25. Your friend works in a cell biology research lab. She is working she calls p125, because its molecular mass is 125 kiloDaltons. She knows that p125 is a transmembrane protein with three membrane-spanning domains. It has been previously reported that p125 interacts with three other proteins called p175, p80, and p50 (again, polyacrylamide gel). These four proteins in the cell. To determine how these proteins interact with the membrane, you perform a set of experiments in which you first lyse the cells and save some of your lysate, which you run in the input lane (labeled "I" in Figure Q25 below). The lysate is then subjected to a low-speed centrifugation so that you separate out the membrane fraction (which ends up in the pellet, "P") from the cytoplasm (which is in the supernatant, "S"). You then wash the pellet from the first extraction with a high-salt wash that does not disrupt the lipid bilayer, and save a little bit to run on the gel. After the high-salt wash, you centrifuge the pellet again. Your results are illustrated on the gel in Figure Q25. protein that on a on the basis of their apparent sizes on an SDS thought to exist as a protein complex 1st extraction after high-salt wash marker S P P 250 kD 150 kD 100 kD 75 kD 50 kD Figure Q25 (a) What types of bonds are most likely to be disrupted by a high salt wash? Explain your answer. I I 1 I | |

: Yeast cells adapt to cold environments by and the length of the phospholipid tails the number of saturated fatty acid tails in the plasma membrane. Increasing....... Decreasing b. Decreasing....... Increasing C. Decreasing ....... Decreasing d. Increasing ....... Increasing Bacterial cells adapt to high temperatures by the length and the amount of saturated fatty acid tails in the plasma membrane. Increasing ...... Decreasing b. Decreasing....... Increasing C. Decreasing....... Decreasing d. Increasing....... Increasing

1. The CFTR protein is a chloride channel in the cell membrane. Use your understanding of the biochemical properties/categories of amino acids and how they interact with membrane phospholipids to predict the distribution of charged/polar, and non-polar amino acids within the domains of CFTR listed below. Consider one category to include the charged amino acids and the polar amino acids and the other category to include the non-polar amino acids. For each domain, predict which category of amino acids is likely to be most abundant. Also, explain the rationale behind your prediction. Protein domain Prediction (Charged/Polar or Non-Polar amino acids?) Explanation for prediction TMD1 and TMD2 (transmembrane domains, parts 1-12)     ECLs and ICLs (extracellular and intracellular loops)         NBD1 and NBD2         R

The role of GTP hydrolysis in actin polymerization is similar to the role of ATP hydrolysis in tubulin polymerization: both serve to weaken the bonds in the polymer and thereby promote depolymerization. Is that true or false? why?