Amino Acid Structure and Classification

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What distinguishes α, β, and δ amino acids?

  • The position of the amino group in the carbon chain (correct)
  • Their side chain composition
  • Their occurrence in prokaryotic organisms
  • The number of carbon atoms in the chain

Why do amino acids have optical activity?

  • They are zwitterionic in nature
  • They contain a chiral carbon atom (correct)
  • They are all saturated compounds
  • They have symmetrical structures

Which statement is true regarding amino acids found in mammalian proteins?

  • Some amino acids do not exhibit amphoteric properties
  • D-amino acids are predominant
  • All standard amino acids have only L-forms (correct)
  • There are 12 standard amino acids in mammalian proteins

Which group is found at the alpha carbon of amino acids?

<p>Carboxyl group and amin group (D)</p> Signup and view all the answers

What unique property do amino acids exhibit due to being zwitterions?

<p>Can act as both acids and bases (C)</p> Signup and view all the answers

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

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

What is the significance of L- and D- amino acids in biological systems?

<p>Only L-amino acids are used to build proteins in mammals (C)</p> Signup and view all the answers

What results from the modification of standard amino acids?

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

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

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

What is the characteristic of complete proteins?

<p>They contain all essential amino acids. (C)</p> Signup and view all the answers

Which of the following amino acids is considered semi-essential?

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

How are amino acids generally grouped?

<p>According to their side chain properties (C)</p> Signup and view all the answers

Which non-polar amino acid has a hydrogen atom as its R group?

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

What type of proteins are most vegetable proteins classified as?

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

Which of the following amino acids is NOT an aromatic amino acid?

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

Which amino acids are involved in hydrophobic interactions due to their hydrocarbon R groups?

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

Which of the following amino acids is classified as basic?

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

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

<p>Essential amino acids must be obtained from the diet. (D)</p> Signup and view all the answers

Which amino acid is known for functioning as a neurotransmitter?

<p>L-Dopamine (A)</p> Signup and view all the answers

What role does the -OH group in tyrosine play in proteins?

<p>It acts as a site for phosphorylation and hydrogen bonding. (B)</p> Signup and view all the answers

Which of the following amino acids is negatively charged at pH 7.0?

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

Which of the following classifications includes both glucogenic and ketogenic amino acids?

<p>Semi-essential amino acids (C)</p> Signup and view all the answers

Which amino acid contains a sulfur atom in its side chain, contributing to hydrophilic interactions?

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

Which amino acid belongs to the polar category?

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

What is a primary source of essential amino acids?

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

What characteristic of proline affects its flexibility in protein structures?

<p>It contains an imino group forming a five-membered ring. (A)</p> Signup and view all the answers

Which statement accurately describes electrically charged amino acids?

<p>Electrically charged amino acids can be either acidic or basic. (C)</p> Signup and view all the answers

Which of the following amino acids is NOT classified as an aromatic amino acid?

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

What is the significance of the side chain properties in amino acids?

<p>They affect the amino acid's solubility and reactivity. (C)</p> Signup and view all the answers

Which amino acid is a dimer of cysteine?

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

What is the pK value of the α-carboxylic group in amino acids typically in the range of?

<p>2.2 (C)</p> Signup and view all the answers

At what point is an amino acid considered electrically neutral?

<p>Isoelectric point (pI) (D)</p> Signup and view all the answers

What occurs in solutions that are more basic than the isoelectric point for amino acids?

<p>The amino acid donates a proton (D)</p> Signup and view all the answers

Which of the following amino acids is polar and uncharged?

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

Which amino acid has a second carboxyl group that affects its acidic properties?

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

What does the term 'zwitterion' refer to in relation to amino acids?

<p>An amino acid with both positive and negative charges (A)</p> Signup and view all the answers

What happens at the pH of an amino acid's isoelectric point?

<p>The positive and negative charges are equal (C)</p> Signup and view all the answers

Flashcards are hidden until you start studying

Study Notes

Amino Acid Structure

  • Amino acids are organic molecules containing both carboxyl and amino groups.
  • Amino acids are the building blocks of proteins.
  • They contain a carboxylic acid group and an amino group on the alpha (α) carbon.
  • Amino acids differ in their properties due to differing side chains.
  • Side chains are called R groups.

α-Carbon

  • The alpha carbon is an asymmetrical carbon atom giving the amino acids optical activity.

Amino Acid Structure

  • Amino acids can be characterized as α, β, or δ depending on the location of the amino group in the carbon chain.
  • α amino acids are found on the carbon adjacent to the carboxyl group.
  • β amino acids are found on the 2nd carbon from the carboxyl group.
  • δ amino acids are found on the 3rd carbon from the carboxyl group.

Amino Acids

  • 20 standard amino acids are present in mammalian proteins.
  • All amino acids have amphoteric properties, meaning they can act as both an acid and a base.
  • All amino acids except glycine have optical activity.
  • Amino acids are dipolar, having both charges.
  • The positive end is NH3+.
  • The negatve end is COO-.
  • Non-standard amino acids come from modifications of standard amino acids.
  • Amino acids have Stereoisomers.
  • All amino acids except glycine have chiral carbon (asymmetrical carbon atom).
  • L-amino acids are natural amino acids found in protein.
  • D-amino acids are found in antibiotics and plant and bacterial cell walls.

Proline

  • Proline is an imino acid, meaning it has a secondary amino group.

Amino Acid Abbreviations

  • Each amino acid has a three letter abbreviation and a one letter symbol.
  • The three letter abbreviation is commonly the first three letters of the amino acid name.
  • The one-letter symbol is typically the first letter of the amino acid name.
  • When these abbreviations are confusing, alternative abbreviations are used.

Amino Acid Functions

  • Amino acids are the building blocks of proteins.
  • Some amino acids and their derivatives function as neurotransmitters and other regulators.
  • Neurotransmitters and regulators include L-dopamine, epinephrine, thyroxine, and histamine.

Classification of Amino Acids

  • Essential or Non-Essential
  • Glucogenic, ketogenic, or Glucogenic & ketogenic
  • Neutral, acidic, and basic
  • According to the side chain properties

Essential & Non-Essential Amino Acids

  • Essential amino acids are not synthesized by the human body and must be obtained from the diet.
  • Essential amino acids are present in dairy products.
  • Sources of protein come from both animal and vegetable sources.
  • Animal sources are complete proteins, meaning they contain all essential amino acids.
  • Vegetable sources usually lack some essential amino acids.
  • They are classified as semi-essential or conditionally essential amino acids, including arginine, cysteine, glutamine, glycine, and proline.

Essential Amino Acids

  • Essential amino acids are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine.
  • Non-Essential amino acids are: alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine.

Complete Protein

  • Complete protein contains all 10 essential amino acids.
  • Incomplete protein lacks one or more essential amino acids.
  • Most vegetable proteins are incomplete proteins with the exception of beans.
  • Beans contain some complete protein.

Classification According to Side Chain Properties

  • Non-polar (Hydrophobic)

  • Side chain does not bind or give off protons.

  • They promote hydrophobic interactions.

  • They are clustered in the interior of a protein when in aqueous solution.

  • They help give 3D shape to the protein structure.

  • Non-polar (Hydrophobic), Aliphatic Amino Acids

  • Glycine (Gly or G)

  • Alanine (Ala or A)

  • Valine (Val or V)

  • Leucine (Leu or L)

  • Isoleucine (Ile or I)

  • Methionine (Met or M)

  • Non-polar (Hydrophobic), Aromatic Amino Acids

  • Phenylalanine (Phe or F)

  • Tryptophan (Trp or W)

  • Proline (Pro or P)

Polar (Hydrophilic) Uncharged Amino Acids

  • Serine (Ser or S)

  • Threonine (Thr or T)

  • Cysteine (Cys or C)

  • Tyrosine (Tyr or Y)

  • Asparagine (Asn or N)

  • Glutamine (Gln or Q)

  • The six amino acids with polar, uncharged R groups are more hydrophilic due to the presence of hydroxyl groups, sulfur atoms, or amide groups.

  • The SH group of two Cysteine residues in proteins can be oxidized to form a covalent disulfide bond.

  • Cys often participates in hydrophobic interactions.

  • Pro has a five-membered ring structure, being rigid in conformation and offering the least flexibility.

  • Pro is often found in the bends of folded protein chains and on the surface of proteins.

Positively Charged (Basic) and Negatively Charged (Acidic) R Groups

  • The most hydrophilic R groups are those either positively or negatively charged.
  • Asp and Glu have a carboxyl group in their R groups.
  • They have a net negative charge at pH 7.0.
  • They are typically named aspartate and glutamate.
  • Arg, Lys, and His have positively charged R groups at pH 7.0.
  • Their R groups contain a guanidino, amino, or imidazole group respectively.
  • The side chain of His can be positively or uncharged depending on the local environment near pH 7.0.

Polar (Hydrophilic) Charged Amino Acids

  • Negatively charged

  • Aspartic Acid (Asp or D)

  • Glutamic Acid (Glu or E)

  • Positively charged

  • Lysine (Lys or K)

  • Arginine (Arg or R)

  • Histidine (His or H)

Cystine

  • Cystine is a dimer of cysteine.

Sickle Cell Disease

  • Sickle cell disease is a pathology that results from the substitution of polar glutamate by the non-polar valine in the B subunit of hemoglobin.

pK Value

  • pK value measures the ability of an acid to donate a proton (dissociate).
  • It is also known as pKa or the acid dissociation constant.
  • pK value represents the pH at which 50% of the acid is dissociated.
  • The pK values of α-carboxylic groups are typically in the range of 2.2.
  • The pK values of α-amino groups are typically in the range of 9.4
  • The smaller the pK value, the stronger the acid.
  • The larger the pK values, the weaker the acid.

Zwitterion

  • Zwitterion is a double ion.
  • Zwitterion is formed when both NH3+ and COO- are ionized.
  • At the isoelectric point (pI), the positive and negative charges in the zwitterion are equal.
  • pI is the pH at which the molecule is electrically neutral.

Amino Acids as Acids or Bases

  • Amino Acids as Acids

    • In solutions that are more basic than the pI, the —NH3+ in the amino acid donates a proton.
  • Amino Acids as Bases

    • In solutions more acidic than the pI, the COO- in the amino acid accepts a proton.

pH and Ionization

  • Acidic amino acids, such as aspartic acid, have a second carboxyl group that can donate and accept protons.
  • The pI for aspartic acid occurs at a pH of 2.8.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Lecture 1 Amino Acids PDF

More Like This

Use Quizgecko on...
Browser
Browser