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BCEM 547 MT#2 Questions With Complete Solutions
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BCEM 547 MT#2 Questions With Complete Solutions
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BCEM 547 MT#2 Questions With Complete SolutionsNitrogenase Correct Answer Bacterial enzyme that derives all
organic nitrogen from atmospheric N2 through reduction to
ammonia (NH3)
Complex enzyme with 2 subunits and multiple redox centers
How does ammonia enter the amino acid pool? Correct Answer
Through glutamine (Gln) or glutamate (Glu)
What does glutamate provide nitrogen for? Correct Answer
Amino acids and proteins
Provides the alpha amino nitrogen for other amino acids
What does glutamine provide nitrogen for? Correct Answer
Amino acids, proteins, purines, pyrimidines
Provides the side chain nitrogen for many compounds
Global Nitrogen Cycle Correct Answer The movement of
nitrogen among terrestrial ecosystems, the oceans, and the
atmosphere
Annammox Reaction Correct Answer Contributes up to 50% of
the removal of fixed nitrogen from oceans
Reactions occur in a membrane bound compartment which are
completely sealed off from oxygen, then metabolites form this
pathway can be released off
,How is nitrogenase produced? Correct Answer By the bacteria
inside infected plant cells or in cyanobacteria in heterocysts
Important points of the nitrogenase enzyme Correct Answer It
is oxygen sensitive, mini ETC, and it takes a huge amount of
energy to catalyze this reaction
Glutamate dehydrogenase Correct Answer What enzyme
catalyzes the reversible oxidative deamination of glutamate and
produces the TCA cycle intermediate α-ketoglutarate
-High Km for ammonia (~1mM)
-In biosynthetic reactions it uses NADPH
-Euk and prok
Glutamine synthetase Correct Answer Incorporates ammonia
into glutamine
-Low Km for ammonia
-Driven by ATP hydrolysis
-Euk and prok
Glutamine 2-oxoglutarate aminotransferase (GOGAT) Correct
Answer Converts glutamine and alpha-ketoglutarate into 2
glutamates
What did Stadman's lab show in 1964? Correct Answer
Glutamine synthetase was partially inhibited by 4 metabolites,
,all being end products of glutamine metabolism: His, Top, 5'-
AMP, and CTP
GS levels are controlled by the nitrogen source within the
growth medium
Glutamine synthetase structure Correct Answer Composed of
12 identical subunits and each metabolite (Top, CTP, AMP, His)
binds to a separate site on the enzyme giving cumulative
feedback inhibition
The adenylation of GS Correct Answer When in nitrogen rich
medium, there was a higher absorbance (260 nm) suggesting a
purine was attached to the enzyme and treatment with
phosphodiesterase released an AMP from the enzyme
converting to a form that was like the enzyme from N-starved
cells
They found activity that would transfer an AMP to the enzyme
from ATP, an adenylyltransferase
Adenylylation site was determined to be a specific tyrosine
residue
Adenylyltransferase Correct Answer The activity in which
removed the AMP from GS consisted of 2 fractions (PI and PII)
and both were required to deadenylylate GS
Reaction relied UTP, alpha-ketoglutarate, and was stimulated by
Pi and inhibited by Gln
, PI adenylylated GS and the reactions were controlled by the PII,
ATP, UTP, alpha-ketoglutarate, and Gln
Exact role of Pi in adenylylation of GS Correct Answer
Phosphorolytic cleavage of the adenylyltyrosine in GS
How does the uridylylation of PII govern the activity of
adenylyltransferase? Correct Answer Protein factor in the PI
fraction in the presence of UTP could stimulate the ability of PII
to cause the adenylyltransferase to deadenylyate GS, and inhibit
the ability of the adenylyltransferase to adenylylate GS
Uridylyltransferase from PI fraction was purified and shown to
add a UMP to PII and this was activated by ATP and alpha-
ketoglutarate and inhibited by Gln
Bifunctionallity of uridylyltransferase Correct Answer Can add
or remove the UMP of PII and is referred to as
uridylyltransferase/uridylyl-removing enzyme (UT/UR)
How does UT/UR enzyme work? Correct Answer
Allosterically sense Gln, while PII binds ATP and 2KG to sense
their level in the cell
ATP is low: PII will not bind to 2KG
ATP is adequate: PII adopts a conformation that exposes a
binding site and will then bind 2KG which makes it a good
substrate for the UT enzyme
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