- when a person is unable to breakdown Phe into Tyr - Tyr becomes an essential AA - solution: limit Phe in diet and supplement with Tyr

- Lysine: involved in the production of carnitine, limiting in grains - Arginine: conditionally essential (for infants) - Histidine: used to produce histamine (inflammation)

- Aspartate - Glutamate both non-essential can react with basic amino groups to form Gln and Asn

- non-essential - used to produce porphyrin (component of heme)

- 1st step in the synthesis of all proteins - limitting in legumes - makes cystine

- sulfur containing - non-essential - made from methionine - used in glutathione synthesis in oxidant defence - "spares" methionine when it is consumed in diet

- phenylalanine: used to make Phe - tyrosine: spares "Phe" - Tryptophan: used for niacin (B3) synthesis - Proline: important for collagen production, aliphatic side chain

- happens on the OH side chains of serine, threonine and tyrosine in peptide chains - needs phosphate

proteins Flashcards by Cassia Di Pierdomenico

phenylketonuria

when a person is unable to breakdown Phe into Tyr
Tyr becomes an essential AA
solution: limit Phe in diet and supplement with Tyr

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liver disease (cirrhosis)

impairs Phe and Met catabolism
Tyr and Cys are usually synthesized from Phe and Met
Tyr and Cys become essential because they cannot be synthesized

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Basic AAs

Lysine: involved in the production of carnitine, limiting in grains
Arginine: conditionally essential (for infants)
Histidine: used to produce histamine (inflammation)

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Acidic AAs

Aspartate
Glutamate
both non-essential
can react with basic amino groups to form Gln and Asn

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Asparagine and Glutamine

both non-essential
made when amino group reacts with asp and glu
glutamate is used to make GABA

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Glycine

non-essential
used to produce porphyrin (component of heme)

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what are the essential amino acids

histidine
isoleucine
leucine
lysine
methionine
phenylalanine
threonine
tryptophan
valine

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branched chain AAs

leucine, isoleucine and valine
- all are essential
- high levels in circulation (not catabolized in the liver)
- promote protein synthesis
- BCAA levels high in protein suppliments

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Methionine

1st step in the synthesis of all proteins
limitting in legumes
makes cystine

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hydroxylated (OH) AAs

Serine and threonine
- OH in their side chains is important for the phosphorylation PTM of proteins

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Cystine

sulfur containing
non-essential
made from methionine*
used in glutathione synthesis in oxidant defence
“spares” methionine when it is consumed in diet

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Aromatic AAs (rings)

phenylalanine: used to make Phe
tyrosine: spares “Phe”
Tryptophan: used for niacin (B3) synthesis
Proline: important for collagen production, aliphatic side chain

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PTM: phosphorylation

happens on the OH side chains of serine, threonine and tyrosine in peptide chains
needs phosphate

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Hydroxylation of lysine

produces hydroxylysine
copper dependent

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hydroxylation of proline

makes hydroxyproline (Pro-OH)
vitamin C dependent
important in collagen subunits
associated with scurvy

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PTM: gamma-carboxylation

vitamin K dependent
required for calcium homeostasis and blood clotting
another carboxyl group is added to glutamate to allow protein to bind to calcium

PTM: iodination

crucial for the formation of thyroid hormones
crucial for regulation of metabolic rate

PTM: ADP ribosylation

dependent on Niacin (vit B3)
adding ADP-ribose to an acceptor protein
when NAD+ is broken down in the cell, ADP-ribose and nicotinamide are the products

Brief protein digestion

Mouth: no enzymatic breakdown, just mechanical
Stomach: HCl in gastric juice is released, denatures proteins and activates pepsin
Pancreas: pancreatic juice containing zymogens (inactive enzymes)
Small intestine: activates zymogens to produce small peptides and AAs

protein digestion in the stomach

HCl is present in gastric juice, it denatures proteins and activates pepsin
pepsin is an endopeptidase - the first enzymatic part of breakdown
pepsin is secreted as pepsinogen (inactive) but is activated by HCl in the stomach
pepsin generates oligopeptides and some free AAs to be further digested in the SI

protein digestion in the small intestine

trypsinogen travels from the pancreas and is converted to trypsin by enteropeptidase in the brush border
once activated, trypsin will activate all other zymogens
the enzymes breakdown oligopeptides from the stomach into free AAs and small peptides

which part of the polypeptide chain does each intestinal enzyme attack

trypsin: basic AAs
elastase: neutral aliphatic AAs
pepsin and chymotrypsin: large neutral AAs
amino peptidase: removes N-terminal end
carboxypeptidase: removes C-terminal end

AA absorption

most are absorbed by active transport
uses PEPT1 transporter - sodium dependent (indirect ATP requirement)
minor amount absorbed by facilitated diffusion

Are all AAs absorbed the same?

essential AAs are absorbed faster than non-essential AAs
free AAs (supplements) have no advantage over food AAs

what is glutamine used in intestine cells for

- generate energy for the cell - stimulate cell proliferation - increase synthesis of Heat shock proteins - drive mucus production

how does the liver use amino acids

- uses 20% to make new proteins, enzymes and make peptide hormones - catabolizes the remaining 80% were NH3 is sent to the urea cycle and the carbon skeleton os sent to the Kreb's cycle or used for gluconeogenesis or lipogenesis

what is the basis of protein quality

1. AA composition: more essential AAs = higher quality 2. digestibility: more digestible = higher quality 3. presence of toxic factors: less toxic factors = higher quality (e.g. soybeans contain inhibitors that interfere with trypsin thus preventing protein digestion) 4. Species consuming the protein: ruminants have different needs than us because bacteria in the rumen can make all AAs

Protein Efficiency ratio

Test - rats fed a diet with adequate nutrients except protein (10% kcal) - pros: sensitive to AA balance, digestibility and toxic factors - cons: don't know WHY the protein is poor quality PER = gain in body mass / total protein intake

Chemical score (CS)

Test: test protein is digested into free AAs then quantified and compares to the AA composition of whole egg protein (perfect protein) - whichever AA gives the lowest % (test/egg) is the CS - pros: identifies limiting AA - cons: doesn't account for digestibility and toxins CS = (amount of limiting AA in test protein/amount of same AA in egg) x 100

Nitrogen balance

NB = N intake - N loss - most people NB = 0 - if you don't have enough protein NB < 0 - during growth and pregnancy NB > 0

consequences of high protein diets

- short term weight loss - improved insulin sensitivity compared to CHO diets - moderate increase in protein is cardio productive - high protein may be a concern longterm

Marasmus

- protein AND calorie deficiency - body switches to starvation mode - characterized by complete loss of body fat and muscle, peeling skin, uneven pigmentation

Kwashiorkor

- sufficient calories but very deficient in protein (1-2% protein) - comes with high CHO foods - characterized by enlarged abdomen, burns on skin and diarrhea - enlarged abdomen due to decreased plasma proteins causing osmotic imbalance (swelling of gut) - liver is enlarged due to inability to export fat from liver (can't make VLDL)