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BIOCH200 Lecture Notes - Lecture 2: Protein Structure, Dipeptide, Peptide

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skycaribou653
11 Dec 2017
School
University of Alberta
Department
Biochemistry
Course
BIOCH200
Professor
Jonathan Parrish

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Document Summary

In the formation of a peptide bond, the c-terminus and the n-terminus only retain their charge. If the side chains have charge, they are also retained. Primary structure: the sequence of amino acids in a polypeptide is its primary structure. The four major levels of protein structure: primary, secondary, tertiary, quaternary. The peptide bonds limit the possible conformations a polypeptide can adopt because free rotation around c-n bond is not possible. In secondary structure, h bonds form between the amino acid peptide backbones. C=o group are hydrogen acceptors and n-h groups are hydrogen donors. Regular patterns in secondary structure satisfy h bond potential and minimise steric repulsion. Steric conflict: h bond forms between backbone co and nh in the same helices. Globular proteins: hydrophobic interactions, hydrophobic side chains found in the interior, hydrophilic side chains found on the exterior, most irregular structures are found on the exterior because they form hydrogen bonds with the water.

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Related Questions

1. A sequence of amino acids in a certain protein is found to be – Ser – Gly – Pro – Gly –

The sequence is most probably part of a(n):

a. beta turn

b. antiparallel beta sheet

c. alpha-helix

d. parallel beta-sheet

e. alapha-sheet

2. Which statement about peptides bonds is NOT TRUE?

There is perfectly free rotation about the peptide bond.

The peptide bond has partial double-bond character.

The peptide bond is shorter than a normal carbon-nitrogen single bond.

The peptide bond usually has a trans configuration with respect to the alpha-carbons of the two amino acids involved in the peptide bond.

Peptide bonds are made via condensation of an amine and a carboxylic acid with loss of water.

3. Which of the following statements about proteins is FALSE?

Active proteins are generally very loosely structured.

In water-soluble proteins, hydrophobic amino acid residues are generally buried and not exposed to water.

Primary structure determines tertiary structure.

Secondary structure is regular, recurring arrangements in space of nearby amino acid residues in a polypeptide.

Quaternary structure involves the interaction of subunits in a protein with more than one polypeptide chain.

It said I had two wrong. Please help.

Proteins are naturally occurring polymers formed by condensation reactions of amino acids, which have the general structure

In this structure, –R represents –H, –CH3, or another group of atoms; there are 20 different natural amino acids, and each has one of 20 different R groups. (a) Draw the general structure of a protein formed by condensation polymerization of the generic amino acid shown here. (b) When only a few amino acids react to make a chain, the product is called a “peptide” rather than a protein; only when there are 50 amino acids or more in the chain would the molecule be called a protein. For three amino acids (distinguished by having three different R groups, R1, R2, and R3), draw the peptide that results from their condensation reactions. (c) The order in which the R groups exist in a peptide or protein has a huge influence on its biological activity. To distinguish different peptides and proteins, chemists call the first amino acid the one at the “N terminus” and the last one the one at the “C terminus.” From your drawing in part (b) you should be able to figure out what “N terminus” and “C terminus” mean. How many different peptides can be made from your three different amino acids?