Proteins Flashcards
What do amino acids consist of?
A hydrogen atom, an amino group, a carboxyl group and a variable R group
What is the monomer for polypeptides?
Amino acids
How do amino acids join?
Condensation reaction between carboxyl group (-COOH) and amino group (-NH) with removal of one water molecule, forming a peptide bond
What is the bond between amino acids?
Peptide bonds
How is a protein’s function determined?
It is determined by its conformation, which is dictated by its amino acid sequence
What are the 4 levels of organisation in proteins?
Primary, Secondary, Tertiary and Quaternary structures
What does primary structure refer to?
It refers to the unique and specific number, sequence and types of amino acids maintained by peptide bonds in a specific polypepetide
What does secondary structure refer to?
It refers to the regular coiling or pleating of a single polypeptide chain. The structure is usually maintained by hydrogen groups between CO and NH groups of polypeptide backbone
What are the 2 examples of secondary structures?
α-helix and β-pleated sheet
What is the structure of α-helix secondary structure?
It is made up of a single polypeptide chain wound into a coiled/spiral structure with each turn linked by hydrogen bonds between CO and NH groups. There are 3.6 amino acid residues in every turn of the α-helix.
What is the structure of a β-pleated sheet secondary structure?
It is formed by 2 or more regions of a single polypeptide chain lying side by side linked together by hydrogen bonds, formed between CO and NH groups of adjacent regions. Chains may run parallel or anti-parallel
What does tertiary structure refer to?
it refers to the further extensive folding and bending of a single polypeptide chain, giving to specific conformation of a protein.
What bonds maintains the tertiary structure?
Hydrophobic interactions, hydrogen bonds, ionic bonds and disulfide bonds formed between R groups of amino acid residues
What does quaternary structure refer to?
It refers to the association between 2 or more polypeptide chains to form one functional protein molecule
What bonds can maintain the quaternary structure?
Hydrophobic interactions, hydrogen bonds, ionic bonds and disulfide bonds formed between R groups of amino acid residues on different polypeptide chains
What are the 2 kinds of proteins?
Fibrous and globular/spherical proteins
What is the quaternary structure of haemoglobin?
4 polypeptide subunits, 2 α-globin subunites and β-globin subunits. Each subunit consist of a polypeptide component called globin and a prosthetic component called haem group
How are the subunits of haemoglobin held together?
They are held together by ionic bonds, hydrogen bonds and hydrophobic interactions.
How does the bonds between subunits in haemoglobin help with its functions?
Ionic bonds, hydrogen bonds and hydrophobic interactions allow subunits to move with respect with each other allowing a change in position that influences its affinity with oxygen. Hence, binding of one oxygen molecule induces a conformation change in remaining subunits so that affinity to oxygen increases.
What is a collagen molecule?
It consists of 3 helical polypeptide chains wound around each other. It is said to have both a secondary and quaternary structure (no tertiary structure).
What is the structure of each helical polypeptide chain in collagen?
It has a loose helix secondary structure that is stabilised by hydrogen bonds. The sequence is usually glycine-X-Y.
What is the assembly of tropocollagen (molecule of collagen)?
- It can form a tight triple helix as almost every third amino acid is a glycine, the smallest amino acid, allowing it to fit into restricted space in triple helix
- Hydrogen bonds between adjacent polypeptide chains increases tensile strength and makes molecule insoluble
What is the assembly to form fibrils in collagen?
Tropocollagen molecules crosslinks with neighbouring molecules running parallel to it. Cross-linking of adjacent tropocollagen molecules results in formation of fibrils, greatly increasing tensile strength.
What is the assembly to form collagen fibre?
Many fibrils in turn assemble to form a fibre, increasing tensile strength of collagen
