A zwitterion is a species that carries both a positive (-NH 3 + ) and a negative (-COO - ) charge on the same molecule. Amino acids form zwitterions in aqueous solution.

Why are amino acids described as amphoteric?

Amino acids contain both a basic amino group (-NH 2 ) and an acidic carboxylic acid group (-COOH). They can act as both acids and bases, which is the definition of amphoteric.

True or False? At low pH, the carboxylate group (-COO - ) of a zwitterion accepts a proton to reform -COOH.

True. Adding acid lowers the pH. The -COO - group accepts an H + to reform the -COOH group, causing the zwitterion to become a positively charged ion .

Define isoelectric point .

An isoelectric point is the pH at which an amino acid exists predominantly as a neutral zwitterion, with no net overall charge.

What happens to the -NH 3 + group of a zwitterion when a base is added?

The -NH 3 + group donates a proton (H + ) to the added base, reforming the -NH 2 group. This causes the zwitterion to become a negatively charged ion .

The general structural formula for naturally occurring amino acids is .......... . There are .......... naturally occurring amino acids.

The general structural formula for naturally occurring amino acids is RCH(NH 2 )COOH . There are 20 naturally occurring amino acids.

True or False? Amino acids are soluble crystalline solids because of the strong intermolecular forces between zwitterions.

True. Zwitterions carry both positive and negative charges, creating strong electrostatic attractions between molecules. This results in amino acids being soluble crystalline solids .

How does an amino acid solution act as a buffer?

The zwitterion can accept protons (via -COO - ) when acid is added or donate protons (via -NH 3 + ) when base is added. This resists changes in pH, making it a buffer solution.

In a zwitterion, the .......... group is protonated to -NH 3 + and the .......... group is deprotonated to -COO - .

In a zwitterion, the amino group is protonated to -NH 3 + and the carboxylic acid group is deprotonated to -COO - .

Define peptide bond .

A peptide bond is an amide bond formed between the -NH 2 group of one amino acid and the -COOH group of another in a condensation reaction, with H 2 O eliminated.

What small molecule is eliminated when two amino acids join to form a dipeptide?

Water (H 2 O) is eliminated. The -NH 2 group of one amino acid reacts with the -COOH group of another in a condensation reaction.

True or False? A dipeptide still contains free -NH 2 and -COOH groups that can undergo further condensation reactions.

True. The dipeptide retains an -NH 2 at one end and a -COOH at the other. These can react with additional amino acids to form a tripeptide or polypeptide.

What is a polypeptide?

A polypeptide is a long chain formed when many amino acid molecules are joined together by peptide bonds through repeated condensation reactions.

A peptide bond is also called an .......... bond. It is formed in a .......... reaction between the -NH 2 and -COOH groups of two amino acids.

A peptide bond is also called an amide bond. It is formed in a condensation reaction between the -NH 2 and -COOH groups of two amino acids.

True or False? A tripeptide is formed when three amino acids join, with two peptide bonds and two water molecules eliminated.

True. Each condensation step eliminates one water molecule and forms one peptide bond. Three amino acids joined in sequence produce two peptide bonds and release two H 2 O molecules.

Which two functional groups on an amino acid take part in forming peptide bonds?

The -NH 2 (amino) group and the -COOH (carboxylic acid) group . The -NH 2 of one amino acid reacts with the -COOH of another to form the peptide bond.

Joining two amino acids forms a .......... . Joining many amino acids forms a .......... .

Joining two amino acids forms a dipeptide . Joining many amino acids forms a polypeptide .

A dipeptide is a molecule formed when two amino acids are joined by a single peptide bond in a condensation reaction, eliminating one molecule of water.

Define electrophoresis .

Electrophoresis is an analytical technique that separates ions by placing them in an electric field. It is used in biochemistry to identify and purify proteins and amino acids.

In electrophoresis, what determines the rate at which an ion moves toward an electrode?

Two factors determine the rate: Size of the ion: larger ions move more slowly. Charge of the ion: more highly charged ions move more quickly.

True or False? In electrophoresis, positively charged amino acid ions move toward the positive electrode.

False. Positively charged ions move toward the negative electrode. Negatively charged ions move toward the positive electrode.

At pH 7, in what direction does lysine (a positively charged amino acid) move during electrophoresis?

Lysine moves toward the negative electrode . Its positively charged side chain means it is attracted to the negatively charged electrode.

An amino acid at its isoelectric point will .......... during electrophoresis. Larger ions travel .......... slowly than smaller ions toward the electrode.

An amino acid at its isoelectric point will remain stationary (in the well) during electrophoresis. Larger ions travel more slowly than smaller ions toward the electrode.

True or False? The charge on an amino acid during electrophoresis depends on the pH of the solution.

True. The pH determines whether the amino acid is positively charged, negatively charged or neutral (at its isoelectric point), which in turn determines the direction and rate of migration.

What is an electropherogram?

An electropherogram is the series of bands observed on the paper or gel after electrophoresis. Each band corresponds to a particular species, separated by charge and size.

Define electropherogram .

An electropherogram is the pattern of separated bands produced on a gel or paper after electrophoresis, where each band represents a distinct species.

Glutamic acid (negatively charged, large) moves toward the .......... electrode more .......... than lysine (positively charged, smaller) moves toward the negative electrode.

Glutamic acid (negatively charged, large) moves toward the positive electrode more slowly than lysine (positively charged, smaller) moves toward the negative electrode.

A LevelChemistryCambridge (CIE)Flashcards34. Nitrogen CompoundsAmino Acids

Amino Acids (Cambridge (CIE) A Level Chemistry): Flashcards

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Define zwitterion.
A zwitterion is a species that carries both a positive (-NH₃⁺) and a negative (-COO^-) charge on the same molecule. Amino acids form zwitterions in aqueous solution.
Why are amino acids described as amphoteric?
Amino acids contain both a basic amino group (-NH₂) and an acidic carboxylic acid group (-COOH). They can act as both acids and bases, which is the definition of amphoteric.
True or False?
At low pH, the carboxylate group (-COO^-) of a zwitterion accepts a proton to reform -COOH.
True.
Adding acid lowers the pH. The -COO^- group accepts an H⁺ to reform the -COOH group, causing the zwitterion to become a positively charged ion.
Define isoelectric point.
An isoelectric point is the pH at which an amino acid exists predominantly as a neutral zwitterion, with no net overall charge.
What happens to the -NH₃⁺ group of a zwitterion when a base is added?
The -NH₃⁺ group donates a proton (H⁺) to the added base, reforming the -NH₂ group. This causes the zwitterion to become a negatively charged ion.
The general structural formula for naturally occurring amino acids is ........... There are .......... naturally occurring amino acids.
The general structural formula for naturally occurring amino acids is RCH(NH₂)COOH. There are 20 naturally occurring amino acids.
True or False?
Amino acids are soluble crystalline solids because of the strong intermolecular forces between zwitterions.
True.
Zwitterions carry both positive and negative charges, creating strong electrostatic attractions between molecules. This results in amino acids being soluble crystalline solids.
How does an amino acid solution act as a buffer?
The zwitterion can accept protons (via -COO^-) when acid is added or donate protons (via -NH₃⁺) when base is added. This resists changes in pH, making it a buffer solution.
In a zwitterion, the .......... group is protonated to -NH₃⁺ and the .......... group is deprotonated to -COO^-.
In a zwitterion, the amino group is protonated to -NH₃⁺ and the carboxylic acid group is deprotonated to -COO^-.
Define peptide bond.
A peptide bond is an amide bond formed between the -NH₂ group of one amino acid and the -COOH group of another in a condensation reaction, with H₂O eliminated.
What small molecule is eliminated when two amino acids join to form a dipeptide?
Water (H₂O) is eliminated. The -NH₂ group of one amino acid reacts with the -COOH group of another in a condensation reaction.
True or False?
A dipeptide still contains free -NH₂ and -COOH groups that can undergo further condensation reactions.
True.
The dipeptide retains an -NH₂ at one end and a -COOH at the other. These can react with additional amino acids to form a tripeptide or polypeptide.
What is a polypeptide?
A polypeptide is a long chain formed when many amino acid molecules are joined together by peptide bonds through repeated condensation reactions.
A peptide bond is also called an .......... bond. It is formed in a .......... reaction between the -NH₂ and -COOH groups of two amino acids.
A peptide bond is also called an amide bond. It is formed in a condensation reaction between the -NH₂ and -COOH groups of two amino acids.
True or False?
A tripeptide is formed when three amino acids join, with two peptide bonds and two water molecules eliminated.
True.
Each condensation step eliminates one water molecule and forms one peptide bond. Three amino acids joined in sequence produce two peptide bonds and release two H₂O molecules.
Which two functional groups on an amino acid take part in forming peptide bonds?
The -NH₂ (amino) group and the -COOH (carboxylic acid) group. The -NH₂ of one amino acid reacts with the -COOH of another to form the peptide bond.
Joining two amino acids forms a .......... . Joining many amino acids forms a ...........
Joining two amino acids forms a dipeptide. Joining many amino acids forms a polypeptide.
Define dipeptide.
A dipeptide is a molecule formed when two amino acids are joined by a single peptide bond in a condensation reaction, eliminating one molecule of water.
Define electrophoresis.
Electrophoresis is an analytical technique that separates ions by placing them in an electric field. It is used in biochemistry to identify and purify proteins and amino acids.
In electrophoresis, what determines the rate at which an ion moves toward an electrode?
Two factors determine the rate:
1. Size of the ion: larger ions move more slowly.
2. Charge of the ion: more highly charged ions move more quickly.
True or False?
In electrophoresis, positively charged amino acid ions move toward the positive electrode.
False.
Positively charged ions move toward the negative electrode. Negatively charged ions move toward the positive electrode.
At pH 7, in what direction does lysine (a positively charged amino acid) move during electrophoresis?
Lysine moves toward the negative electrode. Its positively charged side chain means it is attracted to the negatively charged electrode.
An amino acid at its isoelectric point will .......... during electrophoresis. Larger ions travel .......... slowly than smaller ions toward the electrode.
An amino acid at its isoelectric point will remain stationary (in the well) during electrophoresis. Larger ions travel more slowly than smaller ions toward the electrode.
True or False?
The charge on an amino acid during electrophoresis depends on the pH of the solution.
True.
The pH determines whether the amino acid is positively charged, negatively charged or neutral (at its isoelectric point), which in turn determines the direction and rate of migration.
What is an electropherogram?
An electropherogram is the series of bands observed on the paper or gel after electrophoresis. Each band corresponds to a particular species, separated by charge and size.
Define electropherogram.
An electropherogram is the pattern of separated bands produced on a gel or paper after electrophoresis, where each band represents a distinct species.
Glutamic acid (negatively charged, large) moves toward the .......... electrode more .......... than lysine (positively charged, smaller) moves toward the negative electrode.
Glutamic acid (negatively charged, large) moves toward the positive electrode more slowly than lysine (positively charged, smaller) moves toward the negative electrode.

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