polypeptide

(noun)

Any polymer of (same or different) amino acids joined via peptide bonds.

Related Terms

  • R group
  • amino acid
  • catalyze

Examples of polypeptide in the following topics:

  • Protein Structure

    • A protein's primary structure is the unique sequence of amino acids in each polypeptide chain that makes up the protein.
    • Really, this is just a list of which amino acids appear in which order in a polypeptide chain, not really a structure.
    • For example, the pancreatic hormone insulin has two polypeptide chains, A and B.
    • Rarely does a single secondary structure extend throughout the polypeptide chain.
    • Proteins made from a single polypeptide will not have a quaternary structure.
  • Amino Acids

    • An amino acid contains an amino group, a carboxyl group, and an R group, and it combines with other amino acids to form polypeptide chains.
    • The resulting chain of amino acids is called a polypeptide chain.
    • Each polypeptide has a free amino group at one end.
    • When reading or reporting the amino acid sequence of a protein or polypeptide, the convention is to use the N-to-C direction.
    • Although the terms polypeptide and protein are sometimes used interchangeably, a polypeptide is technically any polymer of amino acids, whereas the term protein is used for a polypeptide or polypeptides that have folded properly, combined with any additional components needed for proper functioning, and is now functional.
  • The Mechanism of Protein Synthesis

    • Catalyzing the formation of a peptide bond removes the bond holding the growing polypeptide chain to the P-site tRNA.
    • The growing polypeptide chain is transferred to the amino end of the incoming amino acid, and the A-site tRNA temporarily holds the growing polypeptide chain, while the P-site tRNA is now empty or uncharged.
    • This causes the polypeptide chain to detach from its tRNA, and the newly-made polypeptide is released.
    • The growing polypeptide chain is attached to the tRNA in the ribosome P site.
    • This creates a peptide bond between the C terminus of the growing polypeptide chain and the A site amino acid.
  • The Central Dogma: DNA Encodes RNA and RNA Encodes Protein

    • These nucleotide triplets are called codons; they instruct the addition of a specific amino acid to a polypeptide chain.
    • Three of the 64 codons terminate protein synthesis and release the polypeptide from the translation machinery.
    • Translation is the process by which mRNA is decoded and translated to produce a polypeptide sequence, otherwise known as a protein.
    • In translation, a cell decodes the mRNA's genetic message and assembles the brand-new polypeptide chain.
    • The main function of tRNA is to transfer a free amino acid from the cytoplasm to a ribosome, where it is attached to the growing polypeptide chain. tRNAs continue to add amino acids to the growing end of the polypeptide chain until they reach a stop codon on the mRNA.
  • The Protein Synthesis Machinery

    • For instance, ribosomes may consist of different numbers of rRNAs and polypeptides depending on the organism.
    • A ribosome is a complex macromolecule composed of structural and catalytic rRNAs, and many distinct polypeptides.
    • The peptidyl-tRNA carrying the growing polypeptide chain is held in the P site.
    • (More accurately, the growing polypeptide chain is added to each new amino acid bound in by a tRNA.)
    • (More accurately, the growing polypeptide chain is added to each new amino acid brought in by a tRNA.)
  • Types and Functions of Proteins

    • These amino acids are covalently attached to one another to form long linear chains called polypeptides, which then fold into a specific three-dimensional shape.
    • Sometimes these folded polypeptide chains are functional by themselves.
    • Other times they combine with additional polypeptide chains to form the final protein structure.
    • Sometimes non-polypeptide groups are also required in the final protein.
    • For instance, the blood protein hemogobin is made up of four polypeptide chains, each of which also contains a heme molecule, which is ring structure with an iron atom in its center.
  • Lipid-Derived, Amino Acid-Derived, and Peptide Hormones

    • The structure of peptide hormones is that of a polypeptide chain (chain of amino acids).
    • The peptide hormones include molecules that are short polypeptide chains, such as antidiuretic hormone and oxytocin produced in the brain and released into the blood in the posterior pituitary gland.
    • Amino acid-derived and polypeptide hormones are water-soluble and insoluble in lipids.
  • The Incorporation of Nonstandard Amino Acids

    • A protein (also called a polypeptide) is a chain of amino acids.
    • For instance, the peptide hormone insulin is cut twice after disulfide bonds are formed, and a propeptide is removed from the middle of the chain; the resulting protein consists of two polypeptide chains connected by disulfide bonds.
    • Also, most nascent polypeptides start with the amino acid methionine because the "start" codon on mRNA also codes for this amino acid.
  • Denaturation and Protein Folding

    • At higher pHs pepsin's conformation, the way its polypeptide chain is folded up in three dimensions, begins to change.
    • It is often possible to reverse denaturation because the primary structure of the polypeptide, the covalent bonds holding the amino acids in their correct sequence, is intact.
    • The chaperonins clump around the forming protein and prevent other polypeptide chains from aggregating.
  • Proteolytic Degradation

    • The breakdown of proteins into smaller polypeptides, or its respective amino acids, are necessary for metabolic and cellular homeostasis.
    • Polypeptides are commonly broken down via hydrolysis of the peptide bonds by utilizing a class of enzymes called proteases.
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