Amino Acids Classification and Properties
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Questions and Answers

Which of the following amino acids is classified as a sulfur-containing amino acid?

  • Methionine (correct)
  • Glutamine
  • Lysine
  • Threonine

What characterizes imino acids compared to other amino acids?

  • Absorb ultraviolet light
  • Always contain a hydroxyl group
  • Contain a basic amino group and a carboxyl group
  • Have a pyrrolidine ring (correct)

Which property of amino acids allows them to exist as zwitter ions in solution?

  • Hydrophobic nature
  • Presence of aromatic side chains
  • Dual acidic and basic functional groups (correct)
  • Classification by biological value

Which type of amino acid is characterized by the presence of a hydroxyl functional group in its side chain?

<p>Hydroxyl group containing amino acids (A)</p> Signup and view all the answers

Which of the following amino acids is classified as an acidic amino acid?

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

Which of the following amino acid classifications contains amino acids that usually absorb ultraviolet light?

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

Which of the following amino acids is NOT part of the aliphatic amino acids group?

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

What is the primary reason amino acids exhibit acidic and basic properties?

<p>Two functional groups: amino and carboxyl (D)</p> Signup and view all the answers

What type of reaction occurs when aspartic acid reacts with ammonia to form asparagine?

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

Which of the following amino acids is primarily involved in the synthesis of serotonin?

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

Which metabolic pathway liberates free ammonia from amino acids?

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

How are amino acids classified if they can be converted into glucose?

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

Which property allows amino acids to exist as zwitterions at a particular pH?

<p>Dual ionic forms of amino and carboxyl groups (C)</p> Signup and view all the answers

Which of the following amino acids is known for its role in detoxification processes?

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

Which type of amino acids typically has aromatic side chains?

<p>Aromatic amino acids (B)</p> Signup and view all the answers

Which amino acid is coded by the codon UGU in the genetic code?

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

Which amino acid is considered critical for the synthesis of catecholamines?

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

Which of the following properties is NOT typically associated with amino acids?

<p>Amino acids are unable to form zwitterions in physiological pH. (B)</p> Signup and view all the answers

Which amino acid is considered semi-essential and plays a role in metabolism as a precursor for nitric oxide?

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

Which of the following amino acids is NOT categorized as electrically charged?

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

In the context of amino acid classification, which of the following statements is correct regarding essential amino acids?

<p>They must be obtained through diet for proper growth and maintenance. (B)</p> Signup and view all the answers

Which of the following amino acids is a nonpolar side chain and does not participate in acid-base reactions?

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

What characteristic of amino acids accounts for their ability to act as both acids and bases?

<p>Presence of both carboxylic and amino groups (A)</p> Signup and view all the answers

What is the charge of an amino acid at a strongly alkaline pH?

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

Which of the following statements about zwitter ions is true?

<p>They exist in a form carrying both positive and negative charges (B)</p> Signup and view all the answers

What is the isoelectric pH (pI) of an amino acid?

<p>The pH at which it forms a zwitter ion and has no net charge (C)</p> Signup and view all the answers

The decarboxylation of amino acids converts them into which of the following?

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

Which factors help determine the pI of an amino acid?

<p>Ionizable groups pK values (C)</p> Signup and view all the answers

Which reaction result is specifically associated with the carboxylic group of amino acids?

<p>Formation of esters (B)</p> Signup and view all the answers

What behavior do amino groups exhibit in relation to acids?

<p>They act as bases (A)</p> Signup and view all the answers

What identifies amino acids as ampholytes?

<p>Able to donate or accept protons (A)</p> Signup and view all the answers

Which of the following amino acids demonstrates the property of existing predominantly as a zwitter ion?

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

Which amino acid is classified as a pure glucogenic amino acid?

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

What type of compounds are produced from the metabolism of amino acids classified as pure ketogenic?

<p>Ketone bodies only (A)</p> Signup and view all the answers

Which statement regarding the solubility of amino acids is correct?

<p>Most are soluble in water and insoluble in organic solvents. (A)</p> Signup and view all the answers

What role do the carbon skeletons of amino acids primarily play?

<p>They serve as precursors for glucogenic or ketogenic paths. (B)</p> Signup and view all the answers

The amino acids selenocysteine and pyrrolysine are classified as which type?

<p>Non-standard amino acids (B)</p> Signup and view all the answers

Which of the following amino acids is known for its bitter taste?

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

Which of the following categories does not classify any of the amino acids?

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

In terms of metabolic pathways, which of the following products is not formed from amino acid metabolism?

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

Which amino acids are characterized as having higher melting points, often above 200°C?

<p>Most amino acids generally melt at higher temperatures (D)</p> Signup and view all the answers

Which of the following amino acids is non-essential?

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

Flashcards

Amino Acid Function Groups

Amino acids contain both an amino group (-NH2) and a carboxyl group (-COOH).

Amino Acid Structure

Each amino acid has a central carbon atom (α-carbon) bonded to an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group).

Amino Acid Classification by Side Chain

Amino acids are grouped by the chemical structure and properties of their side chains (R groups).

Aliphatic Amino Acids

Simple amino acids with hydrocarbon side chains that are generally non-polar.

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Essential Amino Acids

Our bodies can't make these 9 amino acids; we must get them from food.

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Aromatic Amino Acids

Have a ring structure in their side chains, often nonpolar.

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Imino Acid

Proline is the ONLY imino acid; containing a pyrrolidine ring and an imino group (=NH).

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Classification of Amino Acids

Amino acids are classified based on chemical structure of their side chains (R-groups), polarity, nutrition value, etc.

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Reaction with ammonia

Dicarboxylic amino acids react with ammonia to form amides.

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Transamination

Transfer of an amino group to a keto acid, creating a new amino acid.

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Oxidative Deamination

Amino acids break down, releasing ammonia.

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Amino Acid Function

Body uses amino acids to make proteins for digestion, growth, tissue repair and many other functions; also a source of energy.

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Tryptophan to Serotonin

Tryptophan is converted into Serotonin

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Aspartate, Glutamine to Pyrimidines

Aspartate and Glutamine are used in pyrimidine synthesis.

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Glycine, Aspartate, Serine to Purines

Glycine, aspartate, and serine are used to make purines.

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Glycine, Cysteine as Detoxifiers

Glycine and Cysteine are important for detoxification.

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Methionine Methyl Group Transfer

Methionine transfers methyl groups.

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Glutamate to GABA

Glutamate is converted to GABA.

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Non-Essential Amino Acids

These amino acids can be synthesized by the body, so they don't need to be consumed in the diet.

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Glucogenic Amino Acids

Amino acids that can be converted into glucose through metabolic pathways.

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Ketogenic Amino Acids

Amino acids that can be converted into ketone bodies, which are an alternative energy source.

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Mixed Glucogenic & Ketogenic Amino Acids

Amino acids that can be converted into both glucose and ketone bodies.

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Pyruvate

A key metabolic intermediate produced from the breakdown of some amino acids.

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Acetyl-CoA

A key metabolic intermediate produced from the breakdown of some amino acids.

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Alpha-Ketoglutarate

Key intermediate in the citric acid cycle. Produced from the breakdown of some amino acids.

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Selenocysteine

The 21st amino acid, containing selenium. Involved in various biological functions.

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Pyrrolysine

The 22nd amino acid. Found in some bacterial enzymes.

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Optical Isomers in Amino Acids

All amino acids except glycine have optical isomers due to the presence of an asymmetric carbon atom. This means they exist in two mirror-image forms (L and D) that rotate plane-polarized light differently.

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Amino Acids as Ampholytes

Amino acids possess both acidic (-COOH) and basic (NH2) groups. They can act as both acids (donating protons) and bases (accepting protons), making them ampholytes.

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Zwitter Ion: What is it?

A zwitter ion is a molecule with both a positive and negative charge. It arises from the internal transfer of a proton from the carboxyl group to the amino group within an amino acid.

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Zwitter Ion Formation: pH Dependence

The form of an amino acid (neutral, positively charged, or negatively charged) depends on the pH of the solution. In acidic conditions, the amino acid is positively charged. In alkaline conditions, it's negatively charged.

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Isoelectric Point (pI): What is it?

The isoelectric point (pI) is the specific pH at which an amino acid exists as a zwitter ion and carries no net charge. This is when the positive and negative charges balance out.

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Calculating Isoelectric Point (pI)

The pI value for an amino acid is calculated by averaging the pK values of the two ionizable groups involved in zwitter ion formation.

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Amino Acid Reactions: Carboxyl Group (-COOH)

The carboxyl group in amino acids can react with bases to form salts (-COONa) and with alcohols to form esters (-COOR'). These are important reactions in metabolism and synthesis.

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Amino Acid Reactions: Amino Group (-NH2)

The amino group in amino acids can react with acids to form salts. This is due to the basic nature of the amino group.

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Decarboxylation of Amino Acids

Amino acids can undergo decarboxylation, where they lose their carboxyl group (-COOH) to form corresponding amines. This is a crucial step in the synthesis of important bioactive molecules.

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Examples of Decarboxylation Products

Decarboxylation of specific amino acids like histidine, tyrosine, and glutamate produces important biomolecules like histamine, tyramine, and γ-amino butyric acid (GABA), respectively.

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Arginine

It is a basic amino acid, contains a guanidino group, and plays a crucial role in the urea cycle. It's also a precursor for nitric oxide, a vital molecule involved in blood vessel dilation.

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Histidine

Histidine is a semi-essential amino acid, meaning that your body can usually make enough, but you may need to get some from your diet. It has an imidazole ring in its structure and plays a role in regulating pH.

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Nonpolar Amino Acids

This group of amino acids includes Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Tryptophan, Phenylalanine, and Proline. These amino acids have hydrophobic side chains, meaning they don't interact well with water.

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Electrically Charged Amino Acids

This group includes Aspartic Acid, Glutamic Acid, Lysine, Arginine, and Histidine. These amino acids have either a positive or negative charge on their side chains, making them hydrophilic (water-loving).

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Study Notes

Amino Acids: General Overview

  • Amino acids are organic compounds with two functional groups—amino and carboxyl.
  • The amino group (-NH₂) is basic, while the carboxyl group (-COOH) is acidic.
  • There are approximately 300 amino acids found in nature, but only 20 are found in proteins.

Amino Acid Structure

  • Each amino acid has four different groups attached to a central carbon atom (α-carbon).
  • These groups include an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group).
  • The R group is specific for each amino acid and gives it unique properties.

Amino Acid Classification

  • Amino acids are classified based on various properties, including:
    • Chemical structure of the side chain (R group)
    • Polarity of the side chain (hydrophobic, hydrophilic, etc.)
    • Biological value
    • Nutritional value
  • Specific groups include: aliphatic, hydroxyl, sulfur-containing, acidic, basic, aromatic, and imino amino acids.

Aliphatic Amino Acids

  • These are monoamino monocarboxylic acids.
  • Examples include glycine (Gly - G), alanine (Ala - A), valine (Val - V), leucine (Leu - L), and isoleucine (Ile - I).
  • Glycine has a simple side chain, while others have branched chains.

Important Amino Acids: Glycine

  • Small, simple amino acid. Its R group is a hydrogen atom.
  • A non-essential amino acid.
  • An allosteric inhibitor of glutathione synthetase.
  • Crucial for muscle tissue, central nervous system, and digestive systems.
  • A component of collagen, which keeps skin and connective tissue firm and flexible.

Important Amino Acids: Alanine

  • A non-essential amino acid.
  • An allosteric inhibitor of glutathione synthetase.
  • D-Alanine is a constituent of bacterial cell walls.
  • β-Alanine is present in pantothenic acid (vitamin B5).

Branched-Chain Amino Acids (BCAAs)

  • Leucine, isoleucine, and valine are BCAAs.
  • Their metabolic breakdown products have different fates, impacting glucose and ketone body production.

Maple Syrup Urine Disease

  • A metabolic disorder involving branched-chain amino acids.
  • Characterized by a distinctive maple syrup odor in the urine.
  • The enzyme deficiency lies in branched-chain α-ketoacid dehydrogenase.

Hydroxyl-Containing Amino Acids

  • Serine (Ser - S), threonine (Thr - T), and tyrosine (Tyr - Y) are important amino acids.
  • These have hydroxyl groups (-OH) in their side chains.

Sulfur-Containing Amino Acids

  • Cysteine (Cys - C) and methionine (Met - M) contain sulfur atoms in their side chains.
  • Cysteine forms disulfide bonds (-S-S-) with other cysteines, crucial for maintaining protein structure.
  • Methionine starts the production of proteins in the human body.

Methionine

  • An essential amino acid.
  • Coded by the AUG codon (start codon).
  • The first amino acid incorporated into nascent polypeptide chains.

Acidic Amino Acids and Their Amides

  • Aspartic acid (Asp - D), asparagine (Asn - N), glutamic acid (Glu - E), and glutamine (Gln - Q) are vital.
  • These amino acids are important in various reactions throughout the body

Basic Amino Acids

Including Lysine (Lys - K), Arginine (Arg - R), and Histidine (His - H)

  • Imino group amino acids - Proline (Pro- P): containing a pyrrolidine ring, plays a significant role in protein structure.
  • Proline's distinctive cyclic structure and imino group contribute to the rigidity of polypeptide chains.

Aromatic Amino Acids

  • Phenylalanine (Phe - F), Tyrosine (Tyr - Y), and Tryptophan (Trp - W) are aromatically structured.
  • These are precursors for numerous hormones and neurotransmitters.
  • Essential for numerous biological functions.

Protein Structure and Function

  • Primary structure: The amino acid sequence.
  • Secondary structure: Local folding patterns (e.g., α-helices, β-sheets).
  • Tertiary structure: Overall three-dimensional shape of the protein.
  • Quaternary structure: Arrangement of multiple polypeptide chains in a protein.

Nutritional Classification of Amino Acids

  • Essential amino acids cannot be synthesized by the body and must be obtained from the diet.
  • Non-essential amino acids can be synthesized by the body.
  • Ten essential amino acids need to be obtained through diet: Arginine, Valine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, and Tryptophan.

Amino Acid Metabolism and Fate

  • Amino acids can be converted into glucose or fat.
  • They are classified as ketogenic, glucogenic, or both glucogenic and ketogenic.

Amino Acid Properties and Reactions

  • Amino acids possess both acidic and basic properties due to the presence of carboxyl and amino groups.
  • They exist as zwitterions at physiological pH.
  • They undergo various reactions including decarboxylation, transamination, and oxidative deamination, crucial for metabolic pathways.

New Amino Acids

  • Selenocysteine (21st) and Pyrrolysine (22nd) amino acids are newly identified and play roles in protein synthesis.

Physical Properties of Amino Acids

  • Solubility in water and insolubility in organic solvents.
  • High melting points.
  • Variable tastes (sweet, tasteless, or bitter).
  • Monosodium glutamate used as a flavoring agent in food.

Optical and Acid-Base Properties

  • Optical isomers (except glycine) due to an asymmetric carbon atom.
  • Ampholyte (can act as both an acid and a base) due to both carboxyl and amino groups.
  • Zwitterion form at neutral pH.
  • Isoelectric point is the pH where the molecule carries no net charge.

Fill in the blanks and Questions (from student document, and presented in more coherent form):

  • Fill in the blanks for types of amino acids including small, branched-chain, sulfur-containing, etc.
  • Identify the specific amino acids (from provided list) used in the construction of particular molecules or in reactions.
  • Address questions on classifying amino acids, properties of amino acids, and the concepts of ketogenic/glucogenic amino acids.
  • Answer questions concerning the formation of specific molecules (thyroid hormones, niacin) using amino acids.

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Amino Acids - Lecture Notes PDF

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Test your knowledge on the classification, properties, and reactions of amino acids. This quiz covers various aspects, such as sulfur-containing amino acids, imino acids, zwitter ions, and more. Perfect for students studying biochemistry or related fields.

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