Amino Acid I

Question 1

Endopeptidase

Answer 1

cleaves peptide bonds on internal surface of protein; ex. Phe, Tyr, Trp, Leu

Question 2

Cholecystokinin

Answer 2

presence of chyme releases this; stimulates both release of bile from gall bladder and also digestive enzymes (zymogens such as trypsinogen) from the pancreas

Question 3

Secretin

Answer 3

released when chyme is present; stimulates acinar cells of pancreas to release HCO3-, to neutralize acidic chyme

Question 4

Pepsinogen/Pepsin

Answer 4

Pepsinogen = inactive zymogen, autoinhibits itself, comes from chief cells of stomach; Pepsin= active enzyme, endopeptidase

Question 5

Enteropeptidase

Answer 5

membrane anchored protease found on surface of villi; converts trypsinogen to trypsin

Question 6

Endopeptidase/Aminopeptidase

Answer 6

on luminal surface of epithelial cells. Produce a mixture of free AA’s and di/tripeptides

Question 7

Sodium Electrical Gradient

Answer 7

form of energy input used in uptake of free AA’s to epithelial cells

Question 8

L vs. D AA’s

Answer 8

affinity of AA transport much higher for L- than D- AA’s

Question 9

Proton Gradient

Answer 9

form of energy input used in uptake of di/tripeptides

Question 10

Acute Pancreatitis

Answer 10

inflammatory disease; causes = alcohol, infections, gallstones; enzymes activated inside of the pancreas = damage; Treatment = supportive, involving fasting

Question 11

Hartnup Disease

Answer 11

blocks AA transporter normally responsible for uptake of large, neutral AA’s (Phe, Tyr, Trp, Met, Val, Leu, Ile) into intestinal epithelial cells; also transporter found in kidney were it is responsible for reaborption of netural AA’s from ultrafiltrate; malabsorption of dietary neutral AA’s and presnce of neutral AA’s in the urine; symptoms like pellagra so supplementation w/ niacin

Question 12

Celiac Disease

Answer 12

inappropriate immune response to Alpha-gliadin (glycoprotein in gluten); severe cases = loss of villi in intestine; lose ability for good absorption and look like nutrient deficiency possiblity; cramps, bloating; treatment w/ foods avoiding alpha-gliadin

Question 13

Amino Acid Pool

Answer 13

100g in adults; AA’s used for energy metabolism or protein synthesis; N(in) = N(out) equilibrium; Negative balance means inadequate protein intake and positive balance means increase in body protein (ex. pregnant women, growing children or adults recovering from illness; growth stages); human degrades about 400g of protein each day and 75% are recycled in body; the other 50-100g must be replaced by diet

Question 14

Essential AA’s

Answer 14

Pvt Tim Hall; Phe, Val, Trp, Threonine, Isoleucine, Methionine, Histidine, Arginine(infants), Leucine, Lysine; we can make arginine just not in enough amounts during growth stages

Question 15

Pressure Ulcers

Answer 15

can be treated w/ help of arginine supplements

Question 16

Alpha-KG and OAA precursors

Answer 16

Glutamate, glutamine, proline, Arginine, Aspartate, Asparagine

Question 17

Pyruvate and 3-Phosphoglycerate precursors

Answer 17

alanine, serine

Question 18

Alpha-Ketoacid vs. Alpha-Amino Acid

Answer 18

Ketoacid = double bonded O to alpha-C
AA= NH3+ and H boned to alpha-C

Question 19

Glutamate

Answer 19

major source is from diet; also generated by transamination of alpha-KG and deamidation of glutamine

Question 20

Glutamate Dehydrogenase

Answer 20

glutamate –> Alpha-KG; most active in the liver; unlikely very reversible; requires NAD+ and H2O and gives off alpha-KG and NADH, NH4+, enzyme is incredible important for global control of AA catabolism

Question 21

Glutamine Synthetase

Answer 21

Glutamate –> Glutamine (requires ATP and NH4+); replaces O- w/ NH2 on terminal carboxyl;

Question 22

Production of Glutamine

Answer 22

glutamine synthetase; requires ATP and NH4+; important mechanism for removal of ammonium ions from peripheral tissues; absorbed by liver, kidneys and intestine where amide group is hydrolyzed by glutaminase (gives glutamate and NH4+)

Question 23

Glutaminase

Answer 23

glutamine–> glutamate (gives off NH4+); done mainly in intestine, liver and kidneys

Question 24

Aminotransferases

Answer 24

catalyze interconversion of AA’s and their corresponding alpha-Ketoacid; freely reversible; requirement for pyridoxal-5’-phosphate (B6 vitamin: PLP)

Question 25

Synthesis of Alanine (co: alpha-Ketoacid and function of alanine)

Answer 25

Pyruvate + Glutamate –> alpha-KG + Alanine (alanine aminotransferase [ALT]); muscle can generate pyruvate during glycolysis and pyruvate can then be converted to alanine; alanine released into blood and taken up by liver; in liver, ALT reverses back to pyruvate for GNG; this will occur during early fasting states

Question 26

Synthesis of Aspartate (co:alpha-ketoacid)

Answer 26

OAA + glutamate –> alpha-KG + Aspartate (Aspartate aminotransferase [AST]); requires B6 in enzyme;

Question 27

Synthesis of Asparagine (source of nitrogen?)

Answer 27

Aspartate –> Asparagine (Asparagine Synthetase [ATP input]); utilizes amide nitrogen of glutamine instead of NH4+ ion;

Question 28

Clinical Significance of ALT and AST and Where they are mainly found?

Answer 28

AST found in liver>cardiac>skeletal muscle> kidney>other tissues; ALT found mainly in liver; both usually in serum at low conc. however, if tests shows high conc. then there is organ damage; ALT mainly signifies liver damage; AST may be liver disease or also heart attack

Question 29

Synthesis of Serine and what serine is good for?

Answer 29

3-Phosphoglycerate –(NAD+)–> 3-Phosphohydroxypyruvate + Glutamate–>3-Phosphoserine (+ alpha-KG)–(H2O)–>Serine; 3 step rxn 1) phsophoglycerate dehydrogenase (makes a alpha-ketoacid!!) 2) 3-phosphoserine aminotransferase (uses glutamate for -N source), 3) Phosphatase; Serine is important substrate for synthesis of cysteine, selenocysteine, sphingolipids and phospholipids

Question 30

Glycine: Synthesis, Contributions, Enzymes

Answer 30

collagen is major source of this in diet and you get a lot of it; dont synthesize a ton; glycine important for porphyrin rings, creatine, glutathione, purine rings; glycine serine; enzyme requires B6 and THF as methylene acceptor

Question 31

THF/folate/1-Carbon Pool

Answer 31

derived from folate vitamin; folate found in liver, eggs, green veggies, beans; THF serves as acceptor for 1-carbon groups (one-carbon pool); 1-C groups can be oxidized or reduced (most oxidized = N10-formyl THF; most reduced = N5-methyl THF); serine is major source of 1-C pool; carbon sources also come from formaldehyde, formate, histidine; dietary carbohydrate enters pool via 3-Phoshoglycerate

Question 32

N5-Methyl THF

Answer 32

once formed it is NOT readily re-oxidized; thus, will tend to accumulate; only one reaction that can use this as substrate

Question 33

Cysteine: Characteristics, synthesis

Answer 33

only AA that can be reversibly reduced (-SH) and oxidized (S-S); methionine—(Met adenosyltransferase w/ ATP)—>S-Adenosyltransferase (SAM)—(methyltransferases)—>S-Adenosylhomocysteine—–> Homocysteine—(Cystathionine Beta-synthase[PLP/B6] + Serine)—> Cystathione—(Cystathionase)—> Cysteine (+NH4+ + alpha-KG); only -S group of cysteine comes from homocysteine, carbon skeleton of cysteine all comes from serine!

Question 34

Homocystinuria

Answer 34

elevated levels of homocysteine in urine; mutations in cystathione beta-synthase gene; dislocation of optic lens, osteporosis, lengthening/thinning of long bones, thromboembolism, intellectual disability; individuals vary greatly in presentation and those w/ mild symptoms respond to pyridoxine supplementation; low methionine diet suppletmented w/ cysteine and betaine administration;

Question 35

Pyridoxine Supplementation in Homocystinuria

Answer 35

both cystathione beta-synthase (CBS) and the following enzyme in pathway of cysteine synthesis are vitamin B^ dependant

Question 36

Betaine Administration in Homocystinuria

Answer 36

effective b/c there is an alternative pathway of homocysteine metabolism that features an enzyme w/ requirement of betaine

Question 37

Synthesis of Tyrosine

Answer 37

single step from phenylalanine; phenylalanine hydroxylase (found mainly in liver); IRREVERSIBLE (Phe is essential AA); rxn requires tetrahydrobiopterin (THBtn) to oxidize aromatic ring of Phe; THBtn —-> dihydrobiopterin (DHBtn); must be recycled back to THBtn by reduction by NADH and dihydrobiopterin reductase enzyme

Question 38

Phenylketonuria Mechanism

Answer 38

Normal Phe disposal is conversion to Tyr; PKU patients unable to make conversion of Phe–> Tyr; major route of disposal then becomes transamination of Phe—>phenylpyruvate; urine contains high levels of phenylpyruvate; mutations in phenylalanine hydroxylase (more common) and also dihydrobiopterin reductase (less common); one of most common inborn errors of metabolism

Question 39

PKU Symptoms and Results

Answer 39

intellectual disability, recurrent seziures, hypopigmentation, eczematous skin rashes; accumulation of Phe competitively inhibits transport across blood/brain barrier of other AA’s required for protein and/or neurotransmitter synthesis; also leads to reduced synthesis and increased degradation of myelin; competitive inhibitor of tyronsinase (required for myelin synthesis and accounts for hypopigmentation);

Question 40

PKU Treatment and screening

Answer 40

screening require by law since it is both readily detectable and amenable by treatment by dietary modification; prevention of intellectual disability requires treatment w/ low Phe diet supplemented w/ Tyr (before child is 3 weeks of age)

Question 41

Aspartame

Answer 41

dipeptide of aspartate and methyl ester of Phe; it is digested to aspartate, methanol, and Phe