Amino Acids and Protein Structure

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Questions and Answers

Which of the following amino acids is considered highly hydrophilic?

  • Arginine (correct)
  • Leucine
  • Phenylalanine
  • Isoleucine

What characteristic differentiates the N-terminal from the C-terminal of a peptide?

  • The C-terminal has a side chain.
  • The C-terminal is the first amino acid in the sequence.
  • The N-terminal contains a carboxyl group.
  • The N-terminal has an amino group. (correct)

Which of the following statements about peptide bonds is incorrect?

  • Peptide bonds result in the formation of a polypeptide chain.
  • Peptide bonds connect amino acids in proteins.
  • Peptide bonds can be broken by hydrogen bonding. (correct)
  • Peptide bonds are formed by dehydration reactions.

Which property of amino acids is influenced by the functional groups in their side chains?

<p>Solubility in water (B)</p> Signup and view all the answers

Which of the following statements about the molecular weight of amino acids is accurate?

<p>Tryptophan is heavier than Glycine in terms of molecular weight. (B)</p> Signup and view all the answers

Which characteristic distinguishes α-amino acids from other types of amino acids?

<p>They are found in proteins. (D)</p> Signup and view all the answers

How many different combinations can be made with 3 amino acids?

<p>8,000 (C)</p> Signup and view all the answers

Which of the following is true about the stereoisomers of amino acids?

<p>Chiral amino acids have four different substituents. (D)</p> Signup and view all the answers

Which class of biomolecules is NOT categorized with amino acids?

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

What role do proteins serve in biological systems?

<p>They can act as enzymes and antibodies. (C)</p> Signup and view all the answers

What is the significance of the R group in the structure of amino acids?

<p>It determines the identity and characteristics of the amino acid. (D)</p> Signup and view all the answers

Which statement about amino acids is incorrect?

<p>Only β-amino acids are used in protein synthesis. (D)</p> Signup and view all the answers

What type of amino acid is GABA?

<p>γ-amino acid (B)</p> Signup and view all the answers

Which of the following characteristics is true about amino acids in the nonpolar, aliphatic group?

<p>They do not contain a benzene ring. (B)</p> Signup and view all the answers

How does electronegativity influence bond polarity in amino acids?

<p>A larger difference in electronegativity increases bond polarity. (D)</p> Signup and view all the answers

What does it mean when a compound is described as hydrophobic?

<p>It repels water molecules. (A)</p> Signup and view all the answers

Which factor differentiates glutamate from glutamic acid?

<p>Glutamate is the ionized form of glutamic acid. (B)</p> Signup and view all the answers

Which of the following correctly describes the role of water in relation to charged compounds?

<p>Charged compounds are soluble in water due to its polarity. (A)</p> Signup and view all the answers

Which statement about glycine is true?

<p>Glycine is the only amino acid that does not have an isomer. (D)</p> Signup and view all the answers

How can aromatic compounds in amino acids be identified?

<p>They contain a benzene ring or derivatives. (D)</p> Signup and view all the answers

What is a characteristic feature of polar, uncharged amino acids?

<p>They are soluble in water due to the presence of polar bonds. (C)</p> Signup and view all the answers

Flashcards

Amino Acids

Organic molecules that serve as the building blocks of proteins. They contain an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a unique side chain (R group) attached to a central carbon atom (alpha carbon).

Isomers

Molecules that have the same chemical formula but different structural arrangements. They cannot be superimposed on each other.

Enantiomers

A specific type of isomer where the molecules are mirror images of each other and cannot be superimposed.

Chiral Carbon Atom

A carbon atom that is bonded to four different groups or atoms. It is the center of chirality, meaning it can exist in two non-superimposable mirror image forms.

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L-Amino Acids

The configuration of amino acids found in proteins. It is typically represented as L-amino acids, with the amino group on the left side of a Fischer projection.

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Peptide Bond

The bond formed between two amino acids during protein synthesis. It involves a reaction between the carboxyl group of one amino acid and the amino group of another, releasing a water molecule.

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Amino Acid Sequence

The unique sequence of amino acids that makes up a protein. This sequence dictates the protein's shape, function, and properties.

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Protein Sequence Representation

Amino acid sequence is represented using three-letter or one-letter abbreviations to denote each amino acid. For example, Met-Tyr-Ala-Gly-Gly-Trp-Leu represents a sequence of amino acids.

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Hydrophobic interactions

The attraction of molecules to each other caused by non-covalent interactions like Van Der Waals forces, hydrogen bonding, or dipole-dipole attraction.

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Solubility

The amount of solute that can dissolve in a given amount of solvent at a specific temperature.

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N-terminal

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

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C-terminal

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

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Nonpolar, aliphatic R groups

Amino acids with nonpolar side chains that lack functional groups like hydroxyl or amine groups. These side chains are primarily composed of hydrocarbons, making them hydrophobic and less reactive.

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Electronegativity

A measure of an atom's ability to attract electrons within a chemical bond. More electronegative atoms pull electrons closer, creating polarity.

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Aromatic compounds

Organic compounds that contain the benzene ring structure. They often have different properties than compounds without the ring.

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Aliphatic Compounds

Organic compounds that lack the benzene ring structure and are typically composed of straight chains or branched chains of carbon atoms.

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Positively Charged R groups

Amino acids with positively charged side chains due to the presence of protonated amino groups in their R groups. They are usually hydrophilic.

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Negatively charged R groups

Amino acids with negatively charged side chains due to the presence of deprotonated carboxyl groups in their R groups. They are usually hydrophilic.

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Polar uncharged R groups

Amino acids with polar but uncharged side chains. They contain functional groups like hydroxyl or amide groups, making them hydrophilic but not charged.

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Glutamic Acid

The carboxylic acid form of an amino acid. It has a free carboxyl group at the end of its side chain.

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Study Notes

Amino Acids

  • Amino acids are the building blocks of proteins
  • Proteins are composed of 20 different amino acids
  • Each amino acid contains a central carbon atom (α-carbon) bonded to four groups:
    • An amino group (NH2)
    • A carboxyl group (COOH)
    • A hydrogen atom (H)
    • A variable side chain (R group), which differentiates the 20 amino acids
  • Proteins are typically 50-2,000 amino acids long
  • Possible combinations of 20 amino acids in a protein are massive: 20^2 = 400, 20^3 =8,000, 20^100 ≈ 10130, 201000 ≈ ?
  • Proteins have diverse functions including hormones, antibodies, muscle fibers, oxygen transport, ion channels, and enzymes
  • The α-carbon is tetrahedral with bond angles of 109.5°
  • Amino acids in proteins are L-amino acids
  • Amino acids have both positive and negative charges (e.g., H3N+ - C - COO-)
  • Proteins contain various amino acids having different R-groups, defining different classes
  • Classification of amino acids bases on their R groups:

    • Nonpolar, aliphatic

    • Aromatic

    • Polar, uncharged

    • Positively charged

    • Negatively charged

  • Abbreviations are used to represent amino acids (e.g., Ala for alanine)
  • Peptide bonds link amino acids to create polypeptide chains
  • The ends of a peptide chain are different (amino-terminal and carboxyl-terminal ends).
  • Peptides are smaller than proteins and are made from amino acids, using peptide bonds
  • Size of peptides and proteins varies, as shown by examples such as cytochrome c(12,400 MW, 104 residues) and titin (2,993,000 MW, 26,926 residues).
  • Amino acids are important for the structure and function of biomolecules

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