BI SC 002 LECTURE 3—DNA AND MUTATIONS
Draft: October 27, 2010
So, what really IS a gene?
We gave a functional definition of gene in the last lecture, but,
structurally (and chemically) a gene is really a section of DNA that codes for a functional
Proteins are molecules in a living thing that “do stuff”—in other words, just about any
activity that takes place in a living thing, whether it’s allowing chemical reactions to occur,
defense, structure, transport, you name it, a protein does it.
It’s the structure of proteins that lead
to their function, and it’s the function of proteins that basically make every living thing what they
In other words, the proteins lead (either directly or indirectly) to the traits of an organism.
gene can be thought of as a recipe for a protein.
A DNA molecule looks something like this:
The DNA molecule looks sort of like a ladder twisted around on itself (almost like a spiral
The shape of a DNA molecule is called a
, that is, there are two strands
of DNA, and both twisted in a corkscrew manner.
The poles of the DNA ladder are made up of
repeating units of sugars and phosphate groups (called the backbone).
The rungs of the ladder
are made up of chemicals called
There are 4 nitrogenous bases—adenine
(A), guanine (G), cytosine (C), and thymine (T).
In any situation, if, in one strand of the DNA
there is an A, there will always be a T opposite it in the other strand.
If in one strand there is a C,