seema
New Member
Posts: 15
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Post by seema on Apr 23, 2012 17:29:30 GMT -5
Question: Describe how we know that codons are 3 mRNA bases that code for 1 amino acid.
Answer: First of all, we know that there are 4 RNA nucleotide bases and 20 different amino acids. -1 RNA nucleotide can only have 4 different aa sequences (not enough since there are 20) -2 RNA nucleotides can only have 16 different aa sequences (again, not enough) -3 RNA nucleotides can have 64 possible aa sequences
And so, the triplet hypothesis stating that RNA nucleotide bases are read in groups of threes was formed, and proven through experiments by Crick and Brenner. This experiment delt with viruses that were supposed to infect E. Coli; however, the viral DNA sequence needed for the virus to infect the E. Coli was mutated by insertion/deletion of a base. The fact that insertion/deletion of one or two bases prevented the virus from infecting the bacteria, but insertion/deletion of three allowed the virus to work proves that the genetic code is based on multiples of 3 nucleotides that code for one aa.
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carly
New Member
Posts: 9
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Post by carly on Apr 23, 2012 17:58:28 GMT -5
Which of the following is NOT a stop codon:
A) UAA B) UAU C) UAG D) UGA
correct answer B).
Which of the following is NOT associated with a start codon: A) Met B) AUG C) TAC D)Phe
correct answer D)
Great question!! I will keep this in mind for the chapter test.
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Post by maria on Apr 23, 2012 19:34:55 GMT -5
I think a good communication would be describing some different mutations! For example State and compare the 4 types of Chromosomal Mutations, or maybe Differentiate between the effects of Mis sense, non sense, and silent substitution
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Post by Miss DiFederico on Apr 23, 2012 20:28:31 GMT -5
Which of the following is true regarding the difference between prokaryotes and eukaryotes? a) prokaryotes have chromosomes whereas eukaryotes have circular chromosomes b) prokaryotes have membrane bound organelles but eukaryote do not c) eukaryotes control gene expression via operons whereas prokaryotes use other methods of control d) eukaryotes have both coding and non-coding regions whereas prokaryotes only have coding regions, promoters and operators
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Post by maria on Apr 23, 2012 20:46:01 GMT -5
since prokaryotes have NO INTRONS (regions that do not code) I think the answer could be D? Eukaryotes on the other hand, have introns that are removed with spliceosomes in the process known as splicing??
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carly
New Member
Posts: 9
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Post by carly on May 6, 2012 8:23:51 GMT -5
Which is TRUE regarding a bacterial cell that has a recombinant plasmid? A) When put in the growth medium, cells with turn blue B) When X-gal is applied, it turns recombinant plasmids blue C)Cells with recombinant plasmids will not grow in the presence of ampicillin D) Cells with recombinant plasmids will not turn blue in the presence of X-gal
Correct Answer: D) Bacterial cells with recombinant plasmids will grow in ampicillin (they are antibiotic resistant), but will not turn blue in the presence of X-gal (because they cannot break down galactose)
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Post by Lisa Kim on May 6, 2012 18:16:13 GMT -5
what is the role of restriction endonucleus? Restriction endonucleus are molecular scissors that can cut double stranded DNA at a specific base-pair sequence. Molecular biologists can use these enzymes to cut DNA in predictable and precise manner.
Why do we use Restriction Fragment Length Polymorphism (RFLP) instead of gel electrophoresis? DNA sample is too large, therefore too man bands on the gel (appear as a smear)
What is DNA fingerprinting? -used to identify individuals by analyzing their DNA via gel electrophoresis or RFPL -each person's DNA will have a unique banding pattern - used to cmpare DNA at crime scene with a suspect -used to determine paternity
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Post by Miss DiFederico on May 6, 2012 20:26:06 GMT -5
Which of the following correctly compares DNA replication and gene transcription?
a) in replication, DNA helicase unzips the DNA whereas in transcription, heat denatures the helix
b) in replication, new bases are added to the 5’ end of the strand whereas in transcription, new bases are added to the 3’ end of the strand
c) in replication, a primer is not needed whereas in transcription, a primer is used
d) in replication, small fragments of DNA may be produced whereas transcription occurs continuously from one end of the gene to the other
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seema
New Member
Posts: 15
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Post by seema on May 7, 2012 0:30:00 GMT -5
is it D?
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Post by anjali on May 7, 2012 6:36:27 GMT -5
I think that it is D also
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