1. DNA Structure and Replication Reminder…what are the monomer units of a nucleic acid? Nucleotides A long chain of nucleotides strung together ‘phosphate to sugar’ make up one strand of the DNA molecule…the nitrogen base sticks out on its own.

2. DNA is a “twisted ladder”…alternating sugar and phosphate groups make up the uprights of the ladder and the rungs are nitrogen bases hydrogen bonded together (recall hydrogen bonds are weak bonds and can come apart easily). The rungs are always one purine bonded to one pyrimidine…A always to T and C always to G.

3. DNA structure in detail

4. Replication DNA makes an exact copy of itself during the ‘S’ phase of Interphase so that each new cell will get an identical copy of the genetic instructions. Replication is “semi-conservative” meaning that each new DNA molecule is half old DNA and half new (one strand is from the original molecule and one strand is newly synthesized using the old strand as a template). Animation 1 Animation 2Animation 3

5. Building Proteins…turning the DNA sequence into something the cell can use. I. Transcription- turning the DNA sequence into a messenger RNA molecule that can travel out of the nucleus and into the cytoplasm to the ribosomes (site of protein synthesis). (other animation)Transcription(other animation) II. Translation- turning the mRNA sequence into the proper sequence of amino acids (monomers of proteins). (other animation)Translation(other animation) (another animation)