Deoxyribonucleic Acid Chapter 12 Section 1 DNA Deoxyribonucleic Acid Chapter 12 Section 1

Discovery of the Genetic Material Scientists knew genetic information was carried on the chromosomes in eukaryotic cells, but where on the chromosome was unknown Main parts of chromosomes: DNA and proteins Major Contributors: Griffith Avery Hershey and Chase Chargaff Watson and Crick

Frederick Griffith- 1928 First main discovery of DNA as genetic material Working with Streptococcus pneumoniae he discovered that one strain could be transformed: Smooth and Rough strains Smooth killed the host (mouse) Heat smooth strain- host lived Rough did not kill the host Mixture of heated smooth and rough- hostdied

Extracted bacteria and made a culture: -smooth trait appeared Observation: -the disease causing factor was passed from the killed S to the live R cells Conclusion: -bacteria transformed

Oswald Avery- 1944 Avery and colleagues identified the molecule that transformed the R strain into the S strain- not widely accepted Isolated macromolecules (DNA, proteins, lipids) from killed S cells Exposed live R cells to them The exposure to the S strain DNA, macromolecules transformed into S cells Conclusion: In Griffith’s experiment when S cells were killed, they released DNA and the R cells incorporated it into their cells, changing the bacteria into S cells.

Alfred Hershey and Martha Chase- 1952 Provided evidence that DNA indeed was the transforming factor Used bacteriophage made of DNA and protein (virus that attacks bacteria) Viruses cannot replicate themselves, they have to inject DNA into living material into a cell to reproduce Radioactive labeled the bacteriophage to see which part was injected into the bacteria Confirmed the DNA was the genetic material

Bacteriophage manipulation: 32P used to make DNA radioactive b/c proteins do not contain phosphorous 35S used to identify proteins b/c DNA does not contain sulfur Result: viral DNA was injected into the cell and provided genetic information needed to produce NEW viruses Conclusion: DNA is the genetic material passes from generation to generation in visues

DNA Structure & Function

Humans share 50% of their DNA with bananas. Cells can contain 6-9 feet of DNA. If all the DNA in your body was put end to end, it would reach to the sun and back over 600 times. DNA in all humans is 99.9 percent identical. It is about one tenth of one percent that makes us all unique, or about 3 million nucleotides difference. In an average meal, you eat approximately 55,000,000 cells or between 63,000 to 93,000 miles of DNA. It would take a person typing 60 words per minute, eight hours a day, around 50 years to type the human genome.

ANIMATION But, what is DNA? P.A. Levene (1920’s)- Determined DNA is made up of 2 chains of nucleotides Each nucleotide has 3 parts: Deoxyribose sugar Phosphate group Nitrogenous base (1 of 4) Adenine (A) -PURINE Guanine (G) -PURINE Cytosine (C) -PYRIMIDINE Thymine (T) -PYRIMIDINE VIDEO

Erwin Chargaff- 1950 Analyzed the amounts of nitrogenous bases found in DNA Conclusion: the amount of adenine nearly is the same as the amount of thymine and the same for guanine and cytosine. Thus: CHARGAFF’S RULE C=G and T=A

What does DNA look like? Franklin & Wilkins Via the use of x-ray diffraction, Rosalind Franklin and Maurice Wilkins’ photo and data helped James Watson and Francis Crick, solve the structure of DNA. Rosalind Franklin’s Photo 51

DNA Structure WATSON & CRICK DNA is a double helix structure formed of 2 complementary precisely paired strands of nucleotides twisted around each other.

DNA Structure- Cont’d Base Pairing Watson and Crick’s (1953) contributions 2 outside strands consist of alternating deoxyribose and phosphate “backbone” cytosine and guanine bases pair to each other by 3 hydrogen bonds “rung” thymine and adenine base pair to each other by 2 hydrogen bonds “rung”

Functions of DNA

Functions of DNA DNA directs the machinery of a cell to make specific proteins, and, therefore, DNA indirectly controls all of the functioning of all living things.

Functions of DNA 2. DNA stores the hereditary information of an individual

Functions of DNA 3. DNA has the ability to mutate (change). This allows for new characteristics and abilities to appear which may help an individual to survive and reproduce (EVOLUTION).

Functions of DNA 4. Self replication: DNA has the ability to make copies of itself

Chromosomes and DNA Recall: Prokaryotes the DNA is in the cytoplasm and in eukaryotes DNA is organized into chromosomes. Human chromosome= 51-245 million base pairs DNA coils around proteins called histones (negative phosphate group attracts to histone to form a nucleosome) Nucleosome group into chromatin fibers which supercoil to make up DNA structure we know as a chromosome

If all organisms are made of the same 4 nucleotides in their DNA, how are they so different? Every organism has a different DNA sequence, which provides different information The more closely related 2 organisms are, the more similar their DNA nucleotide sequences will be.

DNA Replication Chapter 12 Section 2 Animation

When a cell divides, how does the DNA get copied? Remember that DNA gets copied during the S phase of interphase prior to mitosis or meiosis. This process is called DNA replication. Semiconservative replication: parental strands of DNA separate, serve as templates and produce DNA molecules that have 2 strands.

Semiconservative Replication 3 stages unwinding- hydrogen bonds between nitrogenous bases “unzipped” by the enzyme DNA helicase at the replication fork, RNA primer added to each strand of DNA base pairing- enzyme DNA polymerase adds nucleotides to the 3’ end of the new DNA strand (A T and C  G) joining- nucleotides bond together and DNA polymerases are released when they finish replicating the DNA & DNA ligase binds the pieces of DNA together RESULTS: 2 separate and identical DNA molecules, each containing an original strand and a new strand of DNA.

What is with the 5’ and 3’? It is just the position of the functional group on the 5 ring carbon…

DNA Replication Animation Adds new DNA nucleotides 5’ to 3’ single stranded binding proteins keep helix apart synthesized fragments Replication Fork connects fragments Separates double helix needed to start replication on 5’ end of lagging strand 3’ to 5’

Steps of Replication Summary 1) DNA strands pulled apart by helicase @ rep. fork 2) SSBs bind to keep strands apart 3) RNA primase adds RNA primer 4) DNA polymerase adds DNA nucleotides starting @ primer 5) RNA primer removed 6) Gaps filled in by DNA polymerase 7) DNA ligase joins Okazaki fragments

How does DNA get copied so quickly? Replication begins at thousands of points along a DNA molecule in eukaryotes, requiring thousands of helicases & DNA polymerases In prokaryotes, the chromosome is circular, so replication begins at one site and proceeds in opposite directions until the entire molecule is copied.

How accurate is DNA replication? If a mistake is made, DNA polymerase normally fixes it. There is only about 1 error per billion nucleotide pairs. Any error in DNA replication is called a mutation and it can have serious consequences, some good and some bad.

http://learn.genetics.utah.edu/content/begin/tour/ Read page 283-287 Complete p. 287 #1-6

Question to Ponder We know what dominant and recessive mean, but what actually makes one trait dominant over another trait?

Here’s the brief answer: The gene that produces the dominant trait contains information to make a functional protein. The gene that produces the recessive trait contains information to make a non-functional protein. In a codominant situation, the genes have the information for two different functional proteins.