Protein As A Macronutrient

Front 1

How is nitrogen balanced in the body?

Back 1

uptake by protein, lost in urine (mostly as urea, to a small extent by creatinine, uric acid, and ammonia)

Front 2

What is obligatory nitrogen loss?

Back 2

loss of nitrogen through amino acid catabolism, growing hair and nails, sloughing cells

Front 3

How are amino acids produced?

Back 3

digestion and hydrolysis of dietary protein, hydrolysis of body protein, de novo synthesis of non-essential amino acids

Front 4

How are amino acids used?

Back 4

body protein synthesis, gluconeogenesis, synthesis of other nitrogen containing compounds

Front 5

What makes a protein a high-quality protein?

Back 5

combination and quantity of essential amino acids, digestibility

Front 6

What is protein digestibility?

Back 6

the amount of nitrogen that was absorbed into the body relative to the amount of nitrogen that was consumed

Front 7

What is biological value (BV)(of proteins)?

Back 7

a scale to measure protein quality, measured as the amount of retained nitrogen as proportion of the amount of absorbed nitrogen, corrected by fecal loss of nitrogen (the lower the excreted nitrogen, the higher the BV)

Front 8

What is the protein recommended dietary allowance for adults?

Back 8

0.8 g per kg body weight per day

Front 9

What is the average protein turnover in the human body and what factors affect this rate?

Back 9

400g/day are degraded and replenished, rate depends on half life of protein, and tissue type, age, growth, disease

Front 10

How are body proteins degraded (pathways)?

Back 10

ubiquitin-proteasome pathway degrades short-lived proteins (very ATP dependent),
autophagy-lysosome pathway degrades most long-lived intracellular proteins (less energy consuming)

Front 11

How are protein degradation pathways regulated?

Back 11

low insulin levels activate pathways, starvation (lack of dietary amino acids) increases the rate of autophagy, limiting amino acids activate protein degradation, stress hormones lead to hypercatabolism

Front 12

Which hormones contribute to hypercatabolism of body proteins?

Back 12

stress hormones; cortisol, epinephrine

Front 13

What is glutamine's role during severe stress?

Back 13

acts as the preferred respiratory fuel for lymphocytes, hepatocytes, intestinal mucosal cells (it is a conditionally-essential amino acid)

Front 14

What enzymes are responsible for dietary protein digestion and where are they found?

Back 14

1st: pepsin - stomach
2nd: proteases - pancreas
3rd: aminopeptidases - brush border of enterocytes

Front 15

How are pancreatic proteases activated?

Back 15

enteropeptidase converts trypsinogen to trypsin, then trypsin activates additional trypsin, chymotrypsinogen, proelastase, procarboxypeptidase

Front 16

How does pepsin become active?

Back 16

HCl and other pepsin molecules convert pepsinogen to pepsin

Front 17

What is celiac sprue?

Back 17

immune mediated inflammation and damage of the mucosa in the small intestine, a result of ingestion of gluten, causes malabsorption, diarrhea, vomiting

Front 18

How are free amino acids absorbed into the enterocyte?

Back 18

Sodium dependent transporters

Front 19

How are di- and tri- peptides absorbed into the enterocyte?

Back 19

Hydrogen dependent transporters

Front 20

What is Hartnup disease?

Back 20

a defect in apical amino acid absorption (a defective transporter for neutral amino acids), usually involves tryptophan deficiency

Front 21

What is Cystinuria?

Back 21

defective membrane carrier for dibasic amino acids (cysteine, ornithine, arginine, lysine - COAL), these are usually excreted in urine