Proteins

• Polypeptides are chains of amino acids linked together by peptide bonds between the carboxyl group of one amino acid and the amino group of another.
• Amino acids are simple organic compounds that combine to form proteins.
• Protein synthesis is the process by which cells make proteins, involving transcription and translation.
• The primary structure of a protein refers to its sequence of amino acids.
• Secondary structures refer to localized patterns formed within polypeptide chains due to hydrogen bonding between different parts of the chain.
• Secondary structures refer to the folding patterns formed within polypeptide chains due to hydrogen bonding between different parts of the chain.
• Tertiary structures involve interactions between different parts of the same polypeptide chain.
• Tertiary structures involve the three-dimensional arrangement of secondary structures into complex shapes.
• Quaternary structures describe how multiple polypeptides come together to form functional units called quaternary structures.
• PROTEINS:

  • Monomer: amino acids
  • Covalent bond: peptide
  • Polymer made: protein
  • Polymer examples: haemoglobin, enzymes, antibodies
• Proteins are biological macromolecules consisting of one or more polypeptide chains formed from amino acids linked through peptide bonds. They have diverse functions such as catalysis (enzymes), transport (haemoglobin), storage (myoglobin), movement (actin/myosin filaments), communication (neurotransmitters), defense (antibodies), and structural support (collagen).
• The enzyme endopeptidase hydrolyses bonds within the polypeptide chain.
• A peptide bond is formed by a condensation reaction between an amine group and a carboxyl group.
• Amino acids are the basic monomer units which combine to make up a polypeptide polymer.
• The amine group is the basic functional group from which the amino part of an amino acid is derived (-NH₂).
• The carboxyl functional group is the an acidic group from which the acid part of an amino acid is derived (-COOH).
• A disulphide bridge is a covalent bond between two sulfur atoms (e.g. in cysteine).
• A hydrogen bond is a chemical bond between the positive charge on a hydrogen atom and the negative charge on another atom.
• An ionic bond is the chemical bond formed between any carboxyl and amino groups.
• A peptide bond is the chemical bond formed between amino acids in a condensation reaction.
• A polypeptide is a polymer formed from amino acids joined together with peptide bonds.
• The primary protein structure is the sequence of amino acids that makes up the polypeptides of a protein.
• A protein is a macromolecule formed from many polypeptides.
• The quaternary protein structure is a number of polypeptide chains linked together and sometimes associated with non-protein groups (e.g. the iron-containing haem group in haemoglobin).
• A variable R-group is a side chain consisting of a variety of different chemical groups.
• The secondary protein structure is the way in which the polypeptide's chain of amino acids is folded, into either an α-helix or β-pleated sheet.
• The tertiary protein structure is the folded of a whole polypeptide chain in a precise and 3-dimensional way.
• There are about 20 different amino acids, where each amino acid has the same amine group (NH₂) and carboxylic acid group (COOH) but a different variable (R) group that can make them neutral, acidic, alkaline, aromatic or sulfur-containing.
• The primary structure of a protein is determined by the gene that codes for the polypeptide(s) and influences all following structural properties.
• The secondary structure of a protein is the basic shape that the chain of amino acids takes on as a result of common and predictable hydrogen bonding.
• The shape of a protein's tertiary structure is held together by hydrogen and ionic bonds between R-groups. The protein may be reinforced by strong covalent bonds called disulphide bridges which form between two amino acids with sulphur-containing side chains.
• The quaternary structure is present if a protein is made up of several polypeptide chains.
• Fibrous proteins are generally long, straight chains of amino acids that do not show a tertiary structure and as a result are insoluble. They have structural roles in cells, such as spindle fibres used in cell division and myosin fibres in muscle fibres.
• Globular proteins are generally rounded, soluble and show a 3D structure as a result of their tertiary and quaternary structures. They have numerous roles including as antibodies, enzymes, hormones and receptors.
• Amino acids contain:

  • a central α-carbon
  • a carboxyl group (COOH)
  • an amine group (NH₂)
  • a variable side chain (R)
  • a hydrogen

  
• When two amino acids join together in a condensation reaction a dipeptide and a water molecule are formed.
• Side chains containing hydroxyl groups (-OH) are hydrophilic.
• The greater the number and variety of amino acids, and hence side chains, the greater the scope for folding, so the protein adopts a compact form and is called globular.

  Those that cannot fold remain long and fibrous. These are the tertiary structures.
• Side chains may bond with those on adjacent polypeptides to form a cluster of polypeptides. This is the quaternary structure.
• The amine and carboxyl groups can also be referred to as the N-terminal and C-terminal of a polypeptide.