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.