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What are Proteins?01:55

What are Proteins?

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Amino acids03:42

Amino acids

Amino acids are the monomers that comprise proteins. Each amino acid has the same fundamental structure, which consists of a central carbon atom, or the alpha (α) carbon, bonded to an amino group (NH2), a carboxyl group (COOH), and to a hydrogen atom. Every amino acid also has another atom or group of atoms bonded to the central atom known as the R group. There are 20 common amino acids present in proteins, each with a different R group. Variation in the amino acid sequence is responsible for...
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A peptide bond covalently attaches amino acids through a dehydration reaction. One amino acid's carboxyl group and another amino acid's amino group combine, releasing a water molecule. The resulting bond is the peptide bond. The products that such linkages form are peptides. As more amino acids join this growing chain, the resulting chain is a polypeptide. Each polypeptide has a free amino group at one end. This end has the N-terminal, or the amino-terminal, and the other end has a free...
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Proteins are polymers of amino acids linked together by peptide bonds. Proteins and polypeptides are interchangeably used to refer to long chains of amino acids. However, polypeptides have a molecular weight of fewer than 10,000 daltons, while proteins have greater molecular weight.  Polypeptides with less than 20 amino acids are called oligopeptides or simply peptides. Interactions among the constituent amino acid side chains of proteins help them fold into a stable 3-dimensional structure...
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Proteins are polymers of amino acid residues. They are versatile and responsible for different cellular functions, including DNA replication, molecular transport, catalysis, and structural support. Proteins have a hierarchical structure comprising at least three levels of organization: primary, secondary, and tertiary structure. Some large proteins have a quaternary structure where individual protein subunits are linked together.
The primary structure of a protein is its amino acid sequence.

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Related Experiment Video

Updated: Jul 10, 2026

Peptide Scanning-assisted Identification of a Monoclonal Antibody-recognized Linear B-cell Epitope
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Polypeptide chains containing D-gamma-hydroxyvaline.

Katarzyna Pisarewicz1, David Mora, Fred C Pflueger

  • 1Department of Chemistry & Biochemistry and Center of Excellence in Biomedical & Marine Biotechnology, Florida Atlantic University, 777 Glades Road, Boca Raton, Florida 33431, USA.

Journal of the American Chemical Society
|April 28, 2005
PubMed
Summary
This summary is machine-generated.

Researchers discovered unusual d-amino acids, d-Val and d-gamma-hydroxyvaline (d-Hyv), in cone snail venom peptides. These findings challenge the typical l-homochirality of life and suggest novel enzymatic pathways.

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Area of Science:

  • Biochemistry
  • Peptide Chemistry
  • Venom Research

Background:

  • Life exhibits a distinct l-homochirality, with proteins primarily using l-amino acids.
  • Cone snail venom contains diverse peptides (conopeptides) with various biological activities.

Purpose of the Study:

  • To investigate the presence and structural characteristics of unusual amino acids in newly isolated conopeptides.
  • To elucidate the novel structural motifs and potential enzymatic mechanisms involved in their synthesis.

Main Methods:

  • Isolation and purification of four conopeptides: gld-V/gld-V' and mus-V/mus-V'.
  • Determination of complete amino acid sequences using nano/pico-NMR and MS/MS techniques.
  • Analysis of novel structural motifs and their stabilizing interactions.

Main Results:

  • Discovery of d-Val and d-gamma-hydroxyvaline (d-Hyv) within ribosomally expressed polypeptide chains.
  • Identification of a novel Ser-d-Hyv-Trp motif in gamma-hydroxyconophans, stabilized by specific interactions.
  • Characterization of atypical conophans and gamma-hydroxyconophans lacking typical constraints and exhibiting high hydroxylation.

Conclusions:

  • The presence of d-amino acids in conopeptides challenges fundamental principles of biological homochirality.
  • Novel structural motifs and a potential hyperhydroxylation mechanism in cone snail venom enhance neuronal targeting.
  • The findings suggest the existence of a d-stereospecific enzyme involved in d-Val oxidation.