PROTEINS

• What is a protein?

  A protein consists of one or more polypeptides arranged as complex macromolecules with specific functions.
• What are peptides?

  Polymers consisting of short chains of two or more amino acids linked by peptide bonds.
• What are polypeptides?

  Polymers consisting of longer chains of amino acids linked by peptide bonds.
• What are amino acids?

  Organic compounds consisting of an amine, acidic carboxylic, and unique R functional group; the R group being what determines the amino acid.
• What is a functional group?

  A specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule.
• How many different amino acids can be found in cells?


  Twenty, some are non essential made from other amino acids, while some are essential made from food.
• What is the process of peptide synthesis (the chemical making of)?

  1. Amino acids join when the amine and carboxylic groups connected to the central carbs react; the R groups not being involved at this point.
  2. Hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group.
  3. A peptide bond is formed between the amino acids, with water being produced, forming a dipeptide compound.
• What catalyses polypeptide formation?

  Peptidyl transferase present in ribosomes.
• What happens when the R groups of amino acids join?

  They interact with each other, forming different types of bonds. These bonds lead to long amino acid chains (polypeptides) folding into complex protein structures, which form specific shapes vital for protein function.
• What is the primary structure of a protein?

  The sequence of amino acids, influencing how the polypeptide chain folds to give the final protein shape; contain peptide bonds.
• What is the secondary structure of a protein?


  The oxygen, hydrogen, and nitrogen atoms of the basic repeating structure interact and hydrogen bonds form within the amino acid chain, pulling it into a coil shape, an alpha helix. The polypeptide chains can also lie parallel to each other joined by hydrogen bonds, forming a sheet structure, a beta pleated sheet; forming weak peptide and hydrogen bonds.
• What is the tertiary structure of a protein?


  The coiling of protein sections in their secondary structure cause the R groups of amino acids to become closer, causing them to interact and fold; consisting of hydrophobic and philic interactions, hydrogen, ionic, and disulphate bridge bonds.
• What is the quaternary structure of a protein?


  This is the association of two or more proteins called sub-units, with the subs-unit interaction being the same as the tertiary structure. The subunits can be identical or not, enzymes usually have identical subunits, while hormones (insulin) have two different; containing hydrophobic and philic interactions, hydrogen, ionic, and disulphate bridge bonds.
• What are hydrophobic and hydrophilic bonds?


  Weak interactions between polar and non-polar R groups.
• Are hydrogen bonds strong or weak?


  Weak, consisting of electrostatic attractions between partially charged atoms rather than the transfer or sharing of electrons; these bonds are however strong in large numbers.
• What are electrostatic attractions?


  The force of attraction or repulsion between two charged particles.
• Where do ionic bonds form in proteins?


  They form between oppositely charged R groups.
• What are disulphate bridge bonds?


  Covalent bonds between R groups containing sulfur atoms.
• How do hydrophobic and hydrophilic interactions effect protein assembly?


  Proteins are assembled in aqueous environments, and so the way they are folded depends on whether the R groups are phobic or philic; with philic shielding phobic from water in the cytoplasm.
• How are peptides broken down?


  Peptides are formed by condensation reactions, linking amino acids to form peptide bond. The enzyme protease catalyses the reverse reaction, in which water is added and hydrolysis occurs; converting the peptide back into amine and carboxyl groups.
• What is a globular protein?


  A compact, water soluble, and spherical protein.
• How is a globular protein formed?


  Formed when proteins fold a way in their tertiary stage, which means the hydrophilic R groups are on the outside, making it soluble.
• Why is the solubility of a globular protein vital?


  This solubility is vital for the regulation of many processes; such as, chemical reactions, immunity, and muscle contraction. Eg. insulin, a hormone transported in the blood that must be soluble and fit into specific cell receptors on cell surface membranes in order to have their effect, with specific, complementary shapes.
• What are conjugated proteins?


  These are globular proteins that contain a non protein components, such as a prosthetic group.
• What are examples of these prosthetic groups on conjugated proteins?


  Lipids which bind with proteins to form lipoprotein, and carbohydrates that bind to form glycoprotein. Metal ions and vitamin molecules can also form prosthetics; such as haem groups, contain iron II ions (Fe2+).
• What is haemoglobin?


  An oxygen carrying pigment in red blood cells.
• What is the structure of haemoglobin?


  A quaternary structure consisting of four polypeptides, two alpha and two beta subunits. Each subunit contains a haem group, and the iron II ions present can combine with an oxygen molecule to allow oxygen transport.
• What is catalase enzyme?


  A quaternary protein containing four haem prosthetics, of which the iron II ions allow it to interact with hydrogen peroxide and speed up its breakdown.
• What is hydrogen peroxide?


  A common byproduct of metabolism but damaging to cell if accumulated.
• What are fibrous proteins?


  Proteins formed from long, insoluble molecule, due to a high proportion of amino acids with phobic R groups in their primary structure. They contain a limited range of amino acids with a repetitive sequence, forming an organised structure of strong, long molecules that aren’t folded.
• What are nucleic acids?


  Large polymers made from nucleotide monomers and present in the nuclei, consisting of two types; DNA and RNA.
• What are the roles of DNA and RNA?


  Roles in storage, transfer of genetic material, and synthesis of polypeptides.
• What is a nucleotide?


  It is a pentose monosaccharide (sugar), containing five carbon atoms, a phosphate group, a nitrogenous base.
• What is a phosphate group?


  An organic molecule that is acidic and negatively charged.
• What is a nitrogenous base?


  A complex organic molecule containing one or two carbon rings.
• How are polynucleotides formed from nucleotides?


  A condensation reaction that allows the phosphodiester and covalent bonds between the phosphate group of the pentose sugar of one nucleotide, and the hydroxyl group of the pentose sugar on another nucleotide to interact, forming a strong, long sugar phosphate backbone with a base to each sugar.
• What does deoxyribonucleic acid consist of (DNA)?


  It is a sugar with one fewer oxygen than ribose (hence its name deoxyribose), and the nucleotides in DNA have one of four bases, so there are four different DNA nucleotides.
• What are pyrimidines?


  Smaller, single carbon ring structure; consisting of thymine (T) or uracil (U), and cytosine (C).
• What is a purine?


  A larger, double carbon ring structure; consisting of adenine (A), and guanine (G).
• What is the double helix structure?


  Consists of two strands of polynucleotides coiled into a helix, held together by hydrogen bonds between bases; each has a phosphate group at one end and hydroxyl group at the other, with both strands running in different directions (anti parallel).