BCH210H1 Lecture Notes - Lecture 2: Aromatic Amino Acids, Cystine, Aspartic Acid

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ochreminnow2

2 Oct 2018

School

UTSG

Department

Biochemical Engineering and Applied Chemistry

Course

BCH210H1

Professor

Wright

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BCH210H1 Full Course Notes

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Threonine, thr, t (has beta-branched side chain) Cysteine, cys, c (when oxidized, cystine) Pro (looks hydrophobic, but classified in a diff way) Hydrophobic a. a occurs usually in the interior of globular protein. Hydrophilic a. a occurs usually on the exterior of globular protein. R, k ,e, d, q, n, s, t. Zwitterion changes form pk a of amino acid side chains. Pk a : ph value at which group is half protonated and half unprotonated. Glutamic acid, glu, e: pk a = 4. 3. Aspartic acid, asp, d: pk a = 3. 9. Non - polar groups driven together because water h bonds strongly to itself. Mainly protonated amino and ionized carboxylate groups. Stabilizing, attractive interactions between a proton (usually part of a polarizable bond: -nh, -oh, -sh) & an e- donating species (c=o) Important for protein structure such as the____- helix. Largely from favorable (non-repulsive) interactions between side chains. Based on proximity and packing at the.

Related Questions

1. What is the optimum pH to separate a mixture of lysine, arginine, and cysteine using electrophoresis? (See the table in the image.)

A. At pH about 7.0

B. At pH about 5.1

C. At pH about 9.5

D. At pH about 10.8

2. Choose the structure of lysine in the protonation state that would predominate at the pH you have chosen.

3. Choose the structure of arginine in the protonation state that would predominate at the pH you have chosen.

4. Choose the structure of cysteine in the protonation state that would predominate at the pH you have chosen.

Amino Acid	M.W. g/mol	pK_a for side chain
Alanine	89.1
Arginine	174.2	12.48
Asparagine	132.1
Aspartate	133.1	3.90
Cysteine	121.1	8.37
Glycine	75.0
Glutamate	147.1	4.07
Glutamine	146.1
Histidine	155.1	6.04
Isoleucine	131.2
Leucine	131.2
Lysine	146.2	10.54
Methionine	149.2
Proline	115.1
Phenylalanine	165.2
Serine	105.1
Threonine	119.1
Tryptophan	204.2
Tyrosine	181.2	10.46
Valine	117.1

Take a look at your pK_a table for the amino acids. It turns out that when these side chains are in a protein, they can have very different pK_a values. Explain the following observations:

a. In the enzyme medium chain acyl-CoA dehydrogenase (b-oxidation of fatty acids), E376 has a measured pK_a ~ 8.0. It is found in a very hydrophobic environment. What could account for it elevated pK_a?

b. For the enzyme aconitase (Krebbâs Cycle), a catalytic serine is known to have a pK_a ~ 8. What kind of factors could account for this decrease in pK_a?

lilacbee20

The peptide hormone vasopressin is used in the regulation of Na+ in many vertebrate. Porcine(pig) vasopressin has the sequence Asp-Tyr-Phe-Glu-Asn-Cys-Pro-Lys-Gly.

a) What is the pI of this peptide? Use the pKa values in the table on the last page for your calculations.

b) Could this peptide have an a helical secondary structure? Why or why not.

c) Will this peptide absorb UV light(280nm)? Why?

BCH210H1 Lecture Notes - Lecture 2: Aromatic Amino Acids, Cystine, Aspartic Acid

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