Proteins

    Cards (56)

    • Amino acids are the monomers of protein molecules
    • Monomers are subunits, or “building blocks”
    • Polymers are what you get when you string many monomers together
    • Each amino is composed of a central carbon atom attached to:
      1. Amino group (NH2)
      2. Carboxyl group (COOH)
      3. Hydrogen (H)
      4. R groups
    • There are 20 different amino acids, defined bytheir unique R group
    • The 20 amino acids can be grouped based on:• How they interact with water (hydrophilic vs. hydrophobic)• Whether they are basic or acidic
    • Properties of amino acids are very importantbecause they influence how a proteinfolds into its 3D shape
    • Protein shape determines protein functions
    • By stringing different amino acid monomers together in all kinds of unique ways and combinations to create unique protein polymer
    • The carboxyl group of one amino acid can react with the amino group of another to form a covalent bond called a peptide bond
    • When many amino acids are linked, the resulting polymer molecule is a polypeptide
    • Polypeptide is basically an immature protein
    • The unique sequence of amino acids that make up a polypeptide strand is called the primary structure of a protein
    • A protein’s primary structure determines its shape and thus its function
    • In other words, the primary structure determines:
      • How the protein “folds” into its 3D shape, then....
      • The 3D shape determines which parts of the protein can interact with other molecules or ions in the cell (...thus, determines its function)
    • A change of even one amino acid in the primary structure canmake an entirely different protein
    • The primary polypeptide strand is progressively folded into its final 3D shape in 2-3 “steps,” or “structural levels”
    • A protein’s primary structure is its unique sequence of amino acids that form the linear polypeptide strand
    • Folding the primary structure gives us an intermediate shapecalled the secondary structure
    • A protein’s secondary structure is stabilized (supported) byH-bonding along the polypeptide backbone
    • B/c the peptide backbone is flexible and lined with δ+ and δ- charges, it can twist and bend around itself to allow parts of the peptide backbone to form hydrogen bonds with each other
    • There are 2 common types of secondary structures aprimary polypeptide will fold into
      1. ALpha Helices
      2. Beta Sheets
    • Alpha Helix
      • The carbonyl (C=O) group of each amino acid in the backbone forms a hydrogen bond with the amide group (N-H) of the amino acid 4 residues away
    • Beta Sheet
      • Instead of twisting into a helix, polypeptide bends over,creating parallel, adjacent strands. Hydrogen bonds formbetween carbonyl groups along one length of the strandand the amide groups along the adjacent strand (it’s stillall one polypeptide)
    • Secondary structure results from hydrogen bonding along the backbone (between the carboxyl group of one amino acid and the amide group of another) to form alpha helices and/or beta sheets
    • A polypeptide’s tertiary structure is its final folded 3D shape
    • The tertiary structure of a polypeptide is made up of several secondary structure elements (often a combination of alpha helices and beta sheets)
    • Whereas secondary structures are formed by hydrogen bonding along the polypeptide backbone...A polypeptide’s tertiary structure results from interactionsbetween side groups (R)
    • tertiary structure is mostly determined by:
      • Interactions between R groups and the surrounding water
      • Interactions between different R groups within the polypeptide
    • R groups have different chemical properties so:
      • They can be hydrophilic or hydrophobic
      • They can be polar or nonpolar
      • They can be basic or acidic
    • The R-group interactions that determine the complex, 3D shape of a polypeptide’s tertiary structure can be both short- and long-range
    • Hydrophobic interactions play a HUGE contributing role in the folding and shaping of a protein
    • Hydrophilic R groups seek contact with their aqueous environment
    • Hydrophobic R groups will seek to avoid water and thus position themselves towards center of protein (away from aqueous environment)
    • Hydrogen bonding (and other intermolecular forces, such as van der Waal forces interactions) help to stabilize protein structure
    • H-bonding in polypeptide chain and between amino acid R groups hold the protein in the shape established by hydrophobic interactions
    • van der Waals forces are interactions between attractive and repulsive forces that occur between R groups that become polarized
    • Due to protein folding, ionic bonding can occur between thepositively and negatively charged "R" groups that come in close contact with one another
    • Folding can also result in covalent bonding between the "R" groups of cysteine amino acids, forming a disulfide bridge
    • Protein folding usually happens spontaneously(to some extent)