Download DNA Structure Cornell Notes

Imagine a combination lock with just the numbers 1-4 on it. In the space
below, write as many combinations of those 4 numbers as you can think of.
What 3 items form a
nucleotide?
1.
2.
3.
What is DNA?
Living things contain proteins. Your skin,
muscles and bones all contain protein. All the
actions you perform such as eating, funning and
thinking depend on proteins called enzymes.
But how is this related to DNA? Within DNA
is all the information for life. DNA contains all
the instructions to make all the different
proteins an organism needs.
DNA Structure
What are the 4 nitrogen
bases found in DNA?
1.
2.
3.
4.
Which bases are Purines?
Pyramidines?
DNA is made of nucleotides. In the 1920s,
biochemist P.A. Levene showed that each DNA
nucleotide contains the sugar deoxyribose (dee
ahk sih RI bos), phosphate group, and one of
four nitrogenous bases —adenine (A dun een),
guanine (GWAH neen), cytosine (SI tuh seen),
or thymine (THI meen). RNA also is made of
nucleotides. Each RNA nucleotide contains the
sugar ribose, a phosphate, and one of four
nitrogenous bases—adenine, guanine, cytosine,
and uracil (YOO ruh sihl). The figure on the
left shows the structure of a nucleotide.
Adenine (A) and guanine (G) are double-ringed
bases, which are called purine bases. Thymine
(T), cytosine (C), and
uracil (U) are
single-ringed
bases, which are called
pyrimidine
bases.
Chargaff’s Rule
Erwin Chargaff discovered that the amount of
guanine is almost equal to the amount of cytosine,
and the amount of adenine is almost equal to the
amount of thymine for the DNA of any given
species. This finding is known as Chargaff ’s rule:
According to Chargaff’s Rule if 42% of
an organisms genome (DNA) is Adenine,
than what percentage would be Thymine?
Guanine?
C = G and T = A.
Cytosine?
What does the DNA molecule look like?
In 1953, James Watson and Francis Crick published
a paper correctly describing the shape of a DNA
molecule for the first time. They said that DNA is
made of two strands of nucleotides held together
by the nitrogen bases, the parts that stick out like
zipper teeth. Adenine on one strand always joins
with thymine on the other strand. Likewise, guanine
always joins with cytosine. They also noted that
DNA is shaped like a long zipper that is twisted into
a coil like a spring. The two strand of twisted DNA
are referred to as a double helix.
How can DNA do so much with so little?
If every organisms is made up of the same four
nucleotides, how can organisms be so different
from one another? The key to variety in organisms
is the sequence , or order of the four nucleotides.
For Example, a nucleotide sequence of A-T-T-G-A-C
carries different information that the sequence
T-C-C-A-A-A. It is the sequence of nucleotides
that forms the unique genetic information for every
organism. You can think of it like this some words
have the same letters, but different meanings.
TEA for example is not the same as ATE or EAT.
The order of nucleotides in a DNA molecule therefore determines the enzymes produced (remember!
enzymes are proteins) which in turn control many of
the biochemical reactions in your body. So in a way
the sequence of nitrogen bases controls everything.
What do you call the twisted ladder
structure of a DNA molecule?
In DNA, what determines the traits
(characteristics) of an organism?