DNA and Protein Synthesis

[Ayeshaa]

Hey guys, I’m new to this forum, and would appreciate if you could help me with a few questions. Thanks in advance 🙂 I actually have very simple answers, so if I’ve missed out on anything important, then please tell.

Suppose you knew the makeup of specific proteins in a cell. How would you determine the particular DNA code that coded for them?

^ You would be working backwards, so first you would find the amino acid known, then you would break them down to find the tRNA code, and break that code down to find mRNA, and break this code down to find the base pairs of DNA.

How could one change in a DNA nucleotide alter the formatin of the translated protein?

^ One change in the nucleotide can put a change in the amino acid and that can change the whole function of the DNA.

If DNA never leaves the nucleus during the growth of a cell, explain briefly how it and the nucleus control most of the cells activity like growth, repair, cellular respiration, secretion, and excretion.

^ The mRNA carries the genetic information of the DNA to the ribosomes in the cytoplasm and tells them what to do. It makes protein and functions cell.

[JackBean]

1) theoretically right, but I guess they want something more practical.
If you have AA sequence, you can look for amino acids, which are coded with only few codons (remember, genetic code is degenerated, so you cannot simply reverse-translate!). For this are you would design primers and try to get some amplification from either gDNA or cDNA library.
However, nowadays plenty of genomes are already known, so you can use your protein sequence as query to search nucleotide sequences.

2) First of all, it doesn’t change function of DNA, but of the protein.
Anyway, there are several options. Either the mutation will be silent, i.e. coding for the same amino acid and you will see no change in protein. Or the amino acid may be very similar (Ala and Val), so you will see change in protein sequence, but it’s function won’t be altered. Another possibility is that you get some totally different amino acid (Glu -> Arg; Xxx -> Pro), which will either completely impair the functioning of that protein or it won’t be able to fold (and thus work). Lastly, you can get premature STOP and truncated protein. Question is, how premature the STOP codon would be, whether the fragment would be able of catalysis or not.

[Ayeshaa]

Thanks soo much for the help JackBean, I really appreciate it =)

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