DNA RNA and Proteins The Structure of DNA

DNA, RNA and Proteins The Structure of DNA Ms. Yard

Learning Objectives • The students will be able to identify the substance that makes up genetic material. • The students will be able to name the experiments that led to the discovery of DNA’s structure and the experiments that identified the role of DNA. • The students will be able to relate the structure of DNA to the function of DNA as a carrier of information. • The students will be able to complete a model by creating a replica of DNA and labeling all of the components. • The student will be able to relate the importance of the discovery of DNA to how it has affected their life.

Why does it matter to you? • DNA is the “blueprint” from which all living things are made, so understanding DNA is key to understanding life.

DNA: The Genetic Material • 1800 s, Gregor Mendel showed that traits are passed from parents to offspring. • Many years later, scientists have discovered how these traits are passed on. – The instructions for inherited traits are called genes. • 1950 s, however, scientists did not know what genes were made of. • We now know that genes are made of small segments of deoxyribonucleic acid, or DNA • DNA is the primary material that causes recognizable, inheritable characteristics in related groups of organisms.

Griffith’s Discovery of Transformation • 2 separate strains of bacteria – S Strain- caused pneumonia, covered by a capsule of polysaccharides • Mice that were injected with the S Strain died • Mice that were inject with heat-killed S bacteria did not die but capsule was still present – R Strain-does not cause pneumonia and is not covered by capsule of polysaccharides • Mice injected with R bacteria did not die • Mice were injected with R bacteria and the heat-killed S bacteria did die – Why do you think that this happened?

Griffith’s Discovery of Transformation • Griffith had discovered transformation, which is a change in genotype that is caused when cells take up foreign genetic material. • His experiment led to the conclusion that genetic material could be transferred between cells. • But no one knew that this material was DNA.

Hershey-Chase Experiment The Hershey- Chase Experiment determined that DNA is the hereditary material, at least in viruses.

The Shape of DNA • After the 1950’s most scientists were convinced that genes were made of DNA, but nothing was known about it’s structure. • James Watson and Francis Crick pieced together a model of DNA’s structure • Structure – Winding Staircase – Nucleotide Subunits

The Shape of DNA • How were James Watson and Francis Crick able to determine the doublehelical structure of DNA? -Experiments from Chargaff, Wilkins and Franklin • Chargaff- 1949 - A=T and G=C -Using technology • Franklin and Wilkins- 1952 - high quality X-rays to study the structure of molecules

The Shape of DNA • A DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits. This spiral shape is known as a double helix. • Each nucleotide is made up of three parts 1. Phosphate group 2. Five –carbon sugar molecule 3. Nitrogen-Containing base.

The Shape of DNA

The Information in DNA • The structure of DNA is very important in the transfer of genetic information. • The information in DNA is contained in the order of the bases • Base-pairing structure allows the information to be copied • Each nucleotide has the same sugar molecule and phosphate group, but the nucleotide can have one of four nitrogenous bases – Nitrogenous Bases • Adenine (A) *A and G = purines • Guanine (G) • Thymine (T) *T and C= pyrimidines • Cytosine (C)

The Information in DNA • Base-Pairing Rules • A purine on one strand of a DNA molecule is always paired with a pyrimidine on the other strand. • Pyrimidines= Thymine (T) and Cytosine (C) • Purines= Adenine (A) and Guanine (G) • Adenine always pairs with thymine • Guanine always pairs with cytosine • dictated by the chemical structure of the bases

The Information in DNA • Paired bases are said to be complementary because they fit together • Example: TATGAGAGT • Example: TATGAGAGT ATACTCTCA Pairing insures that each strand of a DNA molecule contains the same information

The Information in DNA

Back to your DNA candy model… • Using your candy DNA model, make adjustments to your DNA. Remember to look back at your notes to determine any necessary changes.

4 -Corners Adenine Cytosine Thymine Guanine

4 Corners Adenine Thymine Cytosine Guanine • 4 - Corners asking the following questions: What is the missing complementary base nucleotide for each of the following? ATCG – What nitrogenous base is considered a purine? • Guanine AND adenine – What nitrogenous base is considered a pyrimidine? • Thymine and cytosine – In the sequence of nitrogenous bases in one strand of DNA is G A G T C, what is the bases in the underlined complementary strand of DNA? Answer: C T C A G

In the Future… • Replication of DNA – Describing the steps of DNA replication – Comparing the role of DNA helicases and DNA polymerases – Comparing the process of DNA replication in prokaryotes and in eukaryotes