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Name ___________________________ Teacher_________________________ Date ____________________________
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1. The model below represents a protein surrounded by water molecules. It curls into a ball like this.
Notice that each white circle represents an amino acid Glycine. Why do you think the protein folds this way? The bonds between amino acids are stronger than those between them and surrounding water molecules. Water molecules are free, therefore, to make multiple hydrogen bonds with each other, effectively pushing the amino acids together.
Scientists substituted the first amino acid (glycine, G) in the chain with another one (E, glutamic acid). Look what happened to the protein (below).
Why do you think this single replacement of an amino acid affected the shape of the protein chain the way it did? The single replacement of an amino acid glycine with glutamic acid has such strong effect on the protein chain because glutamic acid in water carries a strong negative charge and therefore gets attracted to polar water molecules much more than to the rest of the protein chain. This force of attraction pulls the entire chain toward water. How do you think the shape of this protein will change if the same type of amino acid would be placed on the other end of the protein chain? Explain your prediction or draw what you think the protein would look like. If another glutamic acid (E) would be placed on the other
end of the protein chain, both sides of the chain will experience
a strong pull toward water and the chain very likely will be
unwound from both sides and will perhaps look like this:
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2. A piece of DNA was
hit by radiation, breaking the strand of nucleotides.
Will the DNA necessarily produce a different protein now? On what does this depend?
This DNA fragment will very likely produce a different protein. The insertion of a new nucleotide in the DNA changes the genetic code possible creating different triplets of nucleotides (codons), starting with the codon the where the insertion occurred. As the result, the cell may use the wrong amino acids to build the protein.
3. There is a dangerous human disease, called Cystic Fibrosis that affects various organs, making it hard to breathe. It often shortens peoples' lifespan. It is known that Cystic Fibrosis is an inherited disease, that is, one that can be passed on from parents to children. Trying to uncover the cause of the disease and seeking a cure, scientists noticed that those with this disease have very salty (chloride-filled) sweat. Scientists isolated a protein from the skin of healthy individuals and found that it works like a control valve, regulating how much chloride goes out with the sweat. People with Cystic Fibrosis are missing that protein valve. Scientists discovered that, because the protein was misshapen, it could not take its place in the cell membrane, where it controls the flow of salt in and out of the cell.
Box 2: To make protein that serves as a salt valve, the cell transcribes the genetic information from the gene that codes such protein. In people that inherited Cystic Fibrosis, this gene is mutated and when it transcribes the cell use this information to assemble a protein with the wrong sequence of amino acids
B. How you would possibly attempt to cure the illness?
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