Chapter 3
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Questions and Answers

Which amino acid contains a thioether group in its side chain?

  • Serine
  • Tryptophan
  • Cysteine
  • Methionine (correct)

Which of the following amino acids has a side chain that can be positively charged at physiological pH?

  • Asparagine
  • Aspartic acid
  • Glutamic acid
  • Lysine (correct)

Which amino acid contains an imidazole group within its side chain?

  • Lysine
  • Arginine
  • Proline
  • Histidine (correct)

Which of the following amino acids contains a hydroxyl group in its side chain?

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

Which amino acid is characterized by having a unique aliphatic side chain that forms a ring with the amino group?

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

Which amino acid is similar to alanine but contains a hydroxyl group in place of one of its methyl hydrogens?

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

Which of the following amino acids has a side chain containing a guanidinium group?

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

Which pair of amino acids have carboxamide groups in their side chains?

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

Which amino acid is similar to phenylalanine, but contains a hydroxyl group attached to its aromatic ring?

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

Which of the following amino acids has a side chain that ends in an amino group?

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

What is the central carbon atom in an alpha-amino acid called?

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

At neutral pH, which of the following best describes the charge state of an alpha-amino acid?

<p>Dipolar ion or zwitterion with both positive and negative charges (D)</p> Signup and view all the answers

How does a change to acidic pH influence the charge of the carboxyl group in an amino acid?

<p>It is protonated (-COOH) (B)</p> Signup and view all the answers

Which of the following is NOT a key factor in the variability of amino acid R groups?

<p>Molecular weight of the alpha carbon (D)</p> Signup and view all the answers

Which of the following functional groups is NOT commonly found in amino acid R groups?

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

Which characteristic is shared among all hydrophobic amino acids?

<p>Nonpolar R groups (D)</p> Signup and view all the answers

Polar amino acids are described as having a neutral R group. How does the charge distribute in this polar R group?

<p>The charge is concentrated in one area (C)</p> Signup and view all the answers

What is a key characteristic of positively charged amino acids at physiological pH?

<p>They have positively charged R groups. (D)</p> Signup and view all the answers

Which of the following is NOT a classification group of amino acids based on their R group characteristics?

<p>Negatively charged amino acids with acidic R groups (D)</p> Signup and view all the answers

What is the term used to describe amino acids with both positive and negative charges within the same molecule at a neutral pH?

<p>Dipolar ions and zwitterions (A)</p> Signup and view all the answers

Flashcards

Amino acid

An organic compound with a central carbon atom called the alpha carbon, bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom (H), and a unique side chain (R group).

Dipolar ion

A molecule with both a positive and negative charge, such as amino acids at neutral pH, often called 'zwitterions'.

R group

The side chain attached to the alpha carbon of an amino acid, determining its chemical properties and its role in protein structure.

Functional groups in amino acids

Functional groups, such as alcohols, thiols, amides, and carboxylic acids, that define an amino acid's chemical properties and affect its interactions.

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Hydrophobic amino acid

A type of amino acid with nonpolar R groups that repel water, often found in the interior of proteins. Examples include alanine, leucine, valine.

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Polar amino acid

A type of amino acid with polar but uncharged R groups that can form hydrogen bonds. Examples include serine, threonine, asparagine.

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Positively charged amino acid

A type of amino acid with positively charged R groups at physiological pH (7.4). Examples include lysine, arginine, histidine.

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Essential amino acid

These are amino acids that the body cannot synthesize on its own and must be obtained from the diet. Examples include isoleucine, leucine, lysine.

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Nonessential amino acid

Amino acids that the body can synthesize from other molecules. Examples include alanine, asparagine, glutamine.

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Ionizable amino acid

Amino acids with side chains that can ionize (gain or lose a proton) and their charge can change with pH, affecting protein structure and function. Examples include lysine, arginine, histidine, aspartic acid, glutamic acid, cysteine, tyrosine.

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Negatively Charged Amino Acids

Amino acids with R groups that carry a negative charge at physiological pH (pH 7.4). This negative charge is due to the presence of a carboxyl group (-COOH) in their side chains.

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Acidic Amino Acids

Amino acids with side chains containing a carboxyl group (-COOH), which is deprotonated to form a carboxylate (-COO-) at physiological pH. This results in a negative charge.

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Glycine

A simple amino acid with only a hydrogen atom as its side chain. It is considered nonpolar and hydrophobic.

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Alanine

A hydrophobic amino acid with a methyl group (-CH3) as its side chain. It's a simple, nonpolar amino acid.

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Cysteine

An amino acid with a thiol group (-SH) as its side chain. It is typically found in proteins that are involved in redox reactions.

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Histidine

An amino acid with an imidazole group in its side chain. This group can act as both a hydrogen donor and acceptor, making it important for enzyme active sites.

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Study Notes

Amino Acids

  • Amino acids are the building blocks of proteins
  • Twenty common amino acids
  • Each has a central carbon atom bonded to:
    • An amino group (-NH2)
    • A carboxyl group (-COOH)
    • A hydrogen atom
    • A variable R-group (side chain)
  • R-groups determine amino acid properties (e.g., size, shape, charge, hydrophobicity)
  • Amino acids with side chains which can ionize influence pH
  • At physiological pH (7.4), amino acids exist as dipolar ions (zwitterions)
  • Protonation or deprotonation of amino acids depends on pH
  • Amino acids categorized based on side-chain properties
    • Hydrophobic (nonpolar)
    • Polar (neutral)
    • Positively charged (basic)
    • Negatively charged (acidic)
  • Some amino acids essential, meaning they must be obtained from the diet
    • Others nonessential, meaning the body can synthesize them
  • A key aspect for protein function and structure are the twenty amino acids
  • Hydrophobic amino acids primarily have hydrocarbon side chains
  • Other functional groups in amino acids include alcohols, thiols, thioethers, carboxylic acids, carboxamides, and various basic groups.
  • The ionizable side chains of seven specific amino acids enhance reactivity and bonding
  • These amino acids are crucial for forming ionic bonds and acting as acid-base catalysts.

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Chapter 3 Amino Acids PDF

Description

Test your knowledge about amino acids, the fundamental building blocks of proteins. This quiz covers their structure, classification, and importance in biological processes. Understand essential versus nonessential amino acids and their properties related to pH and side chains.

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