BIOC0005 REVISION PACK EXAM QUESTIONS AND
ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
What are the different structures of DNA?
A-DNA, B-DNA and Z-DNA
What is the configuration of B-DNA?
10.5bp per turn of 3.32nm rise. 2nm in width possessing major & minor groves.
What are A-DNA & Z-DNA?
A-DNA is the dehydrated from of B-DNA. While Z-DNA is left-handed double helix
What is a triple helix?
When a 3rd strand of B-DNA is incorporated.
What are the two extra proteinogenic amino acids?
Selenocysteine & pyrrolysine are incorporated into proteins under specific conditions.
why is uracil used in RNA, but replaced by thymine in DNA?
-Due to spontaneous deamination of cytosine to uracil, it can be recognised for repair
easily. So thymine is used in DNA over uracil.
-As mRNA is more transient so mutation/deamination has less lasting damage
-Uracil is more resistant to oxidation
Why can't RNA editing predict the original DNA sequence of the protein?
changes of uracil to cytosine.
Why do we observe codon re-assignments of UGA & UAG which codes for the
STOP codon codes for Top in prokaryotes w/ smaller genomes?
, smaller genomes w/ fewer genes, easier to introduce genomic changes w/out collapsing
What are inteins?
auto-processing domains that carry out protein splicing
what is protein splicing?
self-catalysed excising of intein from a precursor polypeptide sequence while exteins
are ligated together
why is protein sample not visible at wavelength 300nm?
Protein absorbed @ UV range ~280nm, so colourless @ 300nm.
How to use spectrometer to detect DNA sample contamination by tryptophan
containing protein
Use A260:A280 ratio, higher A280, so ratio <1.8
define hyperchromicity
DNA denaturation due to temperature, pH... cause increase in A260:A280
What are some uses of hyperchromicity?
-Estimate G-C % of a genome sampl, as 3x H-bonds, denatures @ higher Temp than A-
T.
-Also used to estimate similarity in two genomes to measure degree of hybridisation
during renaturation.
What does Tm value indicate?
the temperature @ which 50% ss.DNA vs ds.DNA
What is the role of cations in DNA annealing?
to minimise charge repulsion between poly-anionic strands
why is the rate of migration in gel electrophoresis dependent on?
ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
What are the different structures of DNA?
A-DNA, B-DNA and Z-DNA
What is the configuration of B-DNA?
10.5bp per turn of 3.32nm rise. 2nm in width possessing major & minor groves.
What are A-DNA & Z-DNA?
A-DNA is the dehydrated from of B-DNA. While Z-DNA is left-handed double helix
What is a triple helix?
When a 3rd strand of B-DNA is incorporated.
What are the two extra proteinogenic amino acids?
Selenocysteine & pyrrolysine are incorporated into proteins under specific conditions.
why is uracil used in RNA, but replaced by thymine in DNA?
-Due to spontaneous deamination of cytosine to uracil, it can be recognised for repair
easily. So thymine is used in DNA over uracil.
-As mRNA is more transient so mutation/deamination has less lasting damage
-Uracil is more resistant to oxidation
Why can't RNA editing predict the original DNA sequence of the protein?
changes of uracil to cytosine.
Why do we observe codon re-assignments of UGA & UAG which codes for the
STOP codon codes for Top in prokaryotes w/ smaller genomes?
, smaller genomes w/ fewer genes, easier to introduce genomic changes w/out collapsing
What are inteins?
auto-processing domains that carry out protein splicing
what is protein splicing?
self-catalysed excising of intein from a precursor polypeptide sequence while exteins
are ligated together
why is protein sample not visible at wavelength 300nm?
Protein absorbed @ UV range ~280nm, so colourless @ 300nm.
How to use spectrometer to detect DNA sample contamination by tryptophan
containing protein
Use A260:A280 ratio, higher A280, so ratio <1.8
define hyperchromicity
DNA denaturation due to temperature, pH... cause increase in A260:A280
What are some uses of hyperchromicity?
-Estimate G-C % of a genome sampl, as 3x H-bonds, denatures @ higher Temp than A-
T.
-Also used to estimate similarity in two genomes to measure degree of hybridisation
during renaturation.
What does Tm value indicate?
the temperature @ which 50% ss.DNA vs ds.DNA
What is the role of cations in DNA annealing?
to minimise charge repulsion between poly-anionic strands
why is the rate of migration in gel electrophoresis dependent on?
