Zwitterions, Carboxyl Group Reactions and Peptide Bond Formation

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14 Terms

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Cationic Amino Acids

What is cation?

In what type of solution do aa become cationic?

Which part of aa act as cationic?

How can aa be cationic?

Cation: Ion with positive charge

Type of solution: Acidic solution

Part of aa that is cationic: Amine group (NH2+)

How aa be cationic: Amine group acts like a base and gains hydrogen, becoming NH3+

<p><strong>Cation: </strong>Ion with <strong><span style="color: blue">positive charge</span></strong></p><p><strong>Type of solution: <mark data-color="red">Acidic</mark> </strong>solution<strong> </strong></p><p><strong>Part of aa that is cationic: <span style="color: purple">Amine group </span></strong>(NH2+) </p><p><strong>How aa be cationic: <span style="color: purple">Amine group</span> </strong>acts like a <strong><span style="color: blue">base</span> </strong>and <strong><span style="color: blue">gains hydrogen</span></strong>, becoming <strong><span style="color: blue">NH3+ </span></strong></p>

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Anionic Amino Acids

What is anion?

In what type of solution do aa become anions?

Which part of aa act as anion?

How can aa be anion?

Anion: Ion with negative charge

Type of solution: Basic (alkaline) solution

Part of aa that is anionic: Carboxyl group (COOH)

How aa be anion: Carboxyl group acts like acid and loses hydrogen, becoming COO-

<p><strong>Anion: </strong>Ion with <strong><span style="color: red">negative charge</span></strong></p><p><strong>Type of solution: <mark data-color="blue">Basic (alkaline)</mark> </strong>solution<strong> </strong></p><p><strong>Part of aa that is anionic: <span style="color: yellow">Carboxyl group</span><span> </span></strong><span>(COOH)</span></p><p><strong>How aa be anion: <span style="color: yellow">Carboxyl group</span><span> </span></strong><span>acts like </span><strong><span style="color: red">acid</span><span> </span></strong><span>and </span><strong><span style="color: red">loses hydrogen</span><span>, </span></strong><span>becoming</span><span style="color: red"> </span><strong><span style="color: red">COO-</span></strong></p>

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What is the iso-electric point?

the pH at which a particular molecule carries no net electric charge (around pH 7)

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What are zwitterions

A molecule that has separate positively and negatively charged groups giving an overall net charge of 0

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When and how can amino acids form zwitterions?

Amine group

Base or acid?
Gain or lose proton?
Functional group changes to

Carboxylic group

Base or acid?
Gain or lose proton?
Functional group changes to

When: Dissolved in aqueous solution at around pH 7

How:

Amine group:

It’s a base so it will gain a proton (H+), gaining positive charge and changing the functional group from NH2+ —> NH3+

Carboxylic group:

It’s an acid so it will lose a proton (H+), gaining negative charge and changing the functional group from COOH —> COO-

Both of these reactions are happening at the same time so there is no total net charge

<p><strong>When: </strong>Dissolved in <strong><span style="color: green">aqueous solution</span> </strong>at around <strong><span style="color: green">pH 7</span></strong></p><p><strong>How:</strong></p><p><strong><u><span style="color: purple">Amine group:</span></u></strong></p><ul><li><p>It’s a <strong><span style="color: blue">base</span> </strong>so it will <strong><span style="color: blue">gain</span> </strong>a <strong><span style="color: blue">proton</span> </strong>(H+), gaining <strong><span style="color: blue">positive</span> <span style="color: blue">charge</span> </strong>and changing the functional group from<span style="color: blue"> </span><strong><span style="color: blue">NH2+ </span>—> <span style="color: blue">NH3+</span></strong></p></li></ul><p><strong><u><span style="color: yellow">Carboxylic group:</span></u></strong></p><ul><li><p>It’s an <strong><span style="color: red">acid</span></strong> so it will <strong><span style="color: red">lose</span> </strong>a <strong><span style="color: red">proton</span> </strong>(H+), gaining <strong><span style="color: red">negative</span> <span style="color: red">charge</span> </strong>and changing the functional group from <strong><span style="color: red">COOH </span>—> <span style="color: red">COO-</span></strong></p></li></ul><p><strong><span style="color: green">Both</span> </strong>of these reactions are happening <strong><span style="color: green">at the same time</span> </strong>so there is<span style="color: green"> </span><strong><span style="color: green">no total net charge</span></strong></p>

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<p><strong><span style="color: blue">Cation</span></strong>, <strong><span style="color: green">Zwitterion</span> </strong>and <strong><span style="color: red">Anion</span></strong></p>

Cation, Zwitterion and Anion

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<p>Unionized vs <strong>Zwitterion </strong>form </p>

Unionized vs Zwitterion form

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What is decarboxylation and what does it produce?

What: Reaction where CO2 is removed from carboxylic group

Produces: CO2 and Amine (ammonia derivative)

<p><strong>What: </strong>Reaction where <strong><span style="color: yellow">CO2</span> </strong>is <strong><span style="color: yellow">removed</span> </strong>from <strong><span style="color: yellow">carboxylic group</span></strong></p><p><strong>Produces: <span style="color: yellow">CO2 </span></strong>and <strong><span style="color: blue">Amine</span> </strong>(ammonia derivative)</p>

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Decarboxylation of amino acids

Histidine

Tyrosine

Tryptophan

Lysine

Glutamic acid

Histidine —> Histamine + CO2

Tyrosine —> Tyramine + CO2

Tryptophan —> Tryptamine + CO2

Lysine —> Cadaverine + CO2

Glutamic acid —> Gamma Amino Butyric Acid (GABA) + CO2

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What is GABA?

A neurotransmitter

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How can amino acids be formed into amides (carboxylic acid derivative)

Through the reaction between carboxylic group (-COOH) and ammonia

-COOH + NH3 —> Amide

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Amide Formation from Amino Acids

Aspartic acid

Glutamic acid

Aspartic acid + NH3 —> Asparagine

Glutamic acid + NH3 —> Glutamine

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How are peptide bonds form?

Alpha carboxylic group of one aa reacts with alpha amino group of another aa forming the CO-NH bridge (peptide bond)

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How are proteins made?

By the polymerization of amino acids through peptide bonds