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43 Cards in this Set
- Front
- Back
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What is the ultimate source of aa nitrogen?
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-N2 gas from the atmosphere (but most organisms cannot incorporate this into aa)
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How do you incorporate atmostpheric N2 into aa?
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Nitrogen fixation. This can be done:
-Biologically by mircroorganisms (diazotrophs brea down the N2 db to get NH3) -Through lightning (get about 10% of our naturally fixed N2 this way) |
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What are the 3 paths to get NH3 into the biosphere (what are the 3 nitrogen assimilation rxns)?
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1) Synthesis of Glutamate
2) Synthesis of Glutamine 3) Synthesis of Carbamyl Phosphate |
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What happens when lightning breaks down N2?
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When the bond is broken, N is very reactive .: combines with O2 to form NO2 and NO3
-NO2 and NO3 get hydrated into nitrates (but we still can't use this) .: Nitrfying bacteria: can consume nitrates and turn them into ammonia (* nitrifying bacteria can't break the N2 bonds themselves) |
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How do diazotrophs do nirtogen fixation?
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Use Nitrogenases and Fe to do this process
-E cost, however is very high => requires 16 ATP and 8 e- |
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What is Nitrogen balance?
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State of an individual over a 24-h period btw the amt of N2 taken in and amt of N2 released/excreted
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When do u have positive N balance? Negative N balance?
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-Pos. N balance: N intake> N release
happens during growth, pregnancy, bodybuilding -Neg N balance: N in < N out Happens when your sick |
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What are the 2 pools of aa in the body?
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1) Body Proteins
2) Free aa pool (1% of the amount of body ptn) |
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What is the free pool of AA used for?
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1)Make poteins
-Turnover rate of ~300g of ptns 2)Make N-containing compounds: -Purines & pyrimidines (DNA) -Heme (for O2 fixation in RBC) -Creatine (in E-regenerating sys) => After these 2 things are done, the rest of the aa in teh free pool will be catabolized/degraded |
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Where do the aa in the free pool come from?
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-Degraded proteins
-aa consumed in our diet -paths that make non-essential aa (aa made by the organism) |
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What are 3 characteristics of the free aa pool?
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1) Its dynamic (always making and degrading aa to keep the 300g ptn turnover rate cst)
2) All the aa are of equal quality and are indistinguishable (can't tell the source of the aa) 3) Free aa pool is constant (always 100g of free aa) |
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Which aa are in the free aa pool?
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All 20 of them must be there (if even one is missing, get a neg N balance)
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What is special about Arginine? Cystein? Tyrosine?
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Arginine: Only conditionnaly essential (only essential for children)
Cystein: non-essential, but depends on an essential aa (Methionine) to be made Tyrosine: non-essential aa, but depends on an essential aa (Phenylalanine) to be made |
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What aer the 10 non-essential aa?
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{3A, C, 3G, PST}
-Alanine, Asparagine, Aspartate (3A) -Cysteine -Glutamate, Glutamine, Glycine (3G) -Proline -Serine -Tyrosine |
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What are the 10 essential aa?
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A HILL MPT (MP Three) TV
-Arginine -Histidine -Isoleucine -Leucine -Lysine -Methionine -Phenylalanine -Threonine -Tryptophan -Valine |
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How is aa homeostasis maintained?
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-Oxidation
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What area the 2 oxidation paths for aa?
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1) Obligatory oxidation
-post absorptive state -turned on 10hrs after eating -aa are catabolized for E 2) Regulated oxidation: Turned on right after a meal cuz you have too much aa circulating in the free aa pool *Both paths are used tog to maintain aa homeostasis |
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Which aa can be used whole to produce a N-containing cmpd?
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Glycine: can be used to make heme, purine rings and creatine
Tyrosine: used to make hormones and NT |
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If an N-containing cmpd is produced only from the alpha-amino gp of an aa, which aa does it come from?
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Glutamine
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How is glutamine formed from glutamate?
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Glutamate--> y-Glutamylphosphate intermediate --> Glutamine
-Step 1 requires Glutamine synthetase -Requires 1 ATP and you also add an NH2 group => 1st Nitrogen assimilation rxn |
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How can most aa be used to form N-containing cmpds? What are the exceptions?
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-Most aa can transfer their alpha-amino group to glutamate to form glutamine
-Exceptions: Lysine, Threonine |
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What enzyme catalyzes the transfer of the alpha-amino group from one aa to glutamate?
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Transaminase (Aminotransferase)
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Where is the alpha amino group transeferred to?
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-alpha ketogluterate
-From a-KGA can form glutamate through transaminases |
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Once glutamate is formed from the other aa and a-KGA, what rxns can take place?
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1) Glutamine synthetase rxn
2) Glutamate canform glutamine by donating its amino group -This requires Glutamate DH (this enz imp in forming urea) -Form a-KGA and NH4+ (ammonia) in this rxn |
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Why is glutamine important?
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-Used for ptn synthesis
-used as a source of N in the synthesis of N-containing cmpds **-Acts as a non-toxic way to store ammonia** (alternative to the alanine cycle) |
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How is Glutamine Synthetase regulated?
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-Allosterically activated by a-KGA
-Fdbk regulation: glutamine synthetase can sense accumulation of NH3 in the bldstream through the ketoacid -when a-KGA accumulates, activate Gln synthetase to incorporate NH3 into glutamine |
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Why is funneling of a-amino groups by transaminases important?
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1) For synthesis of N-containing cmpds (funnelling through glutamate to get Gln)
2) For aa catabolism (glutamate is the only aa that can undergo oxidative deamination at a fast rate) |
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What is the coenz used by transaminases?
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PLP (Pyridoxal Phosphate)
-formed from vitamin B6 |
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What do all the enz that contain PLP involved in?
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aa metabolism
(exception is glycogen phosphorylase) |
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What are the main components of PLP? What are their functions?
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C 4' aldehyde group
-forms a bond with the enz and then with the substrate (a-amino gp) -covalent imine linkage -planar geometry around the imine bond Pyridine Ring - e- sink tha will delocalize e- pairs during the rxn, .: stability Phosphate gp: -enz forms bonds around the P so that it can hold on to the PLP molec 3' Hydroxyl group -form H-bonds with the a-amino group that's added to the aldehyde. This extends the SA that e- can be delocalized on and also establishes a planar geometry |
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What are general features of transamination rxns?
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1) initially, enz covalently linked to C4' aldehyde of PLP by a Schiff base bond (imine) => internal aldimine bond
2) during the transamination, form an External aldimine bond btw the aa and the PLP => get planar geometry cuz of 3" OH gp that stabilizes the forming carbanion 3) Carbanion forms and is stabilized by PLP |
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What is the Ping-Pong-Bi-Bi mechanism?
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Mechanism used for PLP rxns
Phase 1: -aa binds the PLP enz -rxn proceeds through intermediates -release of the a-keto acid of the aa and the PMP enz Phase 2: -basically phase 1 in reverse: use a-ketoacid and PMP-enz to produce another aa (if same a-ketoacid that was produced in phase 1 is used, then the aa will be the same. If another a-ketoacid is used, the aa formed will be different-> likely because transaminases like a-KGA) *Glutamate will always be the product of transamination, regardless of which aa was used as the subs or which aa-specific transaminase was used |
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What is the overall rxn for transamination?
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Phase 1: aa1 -> a-ketoacid 1
Phase 2: a-ketoacid2 -> aa2 aa1 + a-ketoacid2 -> a-ketoacid 1 + aa2 .: aa1 + a-KGA -> a-ketoacid 1 + glutamate |
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What is Type II tyrosinemia?
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-autosomal recessive
-nonsense mutation in gene for Tyrosine transaminase in liver (either RNA is degraded or aberrant ptn is produced) |
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What enz catalyzes Glutamate's oxidative deamination?
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Glutamate Dehydrogenase
(Produces NH4+) |
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What does GDH do in peripheral cells? In liver cells?
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Peripheral: Involved in the production of N-containing compounds
Liver: in mito, used for urea synthesis |
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What happens to the ammonia that is produced in the peripheral cells?
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Goes through the Glucose-Alanine cycle, to get from the muscles to the liver, where it can be detoxified
(This is esp important in post-absorptive state, cuz obligatory oxid is taking place to prod E from aa) -Produce alanine in the peripheral cells that can then go out into the blood stream and tehn to the liver, where it can be transformed back into urea |
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What are the 2 ways to produce alanine in the peripheral tissues?
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-Degrade body proteins
-Transamination of pyruvate by specific transaminase in muscles :alanine transaminase (ALT is an exception cuz it uses pyruvate as its ketoacid subs instead of a-KGA, .: ALT produces alanine, instead of glutamate) |
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What are the steps of the Glucose-Alanine cycle?
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1) a-amino gp of aa is transferred to pyruvate by ALT, forming alanine
2) Alanine is transported through the blood to the liver 3) Alanine undergoes transamination in the liver. producing pyruvate and glutamate, while the a-amino gp is transferred to an a-KGA 4) Glutamate is used to produce urea using GDH 5) Pyruvate is transformed to glucose, which can be used by the muscles 6) Glucose is then reconverted to pyruvate in the muscles |
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What is another way for a-amino groups to be transported? How?
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-Glutamine
-Produce glutamine form Glutamate using glutamine synthetase -Gln releass NH3 in the liver, which will be incorporated into urea -If Gln reaches kidney first, use Glutaminase enz to release the NH3 directly into urine |
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What is the use of GDH?
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-Allows amino gps to be incorporated into Glutamate (2nd ammonia assimilation rxn)
-Imp for detoxifying the blood -re-incorporating amino gps into aa |
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How is GDH regulated?
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-Allosterically by the E charge of th cell
-If GTP or NAD(P)H binds, enz activity will decrease -Low E (lots of GDP or NAD(P)), GDH activity will be stimulated |
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What happens when there are defects in GDH?
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HyperInsulinism and HyperAmmonemia
Symptoms: hypoglycemia and too much ammonia Caused by: missense mutation, enz becomes insensitive to GTP, get inc amt of a-KGA nd Ammonia |
