3. Enzymes
A section of Biology, 9700
Listing 10 of 276 questions
Arachidonic acid is a fatty acid that is a common component of phospholipids. Phospholipids can be used as a source of arachidonic acid when it is metabolised within cells in an enzyme-catalysed pathway known as the cyclooxygenase (COpathway. The final products of the COX pathway can be different in different cell types, causing a range of responses. In some cells, the products are involved in the inflammatory response, which is a response by the body to infection. In other cells, cell division is stimulated. shows the first reaction in the COX pathway. This reaction is catalysed by an enzyme known as COX-2. COX-2 arachidonic acid + oxygen prostaglandin-H2 The enzymes involved in the COX pathway are located in the membrane of rough endoplasmic reticulum. Suggest the advantages to the cell of enzyme pathways being located in cell membranes, rather than in the cytosol of the cell (fluid portion of cytoplasm). During an inflammatory response, compounds produced by the COX pathway cause an increased sensitivity to pain. Some anti-inflammatory drugs are reversible competitive inhibitors of COX-2. shows how increasing arachidonic acid concentration affects COX-2 activity. Vmax ½ Vmax Km rate of reaction / arbitrary units arachidonic acid concentration / arbitrary units Sketch on the curve obtained if an anti-inflammatory drug, which is a competitive inhibitor, is present with arachidonic acid. Complete the statements to show whether the maximum rate of reaction (Vmaand the Michaelis-Menten constant (Km) of COX-2 increases, decreases, or stays the same in the presence of a competitive inhibitor. In the presence of a competitive inhibitor: Vmax of COX-2 Km of COX-2 . COX-2 is composed of two identical polypeptides. The enzyme is produced when a gene, PTGS2, located on chromosome 1, is switched on and transcription begins. Using gene PTGS2 and enzyme COX-2 as examples, explain what is meant by a gene. Some mutations in PTGS2 lead to an increased rate of transcription. These mutations have been linked to an increased risk of certain types of cancer. Suggest why mutations in PTGS2 may increase the risk of cancer. shows the molecular structure of arachidonic acid. Not all hydrogen atoms are shown. C C C C C C C C C C H H H C C C C C C C C O H O C H H H H H C H H H With reference to , explain why increasing the proportion of phospholipids with arachidonic acid in a cell will increase the fluidity of the cell surface membrane of the cell.
9700_s22_qp_23
THEORY
2022
Paper 2, Variant 3
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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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Questions Discovered
276