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Biochem part 3
Amino acid metabolism
| Question | Answer |
|---|---|
| When does gastrin get secreted | As food enters the stomach |
| What are the two functions of gastrin | facilitates secretion of pepsinogen; cause release of HCl from parietal cell |
| two functions of HCl in stomach | denatures dietary protein; converts pepsinogen to pepsin |
| name the four pancreatic proenzymes | trypsinogen, chymotrypsinogen, procarboxypeptidase, proelastase |
| converts trypsinogen to trypsin | enteropeptidase |
| where is enteropeptidase found/produced | enteropeptidase is synthesized by and present on the luminal surface of intestinal mucosa cells |
| what converts the other 3 pancreatic proenzymes | trypsin |
| what are the enzymes produced in the intestines for protein digestion | aminopeptidases (produced in intestinal tract), dipeptidases, tripeptidases (both within intestinal mucosa cells) |
| chymotrypsin works on the carboxyl supplied by which type of AA | hydrophobic or acidic amino acid |
| trypsin works on the carboxyl supplied by which type of AA | basic or aromatic AA |
| pepsin works on the carboxyl supplied by which type of AA | aromatic or acidic AA |
| how are amino acids brought into intestinal cells | brought in with Na+ ions in a 1:1 ratio |
| what type of transport takes the Na+ back out of the intestinal cell | active transport as a K+ is brought into the cell (1 ATP gets used) |
| how are amino groups removed from peptides | transaminases; glutamate dehydrogenase |
| what two classes of compounds are needed for transamination | alpha-keto acid and amino acid |
| what common AA/alpha-keto acid pair is often used for transamination | alpha-ketoglutarate and glutamate |
| how are aminotransferases named | named after amino acid donor |
| what coenzyme is needed for transamination | PLP |
| where are aminotransferases normally found | intracellular |
| what does the presence of high levels of aminotransferases in the plasma indicate | damage to cells rich in these enzymes |
| what two blood transaminases are used diagnostically | alanine aminotransferase and aspartate aminotransferase |
| other name for alanine aminotransferase | glutamate-pyruvate transaminase |
| other name for aspartate aminotransferase | glutamate-oxaloacetate transaminase |
| what do high levels of AST in the blood indicate | MI |
| what do high levels of ALT and AST indicate | liver disease |
| after transamination, what's the next step in liberation of amino group | oxidative deamination |
| where does oxidative deamination primarily take place | liver and kidney |
| outline what happens to glutamate after transamination | glutamate==> imino acid (via glutamate dehydrogenase) ==> alpha-keto glutarate + NH3 (via hydrolysis) |
| what are the two ways to dispose of ammonia | excrete as ammonium ions in urine; convert to urea and then exrete urea in urine |
| what are the two paths for getting ammonia to the liver or kidneys | glutamine shuttle; glucose alanine cycle |
| what happens in the glutamine shuttle | glutamate is converted to glutamine by the addition of ammonia using ATP. Glutamine is then taken to liver or kidney and broken down to release ammonia. |
| what two enzymes are involved in the glutamine shuttle | glutamine synthetase and glutaminase (which breaks down glutamine) |
| what happens to ammonia in the liver and kidney | ammonia is turned into ammonium ions in the kidney and excreted. it is turned into urea in the liver which is taken to kidney for excretion |
| where does glutamine shuttle take place | brain, muscle, liver |
| outline the steps of the glucose-alanine cycle | pyruvate from glycolysis in muscles is turned into alanine in muscle and alanine is turned back into pyruvate and then glucose in liver and is then sent back to muscle. way of breaking down muscle protein. |
| where does the urea cycle take place | liver only |
| what percentage of our nitrogen is excreted as urea | 80-90% |
| list the order of metabolites in the urea cycle and where they are made | carbamoyl phosphate (M), citrulline (M), citrulline (C), argininosuccinate (C), arginine (C), Ornithine & Urea (C); M=mitochondria, C=cytoplasm |
| name the order of enzymes used in the urea cycle | carbamoyl phosphate synthetase, ornithine transcarbamoylase, argininosuccinate synthetase, argininosuccinase, arginase |
| how many ATP are used in the urea cycle | 3 |
| where do the nitrogens in urea come from | one from free ammonia and the other from aspartate amino group |
| what two reactants make citrulline | ornithine and carbamoyl phosphate |
| what two reactants make argininosuccinate | aspartate and citrulline |
| argininosuccinate is broken down into what two products | fumarate and arginine |
| how is aspartate regenerated for the urea cycle | fumarate => malate =>oxaloacetate => aspartic acid (via transamination) |
| what does BUN stand for | blood urea nitrogen |
| what does elevated BUN indicate | kidney impairment |
| what are some things which may lead to high BUN | liver may be making excessive urea because of high protein diet, infections, physical trauma |
| what are three areas carbon skeletons can be used after an AA has been deaminated | glycolysis, TCA cycle intermediates, Lipid metabolism |
| what are glucogenic AAs | they are converted to glucose during starvation; converted to glucose and stored as glycogen when excess protein is consumed; AAs that are degraded to TCA cycle intermediates |
| what are ketogenic AAs | converted to ketone bodies during starvation;converted to fatty acids and stored as fat when excess protein is consumed; AAs converted to intermediates in lipid metabolism |
| what two AAs are strictly ketogenic | leucine and lysine |
| what AAs are both glucogenic and ketogenic | phenylalanine, isoleucine, tyrosine, tryptophan |
| what AA is used to make GABA | glutamate |
| what is GABA used for | it's a post synaptic inhibitor of nerve transmission in the brain |
| what AA is the precursor for histamine | histidine |
| tryptophan is used to make what neurotransmitter | serotonin |
| what AA shows up in most drug metabolism processes | methionine |
| how is methionine activated to create S-adenosylmethionine | by adding the adenosine from ATP |
| what functional group can SAM give to an amine or a hydroxyl | a methyl group |
| what is SAM used for in Europe | osteoarthritis and depression |
| when a Schiff base is turned into an aldehyde what is added and what is given off | water is added and ammonia is given off |
| when norepinephrine is acted on by SAM what is the product | epinephrine |
| what enzyme is used to convert phenylalanine to tyrosine | phenylalanine hydroxylase |
| what causes PKU | deficiency of phenylalanine hydroxylase causing a buildup of phenylalanine |
| what is phenylalanine converted to via transamination | phenylpyruvic acid (PPA) |
| what amino acid is the precursor to norepinephrine and dopamine | tyrosine |
| name the intermediates in the synthesis of norepinephrine from tyrosine | tyrosine ==> dopa ==> dopamine ==> norepinephrine |
| in the melanocytes, tyrosine is converted to dopa and eventually melanin. what enzyme starts the process | tyrosine hydroxylase |
| what cofactor is needed in melanin synthesis | copper |
| what enzyme converts dopa to dopamine | dopa decarboxylase |
| in what two places is norepinephrine made | brain and adrenal medulla |
| where is epinephrine made | adrenal medulla |
| norepinephrine is inactivated by conversion to what metabolite | VMA (vanillylmandelic acid) |
| what disorder is diagnosed by measuring VMA in the urine | pheochromocytoma |
| where in the thyroid gland does iodination and coupling of tyrosine residues take place | in the follicular space |
| what hormone stimulates the pinocytosis of Tgb with T3 and T4 | TSH |
| what three substances combine to create creatine | glycine, arginine, and SAM |
| how is creatinine formed | creatine and creatine phosphate spontaneously cyclize to form creatinine |
| what enzyme converts creatine into creatine phosphate | creatine kinase using 1 ATP |
| in what parts of the body is creatine kinase found | brain, muscles |
| what is creatine kinase used to diagnose | MI |
| what is serum creatinine levels used for | to diagnose kidney function |
| what is the advantage of creatinine measurement over BUN | rate of synthesis of creatinine is constant |
| what does creatinine clearance measure | rate of glomerular filtration |
| why is creatinine ideal for measuring glomerular filtration rate | it is completely filtered in glomerulus; it is not reabsorbed; it is not secreted |
| what is the relationship between the GFR and volume of urine excreted | GFR x [Cr]plasma = [Cr]urine x volume of urine/min |
| what are the intermediates in the synthesis of heme | aminolevulinic acid and porphobilinogen |
| how is aminolevulinic acid made | succinyl CoA + glycine in the presence of PLP. Co2 and CoA are given off. |
| what is the rate controlling step in the synthesis of heme | creation of aminolevulinic acid (ALA) |
| what is given off when 2 ALAs come together and what is formed | 2 water molecules are given off and porphobilinogen is formed |
| when you link 4 porphobilinogens, what else happens to create heme | lose 4 ammonia, lose 6 CO2, oxidations to introduce double bonds, insert metal ion |
| what are porphyrias | diseases caused by defects in heme synthesis. genetically inherited |
| what substance negatively feeds back to ALA synthase to adjust heme synthesis | heme |
| what happens if one of the enzymes between porphobilinogen and heme are deficient | ALA synthase activity is uncontrolled and an excess of intermediates build up in the blood |
| what are symptoms of porphyria | neurological symptoms; skin photosensitivity |
| where are red blood cells broken down | in liver, bone marrow, spleen (RE system) |
| how is bilirubin carried in the blood | attached to albumin |
| when bilirubin enters the liver it reacts with 2 UDP glucuronic acid to produce what substance | bilirubin diglucuronide (BDG) and gives off 2 UDP |
| BDG enters the intestines and is acted on by bacteria to create which substance | urobilinogen (UB) |
| what can happen to UB after it's made | UB can be taken to the kidney for excretion; it can be excreted from the gut after being turned into stercobilin (brown) |
| what does the presence of BDG in the urine indicate | liver disease |
| true or false. bilirubin-albumin can be excreted by the kidneys | false. complex is too large |
| in prehepatic jaundice, what is the major blood metabolite of heme | bilirubin-albumin complex |
| what happens in prehepatic jaundice | too much bilirubin being produced. being made faster than liver can conjugate it with glucuronic acid |
| what happens to conc. of UB and bilirubin in urine when one has hemolytic jaundice | UB increases; bilirubin absent |
| in hepatic jaundice what happens to blood levels of BDG and urine levels of UB and bilirubin | major blood metabolite is BDG; UB levels in urine increase and bilirubin is also present in urine |
| in posthepatic jaundice, what happens to fecal UB and urine UB. | both decrease |
| what AA is used to make NO | arginine |
| when arginine is acted on by NO synthase, what other reactants are present and what is the result | oxygen and NADPH are used and the result is citrulline |
| where does NO production occur/have an impact | nerve endings; endothelial cells lining blood vessels |
| what impact does NO have on blood vessels | it lowers blood pressure by causing vasodilation |
Created by:
coolnuh
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