1. Molecular Genetics Ch. 16, 17, 18, 19, 20

2. DNA Replication Happens during interphase of mitosis. Semiconservative Replication 3 basic steps  Unwind and Unzip  Build  Rewind

3. Unwind Helicase, an enzyme, unwinds the DNA helix forming a Y-shaped replication fork. Single-stranded DNA binding proteins attach to each strand of the uncoiled DNA to keep them separate. Topoisomerases help to keep the DNA from forming knots.

4. Build RNA primase initiates DNA replication at a special nucleotide sequences called origins of replication with short segments of RNA called RNA primers. DNA polymerase attaches to the RNA primers and begins elongation, the adding of DNA nucleotides to the complementary strand. The leading complementary strand is assembled continuously. The lagging complementary strand is assembled in short Okazaki fragments which are joined by DNA ligase. RNA primers are placed by DNA nucelotides.

5. Leading vs Lagging DNA is antiparallel The uncoiled DNA consists of a 3’  5’ template strand and a 5’  3’ template strand. DNA polymerase moves in the 3’  5’ direction.  5’ or 3’? The location of the carbon sugar next to the phosphate.

6. Leading vs Lagging Continued Leading strand replication occurs regularly. Lagging strand the replication occurs in fragments called Okazaki fragments.

7. Protein Synthesis DNA  mRNA  tRNA  Protein 3 types of RNA  mRNA A single strand of RNA that provides the template used for sequencing amino acids into a polypeptide.  tRNA Is a short RNA molecule that is used for transporting amino acids to their proper place on the mRNA template.  rRNA Molecules are the building blocks of ribosomes.

8. Protein Synthesis (Transcription) Transcribing DNA to RNA Occurs in the nucleus 3 steps  Initiation  Elongation  Termination

9. Initiation The RNA polymerase attaches to a promoter region on the DNA.  TATA Box DNA begins to unzip.

10. Elongation RNA polymerase unzips the DNA and assembles RNA nucleotides using one strand of the DNA as a template. Only one DNA strand is transcribed.

11. Termination Occurs when the RNA polymerase reaches a special sequence of nucleotides that serve as a termination point.

12. Protein Synthesis (Translation) After transcription mRNA, tRNA, and ribosomal subunits are transported across the nuclear envelope. 3 Steps  Initiation  Elongation  Termination

13. Initiation Small ribosomal subunit attaches to a special region near the 5’ end of the mRNA molecule. tRNA with anticodon UAC carrying the amino acid methionine attaches to the mRNA at the start codon AUG with hydrogen bonds The large ribosomal subunit attaches to the mRNA forming a complete ribosome with tRNA- Met, at the P site

15. Elongation Begins when the next tRNA bearing the appropriate amino acid binds to the A site of the ribosome. The old tRNA moves from the A to the E and leaves. The methionine is attached to the new amino acid in the A site. A new tRNA moves into the P site. The cycle continues

16. Termination Occurs when the ribosome encounters one of three “stop” codons. At termination the completed polypeptide and the 2 ribosomal subunits are released.