biochem exam 4/8/24 Flashcards
the more active form of glutamine synthetase is the
- adenylylated form of the enzyme
- de-adenylylated form of the enzyme
- de-adenylylated form of the enzyme
PII is the factor that binds to adenylyl transferase (AT). If PII is uridylylated
- AT preferentially catalyzes the adenylation of glutamine synthetase (GS)
- AT preferentially catalyzes the de-adenylation of GS
- AT preferentially catalyzes the de-adenylation of GS
An elevated glutamine concentration leads to…
A. An increase in the [PII + UMP]
B. A decrease in the [PII + UMP]
C. The de-adenylation of glutamine synthetase
B. A decrease in the [PII + UMP]
When there is a sufficient amount (or more) of gln in a cell, which of the following is true about glutamine synthetase and the associated regulatory enzyme
- AT-PII will be uridylylated, GS will not be adenylylated and GS will be active
- AT-PII will be uridylylated, GS will be adenylylated and GS will be inactive
- AT-PII will not be uridylylated, GS will be adenylylated and GS will be inactive
- AT-PII will not be uridylylated, GS will not be adenylylated and GS will be active
- AT-PII will not be uridylylated, GS will be adenylylated and GS will be inactive
heme is derived from ____ and is broken down to form ____
- arginine, creatine
- glycine, creatine
- glycine, bilirubin
- blirubin, creatine
- glycine, bilirubin
Which of the following statements is incorrect?
A. GABA is derived from glutamate
B. Histamine→histidine
C. Serotonin→tryptophan
D. Dopamine→tryptophan
E. Epinephrine→tyrosine
D. Dopamine→tryptophan
therapies for Parkinson’s disease include
- block formation of L-Dopa
- administer L-dopa to the patient
- accelerate dopamine breakdown
- administer an MAO inhibitor
- administer L-dopa to the patient
- administer an MAO inhibitor
which of the following reactions is part of the normal nucleotide synthesis
- AMP to dAMP
- GDP to dGDP
- TDP to dTDP
- UTP to dUTP
- CMP to CDP
- GDP to dGDP
Folate and/or vitamin B12 is/are required for the synthesis of…
A. dAMP
B. dCMP
C. dGMP
D. dTMP
E. dUMP
D. dTMP
which statement is false
- gout involves uric acid crystals in joints
- purine catabolism leads to uric acid formation
- allopurinol inhibits uric acid breakdown
- allopurinol inhibits xanthine oxidase
- allopurinol inhibits uric acid breakdown
which of the following inhibits the reduction of NDPs to dNDPs
- allopurinol indomethacin
- azaserin, acivicin
- aminopterin, methotrexate
- gemcitabine
- gemcitabine
which of the following are Gln analogs that interfere with nucleotide synthase
- allopurinol indomethacin
- azaserin, acivicin
- aminopterin, methotrexate
- gemcitabine
- azaserin, acivicin
aminopterin, methotrexate, and fluorouracil reduce the synthesis of
- glutamate
- glutamine
- cAMP
- dAMP
- dTMP
- dTMP
Sources of Nitrogen
Ammonia is toxic to mammalian cells and must be immediately used up (assimilated) or converted to urea and removed (Ch 18)
Soluble, biologically useful nitrogen-containing molecules are generally scarce, so organisms are conservative in their use
Ammonia is assimilated into glutamine (major) and glutamate (minor) in mammalian cells.
Glutamine and glutamate are the nitrogen sources for the cellular synthesis of other amino acids and other nitrogenous compounds.
Assimilation of Ammonia into Glutamine (Major Pathway)
Glutamate + glutamine synthetase = acyl-phosphate intermediate
Glutamine is the source of amino groups for most other nitrogenous compounds.
Major Source of Glutamate
Breakdown of excess dietary amino acids by transamination reactions yields high levels of cellular glutamate, shortly after the meal is consumed.
Glutamate is the source of amino groups for most other amino acids.
Assimilation of Ammonia into Glutamate (Minor Pathway)
Km for NH4+ = 1 mM rendering glutamate synthesis only possible when [NH4+] is abnormally high (hyperammonemia).
In cells, both Glutamine and Glutamate are kept at concentrations higher than other amino acids
Allosteric Regulation of Glutamine Synthetase
Each molecule alone partially inhibits the enzyme…
6 of these are derived from glutamine
If all products are present at sufficiently high levels, the enzyme is essentially turned off.
Don’t need it, don’t make it.
Covalent Regulation of Glutamine Synthetase
GS + AMP = OFF
GS = ON
PII + UMP + AT = GS ON (via deadenylation)
PII + AT = GS + AMP = OFF (via adenylation)
Simplified: Covalent Regulation of Glutamine Synthetase
high ATP or high alpha ketoglutarate, low Gln
- AT-PII uridylyated - yes
- GS adenylylated - no
- GS active - yes
low ATP or low alpha-ketoglutarate or high Gln
- AT-PII uridylyated - no
- GS adenylylated - yes
- GS active - no
Essential and Non-Essential Amino Acids
Essential Amino Acids:
- Amino acids that cannot be synthesized (made) by an organism and must be a component of the diet.
Non-Essential Amino Acids:
- Amino acids that can be synthesized by an organism and are not required to be a component of the diet.
Amino Acid Synthesis
Synthesized from 6 common precursors!
- Sometimes more than one way…
We’ve seen some of these already:
Phenylalanine→Tyrosine (PKU) Pyruvate→Alanine (Muscle) Oxaloacetate→Aspartate (Urea Cycle) α-KG → Glutamate (Transamination) Glutamate→Glutamine (Above)
Connections:
Serine→Glycine uses THF (remember?!) Methionine cycle involves SAM, B12, Folate (B9)!
Glycolysis, PPP, CAC, AA Catabolism, etc.
Porphyrins (Heme)
Heme isn’t just for hemoglobin:
Myoglobin, catalase, peroxidase, P450 liver cytochromes
Deficiency in the enzymes in this pathway cause a build-up of toxic porphyrins→ Porphyria
“Mad” King George III
Genetic, can be triggered by meds Different porphyrias, different symptoms Neurological, skin, photosensitivity
heme breakdown
to bilirubin etc.
a stronger antioxidant, but an elevated level in blood may indicate liver disease
heme breakdown color: black/blue/purple
biliverdin breakdown color:
green
bilirubin breakdown in blood:
yellow