Each of these statements was once regarded as a biological fact but is now under

Question

Each of these statements was once regarded as a biological fact but is now understood to be untrue. In each case, indicate why the statement was once thought to be true and why it is no longer considered a fact.

1.)The flow of genetic information in a cell is always from DNA to RNA to protein.

2.)DNA always wxists as a duplex of two strands would together into a right-handed helix.

3.)The genetic code specifying how the information present in the DNA molecule is used to make proteins is universal in the sense that all organisms use the same code.

Explanation / Answer

1. The flow of genetic information was revisited when DNA reverse transcriptase enzyme was found in retro virus. In which RNA is the genetic material and it is reverse transcribed to DNA.

2. Different forms of DNA exists such as A-more compact form, B-right handed, and Z-left handed helix. Previously only right handed helix was found by Watson and Crick.

3. Human mitrochondrial genes are supposed to use different codons after which many slight variations in the genetic code for some amino acids of different species such as Mycoplasma which translate the codon UGA as tryptophan and CUG as a serine rather than a leucine in yeasts. Alternative start and stop codons are also used instead of standard ones. In case of stop codons non-standard amino acids are substituted.

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