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visits member for 1 years, 8 months
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From the era before Sanger sequencing was invented.


1d
comment Do invertebrates dream?
@jarlemag Fowler's Modern English Usage states that "the only acceptable plural in English is octopuses". Octopi is misconceived because it is based on the idea that octopus is a Latin word whereas in fact it is derived from an Ancient Greek word, and the grammatically correct plural would be octopedes (cf centipedes). However, octopedes is used rarely and considered pedantic, just like this comment!
2d
comment What is Saccus in Embryology?
From the Latin saccus, bag, which is in turn from the Ancient Greek sakkos, sack or bag.
Apr
20
comment How were the first primers made
+1 for PlaysDice - this is why the primers that were used in Sanger sequencing were called universal primers. @PlaysDice you should write this as an answer.
Apr
12
comment Why do three nucleotides code for one amino acid? Why not 5 nucleotides?
@Remi.b great! let's see what answers you get. In E coli it takes 40 min to replicate the genome, but they can grow with a doubling time < 20 min by reinitiating before the previous round of replication has ended. I was once told that the limit to growth is the exponential increase needed in ribosome number as more and more ribosomes are tied up just making ribosomes.
Apr
12
comment Why do three nucleotides code for one amino acid? Why not 5 nucleotides?
I'm always bemused by arguments based upon the metabolic cost of maintaining DNA. I estimate that for E. coli less than 0.06% of ATP is used in replicating DNA, so for a 4 base codon system this would rise but would still be well below 0.1 %. This doesn't strike me as the basis of a strong selective pressure.
Apr
12
comment Why do three nucleotides code for one amino acid? Why not 5 nucleotides?
Warning for the uninitiated - that table is not the 'standard code' , it is the mitochondrial code (AUA is Ile in the standard code).
Apr
10
comment Why are many anti-malaria drugs gap junction antagonists?
Could you give specific examples of antimalarials that block gap junctions? If they do, I'm pretty sure that this isn't anything to do with their antimalarial action. Most of the standard drugs interfere with the food vacuole of Plasmodium resulting in haem toxicity.
Apr
8
comment How do nutrients get to the cells they need to get to?
@max Basically, yes.
Apr
6
comment what is the effect of soda water on digestion?
do you have source for this observation?
Apr
4
comment Is there any documented case in which floating substances led to the introduction of a new species?
But not including actual sea-going vessels?
Apr
3
comment What is the energy consumption of the brain?
I'm not denying that brain activity will require more energy (to restore membrane potential), I'm just dubious that it will be a very big difference (the brain is active during sleep too). I await an answer that provides evidence about this.
Apr
2
comment How can a YAC be screened against a cDNA library and a cosmid library of genomic DNA to find a gene?
@Superbest - hybridisation of probe to clone will occur if there is shared sequence. The fact that there might be small differences in sequence (alleles) or missing sequence (no introns in cDNA clone) will be irrelevant. Before transcriptomics this was the standard way to relate genomic DNA mapping to information about transcripts coming from cDNA cloning.
Apr
1
comment What are the roles of guanidine-HCl and ethanol in binding of DNA to silica?
There is an excellent discussion of this in: Melzak et al. (1996) Driving forces for DNA adsorption to silica in perchlorate solutions. J. Colloid Interface Sci. 181: 635 - 644 I've skimmed the paper, and I'm beginning to understand it, but I don't feel up to actually answering the question yet.
Apr
1
comment How do Gram + bacteria use a proton gradient for F-type ATPase?
In response to your first comment, protons would move up a proton concentration gradient if the membrane potential was favourable, until the chemical and electrical potentials were balanced.
Mar
31
comment How do Gram + bacteria use a proton gradient for F-type ATPase?
Don't have an answer, but it seems to me that given that the Gram negative outer membrane is stuffed full of porins, there is no barrier to proton loss in this case either.
Mar
30
comment Cloning a gene of an organism with an nonsequenced genome
Do you want to clone the gene ( genomic DNA) or a copy of the mRNA (cDNA)? (I imagine it's the latter.)
Mar
29
comment E coli cotransformation efficiency
Nothing to back this up with so just a comment: my understanding is that the cells which are competent take up a lot of DNA, so cotransformation is easy to achieve as long as you can select for both plasmids (if they have replication/segregation features from the same incompatibility group they will segregate rapidly). I once did a Tn5 mutagenesis experiment which required propagating the plasmid in a Tn5 strain, preparing plasmid, transforming a recipient at high DNA input and selecting for kanamycin resistance. Many transformants contained more than one plasmid but they resolved easily.
Mar
29
comment Missing 4$H_2O$s (per glucose) in Cellular Respiration… Where can they be?
Can you point to a source that uses the equation in that form? Everywhere that I have looked has no water on the LHS and 6 water on the RHS, and that is the equation that I'm familiar with. Incidentally in your accounting you missed the loss of 1 water at the aldolase step I believe.
Mar
26
comment Structure of biological membranes?
@biogirl yes, it is, but acid-base equilibria are not redox reactions. I don't understand what your point is.
Mar
23
comment What are conditions for a membrane to be settled ? (centrifugation)
What would happen to the membranes if you didn't centrifuge? (Centrifuging simply accelerates the process.)