Kevin Ahern's BB 350 (Nucleic Acids/DNA Replication) 2014 - #15
1. Contact Kevin at [email protected] 2. Kevin's lectures with The Great Courses - https://www.thegreatcourses.com/cours... 3. Kevin's Lecturio videos for medical students - https://www.lecturio.com/medical-cour... 4. Course materials at https://kevingahern.com/biochemistry-... 5. Course video channel at • 1. Ahern's BB 350 at Oregon State Universi... 6. Metabolic Melodies at https://teeheetime.com/category/lyric... 7. Kevin's Free Biochemistry books - https://kevingahern.com/biochemistry-... 8. Kevin's Pre-med Audio course on Listenable - https://listenable.io/web/courses/143... Highlights Nucleic Acids and DNA Synthesis 1. Chromatin is a complex of DNA and proteins called histones. 2. Histones are positively charged proteins that associate with DNA and allow it to coil up. DNA-histone complexes are called nucleosomes. When you put many nucleosomes together, you get chromatin. 3. DNA strands can easily be separated by heat, acid, or base. 4. Single strands of nucleic acid (DNA or RNA) absorb light at 260 nm more strongly than double strands of nucleic acid in the same quantity. Thus, one can monitor the denaturation of nucleic acid by monitoring its absorbance at 260 nm as the denaturation proceeds. 5. The transition temperature (Tm) for a nucleic acid denaturation is the mid-point of the Tm transition 6. RNA differs from DNA in having ribose (instead of deoxyribose) and uracil (instead of thymine). 7. Three main types of RNA found in all cells are transfer RNA (tRNA), ribosomal RNA (rRNA), and messenger RNA (mRNA). mRNAs carry the genetic code necessary for making proteins, tRNAs carry amino acids and translate the genetic code in the mRNA and rRNAs are components of ribosomes that make proteins. 8. Genes are copied into mRNA in the nucleus of eukaryotic cells and transported to the cytoplasm to be translated into protein. 9. Before mRNAs get transported to the cytoplasm, regions that don't code for protein must be spliced out of the mRNA. Regions that are removed are called introns. The parts of the gene that remain and are joined together to make the final mRNA are called exons. 10. In bacteria genes are in one piece and are transcribed and translated in the same place (cytoplasm) since there is no nucleus in bacteria. 11. tRNAs carry an amino acid at one end and a three base sequence at the other end that base pairs with the mRNA during the process of translation. This loop is complementary to a three base codon found in mRNA. An amino acid is specific for each three base sequence. 12. Ribosomal RNA is found in ribosomes and helps the ribosome form by providing a scaffolding for the protein components of the ribosome to attach to. We'll see at least one other function soon. 13. Information in cells flows from DNA to RNA (called transcription) and from RNA to Protein (called translation). This is known as the Central Dogma. Some retroviruses have an enzyme called reverse transcriptase that allows them to make DNA from RNA. This last process is called reverse transcription. 14. DNA replication is catalyzed by an enzyme called DNA polymerase, which reads a strand and joins complementary bases to the growing strand by forming phosphodiester bonds. DNA replication occurs only in the 5' to 3' direction. 15. The semiconservative replication mechanism means that when DNA is made, the two new duplexes would each have one parental strand and one newly synthesized strand. 16. Replication of each DNA strand occurs by a different scheme. The leading strand is made in a single continuous piece. The lagging strand is made in short segments called Okazaki fragments. The two different replication strategies arise from the fact that both must occur in the 5' to 3' direction. The lagging strand segments can only be started after the leading strand synthesis opens up the duplex sufficiently. This occurs repetitively during synthesis, generating multiple lagging strand fragments. 17. Note that leading AND lagging strand synthesis are both occurring at the same replication fork AND that both leading and lagging strand synthesis are occurring exclusively in the 5' to 3' direction. 18. In bacteria, DNA replication occurs at about 1000 nucleotides per second and the error rate is about 1 mismatch per 10,000,000 bases. 19. In order for DNA replication to move this fast, the DNA strands must be unwound ahead of the DNA polymerase at the rate of 6000 rpm.This enzyme is called a helicase. To keep DNA from tangling up, another enzyme called a topoisomerase must relieve the tension caused by the helicase.
