TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > Proteins
Explain the Four levels of structure of proteins and their significance
- Primary
- Nature
- Linear sequence of amino acids with peptide linkages
- Significance
- Changes in sequence may have overall effect on structure and activity
- Almost infinite number of sequences
- Secondary
- Nature
- The formation of the alpha-helix and beta-pleated sheets, held together by hydrogen bonds.
- Significance
- Tertiary
- Nature
- a complex structure, usually globular, resulting from further folding of the secondary structure of protein
- forms spontaneously due to attractions and repulsions among amino acids with different charges on their R groups
- Active sites possible,added strength due to Ionic bonds, disulphide linkages, and possibly prosthetic groups and coenzymes.
- Quaternary
- the overall structure of a globular protein molecule that consists of two or more polypeptide chains.
- Most large, non-structural proteins have more than one polypeptide and this leads to a greater range of biological activity.
Outline the difference between Fibrous and Globular proteins
Outline the difference between Fibrous and Globular proteins, with reference to two examples of each type
|
| Fibrous Proteins
| Globular Proteins
|
| Sequences of amino acids
| Regular
| Irregular
|
| Polypeptide Chains
| Long Parallel Strands
| Folded Into Spherical Shape
|
| Length of Chain
| Varies
| Identical
|
| Structure
| Stable
| Instable
|
| Solubility
| Insoluble
| Soluble
|
| Function
| Structural
| Metabolic
|
| Examples
| Collagen and keratin
| Enzymes and hormones insulin and haemoglobin
|
Explain the significance of Polar / Non Polar Amino Acids
- There are only 20 different amino acids, and the only differences between them lie in their side (-R) groups.
- The side groups in seven of the amino acids have Polar Regions; in acid or basic solution, these regions can become charged.
- In eight of the molecules, the side group consists of short chains or rings of carbon and hydrogen atoms as you would expect, such groups are non-polar and thus hydrophobic.
- The remaining five amino acids have side groups that are either weak acids or weak bases.
State Six functions of Proteins, giving an example of each
- Enzymes - pepsin
- Cell transport - membrane proteins
- Structural - collagen
- Hormones -insulin
- Immunoglobulins - antibodies
- Transport - haemoglobin
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