proteins

Question 1

phenylketonuria

Answer 1

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

Question 2

liver disease (cirrhosis)

Answer 2

• 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

Question 3

Basic AAs

Answer 3

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

Question 4

Acidic AAs

Answer 4

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

Question 5

Asparagine and Glutamine

Answer 5

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

Question 6

Glycine

Answer 6

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

Question 7

what are the essential amino acids

Answer 7

• histidine
• isoleucine
• leucine
• lysine
• methionine
• phenylalanine
• threonine
• tryptophan
• valine

Question 8

branched chain AAs

Answer 8

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

Question 9

Methionine

Answer 9

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

Question 10

hydroxylated (OH) AAs

Answer 10

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

Question 11

Cystine

Answer 11

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

Question 12

Aromatic AAs (rings)

Answer 12

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

Question 13

PTM: phosphorylation

Answer 13

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

Question 14

Hydroxylation of lysine

Answer 14

• produces hydroxylysine
• copper dependent

Question 15

hydroxylation of proline

Answer 15

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

Question 16

PTM: gamma-carboxylation

Answer 16

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

Question 17

PTM: iodination

Answer 17

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

Question 18

PTM: ADP ribosylation

Answer 18

• 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

Question 19

Brief protein digestion

Answer 19

• 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

Question 20

protein digestion in the stomach

Answer 20

• 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

Question 21

protein digestion in the small intestine

Answer 21

• 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

Question 22

which part of the polypeptide chain does each intestinal enzyme attack

Answer 22

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

Question 23

AA absorption

Answer 23

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

Question 24

Are all AAs absorbed the same?

Answer 24

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

Question 25

what is glutamine used in intestine cells for

Answer 25

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

Question 26

how does the liver use amino acids

Answer 26

- 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

Question 27

what is the basis of protein quality

Answer 27

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

Question 28

Protein Efficiency ratio

Answer 28

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

Question 29

Chemical score (CS)

Answer 29

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

Question 30

Nitrogen balance

Answer 30

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

Question 31

consequences of high protein diets

Answer 31

- 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

Question 32

Marasmus

Answer 32

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

Question 33

Kwashiorkor

Answer 33

- 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)