Week 3 Overview 1

Welcome to Week 3! Time to go seriously cellular and molecular. Most human cells are in the range of 5 to 20 micrometers across, so we have to use special technology to see what they look like. There are all sorts of amazing new microscopes; we’ll see the results they get this week, and then in Course 2

of this Program.We try to define life: Whatever it is, it can’t exist below -50C, where the water in cells turns into a glass, or above 140C, where DNA spontaneously falls apart. Along the way we’ll meet a greedy amoeba who bites off more than it can chew. When biologists became able to look at the anatomy of cells, they found they had their own internal structures, called organelles–little organs. The cell even has a skeleton (and since cyto- means cell, it’s called the cytoskeleton.) The cell’s membrane keeps the good stuff in and the bad stuff out, but we have channels and pumps in the membrane to get the right things where they need to be.

Add a nucleus and protein-making factories and we have a tiny space that’s crammed full of goodies! Proteins are long polymers made up of about 20 different building blocks called amino acids–here’s a protein now!–each of which has different chemical properties, so a typical protein with about 200 amino acids in its chain

can do a very specific job: Hemoglobin carries oxygen, myosin contracts muscles, and so on.

Enzymes are the spice of life (or I think I mean splice?): all sorts of chemical reactions go on in the body, which wouldn’t work in the absence of these excellent catalysts. Molecular biology–transcription, translation… is it impossible to understand? Not with the power of analogy! DNA is the precious book that the library won’t lend, but RNA is the photocopy they allow us to make. And proteins are the useful machines we build, reading our photocopied RNA instructions. And we begin to find out why scientists made such a fuss when it was found that DNA comes in the form of a double helix.