Lesson 12 - Levels of protein structure

Question 1

The hierarchical nature of protein structure (and their structures)

Answer 1

Primary structure (Amino acid sequence)
↓
Secondary structure (hydrogen bonds hold the amino acid sequence in a secondary structure – α-helix or β pleated sheet)
↓
Tertiary structure (Secondary structure is twisted and folded into a complex, and often 3D, structure – held in place by disulphide bridges, ionic bonds and hydrogen bonds)
↓
Quaternary structure (Structure formed of more than 1 polypeptide chain and/or non-protein (prosthetic) groups)

Question 2

Primary structure

Answer 2

sequence of amino acids in the
polypeptide chain

Question 3

Type of bonding in primary proteins

Answer 3

Peptide bonds between each amino acid

Question 4

Secondary structure and bonding

Answer 4

Weak hydrogen bonds form between the slightly positive hydrogen in the N-H group of 1 amino acid and the slightly negative oxygen in the C=O group of another amino acid (due to their polarity).
● This pulls the polypeptide chain into either an:
- 𝝰 - helix coil - most common
- 𝝱 - pleated sheets

Question 5

Tertiary structure

Answer 5

● Further twisting and folding of the whole polypeptide chain to give the very specific 3D shape/structure
● Remember shape/structure = function! - It makes each protein unique

Question 6

Bonding in a tertiary protein

Answer 6

The tertiary structure is held together by a number of different bonds between the R-groups of amino acids:
- Disulfide bridges
- Ionic bonds
- Hydrogen bonds
- Hydrophobic interactions

Question 7

2 common shapes of a tertiary protein

Answer 7

• globular (more circular)
• fibrous (long)

Question 8

Quaternary structure

Answer 8

● Many proteins are often made up of more than one polypeptide chains that are linked together
● The association between different polypeptide chains is called the quaternary structure of proteins
● The different polypeptide chains are held together by the same 4 types of bonds as in the tertiary structure
● There may also be non-protein groups associated with the protein, called prosthetic groups

Question 9

Different types of proteins

Answer 9

● Proteins perform many different roles and their role depends on their shape
● Proteins can be divided into two groups based on structure/shape:
- Globular proteins - form spherical/ball shape, with a compact structure and carry out metabolic functions (e.g. enzymes and Haemoglobin)
- Fibrous proteins - form long chains/strands which run parallel to one another and are linked by cross-bridges (so very strong/stable). Fiber-like and have structural functions (e.g. Collagen)