Transcription

1) What types of RNA molecules are made by transcription? Name at least four types.

2) Consider the relationship between a promoter and a coding sequence on a sense strand. Explain how the anti-parallel nature of the double helix, and the binding and polymerization constraints of the RNA polymerase, limit the polymerase to transcribing the sense strand. In other words, why does it go the 'right' way and read the 'right' strand?

3) Why do we see such consensus between the sequences in promoters - both within the genome of a single species and between species...even between prokaryotes and eukaryotes? What happened to organisms that had mutations in their promoter sequences?

4) Explain how transcription is terminated in rho-independent termination. Explain the significance of the G-C rich and A-T rich regions of the DNA template.

5) The presence of introns in eukaryotic genes was revealed by heteroduplex analyses. Explain.

6) How does the "introns early" hypothesis explain the LOSS of introns in bacteria and archaea? Curiously, the most primitive eukaryotes (Giardia) lack mitochondria, and lack introns. Class II introns exist in motochondria and their alpha-proteobacteria ancestors, and may have "jumped" into their host's genome during early eukaryote evolution. This is the "introns-late" hypothesis that explains the split-gene structure of protein-encoding genes in eukaryotes.

7) The first ribozymes discovered by Cech were actually intronic sequences to catalyzed their own excision. How does this occur?

8) What are three differences between cytoplasmic m-RNA in eukaryotes and the initial RNA transcript?

9) What are homopolymers use in discovering the genetic code? How were they made and used?

10) How can you use heteropolymers with two precursur bases in specific ratios to resolve the genetic code?

11) What considerations led scientists to hypothesize that the code was a triplet, non-overlapping code?

12) Consider this gene. Show the m-RNA synthesized from the sense strand.

            3'_________________________________5'....... __________
                |    |    |    |    |    |    |    |    |    |    |    |    |    |            |                    |
                A  A  T  G  C  C  C  A   T  T  G  G  C   A           |                    |
                                                                                          PROMOTER
                T  T   A  C  G  G  G  T   A  A C  C  G   T           |                    |
           5'   |    |    |    |    |    |    |    |    |    |    |    |    |    | 3' ..... |                    |

13)Consider the eukaryotic DNA sense strand below (in colors). Construct the hn-RNA(initial m-RNA transcript) , m-RNA, and Polypeptide encoded by this DNA. You will have access to a genetic code on an exam - use your book or the web for this one.

promoter

1st base transcribed

Exons

Intron

terminator

3' - TATACCCTATCCGTACGCATCCGCGCGATAAAACTGGGCCGCATCCGGATGGCCT - 5'

hn-RNA:

m-RNA:

Polypeptide: