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Old 01-12-2014
drharmonis's Avatar
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Biochemistry Amino acids, protein and enzymes

Hi Guys,
I am a bit confused with the answer given by Kaplan note 2013 in biochem book. In the review questions:-

1)The peptide ala-arg-his-gly-glu is treated with peptidases to release all of the amino acids. The solution is adjusted to ph7, and electrophoresis is performed. In the electrophoretogram depicted below, the amino acid indicated by the arrow is most likely:

a) Glycine
b) Arginine
c) Glutamate
d) Histidine
e) Alanine

Anw: Arginine
Can anyone please help me to understand why is it arganine? Arganine and histidine are both in R- positive groups. On what basis do we know that it is the most basic or acidic? Do we have to memorise them by heart?

2)The reaction catalysed by hepatic phosphofructokinase-1 has a G0 value of -3.5 kcal/mol. This value indicates that under standard conditions this reaction

G: cannot be gluconeogenesis

I cant really understand the concept of this thermodynamically spontaneous/non spontaneous reaction. Any recommended reading, or explanation from anyone?

Your help is much appreciated! Thanxxx

confused mode
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Old 01-12-2014
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i think you have no other option other than memorizing.

to understand the concept of spontaneous and nonspontaneous first understand the change in energy which equals energy of products - energy of substrate.
if you encounter a negative value for deltaG(change in free energy) it meas that the energy of substrates is greater than that of products. understand that things have a natural tendency to acquire a low energy state so if the energy of substrate if higher than formation of the products is 'favored' . in other words, we can say that under standard conditions , the reaction is spontaneous and irreversible.
the reaction
fructose6phos.........................>fructose1,6 phos
catalysed by hepatic phosphofructokinase-1 has a G0 value of -3.5 kcal/mol. This value indicates that under standard conditions formation of the products is 'favored' the reaction is spontaneous and irreversible so cant not be used for gluconeogenesis and some alternative pathway must be there to bypass this irreversibbility . hope this makes sense .
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