3: Structure of proteins Flashcards
What are proteins?
One or more polypeptides arranged as complex macromolecules. All proteins contain carbon, hydrogen, oxygen and nitrogen
What are amino acids?
Molecules that consist of an amine group, carboxyl group and R group (varies between amino acids, resulting in different amino acids). 20 different amino acids are commonly found in cells
What are peptides?
Polymers made up of amino acid molecules (monomers)
How are peptides synthesised?
Amino acids join when the amine and carboxylic acid groups connected to the central carbon atoms react (the hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group of another amino acid). A peptide bond is formed between the amino acids and water is produced (it is therefore a condensation reaction). The resulting compound is a dipeptide
What is formed when many amino acids are joined together by peptide bonds?
Polypeptide
What is the equation for retention value (Rf)
Rf = distance travelled by component/distance travelled by solvent
What is involved in the primary structure of a protein?
The sequence in which the amino acids are joined which influences how the polypeptide folds to give the protein’s final shape which in turn determines its function. Only bonds involved are peptide bonds
What is involved in the secondary structure of a protein?
Oxygen, hydrogen and nitrogen atoms of the basic structure of amino acids interact. Hydrogen bonds may form within the amino acid chain, pulling it into an alpha helix shape. Polypeptide chains lie parallel to one another joined by hydrogen bonds forming beta pleated sheets. Secondary structure is the result of hydrogen bonds
What is involved in the tertiary structure of a protein?
Folding of a protein into its final shape. The coiling/folding of proteins into their secondary structures brings R-groups of different amino acids closer together so they are close enough to interact and further folding of these sections occurs. The following interactions occur between R-groups:
- Hydrophobic and hydrophilic interactions: weak interactions between polar and non-polar R-groups
- Hydrogen bonds: weakest of bonds formed
- Ionic bonds: stronger than hydrogen bonds, form between oppositely charged R-groups
- Disulfide bridges: covalent and strongest of bonds, only form between R-groups that contain sulfur
What is involved in the quaternary structure of a protein?
Results from association of two or more individual proteins (subunits). Interactions between subunits are same as in the tertiary structure except they are between different protein molecules rather than within one molecule. Protein subunits can be identical or different
How are peptides broken down?
Water molecule is used to break the peptide bond in a hydrolysis reaction, reforming the amine and carboxylic acid groups. Proteases catalyse this reverse reaction
How do you test for proteins?
Biuret’s test:
1. Add sodium hydroxide to the sample to make the solution alkaline
2. Add a few drops of Biuret’s reagent (Copper (II) sulfate solution) to the sample
What is a positive result of the Biuret’s test for proteins?
Colour change from blue to lilac
