DNA

DeoxyriboNucleic Acid. DNA? DNA- the genetic material that organisms inherit from their parents. DeoxyriboNucleic Acid. DNA has three major roles: Storing information Copying information Transmitting information

Genes Gene- sequence of DNA that codes for a protein and thus determines a trait. It is a factor that is past down from parent to offspring. In the 1950’s scientists began researching into what makes a gene, and what its purpose was.

Am I out to discover the meaning of the gene!? No. Like everything else important in science, this field of genetics was discovered while trying to find out something else.

Frederick Griffith Frederick Griffith was out trying to discover why bacteria made us sick. He was studying specifically about bacteria that caused certain lung diseases.

What’s your point, Mr. Kinney? Griffith isolated two strains of bacteria that were almost identical, only one was harmless, yet the other caused an often fatal case of pneumonia. (In mice)

The s-strain When he injected the mice with the disease causing s-strain (stands for smooth strain), the mouse died.

The r-strain When he injected the r-strain (stands for rough) into the mouse, it survived.

The heat-killed s-strain When he injected a heat killed s-strain into the mouse, it survived.

The mixture When he injected heat killed s-strain bacteria with nonvirulent r-strain bacteria, the mouse died.

How can this happen if the s-strain was dead???????? Somehow the heat killed bacteria passed the disease causing ability to the nonvirulent strand. He concluded that somehow, the s-strain must have transferred that ability to the r-strain. He called it transformation.

Transformation The process by which one strain of bacteria is changed by a gene or genes from another bacteria.

How does transformation occur? In 1944, A group of scientists at the Rockefeller Institute in New York repeated Griffith’s work. They treated the heat killed bacteria with a variety of lipid, carbohydrates, proteins and other molecules, yet transformation still occurred in the bacteria.

The last thing they tried was using an enzyme that broke down the structure of nucleic acids (…the NA in DNA…) and transformation did not occur.

Mr. Kinney, this cannot be! But it is! Avery and crew figured out with this observation that nucleic acid DNA stored and transmitted information from one generation of bacteria to another.

Bacterial Viruses (Bacteriophage) Bacteriophage- virus that infects bacteria. Virus- nonliving particle that can infect living cells. When a bacteriophage comes in contact with a certain bacteria, the phage will attach to the cell wall of the bacterium, and inject its own genetic information into the bacteria.

The bacteria’s DNA and replicating properties become hijacked, and the virus uses the bacterium as a factory for producing new bacteriophages. Once enough has been produced in the cell, the cell will lyse and release thousands of new phages into the environment.

The Hershey Chase Experiment The Hershey-Chase Experiment was designed to see if phages DNA or protein coat was what would change a bacteria. Their experiment confirmed Avery’s original explanation that the DNA was the cause of the bacterial change and not the protein coat. This confirmed that genetic information of the gene is found in DNA, not just in bacteria and viruses, but all living cells.

end DNA discovery

Discovering DNA structure

DNA composition DNA is made up of nucleotides joined into strains or chains by covalent bonds. Nucleic acids are small units linked together to form chains.

Nucleotide structure Consists of three parts: The phosphate group (or groups) Carbohydrate (sugar) (ribose or deoxyribose) Nitrogenous base.

Nitrogenous bases Contain nitrogen… In DNA we have four nitrogenous bases: Adenine Thymine Guanine Cytosine

Nucleotides are bound together by covalent bonds Nucleotides are bound together by covalent bonds. The nucleotides are bound together by their phosphate bonds.

Chargaff’s Rule Erwin Chargaff discovers equal ratios of nucleotides in DNA strands. Simply put: Amount of Adenine in a DNA molecule equals amount of Thymine. Amount of Cytosine in a DNA molecule equals amount of Guanine.

Rosalind Franklin’s X-rays Purified and stretched out DNA molecules, then focused an intense X-ray of them. Results of x-rays showed DNA in a twisted helix.

Watson and Crick Built the first DNA model from the information they got by reviewing what was discovered by Rosalind Franklin’s work. Helps explain the specific structure of DNA.

What does the double helix model tell us about DNA? The double helix model explains Chargaff’s rule of base pairing and how the two strands of DNA are held together.

Start DNA Replication

DNA replication overview DNA helix is unwound and broken by the enzyme DNA helicase. The site where the DNA is being split in two is referred to as the replication fork. Each nucleotide strand serves as a template for building a new complimentary strand of DNA. At the site where new nucleotides attach to the newly forming strand, an amassing of proteins and enzymes called a replisome forms.

When the primer is in place DNA polymerase starts attaching nucleotides to the old strands, the leading strand will be continually synthesized. (3 prime to 5 prime end) At sites where DNA synthesis occurs, there will be RNA primers that actually start the synthesis. the lagging strand will need to be put together in pieces. (5 prime to 3 prime end)

DNA ligase then fixes any breaks in the sugar backbone of the new DNA molecule. Any errors will then be removed by base excision repair (BER) and repaired by DNA polymerase and DNA ligase.

The process of replication Cells need to divide in order to make new cells. So, in order to make sure the new cell has all of the information it needs in the new cell, it needs to give a copy of it’s DNA to the new cell.

How can copies be created with DNA? When the DNA helix is unzipped, into 2 half strands, we can figure out what bases match with each other based on the Rule of Base Pairs. (A) always matches with (T) and (G) always matches with (C).