Biochemistry 2280A Lecture Notes - Lecture 3: Alpha Helix, Protein Structure, Hydrogen Bond

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sapphirebear815

28 Oct 2016

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To find overall net charge, need to add up net charge of all ionisable groups at a given ph. Proteins are linear polymers of amino acids. Size: 50 to > 30,000 amino acids. Dipeptide: a peptide chain composed of 2 amino acids. Tripeptide: a peptide chain composed of 3 amino acids. Oliopeptide: a peptide chain composted of 3-10 amino acids. Polypeptide: a peptide chain composted of many amino acids (50+) Protein: a molecule composted of one or more polypeptide: some proteins have 1, some have more. All proteins are polypeptides but not all polypeptides are proteins: protein is a functional unit. Condensation reaction: water is the product: new bond formed that links 2 amino acids called the peptide bond. One of the amino acids loses its carboxyl group and the other loses part of its amino group: 3 atoms lost in the form of water, the product only has 2 ionizable groups.

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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?

purpleyak702

It said I had two wrong. Please help.

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

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.

maroonwallaby335

Biochemistry 2280A Lecture Notes - Lecture 3: Alpha Helix, Protein Structure, Hydrogen Bond

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