MBLG1001 Past Paper

1. MBLG1001 Past Paper Questions 33-46 Central Dogma

2. 33. Transcription • Which of the following statements about transcription in procaryotes is TRUE? • After cell division, the entire genome is copied into mRNA as a back-up. • During transcription, both strands of DNA are simultaneously copied in opposite directions. • During transcription, the 3’ end of mRNA remains attached to the DNA template. • Before a gene is transcribed, its entire length must be unwound into single stranded DNA. • As RNA polymerase transcribes a gene, the sigma subunit unwinds DNA ahead of it. crazy! no yes! no sigma falls off after initiation

3. 34. Termination of Transcription • Which of the events results in TERMINATION of procaryotic transcription? • When RNA polymerase reaches a STOP codon. • When the rho protein falls off RNA polymerase • When the RNA polymerase reaches the START codon for the next gene. • When a recently transcribed part of mRNA forms intra-molecular base pairs • When the transcription bubble reaches a section of DNA that is blocked by a group of stationary holoenzymes. translation stop signal rho kicks off RNA pol another translation theme factor independent termination plausible but genes not that close

4. 35. Polycistronic mRNAs • Which statement regarding polycistronic mRNAs is TRUE? • A single polycistronic mRNAs can be translated to give several proteins. • A polycistronic mRNA contains just one start and one stop codon. • Polycistronic mRNAs are the only transcripts that can be produced in multiple copies after initiation of a gene. • Polycistronic mRNAs are the only transcripts that can be simultaneously translated as they are being transcribed • Polycistronic mRNAs are formed by post-transcriptional splicing of small transcripts. the definition of polycistronic! must have one for each protein all mRNAs have this potential all mRNAs have this potential would be interesting, but no! More interesting if bits of protein could!

5. 36. CAP • What does NOT describe the function of the procaryotic catabolite activator protein (CAP)? • CAP binds to the DNA downstream of the initiation site • CAP displaces the repressor from DNA • CAP interacts with the alpha subunits of RNA polymerase • CAP requires cyclic AMP to properly bind to DNA • After binding to DNA, CAP simulates the transcription of genes binds upstream at promoter repressor has its own site it does it does it does

6. 37. Repressor • Which statement BEST describes the function of the repressor used to regulate expression of the gene that codes for lactose metabolizing enzymes? • This repressor also inhibits expression of the genes that code for glucose metabolism. • Binding of lactose to this repressor lessens it’s affinity for DNA. • This repressor is only produced when lactose is around. • This repressor stimulates the termination of transcription. • This repressor displaces CAP from the DNA. glucose not inducible – important! removes the inhibition repressor produced constitutively just inhibits initiation geographically separate binding sites

7. 38. Translation Direction • Which of the following statements about directionality in procaryotic translation is FALSE? • The mRNA is translated in the 5’ to 3’ direction. • Codon:anti-codon base pairing is complementary and anti-parallel • The protein is made in the C- to N- direction. • The ribosome moves down the mRNA in the 5’ to 3’ direction • The tip of a polypeptide chain emerging from a ribosome is a formyl group. it is! all base pairing is other way – N-fmet group at start relatively speaking similar to C

8. 39. Ribosomes • Which of the following statements regarding procaryotic ribosomes is CORRECT? • The 30S and 50S subunits are held together by proteins called initiation factors • The 50 S subunit contains 16 S rRNA • The 30 S subunit contains rRNA that catalyses the formation of the peptide bond • A mixture of ribosomal RNAs and proteins can self assemble to produce functional ribosomes • The 30 S subunit contains the P- and A-sites for tRNA actually kept apart by the initiation factors this is in the 30 S subunit this is in the 30 S subunit they sure can! these caverns are in the big one

9. 40. Translation Elongation • Which statement regarding the elongation phase of procaryotic protein synthesis is FALSE? • In the aa-tRNA coming into the ribosome, the carboxylic acid group of the amino acid is in a bond with the tRNA. • During peptide bond formation, the peptide on the tRNA at the P-site moves onto the tRNA at the A-site. • Empty tRNAs are ejected before the ribosome moves down the mRNA • EF-G catalyses the relative movement of the ribosome and the mRNA • New aa-tRNAs come into the A-site correct. remember N-formy-met on end correct. strange to move the big bit! not until the ribosome moves on translocase yes

10. 41. Translation • Which statement about procaryotic translation is TRUE? • Only polycistronic mRNAs can be translated by more than one ribosome at a time • An mRNA can only be translated once it has been fully transcribed • The rate of transcription of mRNA is much faster than the rate of translation • The rate of translation of mRNA is much faster than the rate of transcription. • The presence of polysomes makes an mRNA less prone to nuclease digestion they all can can be simultaneous both 40 nucleotides/s both 40 nucleotides/s less easy for nucleases to attack

11. 42. Degeneracy & Wobble • Considering that there is degeneracy and wobble in the code, which statement about the relationship between mRNA and protein sequence is TRUE? • Given an amino acid sequence of a protein, it would be impossible to predict the correct nucleotide sequence of its mRNA • Given an amino acid sequence of a protein, it would be possible to predict the correct nucleotide sequence of its DNA. • Given an mRNA sequence, it would be impossible to determine the amino acid sequence of the protein • Sequence predictions are only possible in some species • Given the DNA sequence, it would be impossible to determine the amino acid sequence of the protein. can’t tell which codons used as for A just need the table of Genetic Codes a silly statement if know DNA, know RNA and thus protein

12. 43. Pro vs Eu • Which statement regarding the differences between procaryotic and eucaryotic molecular biology is FALSE? • In eucaryotes, DNA is located in organelles • In eucaryotes, DNA is wrapped around a core of protein • In procaryotes, most of the DNA is in introns • In eucaryotes, mRNA must be transported into the cytoplasm before translation • mRNA molecules tend to be longer-lived in eucaryotes nucleus histones, nucleosomes, chromatin no introns/exons in procaryotes more precisely the endoplasmic reticulum they are

13. 44. Eucaryotic Transcription • Which statement regarding eucaryotic transcription is FALSE? • mRNA is transcribed by RNA polymerase II • Sections of DNA that are being transcribed are more prone to nuclease digestion • Eucaryotic promoters bind multiple transcription factors • Eucaryotic enhancer sequences can be located within the transcribed portion of the gene • The eucaryotic promoter sequence is the same as the procaryotic consensus sequenece. it is made by RNA pol II naked very complicated almost anywhere in fact similar but not identical

14. 45. mRNA Processing • During post-transcriptional processing, what does NOT happen to a primary mRNA transcript? • A guanine nucleotide is attached to the 5’ end • Several hundred adenine nucleotides are attached to the 3’ end • Intronic sequences are cut out and assembled into a mature transcript • The transcript is acted on by spliceosomes • The transcript is cleaved by small nuclear ribonuceloproteins capping tailing splicing… but introns are destroyed! splicing apparatus components of spliceosomes

15. 46. Eucaryotic Translation • Which statement about the initiation of eucaryotic translation is TRUE? • The mRNA binds to the ribosome through the Shine Dalgarno sequence • The first tRNA to come in contains N-formyl-methionine • The first AUG codon in the transcript is normally the first to be translated • The 5’ cap of mRNA is positioned into the P-site • The initiating complex is between the mRNA and the 60 S subunit procaryotic. scanning in eucaryotes just plain old met scanning first AUG in P-site the 40S subunit