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Explain why the steroid hormone estradiol readily crosses membranes by simple diffusion but the much smaller H+ requires transport proteins.

BONUS: Refer to the following paragraph and accompanying figure to answer the following question(s). Since structure correlates well with function, look for new ways to probe the complex structure of proteins in order to understand what they do and how they do it. One of the most powerful techniques in existence today is X-ray crystallography. The main difficulty with this technique is getting the protein to crystallize. Once crystallized, the protein is bombarded with X-rays to create a pattern that can be analyzed mathematically to determine the protein’s three-dimensional structure. This analysis has been performed by Palczewski (2000) on the protein rhodopsin, which is a light-sensitive protein found in species ranging from ancient bacteria (archaea) to humans. The structure (schematically shown above, where each letter represents an amino acid) is characterized by a single polypeptide chain with several α-helical segments that loop back and forth across the cell membrane. Another notable feature is the disulfide bond (—S—S—) that can be seen at the bottom of the third transmembrane segment. [Figure adapted from K. Palczewski et al., Science 289 (2000): 739.]   Which term best describes the type of membrane protein in the figure? (1 point)  [1] Which of the protein regions (the regions are labeled in the figure with a letter and number)  is likely the ligand binding site for the protein? There are 3 possible answers (4 points)? [2] What is a possible function of this protein (4 points)? [3]

Suppose you have two glucose solutions separated by a selectively permeable membrane. If there is a concentration gradient of glucose across the membrane, then the solutions cannot be ________ relative to each other.

Osmosis moves water from a region of

The process in which white blood cells engulf bacteria is termed

Imagine that you fill a shallow tray with water and place a drop of red ink in one end of the tray and a drop of green ink in the other end. Which of the following is TRUE at equilibrium?

The gases O2 and CO2 enter or leave a plant cell by

You are camping and decide you will sample some wild berries. You soon start to feel ill and realize these berries have a toxic substance in them. On your way to the hospital which organelle is detoxifying the toxin?

It is sometimes jokingly said that you could study for your biology test by placing your textbook under your pillow at night and thereby learn by osmosis as the knowledge would flow from the book to your brain while you slept. Aside from the obvious absurdity of this claim, what is wrong with the use of the word “osmosis” in this context? How might you lose knowledge (if knowledge could actually flow along a concentration gradient between a book and a brain) if you tried this technique?

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