Types of Organisms, Cell Composition, excerpt 2 | MIT 7.01SC Fundamentals of Biology
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Types of Organisms, Cell Composition, excerpt 2 | MIT 7.01SC Fundamentals of Biology

September 18, 2019


PROFESSOR: So let’s begin with
trying to introduce you to biochemistry. So I’m going to be thinking
atoms and molecules for a little bit. Let’s begin by thinking about
the composition of a cell, so that’s the basic unit of life. It’s about 60% hydrogen, 20%
oxygen, 12% carbon, 5% nitrogen, and then there’s
a bunch of other stuff– phosphates, sulfur, magnesium,
manganese, et cetera. But that’s not very helpful
way of studying biology. It’s interesting and is relevant
in some contexts, but that’s the atomic composition. If we look instead at the
molecular composition of a cell, then things start
to get interesting. Cells are about somewhere in
the ballpark of 80% water. Water’s going to be
very important– I’m going to be talking
about that. But of the remainder, then about
50% is protein, about 15% are these molecules we call
nucleic acids, and that means DNA and RNA, which most of
you have probably heard of. We’ll be talking about those
in great detail. 15% are carbohydrate– and in fact, we will talk
about those today– and about 10% fall in the
category of molecules known as lipids, which we’ll be talking
about in another day or two. And then there’s a bunch of
other things– vitamins and other things that happen, but
you can sort of see the big classes of proteins that make
up most of a cell are proteins, nucleic acids,
carbohydrates, and lipids.

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