2. Biological molecules
A section of Biology, 9700
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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 α-keratin, which consists of many α-helices, and β-keratin, consisting of many β-pleated sheets. Keratin can be classified as α-keratin or β-keratin based on a study of protein structure. Suggest the level of protein structure used to classify a protein as α-keratin or β-keratin. Protease enzymes hydrolyse proteins. Many proteases are able to hydrolyse more than one type of protein. Suggest why it is possible for a protease to act on different types of protein. 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. To degrade feather waste from industry, it is an advantage to use keratinases that show at least 60% relative activity in conditions where temperature and pH can vary widely. Table 2.1 shows, for each keratinase, the working range of temperature and pH where at least 60% relative activity is obtained. Use and to complete Table 2.1 and use the completed table to: • name the keratinase that has the widest working range of temperature • name the keratinase that has the widest working range of pH. Table 2.1 keratinase temperature range with at least 60% relative activity / °C pH range with at least 60% relative activity K12 41–63 A22 6.0–9.0 P3 29–56 5.3–7.5 Keratinase with a relative activity of at least 60% that has: • the widest working range of temperature • the widest working range of pH Some detergents contain proteases to remove stains from clothes. These enzymes have a high relative activity in alkaline conditions. The scientists reported that K12 and A22 could be suitable for use in the detergent industry. With reference to and , discuss the advantages and disadvantages of using K12 and A22 in the detergent industry.
9700_w23_qp_22
THEORY
2023
Paper 2, Variant 2
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A student wrote four statements about water. Water has a high specific heat capacity which maintains the temperature of water within cells. Mammals rely on water having a relatively low latent heat of vaporisation to keep them cool. When a negatively charged ion is added to water, the  charge on the hydrogen atom is attracted to the ion. When surrounded by water, non-polar molecules tend to be pushed apart from one another. Which statements are correct?
9700_s22_qp_12
MCQ
2022
Paper 1, Variant 2
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748