excerpt from chapter 19: proteins
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Excerpt from Chapter 19: Proteins. University of Louisiana at Lafayette CHEM 125, Leonard All images used with permission of publisher (Cengage Learning). Zwitterion. A zwitterion has two oppositely charged ions which exist in the same molecule. a. O. H 3 N. CH. C. O. R. +. −. - PowerPoint PPT PresentationTRANSCRIPT
Excerpt fromChapter 19:
Proteins
University of Louisiana at Lafayette
CHEM 125, LeonardAll images used with permission of publisher (Cengage Learning)
Zwitterion
2
H3N CH C O
O
R
+ −
•A zwitterion has two oppositely charged ions which exist in the same molecule.
•The zwitterion can only exist in solution which is at the isoelectric pH.
Zwitterion
3
H3N CH C O
O
R
+ −
•If the pH is too low, the solution is too acidic, the carboxylic salt end will gain H+.
+ H+
H3N CH C OH
O
R
+
positive charge
Zwitterion
4
H3N CH C O
O
R
+ −
•If the pH is too high, the solution is too basic.
•The amine salt end will lose H+.
− H+
negative charge
H2N CH C O
O
R
−
Structural Elements of Proteins
I. 1o Structural Elements
•The order and identity of each amino acid in the protein is it’s 1o structural element.
•Diseases like sickle-cell anemia is caused by a minor sequencing error in the hemoglobin protein.
Structural Elements of Proteins
II. 2o Structural Elements
•Alpha () helix – a coil held together by hydrogen bonds.
Small-scale folding patterns along the protein chain are the 2o structural elements:
Structural Elements of Proteins
•Alpha () helix – a coil held together by hydrogen bonds.
Structural Elements of Proteins
II. 2o Structural Elements
Small-scale folding patterns along the protein chain are the 2o structural elements:
•Alpha () helix – a coil held together by hydrogen bonds.
•Beta ()-pleated sheet – a folded sheet-like shape held together by hydrogen bonds.
Structural Elements of Proteins•Beta ()-pleated sheet – a folded sheet-like shape held together by hydrogen bonds.
Structural Elements of Proteins
II. 2o Structural Elements
Structural Elements of Proteins
III. 3o Structural Elements
Large-scale folding patterns which showhow 1 protein chain folds over itself:
A. Disulfide Linkage – 2 cysteine amino acids can link their thiol R groups.
B. Salt Bridge – attractions between the R groups of the acidic and basic amino acids.
C. Hydrogen Bonding – R groups with an H attached to an O, N, or F is attracted to other O, N, or F atoms.
D. Hydrophobic Interactions – nonpolar R groups attract other nonpolar R groups.
Structural Elements of Proteins
III. 3o Structural Elements
Structural Elements of Proteins
III. 3o Structural Elements
If the following two R groups were in close proximity along a protein chain, what 3o attractions would you see?
AA−C−NH2
OHO−CH2CH2−AA
a)
hydrogen bonding
Structural Elements of Proteins
III. 3o Structural Elements
If the following two R groups were in close proximity along a protein chain, what 3o attractions would you see?
b)
hydrophobic interaction
AA−CH2CH3
CH3CH2-CH−AA
CH3
Structural Elements of Proteins
IV. 4o Structural Elements
•Large-scale folding patterns which show how 2 or more protein chains fold over each other.
Hemoglobin: made up of4 protein chains.