Daily Newsletter, February 6, 2012
Administrative Notes: Milestone Exam 1
Tonight at 5pm, you will be able to start your first milestone exam. The exam link will be located on the uLearn course home page. The exam will end on Tuesday at 5pm. You will have 50 minutes for the exam, and only one attempt. I strongly encourage all students to take the exam tonight. If there is a technical difficulty, please contact me ASAP at rmaxwell@gsu.edu.
Do not wait until the last minute! If you wait, I may not be able to help you if there is a technical problem. Remember, the exam is only open for 24 hours and will not reopen. There are no make-ups.
Today's Topic: The basics of cell communication
This week marks our discussion of cell to cell communication. The first thing which must be remembered is that cells must be able to sense their environment, other cells, and process information from other cells. Signal reception occurs in all known organisms (from picking up environmental to cellular signals). For instance, in bacteria, we know of a signal phenomena known as Quorum Sensing. With this signal system, bacteria release chemicals as they grow which other individuals of the same species (and some times other species) pick up; when the concentration of the chemical reaches a critical point, cellular changes can be observed in the community. Basically, as the population increases, cells begin to change (we will talk about this more later in the week).
But how do cells pick up signals? Signal recognition begins with protein receptors. For a cell to pick up, or register, a signal, it must build a receptor for that signal. This sets up another question: what is a signal?
Most of the signals we will talk about are chemical signals, meaning we have a chemical compound that will "fit" a receptor, activating it. There are other signals though: light can be a signal (photoreception), temperature (thermoreception), and even mechanical such as touch (mechanoreception). As mentioned, out discussions for this week will focus on chemical signal pathways.
By far, the most common type of signal system will involve chemicals. Hormones are chemical signals, neurotransmitters are chemical signals, even carbon dioxide is used as chemical signal in the human body. Because there are so many different chemical signals, we have a generic word for any compound that could bind and activate a receptor protein: Ligand. As a general word, ligand is used when we discuss the basic concepts of signal systems.
At their most basic, a chemical signal system (or pathway) will be comprised of a Ligand and a Receptor. When a ligand binds to a receptor (ligand-receptor complex), the receptor changes shape (conformation), which elicits a physiological response in the cell. Remember: The receptor is a protein, and when proteins change shape, they have an effect on the cell. So the basic signal system will be: Ligand binds to receptor, receptor changes shape, cellular response occurs.
Words of the Day: Paracrine & Autocrine
Prepare definitions for these two words and put them in your notes.
Daily Challenge: A Model Signal Transduction Pathway
Review the model signal transduction pathway of the ompC gene in Escherichia coli as discussed in the Sadava textbook. Write a general description of how the signal/receptor complex alters cell physiology. Describe the nature of the ligand and the receptor.
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