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Transformation Principle In 1928 Fredrick Griffith heated the S bacteria and mixed with the harmless bacteria thinking that neither would make the mice.

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Presentation on theme: "Transformation Principle In 1928 Fredrick Griffith heated the S bacteria and mixed with the harmless bacteria thinking that neither would make the mice."— Presentation transcript:

1 Transformation Principle In 1928 Fredrick Griffith heated the S bacteria and mixed with the harmless bacteria thinking that neither would make the mice sick. However; the mice did develop pneumonia. The heat killed bacteria had passed their disease-causing ability to the harmless strain. Material was transferred from the S bacteria (killed) to the live R bacteria. Transforming one strain changed into the disease causing strain.

2 DNA - Transforming Principle Avery experimented by combining living R bacteria with an extract made from S bacteria. Qualitative Tests showed that no proteins was present. Chemical Analysis revealed that the proportions of elements in the extract matched in DNA was present. Enzyme Tests – the team added the enzymes known to break down proteins, the extract transformed the R bacteria to the S form. Transformation did not occur when they added an enzyme that specifically destroys DNA.

3 Avery confirms Transformation Transformation occurred so those molecules were not responsible for the transformation used. He used enzymes to break down the DNA and transformation did not occur. DNA was the transforming factor. Avery discovered DNA (nucleic acids) stores and transmit genetic information from one generation of organism to the next.

4 DNA is Genetic Material Alfred Hershey and Martha Chase were studying viruses that infect bacteria (bacteriophage). Bacteriophage when a virus takes over a bacterium’s genetic machinery and directs it to make more viruses. They conducted experiments using chemical elements found in proteins and DNA using radioactive phosphorous for tagging and radioactivity was present inside the bacteria but not the protein.

5 DNA DNA is composed of 4 nucleotides. Each nucleotide has 3 parts: phosphate group, a 5 carbon sugar, and a nitrogen containing base (single or double ring). The pyrimidines (single ring) are cytosine and thymine. Purines are the larger (double ring ) adenine and guanine. In 1950 Erwin Chargaff found that the same 4 bases are in the DNA of all organisms but the proportion of the 4 bases differ from organism to organism.

6 Double Helix In April 1953 Watson and Crick published their DNA model. The nucleotides always pair in the same way. The DNA nucleotides of a single strand are joined by covalent bonds that connect the sugar of one nucleotide to the phosphate of the next nucleotide. The alternating sugars and phosphates form the sides of a double helix

7 DNA Replication Watson and Crick realized that s single strand of DNA can serve as a template or pattern for a new strand. DNA is copied during the S stage of the cell cycle. Every cell has a complete set of identical genetic information. Proteins carry out the process of replication. DNA does only stores the information. Enzymes and proteins do the actual work of replication. Ex. Enzymes unzip the double helix to separate the strand and proteins hold the strands apart while the strand serves as a templates

8 DNA Replication An amazing feature is there is a built in feature for “proofreading” and correcting errors. If the wrong nucleotide is added to the new strand of DNA then DNA polymerase can detect the error and remove the incorrect nucleotide and replace it with the correct one.

9 Transcription RNA carries DNA’s instructions Francis Crick defined the Central Dogma of molecular biology. There are 3 processes 1. Replicates or copies DNA 2. Transcription converts DNA message into RNA 3. Translation interprets an RNA message into a string of amino acids called polypeptides. The polypeptides makeup a protein.

10 Transcription In prokaryotic cells, replication, transcription, and translation all occur in the cytoplasm at the same time. In eukaryotic cells, where DNA is located inside the nuclear membrane, these processes are separated in location and time. Replication and transcription occur in the nucleus whereas translation occurs in the cytoplasm. The RNA goes through a processing step before it can be transported out of the nucleus. RNA acts as a temporary copy of DNA that is used and then destroyed.

11 RNA vs DNA RNA differs from DNA in 3 ways: 1. The sugar for RNA is ribose 2. The base Uracil is used instead of Thymine 3. RNA is a single strand of nucleotides whereas DNA is a double strand

12 Transcription Transcription the process of copying a sequence of DNA to produce a complementary strand of RNA. In this process a gene not the entire chromosome is transferred into the RNA message. RNA polymerase is the enzyme that bond nucleotides together in a chain to make a new RNA molecule.

13 3 Steps of Transcription I. In eukaryotic cells, RNA polymerase with the of other proteins and DNA sequence the start site of a gene. RNA polymerase assembles on a DNA strand and begins to unwind a segment of the DNA molecule until the 2 strand separate from each other. II. RNA polymerase wing one strand of the DNA as a template, string together a complementary strand of RNA nucleotides. (RNA pairing follows the same rule and DNA but the uracil will replace the thymine). The strand hangs freely as it is transcribed and then the DNA helix zips back together.

14 Transcription III. After the gene has been transcribed, the RNA strand detaches completely from DNA. Transcription produces 3 types of RNA molecules. Not all RNA code for proteins. 1. Messenger RNA (mRNA) is a message that is translated to form a protein. 2. Ribosomal RNA (rRNA) forms part of the ribosomes (a cell’s protein factory). 3. Transfer RNA (tRNA)brings amino acids from the cytoplasm to a ribosome to help make proteins.

15 Replication & Transcription Both occur within the nucleus of eukaryotic cells Both are catalyzed by large complex enzymes Both involve the unwinding of DNA Both involve the complementary base pairing to the DNA strand Both processes are highly regulated by the cell The end results of the 2 processes are very different

16 Replication & Transcription Replication ensures that each new cell will have one complete set of genetic instructions. Replication occurs only once during each round of the cell cycle because each cell needs only one copy of its DNA. A cell may nee hundreds of copies of a certain proteins so transcription enables a cell to adjust to changing demands. This process can occur over and over again.

17 Translation Translation is the process that converts or translates and mRNA message into a polypeptide. Codons are made up of 3 nucleotides which codes for an amino acid. RNA can code for 4 3 = 64 amino acids Start Codon which signals for the start of translation and the amino acid methionine. Stop Codon – there are 3 which signal the end of the amino acid chain.

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