Tutor profile: Kristen M.
When performing size exclusion chromatography why do the larger products elute faster than the smaller ones? I would expect the larger ones to get 'stuck' in the resin and the smaller ones to flow faster.
Hi, student. Thank you for your question and I would be happy to work through this with you. At first thought, it does seem that the smaller products would elute faster than the larger ones, almost how protein or DNA electrophoresis works. However, size exclusion chromatography (SEC), uses a different mode of separation. Using this technique, a gel resin is typically packed into a column, washed with a buffer or water, the sample is loaded, and fractions are collected. One important feature of the resin is that they are composed of beads with pores (think of them as pumpkins with holes cut into them). The size and frequency of these holes are dependent on different resin types and the sizes of what types of products you are trying to separate. When the sample (a mixture of different sized products) is loaded onto the resin, the smaller sized products will 'fall' into the holes in the beads and remain stuck there for a period of time and buffer washes. However, since the larger products cannot fit into the holes, they will circumvent the beads and elute faster. If necessary, this process can be repeated multiple times or using a range of SEC resins to obtain your desired product at a certain level of purity. Hope that helps! Let me know if you are still unsure and we can work through it some more.
Why do plants grow poorly in green light? I would think that since they are green, they prefer that color to grow. (this was a common question I had in my plant biology class)
Hi, student. Thank you for your question and I would be happy to work through this with you. I know it may seem that plants prefer green light to grow, since the majority of plants in nature are green, but it is in fact the opposite. You may recall from an overview of plant versus animal cells is that plant cells are unique in that they contain an organelle called a chloroplast, the organelle responsible for photosynthesis. In some microscopic images these look like green circles or ovals floating around in the cell. Within the chloroplast there are pigments, kind of like a dye, called chlorophyll. The chlorophyll have a specific chemical composition where they REFLECT GREEN LIGHT and preferentially ABSORB RED AND BLUE LIGHT. Thus, when we look at plants using our eyes we see the green hue. Photosynthesis is the process of converting light, water and carbon dioxide into sugars for the plant for it to grow and develop properly. In fact, plants grow the best in red and blue light because of the chemical composition of the chloroplasts. Therefore, when placed in green light, the plants cannot utilize it as efficiently and the photosynthesis rate is declined, less sugar is made, and the plant grows poorly.
I am having difficulty understanding the difference between the equations (X^2)(X^4) and (X^2)^4. What is the difference and how do I calculate them correctly?
Hi, student. Thank you for your question and I would be happy to work through this with you. You are right in that the equations look similar, but we have to be careful and take our time in looking at the notation. In the first example, you have two independent values that are being multiplied, X^2 and X^4. Because they have the same root, X, the expression can be reduced by ADDING their exponent values. Thus, it would be written as X^6 For the second example, it would be tempting to simply add the exponents, but notice how X^2 is located inside the parentheses, with its entirety being raised to the power of 4. Because the X^2 is located inside the parentheses and is being modified by the exponent of 4, the exponent within the parentheses, 2, is also affected. Therefore, the exponent values are MULTIPLIED, resulting in reduced expression of X^8. Hope that helps! Let me know if you are still unsure and we can work through it some more.
needs and Kristen will reply soon.