3.2. Factors that affect enzyme action
A subsection of Biology, 9700, through 3. Enzymes
Listing 10 of 202 questions
Liver cells contain membrane-bound organelles called peroxisomes, which contain the enzyme catalase. This enzyme hydrolyses hydrogen peroxide into water and oxygen gas. A student cut two identical sized pieces of liver and placed one in a refrigerator at 5 °C and the other in a freezer at –18 °C. After 12 hours both pieces were raised to room temperature and placed in equal volumes of hydrogen peroxide. The liver that had been at –18°C produced bubbles of oxygen more rapidly than the liver that had been at 5 °C. Which statement explains why the liver that had been at –18 °C produced bubbles of oxygen more rapidly than the liver that had been at 5 °C?
9700_w17_qp_13
MCQ
2017
Paper 1, Variant 3
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Hydrolytic enzymes can function within the cell or can be secreted by the cell, where they are able to catalyse reactions. State the term used to describe an enzyme that functions within the cell. The rates of reaction of two different hydrolytic enzymes, enzyme G and enzyme H, were measured at different substrate concentrations. The results are shown in . The two enzymes have different values of the Michaelis–Menten constant (Km). substrate concentration / mmol dm–3 0.2 0.4 0.6 0.8 1.0 rate of reaction / arbitrary units enzyme H enzyme G The Km value of enzyme G is 5 mmol dm–3. Use to derive the Km value for enzyme H. Show your working. With reference to , explain how the values of Km for these enzymes provide information about the relationship between the enzyme and their substrates. Cells can break down an old or damaged organelle, such as a mitochondrion, by enclosing the organelle in a membrane formed from the endoplasmic reticulum. This forms a vacuole. Vesicles containing hydrolytic enzymes fuse with the vacuole and the organelle is then digested. Name the vesicles in the cell that contain hydrolytic enzymes. The cell has internal chemical messengers that signal when an old or damaged mitochondrion should be broken down. Suggest one feature involving mitochondrial structure or function that could lead to the release of these internal signals. Question 3 continues on page 8 Glucocerebrosidase is an enzyme synthesised by macrophages to hydrolyse glucocerebroside, a glycolipid found in cell membranes. The GBA gene codes for glucocerebrosidase. There are a number of different mutations of the GBA gene. Some mutations result in a single amino acid change in the enzyme molecule produced, and this causes a disorder known as Gaucher’s disease. Two of these mutations, at different positions in the GBA gene, are shown in Table 3.1. Table 3.1 amino acid change caused by mutation severity of Gaucher’s disease from to mutation 1 asparagine (Asn) serine (Ser) mild mutation 2 leucine (Leu) proline (Pro) severe With reference to Table 3.1, • outline how a mutation leads to a single amino acid change in the enzyme glucocerebrosidase and • suggest why the two different amino acid changes, Asn to Ser and Leu to Pro, will result in differences in the tertiary structure of the enzyme.
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THEORY
2017
Paper 2, Variant 2
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Questions Discovered
202