Module 1 - Proteins Flashcards
What is a protein?
Proteins are a diverse group of large and complex polymer molecules made up of a long chain of amino acids.
They have a wide range of biological roles including:
Structural = main components of body tissue Catalytic = all enzymes are proteins that catalyse many chemical reactions Signalling = many hormones and receptors are proteins Immunological = all antibodies are proteins. Help with immunity
What is the ‘R’ group?
Represents a side chain from the centre of the alpha carbon atom, and can be anything from a simple hydrogen to a complex ring sturcture.
What are polypeptides?
long chains of amino acids
What is the bond formed between two amino acids?
Peptide bond
What is the reaction that forms peptides bonds?
Condensation reaction
Describe the reaction between 2 amino acids
Condensation reaction between 2 amino acids forming one peptide bond. The reaction site takes place at the carboxylic and the amine group (specifically the reaction between the hydroxyl in the carboxylic group and hydrogen in the amine group).
What forms from the condensation of 2 amino acids
Dipeptides
Describe the primary structure of proteins
The sequence of amino acids in a polypeptide chain form the primary structure of any protein. Many of the 20 amino acids in a polypeptide chain joined in different sequences, limitless combos and so limitless primary protein structures. Determines shape and function.
Describe the secondary structure of proteins
Linked amino acids in a polypeptide bond possess -NH and -C=0 group. H of -NH is positive charge, O of -C=O is negative charge. Form weak bonds, called hydrogen bonds. Causes the long polypeptide to be twisted into a 3D shape (a-helix)
Describe the tertiary structure of proteins
The a-helixes of the secondary structure can be twisted even more to form an even more complex structure, 3D shape of a protein. Structure maintained by number of different bonds.
The role of hydrogen bonds - teritary sturcture
Makes each protein distinctive and allows it to recognise and to be recognised by other molecules.
The role of Ionic bonds - tertiary structure
Formed between carboxyl and amino acid groups that are not involved in forming peptide bonds. Weaker than disulfide bonds and easily broke by change in pH
The role of disulfide bonds - tertiary structure
Fairly strong and so are not easily broken
Quaternary structure of a protein
Large proteins form complex molecules containing a number of individual polypeptide chains linked in many ways. Non-protein groups associated with the molecules called prosthetic groups
What is the name of the test for proteins? What does it detect?
Biuret test. Detects peptide bonds
Describe the biuret test in proteins
Place a sample of solution into a test tube and add an equal volume of sodium hydroxide solution at room temp. Add a few drops of very dilute copper sulfate solution and mix gently. Purple colour indicates presence of peptide bonds. If no protein present, colour remains blue
What causes the changes in protein structure through the three or four levels of structure?
The primary chains form a-helix and b-pleated sheets which fold onto each other forming the tertiary structure.
How does a chaperone work with proteins?
Chaperones assists proteins in folding
What are 2 characteristics of globular proteins?
Spherical proteins that are soluble in water
How are globular proteins soluble in water?
Globular proteins have hydrophilic amino acids on their surface. This means that hydrophilic ‘R’ group of the amino acid can interact with water. Hydrophobic amino acids in centre of amino acids.
Give 3 characteristics of fibrous proteins
They play a structural role, long-rope like molecules and insoluble in water
Why are fibrous proteins insoluble in water?
High proportion of amino acids with hydrophobic R groups meaning it repels water and so they are insoluble in water
Describe collagen
Strong as polypeptide chains wrap tightly forming triple helix. Large number of hydrogen bonds between polypeptide chains which stabilises quaternary structure forming microfibrils and fibrils.
Describe Keratin
Strong and insoluble that are long strained molecules. High amount of amino acid cysteine used to form large number of disulfide bonds.
Describe Elastin
Elastic and can stretch. Long strands containing hydrophobic regions. The strands are crosslinked with each other.
