How do we know it’s our genetic material? DNA How do we know it’s our genetic material?

Several Experiments Science is not linear Many tests were done Some right Some wrong Eventually we came to know about what DNA does

But, what factor in the nucleus controls all of the actions? The Nucleus was the key a series of experiments with algae showed that the nucleus controlled the actions of the cell But, what factor in the nucleus controls all of the actions?

Griffith’s Experiment (1928) experiments with Streptococcus (bacteria) bacteria does not have a “nucleus” genetic material floats around cytoplasm two types of this bacteria

TYPE 1- Smooth (S) S (smooth) has protective capsule causes pneumonia in mice= mice die

TYPE 2- Rough (R) R (rough) has no capsule does not cause pneumonia in mice

S type is heat killed

S is heat killed and mixed with R

Findings dead bacteria could not come back to life somehow, the R absorbed the information from the S and became like S type ( it was transformed) There is some kind of controlling factor in the S type that makes it cause pneumonia

Avery and Colleagues(1944) Knew chromosomes were made of DNA and proteins expanded Griffith’s experiments to find out which one was the genetic material

Mixed Heat killed S and R with DNA destroying enzymes Mixed heat killed S (harmful) and R (harmless) with protein killing enzymes Results- R became deadly (R was Transformed) Mixed Heat killed S and R with DNA destroying enzymes Results- No Transformation- mice weren’t harmed DNA must be genetic material but………many people were still skeptical

Hershey and Chase (1952) supported Avery’s findings experimented with viruses discovered that viruses could use bacterial DNA to replicate more viruses Knew bacteria infecting viruses (bacteriophages) were made of protein and DNA

Hershey and Chase used radioactive labeling to identify the DNA and protein coats of viruses. Viral DNA injected into bacterium will direct the production of viruses, using bacterial DNA.

The bursting of a cell is called Lysis The protein coat of the viruses remained outside the bacterium, but the bacterium produced new viruses. The viruses contained the radioactive DNA.

Also first to identify the actual material as DNA using radioactive tracers Concluded that DNA was the actual control molecule FINALLY!

Discovery of Structure Erwin Chargaff (1949) – determined base pairing Rosalind Franklin (50’s) -discovered DNA was a double helix Watson and Crick (50’s)- created first model

THE DOUBLE HELIX

DNA STRUCTURE DNA is composed of a 3 part unit called a NUCLEOTIDE -5 carbon sugar = DEOXYRIBOSE -PHOSPHATE -NITROGEN BASE (1 OF 4) NB S P NB NB S S P P NB NB S S

Bonds that hold DNA together Sugar (Deoxyribose)-Phosphate = Covalent Sugar (Deoxyribose)-Nitrogen Base=Covalent Nitrogen Base(1 strand)-Nitrogen Base (2nd Strand)= Hydrogen Bond

NITROGEN BASES PURINES PYRIMIDINES ADENINE (A) GUANINE (G) CYTOSINE (C) THYMINE (T) Large, double rings Small, single rings

CHARGAFF’S RULE When forming the “rungs” of the “ladder”.. A always bonds with T A is “complementary” to T 2 Hydrogen bonds hold them together C always bonds with G C is “complementary” to G 3 Hydrogen bonds hold them together there will always be equal numbers of A and T; and of C and G

THINK ABOUT IT! EVERY LIVING THING ON THIS PLANET IS COMPOSED OF ONLY 4 NITROGEN BASES. THE ONLY DIFFERENCE IS THE SEQUENCE OF AND NUMBER OF BASES

DNA REPLICATION in order for a cell to duplicate, DNA must make a copy of itself the process is called DNA REPLICATION an identical strand of DNA is produced

DNA unzips Happens before the cell divides(mitosis), the whole strand unzips An enzyme HELICASE does the unzipping Many enzymes are involved in the rest of the process

DNA POLYMERASE does this free nucleotides in the nucleoplasm(material in the nucleus) attach to the unzipped strands DNA POLYMERASE does this

the “backbone” of sugars and phosphates will bond two, identical, complete strands will form each has half of the original