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Brad F.
Scientist, PhD in Biochemistry
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Biochemistry
TutorMe
Question:

Which of the following are true? The binding of a hormone to a receptor must be: A. Specific, meaning it only binds molecules with specific chemical structures B. Saturable, meaning once the receptor sites are occupied, no more hormone will bind C. High affinity, corresponding to the biological potency of the hormone D. Elicit a biological response E. All the above

Brad F.
Answer:

All the above. If a binding interaction does not meet all these requirements it is likely due to a non-receptor binding protein or a non-specific binding.

Basic Chemistry
TutorMe
Question:

You need 2 l of a 150 mM NaCl solution in water. You have water and a 5 M stock solution of NaCl. How do you make the solution?

Brad F.
Answer:

The formula is M1 (Molarity of the dilution) X V1 (Volume of the dilution) = M2 (Molarity of the stock) X V2 (Volume of the stock). Be sure all the units are the same on both sides of the equation for M and V. M1 is 150 mM, the molarity of the solution you want after dilution. V2 is 2 l, the amount of the diluted solution you want. Using 2000 ml (there are 1000 ml in a l) will make the final number easier to work with. M2 is 5 M, the concentration of the stock solution. Convert this to 5000 mM to match the units for M1. V2 is unknown. This gives us 2000 X 150 = 5000 X unknown. Using algebra, unknown = (2000 X 150)/5000 = 60 ml (the units are the same as V1). To make your solution, add 60 ml of 5 M NaCl to a graduated cylinder, and add water to a total volume of 2 l (1940 ml water).

Biology
TutorMe
Question:

Why do leaves turn colors in the fall?

Brad F.
Answer:

Leaves contain chlorophyll (green), carotene (yellow) and anthocyanins (red). In the spring and summer, the level of chlorophyll is high, so leaves look green. in the fall, the levels of chlorophyll goes down, letting the other colors come out.

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