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DNA Discovery • The scientists Watson and Crick figured out the structure of DNA in 1953. Structure • DNA is in the shape of a twisted ladder or a spiral staircase. • We call it the double helix Sides • The sides of the “ladder” are composed of a sugar (deoxyribose) and a phosphate molecule Rungs • The “rungs” of the ladder contain the nitrogen bases • Adenine (A) • Thymine (T) • Guanine (G) • Cytosine (C) Pairing of the Bases • Adenine always pairs with Thymine • Guanine always pairs with Cytosine • A-T • G-C Replication • When DNA replicates (or makes an exact copy of itself) it must go through a few steps: • 1. The two sides unwind and “unzip” • 2. The nitrogen bases (remember A, T, G, & C) that are floating in the nucleus will “hook up” with the now one sided DNA strand. • 3. The new copy will be an exact copy of the original!!!! Replication Order of the Bases • The order of the bases form a code that specifies what type of protein will be made. • For example CGT always means make a Alanine amino acid. The other pairings of three letters code for other amino acids. • Amino acids hook together like beads on a necklace to make a protein (the protein is the completed necklace). Amino Acid Codes DNA • DNA is in the nucleus right? • Well remember how ribosomes make proteins? And they are floating in the cytoplasm? • How does the DNA message get to the ribosome when DNA is too big • to fit out of the nucleus???? • A MESSENGER!!!! Messenger RNA • RNA is a lot like DNA, but it has only one strand instead of two, so it is “skinnier” and can fit out of the nucleus. • RNA has the same nitrogen bases as DNA except it does not have Thymine, it has URACIL instead. So A pairs with U in DNA. Instead of Thymine!!! Types of RNA • Messenger RNA (mRNA) - takes the message about what type of protein to make out of the nucleus to the ribosome. • Transfer RNA (tRNA) takes the amino acids (small parts that make up proteins) to the ribosome and adds them to the growing protein. Protein Synthesis (Making Proteins) • DNA unzips and an RNA strand pairs up with the DNA strand (G pairs with C, but remember A pairs with U b/c there is no T in RNA) • The mRNA then leaves the nucleus and attaches itself to a ribosome and passes on the message Protein Synthesis (Cont’d) • The tRNA attaches to mRNA and hooks up the amino acids in the right order. Then it goes back out to pick up some more (like a taxi cab picking up more people to bring to the location) • The amino acids get strung along into a “necklace” and when it is complete you have a protein Mutations • Sometimes mistakes happen during the process of protein synthesis. • The mistake is called a mutation. • This may cause an incorrect protein to be made which will cause a different trait than intended in the organism. Mutations • Sometimes they do not affect the organism either way. • Sometimes they can be helpful – like resistance to an antibiotic if you were a bacteria. • Sometimes they can be harmful, like if a rabbit were born as an albino and lived in the forest.