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Lecture 4 - Amino Acid Peptide & Proteins

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p.4

Which of the following describes the general structure of an α-amino acid?

A. A central α-carbon bonded to an amino group, a carboxyl group, a hydrogen, and a variable R-group.
B. A straight chain of carbon atoms with alternating amino and carboxyl groups.
C. A ring structure containing an imino group in all amino acids.
D. A central carbon bonded to two amino groups and two carboxyl groups.
E. A peptide backbone with repeating -CO-NH- units.

Select an answer

p.4

Explanation

Standard α-amino acids have a central α-carbon bonded to an amino group, carboxyl group, hydrogen, and variable R-group; proline is a notable exception as an imino acid.

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1 / 46
p.4

Which of the following describes the general structure of an α-amino acid?

A

p.8

Which amino acid is achiral and lacks optical activity among the standard amino acids?

C

p.6

Which category includes Tyrosine and Tryptophan, and what is a key property of these residues?

B

p.7

Which amino acid contains a sulfhydryl group and can form disulfide bonds?

D

p.10

At the isoelectric point (pI), an amino acid:

E

p.15

For an amino acid with a non-ionizable R-group, the isoelectric point (pI) is calculated as:

B

p.14

Which amino acid has a pKR near physiological pH and often acts as a buffer in biological systems?

A

p.17

Which statement best explains why peptide bonds are planar and restrict rotation?

C

p.18

When naming peptides, the sequence is written from:

B

p.19

Which of the following peptides is an antioxidant composed of three residues?

D

p.21

Which level of protein structure is defined solely by the linear amino acid sequence?

A

p.23

Which secondary structure is stabilized by hydrogen bonds between the C=O of residue i and the N–H of residue i+4?

C

p.25

Which amino acid is commonly found in β-turns at position i+1 due to its cyclic structure?

B

p.26

On a Ramachandran plot, glycine differs from most amino acids because:

D

p.28

Which of the following interactions is the major driving force for protein folding, tending to bury nonpolar side chains in the protein interior?

B

p.28

Which covalent bond stabilizes tertiary structure by linking two cysteine residues?

A

p.29

Domains in proteins are best described as:

C

p.30

Hemoglobin is an example of which quaternary structure arrangement?

D

p.31

Which denaturing agent specifically breaks disulfide bonds?

E

p.31

Anfinsen's experiment supports which conclusion about protein folding?

B

p.30

Which pair of forces stabilizes quaternary subunit interfaces?

C

p.21

Which amino acid substitution causes sickle cell anemia by altering primary structure and protein function?

A

p.29

Which structural motif is commonly involved in DNA binding and consists of two α-helices connected by a short turn?

B

p.24

Which statement about β-sheets is true?

D

p.19

Which of the following peptides is a hormone that lowers blood glucose and consists of about 51 residues?

A

p.23

Which residue is most likely to disrupt an α-helix due to its rigid cyclic structure?

B

p.10

Which of the following best defines amphoteric behavior of amino acids?

C

p.9

Which of the following non-standard amino acid modifications is important for collagen stability?

D

p.6

Which of the following is true about proline compared to other amino acids?

A

p.15

Which technique exploits the isoelectric point (pI) of proteins to separate them?

B

p.28

Which amino acid side chains are typically involved in forming salt bridges (ionic bonds) in tertiary structures?

C

p.25

Which of the following best describes a β-turn?

A

p.18

Which statement about peptide bond directionality is correct?

D

p.33

Which of the following best explains cooperative oxygen binding in hemoglobin?

B

p.31

Which of the following is NOT typically a denaturing condition for proteins?

E

p.28

Which amino acid side chains are likely to be found on the surface of soluble globular proteins interacting with water?

A

p.9

Which post-translational modification is commonly involved in cell signaling by changing residue charge?

B

p.34

Which region of an antibody binds antigen with high variability and specificity?

C

p.31

Which is the main reason proteins lose function upon denaturation?

A

p.29

Which of these motifs is formed by repeating α-helices wound together and often mediates protein-protein interactions?

D

p.33

Which amino acids commonly participate in catalytic triads of serine proteases?

B

p.34

Which structural feature allows transmembrane GPCRs to span the membrane?

A

p.26

Which statement about the Ramachandran plot is FALSE?

E

p.28

Which amino acid is most likely to be found within the hydrophobic core of a globular protein?

B

p.9

Which of the following is an example of a non-proteinogenic biologically active amino acid mentioned in the lecture?

C

p.6

Which of the following best describes why Tyr and Trp are useful in protein concentration assays?

A

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