 DNA is the blueprint for life – it contains your genetic information  The order of the bases in a segment of DNA (GENE) codes for a particular protein; these proteins then determine your traits  How do you get from a 4-letter code to an entire organism? PROTEIN SYNTHESIS! A GENE IS A SEGMENT OF DNA THAT CODES FOR A PROTEIN. NOT ALL DNA CODES FOR PROTEINS.

 In the first step of protein synthesis, the code of DNA is transcribed onto a molecule of RNA – this step of the process is known as transcription  DNA is too big to leave the nucleus (but proteins are made in the ribosome), so the information in DNA must be transferred to a molecule of RNA

 RNA = Ribonucleic Acid  It contains a RIBOSE sugar (instead of Deoxyribose)  It is a SINGLE HELIX (which makes it half the size of DNA)  RNA does NOT contain the base Thymine(T); instead, it contains the base URACIL (U)

 In transcription, a segment of DNA (gene) is unwound to expose the bases  The DNA is used as a template to make the strand of RNA  RNA nucleotides arrange themselves in order, according to the order of bases on the DNA strand to make a strand of MESSENGER RNA (mRNA)  This mRNA will then leave the nucleus and travel through the cytoplasm to the ribosome to direct the making of the protein  If the order of bases on a strand of DNA is ATCATG, what would its complementary mRNA be?...

 Remember, proteins (polypeptides)are made of AMINO ACIDS ! There are 20 different amino acids that serve as the building blocks of proteins.  In translation, the mRNA travels to the ribosome, where it meets up with the TRANSFER RNA (tRNA)  The mRNA and the tRNA meet in the ribosome (site of protein synthesis) – the ribosome is made up of a third type of RNA, known as RIBOSOMAL RNA (rRNA)

 Transfer RNA is the molecule that carries the amino acids to the ribosome to be added to the protein  tRNA “reads” the code on the mRNA to make sure that the amino acids are assembled in the correct order  On one end of the tRNA molecule, there is a special three-base sequence, known as the ANTI-CODON  This anti-codon the the tRNA will bond only with is matching 3-base sequence on the mRNA strand (which is called a CODON ).  If the mRNA codon is AUG, what tRNA anti-codon will bond to it?... Transfer RNA is an RNA molecule that is ‘bent’ into a unique shape. On one end it carries a specific amino acid, and on the other end is the anti-codon that will determine where in the protein chain that amino acid is placed

 So, the tRNAs, each carrying an amino acid, come to the ribosome and hunt for the correct place on the mRNA strand to put their amino acid  Once they find the correct codon on the mRNA, they leave their amino acid behind, adding it to the growing chain  This process repeats, assembling the correct sequence of amino acids, until a STOP codon is reached  A STOP codon is a 3-base sequence on the mRNA that tells the ribosome to stop adding amino acids to the chain  The amino acids are bonded together using peptide bonds, and a protein (polypeptide) is made!  The CENTRAL DOGMA of Biology: › DNA  RNA  PROTEIN  TRAIT