C14 Genomes and Genomics

25 important questions on C14 Genomes and Genomics

Pyrosequencing
  1. How are the DNA strands in step 1 obtained?
  2. why is there a PCR reaction in step 2?
  3. why is each bead placed in a single well in step 3?

  1. This is e.g. Genomic DNA (to make sure the whole genome is sufficiently represented a high coverage is needed), or exomic (only exons, for protein encoding genes) ....
  2. to amplify the fragment so that a stronger signal will be obtained in the following reactions
  3. you want to study individual beads for whether a base is incorporated or not

Why do not all wells show light in every round?

Not in every well the base is complementary to the base in the template giving a reaction and light flash

Where does gene transcription start and stops in this figure?

Transcription starts with the 5' UTR, stops after 3' end (when ply-A is added to a polyadenylation site)
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How many 5' and 3' splice sites are there in this figure?

2 5' and 2 3' splice sites

WHy are there no codons in the intron?

Introns are spliced out, so it is not in the mature mRNA and will not be translated

What is the 3' UTR between the translation termination site and the polyadenylation site?

3' UTR is at the other end of the mRNA. Again not-translated (after the termination), but before poly-A.

Function of UTRs is not yet clear but may have regulatory functions and affect stability of the mRNA

What is the 5' UTR and why is it located behind the promoter and before the translation initiation site?

5' UTR is the untranslated region of the 5'end of the mRNA, it is part of the mRNA but does not contain codons and is not part of the ORF and therefore not translated in protein.

Indicate which binding site is DNA and which RNA

RNApol binding site is in DNA (promoter), ribosome binding site is in mRNA

Why are the ribosome binding site and ORF drawn on the non-template strand of genomic DNA?

Because it had the same sequence (except T>U) as the corresponding mRNA, it is of course copied from the template (note that the RNApol binding site is on drawn on the template)

What is synteny? Which chromosome had diverged more since the last common ancestor, the human chromosome 17 or the mouse chromosome 11?

Synteny boten mouse and human indicated similar order of DNA sequence (and genes) in the chromosome. The human chromosome has changed much more. In fact, this is an atypical example: most chromosomes of the mouse have more rearrangements compared to the ancestor.

Why fo mainly exonic fragments bind to the immobilised probes?

Probes have affinity to specific exon sequence, biotin helps purifying the fragments

Why would you sequence only the exome if you want to study the causal mutation of a patient?

If protein mutation is suspected, much cheaper than whole genome sequencing (exome ± 1% of the genome)

  1. What is the control in step 2?
  2. why is the intensity of the green colour lower in some wells than in others in step 5?
  3. why are some wells green and others red in step 6?

  1. E.g. Cells that have been grown under normal rather than 'experimental' conditions
  2. because less mRNA was present, lower expression --> less cDNA
  3. some have higher (red) expression than control, others lower (green)

  1. How can you select a yeast cell that carries both plasmids?
  2. why is there only expression of the lacZ reporter when the two proteins interact in the cell?

  1. By transforming the plasmids to yeast and selecting for transform ants that are both Trp+ and Leu+ (can grow in the absence of tryptophan and leucine)
  2. when both proteins are present in the cell and interact, the Gal4 binding domein and Gal4 activation domein will be together and form an active transcription factor for the expression of the LacZ gene.

In the ChIP procedure, why is the protein cross-linked to the DNA in step 1?

To keep proteins attached to their DNA sequence

Why does the antibody only bind to the orange protein in step 3?

It is an antibody that recognised the specific proteins that you are interested in

Why is DNA amplified and sequenced at step 4?

To find out what DNA sequence was recognised by the protein of interest.

What is the light-green 'mutant' segment in gene A?

Light green indicated a mutant sequence, e.g. a deletion of part of the gene that knocks out the gene, or a nucleotide change that alters a specific codon. This is termed targeted mutagenesis.

Why are two crossovers required for gene replacement?

1 crossover would result in incorporation of the circular plasmid in the genome

What happend to the plasmid DNA (indicated in red) in the lower part?

That will be lost if not selected for during cell division

What would you do after isolating a mutant with the disrupted gene A?

Check its phenotype

Why is this an example of 'reverse genetics'

Because you start with known sequence of a gene and make a mutant of the gene to find out its function. A forward genetics approach would be: isolate a mutant phenotype and then figure out the genotype.

What dsRNA sequence is synthesised in vitro (left part of the figure)

DsRNA corresponding to (part of) the gene of interest

What does it mean that the arrows point in different directions (middle part of the figure)?

Reverse repeat, so that the formed RNA will fold and form intramolecular dsRNA

What is the template for the transcription of the two RNA molecules?

Both strands of the indicated dsDNA fragment will be used as template (RNA synthesis is form 5' > 3'), giving complementary RNA --> dsRNA

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