8.2 Structure of DNA TEKS 3F, 6A, 6B

8.2
Structure of DNA
TEKS 3F, 6A, 6B
8.2
Structure of DNA
TEKS 3F, 6A, 6B
The Big Ideas…Characteristics of Living Things
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Made of Cells
Reproduce (sexually or asexually)
Have DNA (genetic information)
Grow & Develop
Need/Use Energy (metabolism)
Respond to Environment
Maintain Homeostasis (constant internal environment)
Change Over Time (evolve)
Form Systems & Have Systems (related parts)
Structure & Function are Related
8.2
Structure of DNA
TEKS 3F, 6A, 6B
As you can see from the
model, the structure is
basically a long, …twisted
ladder type thing.
1953: The structure of the DNA molecule is first
described.
8.2
Structure of DNA
TEKS 3F, 6A, 6B
KEY CONCEPT
DNA structure is the same in all organisms.
8.2
Structure of DNA
TEKS 3F, 6A, 6B
The monomer for DNA is a nucleotide
• Each nucleotide has three parts.
– nitrogen-containing base
– deoxyribose sugar
– phosphate group
phosphate group
• The base is the only part of a
nucleotide that will change.
deoxyribose (sugar)
nitrogen-containing
base
8.2
Structure of DNA
TEKS 3F, 6A, 6B
• The nitrogen bases are the only difference in the four nucleotides.
8.2
Structure of DNA
TEKS 3F, 6A, 6B
• Those are the basic parts of DNA, but how did we figure out how it was put
together?
8.2
Structure of DNA
TEKS 3F, 6A, 6B
X-Ray Evidence
• In the early 1950’s a British scientist named Rosalind Franklin began to
study DNA.
• Rosalind wanted to see what she was studying, so she took pictures of
DNA with an X-ray.
• Franklin’s x-ray images suggested that DNA was a double helix.
8.2
Structure of DNA
TEKS 3F, 6A, 6B
Chargaff’s Rules
• Erwin Chargaff was also studying the molecules present in DNA.
• He realized that the frequency of Adenine bases equaled Thymine bases
/ Same for Cytosine and Guanine.
• Number of A = Number of T
• Number of G = Number of C
8.2
Structure of DNA
TEKS 3F, 6A, 6B
Nucleotides always pair in the same way.
• The base-pairing rules show how
nucleotides always pair up in DNA.
– A pairs with T
– C pairs with G
G
C
A T
8.2
Structure of DNA
TEKS 3F, 6A, 6B
Watson and Crick determined the three-dimensional
structure of DNA by building models.
• They realized that DNA is a double helix
that is made up of a sugar-phosphate
backbone on the outside with bases on
the inside.
100 Greatest Discoveries - DNA
8.2
Structure of DNA
TEKS 3F, 6A, 6B
• The backbone is connected by covalent bonds (STRONG).
• The bases are connected by hydrogen bonds (weak).
Sugar/Phosphate
Backbone
Nucleotide
(monomer)
hydrogen bond
Amoeba Sisters - DNA Structure
covalent bond
CC - DNA & Replication