Identify the section of a phospholipid molecule, labelled A in Fig. 1.1, that forms bonds with the phosphate heads and the fatty acid tails.
Using the information in Fig. 1.2, explain how cholesterol molecules are positioned in the phospholipid bilayer shown in Fig. 1.1.
State one function of cholesterol in phospholipid bilayers.
Explain why sodium ions are unable to cross phospholipid bilayers by simple diffusion.
Ions and some molecules cross cell surface membranes by facilitated diffusion and active transport. Compare facilitated diffusion and active transport by giving one similarity and two differences between facilitated diffusion and active transport.
Suggest one advantage of this reaction pathway taking place in the smooth endoplasmic reticulum of a cell rather than in the cytoplasm.
Compare facilitated diffusion and active transport by giving one similarity and two differences between facilitated diffusion and active transport.
Prostaglandins are small lipids made in many tissues of the body. One role of prostaglandins is to trigger inflammation at the site of an injury or infection. Inflammation is the normal first response of the immune system to injury or infection. Cyclooxygenase (COX) is an enzyme that catalyses one stage in the reaction pathway for the formation of prostaglandins from phospholipids. This reaction pathway takes place in the smooth endoplasmic reticulum (SER) of cells. A section of the reaction pathway is shown in Fig. 1.3.
Aspirin lowers the catalytic activity of the COX enzyme by altering the R-group of one of the amino acids. Suggest how changing the R-group of an amino acid in the COX enzyme can lower the catalytic activity of the enzyme.
Prostaglandins are examples of cell-signalling molecules. Outline the signalling process that leads to a response in the cells involved in inflammation.