Week 3 Homework Flashcards
True or false? There is a limited range in the size and shape of proteins.
False
True or false. Amino acid properties determine what a protein looks like and what it does.
True
True or false. A protein is a polymer and amino acids are the monomers.
True
True or false. Covalent bonds join amino acids together.
True
True or false. Only the α-carboxyl group in an amino acid can act as an acid.
False
What is the conjugate acid of C6H5NH2?
C6H5NH3+
The pH inside cells is normally near pH 7. At pH 7 which answer choice is TRUE about the charges (ionization state) of the α-carboxyl and α-amino groups of an amino acid?
I. The α-carboxyl group has a charge of +1 and the α-amino group has a charge of -1.
II. Both groups are uncharged (not ionized) at pH 7.
III. The α-carboxyl group has a charge of -1 and the α-amino group is uncharged.
IV. The α-carboxyl group has a charge of -1 and the α-amino group has a charge of +1.
IV
Ionizable amino acid side chains in aqueous solution become increasingly protonated as the pH ___.
Decreases
As pH drops, an increase in protonation leads to more carboxyl groups becoming ___ and more amine groups becoming ___.
Neutral, positively charged
On the other hand, if pH increases, proteins become more ___ because more carboxyl groups lose protons and become ___ while amine groups lose protons and become ___.
Negatively charged, negatively charged, neutral
Calculate the value of pKa for an acid when Ka = 2.6 × 10-4.
+3.59
Which statements regarding the Henderson-Hasselbalch equation are true?
1) If the pH of the solution is known as is the pKa for the acid, the ratio of conjugate base to acid can be determined.
2) At pH = pK a for an acid, there is an equal amount of conjugate base to acid in solution.
3) At pH»_space; pK a for an acid, the acid will be mostly deprotonated.
4) At pH «_space;pK a for an acid, the acid will be mostly deprotonated.
1, 2, and 3 are true
Use these two points to answer the question.
-Ka describes the equilibrium constant for the dissociation of an acid.
-pKa is related to Ka by the following equation: pKa = -log(Ka).
Which of the following statements about Ka and pKa is/are true?
I. Ka is quantified by measuring the concentration of reactants over the concentration of products in an acid-base reaction.
II. weaker acids will have a higher pKa values
III. stronger acids will have a higher Ka values
II and III
Which of the following statements correctly compares ACIDIC and BASIC amino acids?
I. All amino acid R groups in both categories can ionize.
II. All amino acid R groups in both categories can possess an overall charge of -1.
III. Only amino acid R groups in the ACIDIC category can donate a proton (H+).
IV. All of the statements are correct.
I
True or false? The higher the Ka value, the weaker the acid.
False
True or false? pKa is calculated by taking the logarithm of Ka.
False
True or false? A large Ka has a small pKa.
True
At a midpoint on a titration curve ________.
the pH equals the pKa
Which of the following amino acid functional groups react to form a peptide (amide) bond?
I. R group and α-carboxyl group
II. α-amino group and α-carboxyl group
III. R group and α-amino group
IV. Either an R group and α-carboxyl group OR an R group and α-amino group
II
True or false? A peptide bond can rotate freely; this free rotation gives the polypeptide chain flexibility when folding.
False
True or false? A polypeptide chain has direction, meaning the ends are different.
True
True or false? Formation of the peptide bond is classified as a hydrolysis reaction.
False
Calculate the overall charge of the following peptide at pH = 6.0. The N-terminus is on the left and C-terminus is on the right. Please use Table 5.1 in your textbook or eText for any pKa values you might need. Also, please refer to Figure 5.3 to interpret the 3-letter amino acid abbreviations.
Met - Arg - Lys - Asp - Val - Gln
+1
