BIOLOGY 151 Lecture Notes - Lecture 27: Beta Sheet, Alpha Helix, Tyrosine Kinase

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champagnemole443

26 Apr 2017

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Use this to decide which amino acids would be found on the inside/outside of the protein. Glycine is not really all that nonpolar just has a hydrogen. Tyrosine has a benzene ring which is hydrophobic, but because it has an oh it can be considered polar or hydrophilic. Tyrosine kinase put phosphate on tyrosine of another protein (means more likely to be on outside, not going to go digging on inside to add phosphate to another) Primary structure- amino acid sequence in the protein. If we say the primary structure is changed, this means the amino acid sequence in the protein is changed, usually by a mutation. Secondary structure- consists of beta pleated sheets or alpha helices. The things holding alpha helices and beta pleated sheets together is hydrogen bonds between backbones. Quaternary structure- multiple polypeptides making up a protein.

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1. A polypeptide chain has a large percentage of acidic and basic amino acids in it. The R groups of these amino acids form ionic interactions, which helps the protein to maintain itâs structure. This particular polypeptide works well under an optimum pH of 7. Ignoring effects of strong acids and bases on peptide bonds, what will happen to the tertiary structure of the protein if you move it stomach acid, which has a pH of 1-2. Why? Be specific regarding what influence the pH will have on the bonds maintaining tertiary structure in the molecule. Include the amino acid charges of the acidic and basic amino acids at the acidic pH, as well as the concept of pK in your answer. Assume that acidic amino acids have a pK of approximately 4.7 and basic amino acids have a pK of approximately 10.

2. Ignoring peptide length (or lack thereof) where would this portion of a polypeptide be most likely to be found: On the inside or on the outside surface of a protein floating around in the cytoplasm? Explain

3. A mutation occurs in the SRC kinase such that the tyrosine on the loop over the active site is changed to aspartic acid. This mutation mimics phosphorylation.
a. knowing what you know about the properties of phosphate groups and aspartic acid, why does aspartic acid mimic phosphorylation?
b. What would be the implication of this mutation on the function of the SRC kinase?

1. Amino acid changes in the primary structure of the protein arenot capable of causing changes in the
overall shape of a protein.
a.) True
b.) False

2. An alpha helix:
a.) is destabilized by the amino acid alanine
b.) can only form by hydrogen bonding between different polypeptidechains
c.) can only form when cysteines form disulfide bridges within thisstructure
d.) all of the above
e.) none of the above

3. What will likely happen if two aspartates at pH 5 are next toeach other in a polypeptide chain?
a.) The side chains of these amino acids will be uncharged andthere will be no effect.
b.) The side chains of these amino acids will be charged and theywill attract each other.
c.) The side chains of these amino acids will be charged and theywill repel each other.
d.) Not enough information is given to determine the effect.

4. Consider the amino acid phenylalanine. Which of the followingbest describes where you predict this
amino acid would be found?
a.) This amino acid is hydrophobic and would be on the surface of aprotein that is in the middle
of a membrane.
b.) This amino acid is hydrophilic and would be on the surface of aprotein that is in the middle
of a membrane.
c.) This amino acid is hydrophobic and would be in the interior ofa protein that is in the middle
of a membrane.
d.) This amino acid is hydrophilic and would be in the interior ofa protein that is in the middle of
a membrane.
e.) Not enough information is given to determine.

5. The difference between fetal and adult hemoglobin with regard tooxygen binding occurs because fetal
hemoglobin has an amino acid substitution in one of its chains thatresults in a histidine being replaced by a
serine.
a.) True
b.) False

1. The side chain of tyrosine is considered to be polar because even though it is reminiscent of phenylalanine it also has two types of atoms that have large differences in electronegativity with asymmetry at the terminus.

a.) True

b.) False

2. Which of these changes in primary structure will be certain to cause a loss of protein activity?

a.) Asp to Glu

b.) His to Lys

c.) Trp to Ser

d.) Gly to Pro

e.) Not enough information is given since any one of these changes could be severe depending on the context of the situation

3.The difference between fetal and adult hemoglobin with regard to oxygen binding occurs because fetal hemoglobin has an amino acid substitution in one of its chains that results in a histidine (adult version) being replaced by a serine (fetal version).

a.) True

b.) False

4. What will likely happen if the side chains of aspartate and histidine at pH 5 are next to each other in a polypeptide chain?

a.) The side chains of these amino acids will be uncharged and there will be no electrostatic effect.

b.) The side chains of these amino acids will be charged and they will attract each other.

c.) The side chains of these amino acids will be charged and they will repel each other.

d.) Not enough information is given to determine the effect.

5. A beta pleated sheet:

a.) can occur between two different polypeptide chains
b.) can be formed by either intramolecular or intermolecular hydrogen bonds
c.) can only form when cysteines form disulfide bridges within this structure
d.) forms when side chains of D and E attract each other
e.) both a and b

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BIOLOGY 151 Lecture Notes - Lecture 27: Beta Sheet, Alpha Helix, Tyrosine Kinase

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