CHAPTER 12 POWERPOINT MR. GUILLEN BIOLOGY 9

EXPERIMENTS AND THEIR RELEVANCE Frederick Griffith: discovered that bacteria can get DNA through a process called transformation (process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria) Oswald Avery, Alfred Hershey, Martha Chase: discovered that DNA stores and passes genetic information from one generation of bacteria to the next. DNA IS THE TRANSFORMING MOLECULE. Bacteriophage: a kind of virus that infects bacterial cells. It sticks to the surface of the cell and injects its’ genetic information into it.

THE ROLE OF DNA Storing Information Copying Information A cell must make a complete copy of every one of its genes before the cell divides. Transmitting Information Genes are passed down from parent to offspring. Therefore, must be carefully passed along and stored.

STRUCTURE OF DNA Nucleotides are made up 3 basic parts: 1. 5-carbon sugar (deoxyribose) 2. phosphate group 3. nitrogenous base There are 4 bases: adenine (A), guanine(G), cytosine(C), and thymine(T).

CHARGAFF’S RULE Erwin Chargaff discovered that the percentages of adenine and thymine are equal in any sample of DNA. The same can be said about guanine and cytosine. Therefore, A = T and G = C

CONNECTION B/W FRANKLIN, WATSON, AND CRICK Rosalind Franklin used x-ray diffraction to discover that strands in DNA are twisted around each other in a shape known as a helix. James Watson and Francis Crick were trying to understand the structure of DNA. The clues in Franklin’s x-ray pattern allowed Watson and Crick to build a model that explained the specific structure and properties of DNA.

HYDROGEN BONDING Watson and Crick could not understand what forces held together the strands of DNA’s double helix. They then discovered that hydrogen bonds have just enough force to hold together the strands of DNA.

BASE-PAIRING Plain and simple: Adenine paired with Thymine. Guanine paired with Cytosine.

DNA REPLICATION Before a cell divides, it makes a copy of its DNA in a process called replication. DNA replication is carried out by special proteins called enzymes. These enzymes break hydrogen bonds and pull apart a molecule of DNA. The main enzyme involved in this is called DNA polymerase.

DIFFERENCE IN DNA REPLICATION Prokaryotic vs Eukaryotic Replication: In prokaryotic cells, replication starts from a SINGLE point and continues in 2 directions until the entire chromosome is copied. In eukaryotic cells, replication may begin in MANY places and continues in BOTH directions until the chromosome is copied. https://www.youtube.com/watch?v=5qSrmeiWsuc