Keratin is the structural protein in feathers of birds. Keratin polypeptides are composed of a high proportion of cysteine amino acids, which have sulfur-containing $$$R$$$ groups. Keratin polypeptides form filaments. The two main types of keratin in feathers are $$$\alpha$$$-keratin, which consists of many $$$\alpha$$$-helices, and $$$\beta$$$-keratin, consisting of many $$$\beta$$$-pleated sheets. Proteases known as keratinases vary in the extent to which they can hydrolyse keratin. Feathers are not easily degraded (broken down) because keratin is a very stable protein. Suggest features of keratin structure that contribute to its stability. Keratinases are used to degrade the large quantities of waste feathers from chickens and turkeys that are processed in the food industry. The products of feather degradation can be used in animal feed. Scientists investigated whether three different keratinases, K12, A22 and P3, were suitable as industrial enzymes. These enzymes were extracted from three different soil bacteria. The effects of temperature and $$$\mathrm{pH}$$$ on the activity of each keratinase were investigated. The results are shown in Fig. 2.1 and Fig. 2.2.

Biology

IGCSE&ALevel

CAIE

Exam No：9700_w23_qp_22 Year：2023 Question No：2(c)

Answer:

Knowledge points:

2.3.1 describe and draw the general structure of an amino acid and the formation and breakage of a peptide bond

2.3.2 explain the meaning of the terms primary structure, secondary structure, tertiary structure and quaternary structure of proteins

2.3.3.1 hydrophobic interactions

2.3.3.2 hydrogen bonding

2.3.3.3 ionic bonding

2.3.3.4 covalent bonding, including disulfide bonds

2.3.4 state that globular proteins are generally soluble and have physiological roles and fibrous proteins are generally insoluble and have structural roles

2.3.5 describe the structure of a molecule of haemoglobin as an example of a globular protein, including the formation of its quaternary structure from two alpha (α) chains (α–globin), two beta (β) chains (β–globin) and a haem group

2.3.6 relate the structure of haemoglobin to its function, including the importance of iron in the haem group

2.3.7 describe the structure of a molecule of collagen as an example of a fibrous protein, and the arrangement of collagen molecules to form collagen fibres

2.3.8 relate the structures of collagen molecules and collagen fibres to their function

Answer:

Knowledge points:

Solution:

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