The structure of a peptide is given below.

If the absolute values of the net charge of the peptide at $p H = 2, p H = 6$ and $p H = 11$ are |𝑧₁|, |𝑧₂| and |𝑧₃|, respectively, then what is |𝑧₁| + |𝑧₂| + |𝑧₃|?

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Solution

(i) At pH = 2 (Highly acidic)
In highly acidic medium, the given tripeptide exists as cationic form.

Net charge +2

|Z₁| = 2 at pH = 2

(ii) At pH = 6 (isoelectric point)

At isoelectric point, the given tripeptide exists as Zwitter ion.

net charge = 0

|Z₂| = 0 at pH = 6

(iii) At pH = 11 (basic medium)

In basic medium the given tripeptide exists in anionic form.

Net charge = –3

|Z₃| = 3

Therefore, |Z₁| + |Z₂| + |Z₃| = 2 + 0 + 3 = 5

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Q. The substituents

R_{1}

and

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for nine peptides are listed in the table given below. How many of these peptides are positively charged at pH=7.0?

Peptide	$R_{1}$	$R_{2}$
I	H	H
II	H	$C H_{3}$
III	$- C H_{2} C O O H$	H
IV	$- C H_{2} C O N H_{2}$	$(C H_{2})_{4} N H_{2}$
V	$- C H_{2} C O N H_{2}$	$- C H_{2} C O N H_{2}$
VI	$(C H_{2})_{4} N H_{2}$	$(C H_{2})_{4} N H_{2}$
VII	$- C H_{2} C O O H$	$- C H_{2} C O N H_{2}$
VIII	$- C H_{2} O H$	$(C H_{2})_{4} N H_{2}$
IX	$(C H_{2})_{4} N H_{2}$	$C H_{3}$

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Q. Structure of alanine at

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R_{1}

, and

R_{2}

for nine peptides are listed in the table given below. How many of these peptides are positively charged at pH = 7.0?

$P e p t i d e$	$R_{1}$	$R_{2}$
I	$H$	$H$
II	$H$	$C H_{3}$
III	$C H_{2} C O O H$	$H$
IV	$C H_{3} C O N H_{2}$	${(C H_{2})}_{4} N H_{2}$
V	$C H_{2} C O N H_{2}$	$C H_{2} C O N H_{2}$
VI	${(C H_{2})}_{4} N H_{2}$	${(C H_{2})}_{4} N H_{2}$
VII	$C H_{2} C O O H$	$C H_{2} C O N H_{2}$
VIII	$C H_{2} O H$	${(C H_{2})}_{4} N H_{2}$
IX	${(C H_{2})}_{4} N H_{2}$	$C H_{3}$

Enzymes are proteins. Proteins are long chains of amino acids linked to each other by peptide bonds. Amino acids have many functional groups in their structure.

These functional groups are many of them at least, ionisable. As they are weak acids and bases in chemical nature, this iohisation is influenced by pH of the solution. For many enzymes, activity is influenced by surrounding pH. This is depicted in the curve below, explain briefly.

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The structure of a peptide is given below. If the absolute values of the net charge of the peptide at pH=2, pH=6 and pH=11 are |𝑧1|, |𝑧2| and |𝑧3|, respectively, then what is |𝑧1| + |𝑧2| + |𝑧3|?

The structure of a peptide is given below.

If the absolute values of the net charge of the peptide at $p H = 2, p H = 6$ and $p H = 11$ are |𝑧₁|, |𝑧₂| and |𝑧₃|, respectively, then what is |𝑧₁| + |𝑧₂| + |𝑧₃|?