Flashcards in Lecture 46 Deck (54)
What is the average amount of dietary protein that should be taken in per day?
100g per day
How much body protein is broken down per day?
250-300g are broken down per day, but are reestablished by circulating amino acids in the body
Aside from body protein, what can amino acids be used to form within the body?
100g/day of each of the following are produced:
1) Biosynthetic products: Creatine, neurotransmitters, purines, pyrimidines, & other N-containing compounds
2) Nitrogen-free intermediates: Glucose, CO2 + H2O, & Ketone bodies
3) Ammonia, which is converted to urea in the liver and excreted by the kidney
How much urea is excreted by the kidney each day?
30g per day
What is an essential amino acid?
An essential amino acid is an amino acid that cannot be synthesized de novo by humans, and therefore must be supplied in the diet
What are the essential amino acids?
Phenylalanine, Valine, Threonine, Isoleucine, Methionine, Histidine, Arginine, Leucine, & Lysine
What is a pneumonic device to remember the essential amino acids?
The Ten Acid Pornstars Liked Very Hot Ladies In Mini-skirts
In the stomach, what proteolytic enzyme cleaves dietary protein into polypeptides and amino acids?
Pepsin: enzyme whose zymogen (pepsinogen) is released by the chief cells in the stomach and that degrades food proteins into peptides
Upon entering the small intestine, polypeptides are cleaved by what pancreatic enzymes?
What is the function of trypsin?
Cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine, except when either is followed by proline
What is the function of chymotrypsin?
Cleaves peptide amide bonds where the carboxyl side of the amide bond (the P1 position) is a large hydrophobic amino acid (tyrosine, tryptophan, and phenylalanine).
What is the function of elastase?
1) Elastase breaks down elastin, an elastic fibre that, together with collagen, determines the mechanical properties of connective tissue
2) The specific peptide bonds cleaved are those on the carboxy side of small, hydrophobic amino acids such as glycine, alanine, and valine.
What is the function of carboxy-peptidase?
A protease enzyme that hydrolyzes (cleaves) a peptide bond at the carboxy-terminal (C-terminal) end of a protein or peptide
Once polypeptides have been broken down to oligopeptides, what additional enzymes ensure oligopeptide breakdown to form amino acids?
2) Di- and tri-peptidases
What is the function of an amino-peptidase?
Aminopeptidases catalyze the cleavage of amino acids from the amino terminus of protein (N-terminus) or peptide substrates
What is the function of a di-peptidase?
1) Dipeptidases are enzymes secreted by enterocytes into the small intestine
2) Dipeptidases hydrolyze bound pairs of amino acids, called dipeptides
What is the function of a tri-peptidase?
Tripeptidases hydrolyze bound trios of amino acids, called tripeptides
Where are amino acids sent once they have been formed from the cleavage of protein in the small intestine?
How is nutrient digestion in the small intestine hormonally controlled?
Upon digesting food or liquid, the body produces cholecystokinin & secretin in the blood
What are the functions of cholecystokinin?
1) Negatively regulates gastric motility, to allow for digestion of what is already contained within small intestine
2) Positively regulates the gall bladder to secrete bile into the small intestine
3) Positively regulates the pancreas to secrete pancreatic enzymes into the small intestine
What promotes the production of cholecystokinin & secretin?
Dietary lipids from substances being digested in the small intestine
What is the function of secretin?
Positively regulates the pancreas to secrete bicarbonate into the small intestine (to increase pH, since pancreatic enzymes are optimal at a less acidic pH)
What is cystinuria?
Cystinuria is a disorder of the proximal tubule's reabsorption of filtered cystine and dibasic amino acids (ornithine, arginine, lysice)
What causes cystinuria?
1) Cystinuria is a genetically inherited recessive disorder
2) Cystinuria results in 4 (out of a total 7) defective transporters (cystine, ornithine, arginine, & lysine) that are required for amino acid uptake from the gut and re-uptake into the kidney tubules
What does cystinuria result in?
1) Cystine, ornithine, arginine & lysine appear in the urine
2) Cystine precipitates in the acidic urine, forming stones (calculi)
What is an example of a disulfide linked peptide hormone?
What are characteristics of Hartnup disorder?
1) Defective absorption of tryptophan (required for the liver synthesis of niacin)
2) Deficiency of niacin causes pellagra involving skin, GI tract & CNS
3) Pellagra symptoms: Dermatitis, diarrhea, & dementia (death if untreated)
What can of diet can cause pellagra?
A corn-based diet, since it is low in niacin & tryptophan
What conditions cause a negative balance in nitrogen equilibrium within the body (equilibrium occurs between dietary protein, body protein, urea, and the amino acid pool)?
1) Protein deficiency
2) Essential amino acid deficiency
3) Wasting diseases
What conditions cause a positive balance in nitrogen equilibrium within the body (equilibrium occurs between dietary protein, body protein, urea, and the amino acid pool)?
What is kwashiorkor?
A negative effect of nitrogen balance within the body caused by a deficiency of protein nutrition (intake)
What are physical symptoms of kwashiorkor?
1) Failure to gain weight
2) Stunted linear growth
3) Generalized edema
4) Swollen abdomen
6) Skin depigmentation
7) Reddish pigmentation of hair
8) Decreased muscle mass
What are mental changes that arise in kwashiorkor?
What are physiological changes that arise in kwashiorkor?
1) Fatty liver
What can patients experience in the final stages of kwashiorkor?
How can one treat kwashiorkor?
Gradual re-introduction of protein and amino acids, but irreversible damage may occur
How is nitrogen (amino group) removed from amino acids in a transamination?
1) An amino acid reacts with an alpha-keto acid (usually alpha-ketoglutarate) to transfer its amino group (N) to alpha-keto acid
2) Reaction is catalyzed by aminotransferase (transaminase)
3) In the example of alpha-ketoglutarate:
amino acid + alpha-ketoglutarate --> alpha-keto acid + glutamate
What can alanine be used to form?
Alanine + alpha-ketoglutarate --> Pyruvate + Glutamate through the use of alanine aminotransferase (commonly found in liver; enzymes can be used to test for liver function - lower levels indicates a liver dysfunction)
What can aspartate be used to form?
Asparate + alpha-ketoglutarate --> Oxaloacetate + Glutamate through the use of aspartate aminotransferase (commonly found in liver; enzymes can be used to test for liver function - lower levels indicates a liver dysfunction)
How does pyridoxal phosphate take part in transamination reactions?
The cyclic interconversion of pyridoxal phosphate and pyridoxamine phosphate can transfer amino groups between amino acids and other groups:
1) Glutamate + Pyridoxal phosphate --> Alpha-keto glutarate + Pyridoxamine phosphate
2) Pyridoxamine phosphate + Oxaloacetate --> Pyridoxal phosphate + Aspartate
Following poisoning with the toxic mushroom Amanita phalloides, what happens in the body?
1) Serum concentrations of Alanine amino transferase (ALT) rise gradually and continually until reaching a peak of about 20x higher levels than normal at about 30 hours after ingestion; after this point, levels decrease back to normal, gradually
2) Serum concentrations of bilirubin do not begin to elevate until after 36 hours of ingestion, at which point they rise gradually
What can elevated levels of bilirubin cause?
How can the body use oxidative deamination of an amino acid?
1) Glutamate + NAD+ --> alpha-ketoglutarate + NADH + NH3
2) alpha-ketoglutarate + NH3 + NADPH --> glutamate + NADP+
3) Enzyme: Glutamate dehydrogenase
What are two steps that lead to the disposal of amino acids?
2) Oxidative Deamination
What are allosteric modulators of oxidative deamination?
1) Guanosine triphosphate (GTP) is an allosteric inhibitor of glutamate dehydrogenase
2) Adenosine diphosphate (ADP) is an allosteric activator of glutamate dehydrogenase
How does glutamate dehydrogenase function in comparison to cell energy levels?
When energy levels are low in the cell, glutamate dehydrogenase activity is high, facilitating energy production from the carbon skeletons derived from amino acids
What is the role of D-serine in the brain?
1) D-serine is present in the diet and is also made in brain by serine racemase from L-serine
2) D-serine modulates N-methyl-D-aspartate (NMDA)-type glutamate receptors
3) D-amino acid oxidase (DAO) is a FAD-dependent peroxisomal enzyme that catalyzes the oxidative deamination of D-AA producing alpha-keto acids, ammonia, & hydrogen peroxide
4) Increased DAO activity has been linked to increased susceptibility to schizophrenia
How do transamination and oxidative deamination work together to dispose of amino acids?
1) Transamination: alpha amino acids transfer their amino group to alpha ketoglutarate to form an alpha-keto acid and glutamate (with the amino group)
2) Oxidative deamination: glutamate is oxidized to alpha-ketoglutarate, causing its loss of its amino group in the form of ammonia
3) Oxidative deamination: NAD+/NADP+ is reduced to NADH/NADPH by the oxidation of glutamate
What are two mechanisms to transport ammonia from muscle to the liver?
1) Glutamine synthetase pathway
2) Alanine to the liver
What is the glutamine synthetase pathway to transporting ammonia from muscle to liver?
1) ATP + NH3 + Glutamate --> ADP + Pi + Glutamine (uses Glutamine synthetase in the muscle)
2) Glutamine + H2O --> Glutamate + NH3 (uses Glutaminase in the liver)
What is the alanine amino-transferase pathway to transporting ammonia from muscle to liver?
1) Alanine + alpha-ketoglutarate --> Glutamate + Pyruvate (uses Alanine amino-transferase)
2) Glutamate --> alpha ketoglutarate (uses glutamate dehydrogenase)
What are two functions of amino acids?
2) Precursors of monoamine neurotransmitters
What are examples of neurotransmitters, what are their functions, and where are they localized?
1) Glycine; Inhibitory; Spinal Cord
2) Glutamate; Excitatory; CNS
3) GABA; Inhibitory; CNS