Searching for the “Secret of Life” 1.What is the fundamental unit of all living things? The cell 2.What evidence supports this answer? All living things are made of cells, are the small independently functioning structures that possess all the characteristics of life. 3.How is this fundamental unit controlled? Which cellular structure is responsible? By the nucleus

4.How do we know the nucleus controls the cell? When we remove the nucleus the cell cannot reproduce and dies? When we remove other organelles this does not happen. 5.What is this structure composed of? DNA and protein 6.How did scientist determine the composition of this structure? Chemical analysis after using centrifugation to separate the nuclei from other cellular components. Feulgen stain indicated that all nuclei contained DNA, and several test indicated that protein was present in all nuclei.

Nucleic Acids and their Structure A.It must be able to pass information from parent to offspring and therefore must be very large to carry all of that information. B.It must be able to self replicate with each cell division, and this should happen with very few mistakes or offspring would not resemble the parents. C.It must be very stable in order to last the life of the cell and the organism. D.When a mistake does occur, it must be copied faithfully otherwise there would be no variations and no evolution. I.What properties must the hereditary material possess?

Griffith’s Transformation Experiment

Bacteria and Bacteriophages

Hershey and Chase

Hershey/Chase hill.com/classware/ala.do?isbn= &alaid=ala_661237&showSelfStudyTre e=truehttp://highered.mcgraw- hill.com/classware/ala.do?isbn= &alaid=ala_661237&showSelfStudyTre e=true CONCLUSION

IV. What is the chemical composition of DNA? A. Levine determine that DNA was made out of repeating units we now call nucleotides. B.Nucleotides have three parts: 1.A nitrogenous base 2.A sugar 3.A phosphate group

The nitrogenous bases (page 227) The Purines Why are these called nitrogenous bases?

The nitrogenous bases (page 227) The Pyrimidines How are the pyrimidines different from the purines?

The sugar The phosphate RiboseDeoxyribose

Four different Nucleotides

Chargaff’s Rules The amounts of A, T, G, and C in DNA: –Identical in identical twins –Varies between individuals of a species –Varies more from species to species In each species, there are equal amounts of: –A & T –G & C All this suggests DNA uses complementary base pairing to store genetic info Human chromosome estimated to contain, on average, 140 million base pairs Number of possible nucleotide sequences 4,140,000,000

X-Ray Diffraction of DNA

Some important scientific history Dark lady of DNA

Figure 13.6

Watson and Crick Model Watson and Crick, 1953 –Constructed a model of DNA –Double-helix model is similar to a twisted ladder Sugar-phosphate backbones make up the sides Hydrogen-bonded bases make up the rungs –Received a Nobel Prize in 1962

Semiconservative Replication of DNA

Meselson and Stahl’s DNA replication experiment

Meselson and Stahl hill.com/classware/ala.do?isbn= &alaid=ala_661238&showSelfStudyTre e=truehttp://highered.mcgraw- hill.com/classware/ala.do?isbn= &alaid=ala_661238&showSelfStudyTre e=true CONCLUSION

The process of replication

A.Just prior to cell division, promoter proteins are produced. These proteins bind to DNA at several sites. B.Enzymes called helicase are produced and attach to DNA, where the promoter proteins are located. C.These enzymes break the hydrogen bonds linking the bases and the helix opens up at many sites along the DNA molecule. D.Now another enzyme, RNA primase reads the exposed nucleotides and produces a RNA primer (about 10 nucleotides long).

E.DNA polymerase now starts to replicate the DNA (base pairing) forming the new strand in the 5’ - 3’ direction. 1.So it reads the parent DNA in which direction? F.There is a directional problem! G.One molecule of DNA polymerase produces a continuous (leading) strand of DNA. H.The problem is that DNA polymerase only forms DNA in the 5’-3’ direction.

So what happens on the other side of the molecule? Page 232

I.On the lagging strand, new primers have to form at many sites and DNA polymerase forms many small (Okazaki) fragments (1,000- 2,000 long in prokayotes and long in eukaryotes). J.This process occurs at many sites (replication bubbles) along the DNA molecule. 1.A.Why not just start at one end and go to the other end? Takes too much time. K.In humans, DNA polymerase only incorporates 50 nucleotides per second and prokaryotes 500 per second.

L.When DNA polymerase reaches the 5’ end of the RNA primer it is released and other enzymes remove the RNA primers and replace them with DNA nucleotides. 1. Next, DNA ligase joins together all of the large leading fragments and the many Okazaki fragments to form the two new daughter strands.

M.DNA polymerase also checks and corrects any mistakes in base pairing. A better understanding of this enzyme could lead to better treatments for certain disease. Any ideas?

Topoisomerase prevents kinks as the parent DNA is unzipped. See it again See it again

Reforming into chromatin

Animation from text hill.com/classware/ala.do?isbn= &alaid=ala_661235&showSelfStudyTre e=truehttp://highered.mcgraw- hill.com/classware/ala.do?isbn= &alaid=ala_661235&showSelfStudyTre e=true

Figure 3.19c

Figure 3.20

Figure 3.21

Figure 3.21a

Figure 3.21b

CELL CYCLE ANIMATIONS Cell Cycle Mitosis

Causes of Cancer

The Cell Cycle

Duplicated Chromosome

Mitosis in Animals