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My two cents. Good luck
1 b (d is wrong- Immunoglobulins are proteins)
2 b (http://en.wikipedia.org/wiki/File:Amino_Acids.svg)
3 Not sure I understood the question very well. But, I would go with C as Leu carries a hydrophobic side chain
5 d (Hydrogen bonds make up secondary structure)
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they look good to me but i took bio a year ago so i might be wrong.
1. Proteins don't usually serve as an energy source, except in cases of malnutrition and starvation. Also, relliknaip is right, imminoglobulins are proteins and they serve in defense since they are a major part of your adaptive immune response.
2. Arg is a positive amino acid. So, unless you were replacing a positive amino acid, putting arg in would make your protein more positive.
3. Leu is a hydroPHOBIC amino acid. Think about the word hydrophobic. Hydro means "water" and phobic means "fearing". So being hydrophobic means it doesn't like water and it probably has no over all charge. Lipids are also hydrophobic so you can think about the phospholipid bilayer here to think about what your Leu is going to do. If your protein gets dissolved in water, it's going to avoid contact with the H2O molecules because they are polar. (phobic=fearing, it's going to run away) But also remember from your chemistry classes that like dissolves like; meaning that hydrophobic molecules stick together and hydrophilic molecules stick together. So, Leu is going to avoid contact with both the water and any hydrophilic side chains. (hydro=water, philic=loving, hydrophilic molecules are most likely charged or polar and are attracted to the polar water molecules)
4. You need to look at the chemical arrangements of the amino acids, but that answer is correct. Amino acids don't use aldehydes as functional groups.
5. Peptide bonds are the bonds formed between adjacent amino acids. In other words, it is the bond formed between the NH2 group of one amino acid and the COOH of the adjacent amino acid. When the two amino acids become linked, a dehydration reaction occurs and a peptide bond is formed. Disulfide bonds help stabilize the tertiary structure, but don't do much for the secondary structure. Hydrogen bonds are extremely important in the stabilization of the secondary structure.
6. It's true that quat- means four. But don't be misled by the the term "four fold symmetry" here. That term don't really mean anything which relates to the question. First off, proteins rarely have anything which resembles symmetry. Secondly, when I think about the different levels of protein structure, I find it easiest to think about them like this:
primary: amino acid sequence
secondary: alpha-helicies and beta-sheets, small structures
tertiary: 3-D structure of amino acid chain as a whole
quaternary: the way all the sub-units of the protein interact with each other
7. E is what I would choose, although it's a somewhat misleading question.
8. Disulfide bridges can only be made when there are two sulfur containing amino acids near enough. Cystine is the only amino acid which can do that, even though methionine has S also. The reasons for this are bit complicated.
9. Technically, you're correct here. But there's a possibility that they're actually looking for just b. Personally, I'd put down e and then fight it if I got marked wrong.
10. Possible, but you're going to be marked wrong for this one. It is true that cystine in a protein structure, i.e. not free-floating, is not charged. Sulfur also has a low electronegativity compared to hydrogen, which it's bound to, so it is also non-polar. However, being uncharged and non-polar, is it also hydrophobic. Remember that earlier we decided that hydrophobic means "water fearing" and we discussed that lipids, such as those in the phospholipid bilayer, are also hydrophobic. Remember also that we discussed the fact that similar molecules are attracted to one another. So, they hydrophobic lipids in the bilayer are going to attract hydrophobic amino acids.