Copying DNA?

Question

Explain how an error in copying DNA for an egg or sperm could result in an offspring with a
protein that works differently than the same protein in the parents.

Answer 1

Let's assume that there is a one base error introduced into the DNA during replication. An error in even one base can possibly affect the way that the genetic code is read. So, when the offspring's DNA is being transcribed into mRNA, this error will also be included. Likewise, the error will be incorporated during translation, the process where mRNA is read by ribosomes and made into a string of corresponding amino acids. During translation, three nucleotides (called a codon) code for one amino acid. So, for example, let's assume that in the parent, the original codon was GGG, or three guanine residues. This codon codes for the amino acid glycine. If the first guanine was changed into a cytosine through an error, we would get the codon CGG. This codon codes for the amino acid arginine instead. So just by changing one nucleotide, the amino acid sequence of a protein can be affected. Introducing a different amino acid can, in turn, affect the way a protein folds, and therefore the way it functions (i.e. a protein might not fold correctly, and therefore will not work.).

Sorry for the long-winded explanation, hope it helps a bit.

Answer 2

Just like any DNA error, a flawed copy can be made during Meiosis. It's possible then that this would affect the protein produced by one of the two alleles in the offspring in the following way: The mutation could cause a protein to be made that is not functionally different at all than those made by its parent's DNA. It could cause a comepletely non-functional protein to be made, or it could make a protein that does something different. If a nucleic acid or two are missing (deletion) there will be a reading error in the translation of the protein made from the RNA (made from the DNA). If 3 base pairs are missing, one single amino acid will be missing, and it may or may not affect the protein's function. If one nucleic acid is substituted for a different original one, then the protein may or may not be different. Consult your biology book to see the chart for which triplets code for which amino acids. Often more than one triplet is codes for one amino acid.

Answer 3

This is called a germ-line mutation. Since the germ cells (egg and sperm) get together and form and embryo, a mutation in the DNA of either cell or a mutation during the first few rounds of division following fusion of the two cells leads to an embryo carrying the mutated DNA. Therefore, the offspring may have a protein that is not exactly the same as what is produced in the parents. This is due directly to the mutation in the germ-line DNA since it is transcribed into RNA and then ultimately translated into protein.

Answer 4

We use the "polymerase chain reaction" technique. We do this when we want to amplify a limited DNA sample, so we can make a "DNA fingerprint" gel. Very useful in criminal investigation these days. Or do you mean naturally? In your cells, you copy your DNA using DNA polymerase. You do that prior to cell division, so each new daughter cell can have a full complement of all the DNA of the parent (assuming mitosis here).