breakdown & softening via teeth and saliva 2. swallow bolus 3. enter stomach, presence triggers gastrin release which releases gastric juice (HCl, pepsinogen, mucus); HCl denatures proteins, pepsinogen in the presence of HCl turns into pepsin; pepsin hydrolyzes peptide bonds between amino acids to create smaller peptide chains 4. chyme enters small intestine, presence releases secretin (bicarbonate release) and cck (release trypsinogen, chymotrypsinogen, procarboxypeptidase); trypsinogen goes to tyrpsin w/ enteropeptidase & more trypsin; chymotrypsinogen - chymotrypsin with trypsin; procarboxypeptidase - carboxypeptidase with trypsin - all of these then cleave into tripeptides, dipeptides, and free amino acids 5. some tripeptides are hydrolyzed at brush border but others are absorbed into the enterocyte and then broken down; absorbed into capillaries of villi as free aa's and sent to portal vein to liver


how much of the amino acids in a food are absorbed following ingestine

interorgan flow of amino acids

the flow of aa's between organs to provide for synthesis of nonessential amino acids, protein, Ncontaining compounds, glucose, fat, ketones, energy; dictated by nutritional status & hormones

what are the 2 major amino acids of nitrogen?

glutamine, alanine


a major nitrogen carrier between cells that can diffuse out of cells for inter-tissue transport; also provides fuel for enterocytes, contributes to alpha-ketoglutarate production for krebs, can transaminate pyruvate to form alanine, part of glutathione


a tripeptide antioxidant important in membranes

amino acid catabolism

after a meal, the liver takes about half of amino acids from portal blood and gets half its energy from aa oxidation; another 20% goes toward synthesizing proteins/N-containing compounds, 23% released into circulation

trans vs. deamination

the direct transfer of the amino group to another compound (carbon skeleton, alpha-ketoacid) vs. just removing the group

transamination is important for

the synthesis of the body's dispensable amino acids


the enzymes that catalyze transamination processes; require B6 as a coenzyme; often the alpha-ketoacid is alpha-ketoglutarate so the new amino acid is often glutamate

branched chain amino acid catabolism

much slower

protein turnover

the process of continuously breaking down and resynthesizing protein; by regulating this our bodies can adapt to periods of growth

negative vs. positive nitrogen balance

the condition in which protein intake is less than protein loss (starvation, illness, stress) vs. intake greater than loss (growth, recovery from illness)

the urea cycle: overview

a process in the liver's mitochondria and cytosol important for the removal of ammonia from the body, as too much can be toxic and lead to brain malfunction and coma

the urea cycle

In mitochondria: 1. ammonia + CO2/HCO3- = carbamoyl phosphate 2. carbamoyl phosphate + ornithine via ornithine transcarbamoylase = citrulline, moves to cytosol 3. citrulline + aspartate + ATP via argininosuccinate synthase = argininosuccinate + AMP + PPi 4. argininosuccinate + fumarate via argininosuccinate lyase = arginine 5. arginine + H2O = urea + ornithine

how expensive is the urea cycle?


once formed, urea travels

in the blood to the kidneys for excretion in the urine


blood-urea-nitrogen; healthy range 8-20mg/dL; low protein diets/acidoses diminishes urea synthesis/urinary urea nitrogen excretion; people with advanced renal disease experience diminished urea synthesis and increased blood ammonia concentrations (need low protein diet)

ketogenic vs. glucogenic products of amino acid catabolism & what they provide

acetyl coa/acetoacetyl coa for lipids and energy vs. pyruvate, oxaloacetate, fumarate, alpha-ketoglutarate, succinyl coa for lipids, energy, glucose


source of methyl groups in metabolism; precursor of cysteine


member of the urea cycle; precursor of nitric oxide


storage and transport form of ammonia; precursor of purines and pyrimidines


precursor of tyrosine; elevated in PKU


precursor of histamine


precursor of serotonin


transport form of ammonia from muscle

disadvantages of protein supplementation

amino acids compete for absorption, less efficient absorption, expensive, bad taste

where is albumin made + what are its functions?

liver, maintain oncotic pressure in blood, transport protein for nutrients (Ca, Zn, B6), transport for some drugs/hormones

list the three branched amino acids

isoleucine, leucine, valine

list the three aromatic amino acids

tryptophan, phenylalanine, tyrosine


aspartate aminotransferase found in the heart for transamination of aspartate to alpha-keto acid to form oxaloacetate + amino acid vs. alanine aminotransferase found in the liver for transaminating alanine + alpha-ketoacid to form pyruvate + amino acid

argininosuccinate synthase requires ___ as a cofactor


what is the name of the N containing compound which serves to replenish ATP in exercising muscles?


the oxidation of ___ in muscle yields acetyl coa + acetoacetate


kidney function is often estimated by measuring the clearance of its breakdown product, _____


muscle breakdown can be estimated by the urinary excretion of the compound known as


the amino acid precursor for epinephrine, norepinephrine, dopamine


protein nutrient density problems

divide grams of protein by total kcal (per serving) for nutrient density

if you're given the mg/g protein of amino acids of a food + their requirements for a 1-3 year old, how do you determine %DV?

1. AA profile/requirement 2. Take the lowest one and multiply it by digestibility for PDCAAS 3. adjust for serving by multiplying grams of protein per serving by PDCAAS 4. find %DV by dividing the adjusted protein g by the DV (50)


precursor for GABA (inhibitory neurotransmitter)

pyrimidines vs. purines

6 membered rings (N @ 1, 3): uracil, cytosine, thymidine vs. 2 fused rings (N @ 1,3,7,9): adenine, guanine

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