1. DNA By: Ms. K. Massey

2. Even though DNA is microscopic and too small to see with the naked eye, its importance is un- measurable. It forms the backbone of our genetic code and the makeup of who we are. DNA is an acronym for Deoxyribonucleic acid. DNA has a unique shape. It’s a double helix. It is made up of two strands of adjoining nucleotides. Remember a nucleotide is a sugar, phosphate and base.

3. Below is the structure of DNA Sides of the DNA Ladder: alternating deoxyribose sugar and a phosphate molecule. Rungs of the DNA: 4 nucleotide bases. Adenine, thymine, guanine and cytosine. They are all made up of nitrogen compounds.

4. Phosphate Group Sugar: Deoxyribose Nitrogen bases: A, T, C, G

5. The nitrogenous bases The Purines

6. The nitrogenous bases The Pyrimidines

7. The history of how DNA was discovered is quite interesting. In the 1940’s, Oswald Avery discovered that DNA, and not protein or RNA, is the genetic material that codes for proteins in organisms. In 1949 Erwin Cargaff observed that amount of adenine and thymine are equal and guanine and cytosine are always found in equal amounts. Based on his observations he came up with the following base pairing rules: adenine always pairs with thymine_ and cytosine always pairs with guanine.

8. A few years later, Rosalind Franklin - 1952 developed x-ray diffraction images of strands of DNA, along with her assistant, Maurice Wilkins. Their picture and discovery helped suggest DNA was a tightly coiled helix. James Watson and Francis Crick built a model of DNA in 1953, using information from Chargaff and Franklin. They are credited to discovering the double helix structure of DNA.

9. DNA ultimately codes for the making of proteins, called protein synthesis. This takes place in several steps: Replication, transcription and translation.

10. Replication : Making of two DNA molecules - In the nucleus

11. Step 1: Unwinding and separating DNA strands DNA replication begins with the “unzipping” of the parent molecule as the hydrogen bonds between the base pairs are broken. This is done with enzymes.

12. Step 2: Adding complementary Base Pairs An enzyme DNA Polymerase “reads” the bases and new ones are added to each side of the parent molecule. The nucleotides are added according to the base pairing rules. The original strand serves as a template for the two new strands

13. Step 3: Produces 2 identical DNA strands When the process is complete, two DNA molecules have been formed identical to each other and to the parent molecule.

14. Transcription : Transcription is the synthesis of RNA from a DNA template. It is similar to DNA replication however there are a few small differences. DNA will code for RNA – Ribonucleic acid. It is a molecule made of the sugar ribose, phosphate and 4 nitrogen bases. Uracil, a nitrogen base that replaces thymine. RNA is also single stranded.

15. How are DNA and RNA different?

16. Step 1: Reading the DNA An enzyme will come and separate the DNA

17. Step 2: Making an RNA strand An enzyme RNA polymerase “reads” the DNA molecule and, assembles ribonucleotides into a strand of RNA. Each ribonucleotide is inserted into the growing RNA strand following the rules of base pairing. Thus for each C encountered on the DNA strand, a G is inserted in the RNA; for each G, a C; and for each T, an A. However, each A on the DNA guides the insertion of the uracil ( U ). There is no T in RNA.

19. Step 3: mRNA is on the move The new strand of RNA is called mRNA – messenger RNA _. It will carry the DNA code to synthesize (make) a protein. mRNA will move out of the nucleus through a nuclear pore to a ribosome out in the cytoplasm.

20. Translation - Translation is the process through which ribosomes synthesize proteins. Translation is the third stage. In translation, mRNA produced by transcription decoded by the ribosome to produce a specific amino acid chain, or protein.

21. Step 1: Onto a ribosome The mRNA leaves the nucleus and finds a ribosome

22. Step 2: tRNA and mRNA meet The bases on the mRNA strand are grouped into 3’s. This is called a codon. It will code for a molecule of tRNA carrying a matching amino acid.

23. Step 3: tRNA matches with mRNA A molecule of tRNA – transfer RNA will match with the corresponding mRNA codon. This molecule is called an anticodon. It carries an amino acid. Example: mRNA codon is TAG. Therefore the tRNA anticodon is AUC

24. Step 4: Building a protein chain The tRNA carries specific amino acids that are chained together into a protein as the mRNA passes through and is "read" by the ribosome.

25. Each mRNA codon codes for a specific amino acid. There are 20 amino acids. A codon chart is used to determine which codon goes with each amino acid. There are many different charts. Two are shown for example. Within the chart are a start codon (Methionine) and a stop codon. The start means this the start of the protein and the stop means it is the end of the protein. One DNA molecule can ultimately code for hundreds of different proteins. It all depends on where the DNA molecule you are looking at.

26. Codon = mRNA Anti-codon = tRNA