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Unit Chunk 1B: The Structure and Function of DNA
Day One: The Structure & Function of DNA
EQ - What are the two main functions of DNA?
* DNA stores a cell’s genetic information; it contains the genetic code for making
the cell’s proteins.
* DNA transmits a cell’s genetic information for both asexual and sexual
reproduction.
DNA is a very long polymer--a molecule made up of other monomers. It is a double helix
polymer. The backbone strands of the DNA molecule are alternating phosphate
molecules, and deoxyribose (a sugar) molecules. The ladder rungs are pairs of
molecules called nitrogen bases.
EQ - What are the monomers for the polymer DNA? Describe the structure of this
monomer.
Nucleotides - DNA Monomers - The building blocks for DNA
One deoxyribose together with its phosphate and base make a DNA nucleotide.
DNA has four nitrogen bases: Thymine – T, Adenine – A, Guanine – G, Cytosine – C
The nitrogen bases attract each other because of hydrogen bonds.
•Adenine and Thymine always join together – A & T; T & A
•Cytosine and Guanine always join together – C & G; G & C
Day Two: The Structure & Function of DNA
EQ - What two types of DNA are in animal eukaryotes? What three types are in
plant eukaryotes?
EQ - What is the relationship between the DNA in prokaryotes and the DNA in
mitochondria and chloroplasts?
In prokaryotic cells, DNA is located in the cytoplasm. Most prokaryotes have a single
DNA molecule containing nearly all of the cell’s genetic information.
Eukaryotic DNA is located in the cell nucleus inside chromosomes. Each
chromosome contains a single, long, coiled DNA molecule.
The mitochondria and chloroplasts of eukaryotes also contain DNA. This DNA is
similar to the structure of prokaryotic DNA, a single DNA molecule.
Chromosome Structure - Eukaryotic chromosomes contain DNA and protein, tightly
packed together to form chromatin. Chromatin is what forms chromosomes when
eukaryotic cells get ready to divide.
EQ - Construct an explanation based on scientific evidence for how the structure
of DNA determines the structure of proteins that carry out the essential functions
of life through specialized cells.
Genes are segments of DNA that code for the formation of specific proteins, which carry
out most of the work of cells. The structure of each protein is determined by the
sequence of the DNA bases that make up each gene. Groups of specialized cells use
proteins to carry out the functions of life that are essential to the organism.
Day Three: The Discovery of DNA
The Discovery of DNA
Frederick Griffith – Discovered a factor that contained information that
transformed harmless bacteria into deadly bacteria. Griffith called the process
transformation because the harmless strain of bacteria had changed permanently
into the disease-causing bacteria. (1928)
Other scientists discovered that the nucleic acid DNA is the transforming factor
that transmits genetic information from one generation of an organism to the next.
EQ - What was Franklin’s contribution to the discovery of DNA?
Rosalind Franklin - Used X-ray diffraction to get information about the DNA
molecule, and proceeded to make X-ray photographs of DNA molecules. Franklin
worked hard to perfect her methods until the DNA patterns became clear. In her Xray diffraction photograph, the X-shaped pattern in the center shows that the
structure of DNA is helical (like a spiral). (1952)
EQ - What was Watson and Crick’s contribution to the discovery of DNA?
Watson and Crick - While Franklin was doing her research, James Watson and
Francis Crick were building 3-dimensional models of DNA to explain its properties,
but were unsuccessful. Then, they saw Franklin’s X-ray photo and within weeks
built the double helix model that described the structure of the DNA molecule and
how it carried information and how this information was copied. (1953)