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Amino Acids

The substitue...

Question

The substituents R₁ and R₂ for nine peptides are listed in the table given below. How many of these peptides are positively charged at Ph = 7.0? ___

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Solution

The amino acid remain completely in Zwitter ionic at its isoelectric point. Amino acids with additional acidic group have then isoelec tric pH less than 7.0 and increasing pH above isoelectric point makes them anionic.
On the other hand, amino acids with additional basic group have their isoelectric pH greater than 7.0 and decreasing pH below isoelectric point (by adding acid solution) makes them cationic. The given peptide with followings R₁ and R₂ are basic, will remain protonated (cationic) at pH = 7.0.Thus, 4 is the correct integer.

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Q. The substituents

R_{1}

R_{2}

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	$(C H_{2})_{4} N H_{2}$	$C H_{3}$

Q. The substituents

R_{1}

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	${(C H_{2})}_{4} N H_{2}$	$C H_{3}$

Q. The substituents R₁ and R₂ for nine peptides are listed in the table given below. How many of these peptides are positively charged at Ph = 7.0? ___

Q. 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

p H = 11

are |𝑧₁|, |𝑧₂| and |𝑧₃|, respectively, then what is |𝑧₁| + |𝑧₂| + |𝑧₃|?

Q. Peptide A and peptide B is linked by how many disulfide linkages in insulin?

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