1. Genetics 3: Transcription: Making RNA from DNA

2. Comparing DNA and RNA DNA nitrogenous bases: A, T, G, C RNA nitrogenous bases: A, U, G, C DNA: Deoxyribose vs RNA: ribose sugar DNA: double stranded vs RNA: single DNA: full set of chromosomes vs RNA: just single genes DNA: stays in nucleus vs RNA: can leave nucleus and go to endoplasmic reticulum and cytoplasm

3. Types of RNA All are made in the nucleus first mRNA: (messenger) template for translation tRNA: (transfer) brings amino acids to ribosome in translation rRNA: (ribosomal) with proteins, it makes up the ribosome snRNA: (small nuclear) modifies mRNA miRNA: (micro) regulates gene expression siRNA: (small interfering) also regulates gene expression

4. Main Point of Transcription: To copy only the one section of DNA that we need To make RNA that is allowed to leave the nucleus

5. Transcription Phase 1: Initiation For each gene, only one strand of the DNA is transcribed and is called the template strand.  The other strand is called the coding strand because the mRNA you make will actually match this strand (with T’s being replaced by U’s of course…) Either side can work as the template. It depends on the gene. Transcription begins when an RNA polymerase binds tightly to the promoter region and unwinds and opens up a section of the double helix. The promoter region consists of a sequence of nucleotides in DNA that indicates where the RNA polymerase complex needs to bind.

6. Transcription Phase 2: Elongation The RNA polymerase complex works its way along the DNA molecule, making a strand of mRNA that is complementary to the template strand of DNA. They work in the 5’ to 3’ direction (adding a new nucleotide to the free -OH group) They only transcribe one strand, so no Okazaki fragments this time. As soon as the RNA polymerase complex moves from the promoter region, another complex can bind on. No proofreading, so this process is much faster than DNA replication An error would only result in a messed up protein, so it’s not a big deal

7. Transcription Phase 3: Termination Specific nucleotide sequences in the template DNA serve as a stop signal to transcription. When the RNA polymerase complex reaches this signal, they detach from the DNA strand and the mRNA is released. Double helix reforms.

8. Diagram

9. mRNA Modification in Eukaryotes. In prokaryotes, the mRNA is used right away in protein synthesis. In eukaryotes, what we have just made is known as precursor mRNA (pre-mRNA). In order to get our mature mRNA we have to:  Add a 5’cap: modified G nucleotide added to the 5’ end which enables our protein synthesis machinery to recognize it.  Add a 3’ poly-A tail: series of A nucleotides added the the 3’ end that keep the mRNA stable  Remove introns: introns are non-coding regions that are interspersed among the coding regions (exons) through splicing

10. Splicing Particles composed of snRNA (small nuclear RNA) and proteins called snRNPs (pronounced “snurps”) recognize regions where exons and introns meet and bind on. snRNPs interact with other proteins to form a larger spliceosome complex and removes the introns.

11. Diagrams:

13. Questions: Page 250: 8, 10, 11, 12, 14. Page 254: 7, 9, 12 Page 256: 3, 5, 7