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Biochemistry Questions

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Biochemistry
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University of Arizona
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Overview of Enzymes
Q6.1:
Enzymes provide active sites that allow optimal spatial orientation of substrates and away from
excess solvent like in aldolase catalyzed conversion of glyceraldehydr-3-phosphate to fructose-
1,6-biphoshate. Some enzymes also provide active sites that form bonds with the substrate and
break existing bonds that lowers activation energy such as in adenosine deaminase in purine
degradation. Nearby reactive chemical groups or coenzymes in active sites also acts to further
aid in catalyzing the reaction, like Zn
2+
in carbonic anhydrase to convert CO
2
to carbonic acid.
Q6.2:
One is through acid-base catalysis wherein enzymes add or remove a proton from its substrate
such as in the hydrolysis of polypeptides by chymotrypsin. In covalent catalysis, enzymes bind
with the substrate to create an unstable intermediate like in the catalysis of glyceraldehyde-3-
phosphate from 1,3-bisphosphoglycerate with glyceraldehyde-3-phosphate dehydrogenase.
Metalloenzymes are those involved in catalytic reactions regulated by metal ions, such as
carbonic anhydrase activated by Zn
2+
to convert CO
2
to bicarbonate.
Q6.3:
The turnover number,

, describes the rate at which substrates are catalyzed by a single
enzyme, while the Michaelis constant,
, describes the affinity of the substrate to the active site
of an enzyme. High

and low
both describe high enzyme efficiency, thus


or
specificity constant, is a good measure of overall enzyme efficiency. Triosephosphate isomerase
and pepsin have comparable substrate affinities or
values (  

and   

M,
respectively) but pepsin has a much lower turnover rate.
Regulation of Enzyme Activity
Q7.1:
ATCase catalyzes the formation of a precursor to CTP and is also inhibited by CTP as a signal
that biosynthesis of nucleic acid reaches saturation. Meanwhile, presence of ATP activates
ATCase to balance purine and pyrimidine nucleotides and promote DNA synthesis. Both are
heterotrophic allosteric effectors because are non-substrate regulators of ATCase.
Overview of Cell Signaling Pathways
Q7.2:
Transcription factor











Inactivation of half of Enzyme D causes Enzyme C to yeald 37.5 units of enzyme D instead of
75, reducing the final transcription factor to 18,750,000.

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Overview of Enzymes Q6.1: Enzymes provide active sites that allow optimal spatial orientation of substrates and away from excess solvent like in aldolase catalyzed conversion of glyceraldehydr-3-phosphate to fructose1,6-biphoshate. Some enzymes also provide active sites that form bonds with the substrate and break existing bonds that lowers activation energy such as in adenosine deaminase in purine degradation. Nearby reactive chemical groups or coenzymes in active sites also acts to further aid in catalyzing the reaction, like Zn2+ in carbonic anhydrase to convert CO2 to carbonic acid. Q6.2: ...
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