Amino Acids and Their Classification
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Questions and Answers

Which group is responsible for the formation of a peptide bond?

  • Side chain (R)
  • Amino group (correct)
  • Carboxyl group (correct)
  • Hydrogen atom

What happens to the carboxyl group at physiological pH?

  • It loses its hydrogen atom entirely
  • It remains protonated
  • It forms a negatively charged carboxylate ion (correct)
  • It becomes an imino group

Which of the following statements correctly describes a zwitter ion?

  • It contains no dissociated groups.
  • It is neutral overall but has both positive and negative charges. (correct)
  • It is formed only under acidic conditions.
  • It has a net positive charge.

Which classification of amino acids is characterized by a single carboxyl group and a single amino group?

<p>Monobasic monocarboxylic amino acids (C)</p> Signup and view all the answers

What distinguishes proline from the other amino acids?

<p>It is classified as an imino acid. (A)</p> Signup and view all the answers

Which of the following amino acids is classified as basic due to its side chain containing an NH2 group?

<p>Lysine (C)</p> Signup and view all the answers

What is a common characteristic of acidic amino acids at physiological pH?

<p>They carry a negative charge. (B)</p> Signup and view all the answers

Which amino acid contains a guanido group in its structure?

<p>Arginine (B)</p> Signup and view all the answers

Which amino acid is considered a neutral amino acid due to its side chain being amidated?

<p>Glutamine (C)</p> Signup and view all the answers

What is the R group for Glycine?

<p>H (C)</p> Signup and view all the answers

What functional groups are primarily associated with polar amino acids?

<p>Hydroxyl and amide groups (A)</p> Signup and view all the answers

Which amino acid has an isopropyl group as its R group?

<p>Valine (B)</p> Signup and view all the answers

Which of the following amino acids falls into the category of non-polar amino acids?

<p>Leucine (D)</p> Signup and view all the answers

What distinguishes Serine from Threonine in their structures?

<p>Threonine has an additional methyl group in its R group. (C)</p> Signup and view all the answers

Which amino acid is characterized by a sulfur atom in its structure?

<p>Cysteine (D)</p> Signup and view all the answers

Which amino acid is an example of a basic heterocyclic amino acid?

<p>Histidine (A)</p> Signup and view all the answers

What is the primary charge of aspartic acid at physiological pH?

<p>Negative (A)</p> Signup and view all the answers

Which of the following amino acids is branched chain?

<p>Isoleucine (B)</p> Signup and view all the answers

What is the primary function of the phenyl group in Phenylalanine?

<p>To confer aromatic properties (A)</p> Signup and view all the answers

Which amino acid has the structure HO-C-C-N with a hydroxyl group in its R group?

<p>Serine (B)</p> Signup and view all the answers

Which of the following statements about the neutral hydroxy amino acids is true?

<p>They include amino acids like Serine and Threonine. (A)</p> Signup and view all the answers

Which of the following amino acids is classified as non-polar?

<p>Alanine (A)</p> Signup and view all the answers

Which amino acid is essential and cannot be synthesized by the body?

<p>Methionine (B), Isoleucine (D)</p> Signup and view all the answers

What distinguishes polar amino acids from non-polar amino acids?

<p>Presence of a hydroxyl group (D)</p> Signup and view all the answers

Which of the following amino acids contains sulfur in its structure?

<p>Cysteine (D)</p> Signup and view all the answers

Which amino acid is considered to be the most hydrophobic?

<p>Phenylalanine (D)</p> Signup and view all the answers

In which category does methionine fall?

<p>Both B and C (A)</p> Signup and view all the answers

Which amino acid has a side chain that contributes to protein structure through disulfide bonds?

<p>Cysteine (A)</p> Signup and view all the answers

Which of the following amino acids is non-polar and branched?

<p>Valine (C)</p> Signup and view all the answers

Lysine is often characterized as which type of amino acid?

<p>Both B and C (A)</p> Signup and view all the answers

Which amino acid is noted for having an aliphatic side chain?

<p>Methionine (B)</p> Signup and view all the answers

Which amino acids are classified as essential amino acids?

<p>Leucine and Threonine (A), Valine and Lysine (C)</p> Signup and view all the answers

What characterizes semiessential amino acids?

<p>They are formed in the body but insufficient for requirements. (A)</p> Signup and view all the answers

Which group does not include ketogenic amino acids?

<p>Threonine (B)</p> Signup and view all the answers

What type of amino acids yield both ketone bodies and glucose?

<p>Mixed ketogenic and glucogenic amino acids (B)</p> Signup and view all the answers

What property of amino acids allows them to act as both acids and bases?

<p>Amphoteric nature (C)</p> Signup and view all the answers

How is a peptide bond formed between two amino acids?

<p>By the removal of water (B)</p> Signup and view all the answers

Which of the following statements about peptide chains is correct?

<p>Proteins are formed from chains longer than 50 amino acids. (A)</p> Signup and view all the answers

What is the significance of the isoelectric point (IEP) for amino acids?

<p>It describes the pH at which amino acids do not migrate in an electric field. (A)</p> Signup and view all the answers

What type of bond connects amino acids in a dipeptide?

<p>Peptide bond (C)</p> Signup and view all the answers

Which term describes the end of a polypeptide chain that has a free amino group?

<p>N-terminus (C)</p> Signup and view all the answers

What do all proteins share in common regarding their amino acid components?

<p>They are composed of different amino acids (D)</p> Signup and view all the answers

Which group of amino acids is likely to possess a net negative charge at physiological pH?

<p>Acidic amino acids (D)</p> Signup and view all the answers

Which amino acid is considered optically inactive due to its structure?

<p>Glycine (D)</p> Signup and view all the answers

What type of amino acids are predominantly found as dipolar ions at neutral pH?

<p>Dipolar amino acids (C)</p> Signup and view all the answers

Which amino acid is an example of a sulfur-containing amino acid?

<p>Methionine (A)</p> Signup and view all the answers

At which end of a polypeptide chain does protein synthesis begin?

<p>N-terminus (D)</p> Signup and view all the answers

Flashcards

Amino Acid Structure

Amino acids have a central carbon atom (alpha carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group).

Amino Acid Classification

Amino acids can be classified based on their side chain chemical characteristics, whether they need to be consumed or what part of metabolism they play a role in, and also their net charge.

Zwitter Ion

At physiological pH, amino acids exist as dipolar ions (zwitterions) with both a positive and negative charge.

Peptide Bond Formation

Amino acids are linked together by peptide bonds, forming proteins. These bonds are formed between the carboxyl group of one amino acid and the amino group of another.

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Number of Amino Acids in Proteins

Twenty amino acids are commonly found in proteins, despite hundreds of amino acids naturally occurring.

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Glycine

The simplest amino acid with a hydrogen atom as its side chain (R group). It is the only achiral amino acid.

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Alanine

A simple amino acid with a methyl group (CH3) as its side chain (R group).

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Valine

A branched-chain amino acid with an isopropyl group as its side chain (R group).

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Leucine

A branched-chain amino acid with an isobutyl group as its side chain (R group).

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Isoleucine

A branched-chain amino acid with an isobutyl group as its side chain (R group), but with a different arrangement of the atoms, making it a stereoisomer of leucine.

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Cysteine

A neutral amino acid with a sulfhydryl group (SH) as its side chain (R group).

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Methionine

A neutral amino acid with a thioether group (S-CH3) as its side chain (R group).

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Serine

A neutral amino acid with a hydroxyl group (OH) as its side chain (R group).

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Acidic Amino Acids

Amino acids with a negatively charged side chain at physiological pH. This side chain usually contains a carboxyl group (COOH).

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Examples of Acidic Amino Acids

Aspartic acid (Asp) and Glutamic acid (Glu) are the primary examples of acidic amino acids.

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Basic Amino Acids

Amino acids with a positively charged side chain at physiological pH. This side chain usually contains a nitrogen atom that can accept a proton.

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Examples of Basic Amino Acids

Lysine, Arginine, and Histidine are the main basic amino acids.

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Arginine's Unique Feature

Arginine contains a guanido group (-NH-C(NH2)2) in its side chain, which gives it unique properties.

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Histidine's Speciality

Histidine is a basic heterocyclic amino acid, meaning its side chain contains a ring structure with a nitrogen atom.

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Asparagine & Glutamine

The amide forms of aspartate and glutamate, where the side chain carboxyl group is replaced with an amide group.

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Polar Amino Acids

Amino acids with side chains containing polar hydrophilic groups that can form hydrogen bonds with water. These side chains can contain OH, SH, amide, or basic/acidic groups.

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Essential Amino Acids

Amino acids that cannot be synthesized by the body in sufficient amounts and must be obtained from the diet. They are crucial for growth, health, and protein synthesis.

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Semiessential Amino Acids

Amino acids that can be synthesized by the body but not always in sufficient amounts, particularly in children. They are important for growth and development.

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Nonessential Amino Acids

Amino acids that can be synthesized by the body in sufficient amounts for adults and children.

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Ketogenic Amino Acids

Amino acids that are broken down into ketone bodies, which are used as an energy source when glucose is scarce.

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Glucogenic Amino Acids

Amino acids that are broken down into glucose, which is used as an energy source by the body.

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What is an amino acid's Isoelectric Point?

The pH at which an amino acid exists as a zwitter ion, having no net charge.

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Peptide Bond

The covalent bond that links amino acids together to form peptides and proteins, formed by the removal of a water molecule.

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Phenylalanine

A nonpolar amino acid with a benzene ring side chain.

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Tryptophan

A nonpolar amino acid with a fused ring system containing an indole group.

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Dipeptide

Two amino acids linked by one peptide bond.

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Tripeptide

A chain of three amino acids linked by two peptide bonds.

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Polypeptide

A chain of many amino acids linked by peptide bonds.

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N-terminus

The end of a polypeptide chain with a free amino group (-NH2).

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C-terminus

The end of a polypeptide chain with a free carboxyl group (-COOH).

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What are the 20 amino acids used to build proteins?

The 20 common amino acids are all L-alpha amino acids.

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What makes Glycine unique?

Glycine is the only achiral amino acid, meaning it doesn't have a stereoisomer.

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What are the different types of amino acids?

Amino acids are categorized based on their side chain properties: neutral, acidic, basic, polar, nonpolar, aromatic.

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Study Notes

Amino Acids

  • Amino acids are the building blocks of proteins
  • There are about 300 amino acids found in nature, but only 20 are used in proteins
  • Each amino acid has four different groups attached to its central carbon atom. These groups are: an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group). The side chain is specific to each amino acid.

Classification of Amino Acids

  • Chemical Classification: Based on the number of carboxyl and amino groups, amino acids are classified as neutral and charged.

    • Neutral: Monobasic, monocarboxylic (neutral or uncharged). These can be

      • Simple: Glycine, Alanine.
      • Branched Chain: Valine, Leucine, Isoleucine.
      • Sulfur containing: Cysteine, Methionine.
      • Hydroxy: Serine, Threonine.
      • Aromatic: Phenylalanine, Tyrosine, Tryptophan.
      • Heterocyclic: Proline.

    • Charged: These can have either a positive or negative charge.

    • Basic: Lysine, Arginine, Histidine.

    • Acidic: Aspartate, Glutamate.

  • Essential Amino Acids: These cannot be synthesized by the body and must be obtained from the diet. Examples: Valine, Leucine, Isoleucine, Threonine, Methionine, Lysine, Phenylalanine, Tryptophan.
  • Semi-Essential Amino Acids: Can be synthesized by the body but in insufficient amounts for certain age groups, especially children. Examples are Histidine, Arginine).
  • Non-Essential Amino acids: The remaining amino acids that the body synthesizes in sufficient amount for adults and children.

Metabolic Classification

  • Ketogenic Amino Acids: These yield ketone bodies during metabolism. Examples: Lysine, Leucine.
  • Mixed Ketogenic and Glucogenic Amino Acids: These yield both ketone bodies and glucose, e.g., Isoleucine, Phenylalanine, Tyrosine, Tryptophan.
  • Glucogenic Amino Acids: These yield glucose during metabolism, representing the remainder of the amino acids.

Properties

  • Amphoteric: Amino acids are amphoteric molecules, meaning they exhibit both acidic and basic properties.
    • At physiological pH, neutral amino acids exist as zwitterions (molecules bearing both positive and negative charges).
    • Isoelectric point (IEP) is the pH at which the zwitterion has a net zero charge.
  • Physical Properties: Includes the ability to form hydrogen bonds with water, polarity, and hydrophobic/hydrophilic characteristics.
  • Chemical Properties: The reactions based on the carboxyl group, the reactions based on the amino group, reactions based on the side chain (R) group, and peptide bond formation.

Peptides and Proteins

  • Peptides and proteins are formed from linked amino acids through peptide bonds.
  • Short chains (less than 50 amino acids) are called peptides.
  • Long chains (more than 50 amino acids) are called proteins.
  • A peptide bond forms between the carboxyl group of one amino acid and the amino group of another, releasing a water molecule.

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Related Documents

Amino Acids Classification PDF

Description

Explore the fascinating world of amino acids, which serve as the building blocks of proteins. This quiz covers the different types of amino acids, including their chemical classification into neutral and charged categories. Test your knowledge on specific amino acids and their unique properties.

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