Download Answer Key to Problem Set 2

The Saylor Foundation’s “Answer Key to Problem Set 2”
1.
What is the chemical structure of caffeine?
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2.
What is the structure of a typical cell membrane? What are the major
components?
A typical cell membrane is composed of two phospholipid layers (known as a
bilayer) that have a non-polar hydrophobic “tail” and a polar hydrophilic “head.”
The heads are oriented towards the extracellular and intracellular (cytosolic)
regions. There are protein pores and channels within the membrane allowing
substances (e.g. amino acids, proteins, carbohydrates) to move through the
membrane.
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License. It is attributed to Jerome Walker and the original version can be found here.
3.
What is the primary role of a membrane?
The primary function of the membrane is to regulate what moves into and out of
the cell.
The Saylor Foundation 1
4.
Based on caffeine's structure, does it readily move across brain cell membranes?
Would this movement require the cells to invest energy to transport caffeine
inside?
Caffeine will not move across the cell membrane passively (diffusion).
Therefore, it will require energy to move caffeine through the membrane into the
cell.
5.
What properties of caffeine, the membrane, and membrane components either
allow caffeine to move easily across or hinder its movement across the
membrane?
Caffeine is a large polar molecule and will not readily diffuse across the non-polar
lipids of the cell membrane.
6.
Are there components of brain cells with which caffeine interacts?
Yes, caffeine interacts with adenosine receptors within the brain.
7.
Is caffeine normally produced by the brain or is it a foreign substance that
interferes with normal cellular/molecular processes?
No, caffeine is not produced by the brain and does affect normal cellular
processes. Caffeine is a chemical produced by plants (e.g. coffee, tea, cacao
beans, etc.) and acts as a natural pesticide within the plants.
8.
How does caffeine keep people awake?
When a person is under stress, they accumulate the nucleoside “adenosine” in
the brain. When adenosine binds to receptors in the brain, it triggers a
transduction pathway that eventually causes reduced brain activity that may lead
to drowsiness (to counter the effects of the stress). However, caffeine has a
structure similar to adenosine and can bind to the same receptors in the brain but
does not activate the receptor. Therefore, caffeine does the opposite of what
adenosine does, causing alertness instead of drowsiness.
9.
Sam has never had a biology class. How could you explain this to him in a way
that he might understand?
Sam, moderate levels of caffeine (100mg) are perfectly safe. However, larger
doses such that you are getting throughout the day could lead to adverse effects.
You could become tolerant to the effects of the caffeine, which may cause you to
consume more. High doses of caffeine can cause an increase in heart rate,
increased blood pressure, insomnia, and nervousness. Withdraw from high
doses of caffeine can lead to health problems, such as a blood pressure drop
and headaches.
The Saylor Foundation 2