Question 1

Which amino acid residues are used as attachment sites for covalently bound oligosaccharides in glycoproteins?

Accepted Answer

N-linked carbohydrate is bound to asparagine, and O-linked carbohydrate is bound to serine or threonine (or, in collagen, to hydroxylysine).

Question 2

An amino acid whose side chain is most likely to be found in the center of a tightly packed, water-soluble globular protein such as myoglobin is:

Accepted Answer

Hydrophobic amino acid side chains aggregate in the core of globular proteins, to avoid contact with the surrounding water.Better start: The leucine side chain is hydrophobic. Hydrophobic …

Question 3

Which of the following is true regarding the structure shown? -CH₂-CH₂-COO-

Accepted Answer

Unlike glutamine, glutamate is negatively charged.All negatively charged amino acid side chains prefer the surface of globular proteins, where they can interact with water and dissolved ions.

Question 4

Amino acids at the isoelectric point in the titration curve have a net charge of:

Accepted Answer

This is the definition of the isoelectric point.

Question 5

Which of the following statements about protein structure is correct?

Accepted Answer

Protein conformation is established by noncovalent interactions between functional groups of the polypeptide, sometimes aided by helper proteins called chaperones.Disulfide bonds are formed between cysteine side chains that have been brought into close proximity during the initial folding process.

Question 6

Which of the following is true about the tertiary structure of proteins?

Accepted Answer

Hydrophobic groups associate with one another to minimize the thermodynamically unfavorable interface between lipid and water.Hydrophobic interactions and van der Waals interactions prevail in the core of globular proteins.

Question 7

The secondary structure of proteins:

Accepted Answer

The hydrogen bonds are formed between the components of the peptide bonds.

Question 8

In the tripeptide glutathione (γ-glutamyl-cysteinyl-glycine), the side chain carboxyl group of glutamate forms a peptide bond with the α-amino group of cysteine.The α-amino and α-carboxyl groups of glutamate do not participate in peptide bonds.Approximately what is the isoelectric point (pK) of glutathione?

Accepted Answer

There is an α-amino group (of glutamate) with a pK near 9 or 10, an α-carboxyl group (of glutamate) with a pK near 2, a carboxyl terminus (formed by glycine) with a pK near 4, and a cysteine sulfhydryl group (SH) with a pK near 8.The isoelectric point is halfway between the pK values of the two carboxyl groups.

Question 9

Histones are proteins that bind to negatively charged phosphate groups of DNA.An amino acid in the histones that can mediate this binding is:

Accepted Answer

The lysine side chain carries a positive charge at pH values near 7.

Question 10

Which of the following statements is correct for protein structure?

Accepted Answer

Glycine is too flexible, and proline is too rigid to fit comfortably in an a helix.

Question 11

All naturally occurring amino acids:

Accepted Answer

Only glycine has no asymmetrical carbon.

Question 12

Noncovalent bonds essential for the formation of the α helix and b-pleated sheet are:

Accepted Answer