DNA Structure Standard 3.1.1 Explain the double-stranded, complimentary nature of DNA as related to its function in the cell.

Discovery of DNA Frederick Griffith (1928) - based his research on how bacteria causes pneumonia Griffith’s Experiment Injected mice with disease causing bacteria (all cells died) and again with harmless bacteria (no sickness) Heated disease-causing bacteria to kill bacteria and injected it into mice (mice lived) Mixed heat-killed bacteria with live, harmless bacteria and injected into mice (all died)

Discovery of DNA Oswald Avery (1944) – based his research on how DNA is the hereditary material that transfers information between bacterial cells. Before this, it was believed proteins transferred hereditary material since proteins code for our traits and are more diverse.

Discovery of DNA Alfred Hershey and Martha Chase – based their experiments using radioactive viruses to infect bacteria (bacteriophages) Used radioactive markers to determine what actually entered a bacterial cell Was able to support that DNA is the genetic material of all living things.

Discovery of DNA Now we know: DNA is the hereditary material of all living things DNA can pass from one bacterial cell to another which is known as transformation

DNA Structure Watson and Crick (1953) – created a model of DNA by using Franklin’s and Wilkson’s DNA diffraction X- rays. DNA is made up of nucleotides Consisting of a deoxyribose sugar, phosphate group, and nitrogenous base. DNA is made of two nucleotide strands that are twisted around each other forming a double helix.

DNA Structure A DNA nucleotide is made up of a 5-carbon deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T).

DNA Structure Two kinds of bases in DNA: thymine C N O cytosine Two kinds of bases in DNA: Pyrimidines are single ring bases Thymine and Cytosine Purines are double ring bases Adenine and Guanine Thus, Adenine pairs with Thymine (A-T) and Guanine pairs with Cytosine (G-C) C N O Guanine C N Adenine

DNA Structure Nucleotides along each DNA strand are linked by covalent bond. Hydrogen bonding is found between the complementary base pairs (G-C and A-T) holding the two strands of nucleotides of a DNA molecule together.

Erwin Chargaff Worked with DNA nitrogen bases, discovered (1950): Chargaff’s Rule: In any sample of DNA, the number of adenine will match the number of thymine and the number of cytosine will match the number of guanine. Therefore, in DNA, the bases are always paired: A – T C- G

DNA Replication

DNA Replication DNA replication is the process in which DNA is copied in a cell before a cell divides. DNA will separate into 2 strands: Replication begins with the separation of the DNA strands by helicases. Then, DNA polymerase forms new strands by adding complementary nucleotides to each of the original strands through base pairing (Chargaff’s Rule)

DNA Replication Each new DNA molecule is made of one strand of nucleotides from the original DNA molecule and one new strand. This is called semi- conservative replication. After DNA is replicated, DNA will have 1 old strand and 1 new strand

Replicate the following strand of DNA: TACGTTACTGCA

Errors during Replication When there are errors in the DNA caused during replication, this is called mutations. DNA proofreading and repair mechanisms help prevent many replication errors. Unrepaired mutations in body cells that affect genes that control cell division can cause diseases such as cancer. Unrepaired mutations in sex cells (eggs and sperm) can cause genetic diseases or birth defects in offspring.