Upload
blanche-west
View
214
Download
2
Embed Size (px)
Citation preview
The Structure of DNA
What is DNA?
• It is a nucleic acid that contains deoxyribose sugar and holds an organisms genetic information
• DNA achieves its control by producing proteins called enzymes
Structure of DNA• In the 1950’s, Rosalind Franklin used a
technique called X-ray diffraction to get information about the structure of DNA
• The x-ray pattern revealed the X-shaped pattern and gave clues that the DNA strands are twisted
• The twisted shape is known as a helix• James Watson and Francis Crick used
Franklin’s x-ray to develop a model of the DNA structure
Description of the DNA molecule
• DNA is a polymer of repeating subunits called nucleotides arranged in a double helix
• Nucleotides have three basic parts:– 5 carbon sugar called deoxyribose– Phosphate group– Nitrogenous base
• The deoxyribose sugar and phosphate groups form the backbone of a DNA chain in an alternating pattern
• The nitrogenous bases are attached to the deoxyribose sugar which stick out sideways from the chain
Description of the DNA molecule
• Four nitrogenous bases in DNA– Adenine– Guanine– Cytosine– Thymine
• Adenine bonds to Thymine by forming hydrogen bonds
• Cytosine pairs with Guanine in the same way
Purines (double rings)
Pyrimidines (single ring)
Solving the Structure of DNA• When trying to understand the
structure of DNA, one scientist Erwin Chargaff discovered that the percentages of adenine (A) and thymine (T) were almost equal and that the same was true of guanine (G) and cytosine (C)
• The observation that A = T and G = C became known as Chargaff’s rule
Chromosomes
and
DNA
Where is DNA found?
• In prokaryotic cells
• In eukaryotic cells
In the cytoplasm of the cell
It is also referred to as the chromosome
In the nucleus
In the chromosomes
one
more than one
Chromosome Structure
• What is a chromosome?
• What does it look like?
A threadlike structure within the nucleus containing genetic information
DNA and proteins (histones) tightly coiled into beadlike structures called nucleosomes that loop around
Chromosome structure