24 Questions
A cell needs to store 1000 glucose units of fuel. To minimize osmotic pressure on the cell, the glucose should be stored as
One polysaccharide molecule (eg. starch)
What is the concentration of [OH-] in an aqueous solution of pH 6?
10 ^-8
Which of the following aqueous solutions has the lowest pH?
0.1M HCl
Why is ethanol more soluble in water than ethane?
Ethanol possesses a polar hydroxyl group to which water can hydrogen bond.
Which of the following aqueous solutions has the highest pH?
0.1M Acetic acid (pKa = 4.86)
Which of the following compounds is more soluble in aqueous 0.1M NaOH than aqueous 0.1M HCl?
Benzoic acid and Naphthol
The components of poison ivy and poison oak that produce the characteristic itchy rash are catechols substituted with long chain alkyl groups. If you were exposed to poison ivy, which of the treatments below would you apply to the affected area?
Wash with soap, water, and baking soda (sodium bicarbonate; pH ~9)
Aspirin is a weak acid with a pKa of 3.5. It is absorbed into the blood through the cells lining the stomach and small intestine. Absorption requires passage through the plasma membrane, the rate of which is determine by the polarity of the molecule: charged and highly polar molecules pass slowly, whereas neutral hydrophobic ones pass rapidly. Is more aspirin absorbed into the bloodstream from:
The stomach (pH 1.5) because aspirin is mostly protonated
Identify the following amino acid:
Proline
Identify the following amino acid:
Cysteine
Identify the following amino acid:
Glutamate
Identify the following amino acid:
Lysine
The best method to determine the purity of a protein is:
SDS-Page
When different folded polypeptides interact noncovalently to form a multisubunit protein, this is an example of:
Quaternary Structure
A disulfide bond in a protein is:
A bond between oxidized cysteines
Amino acids placed on a cation exchange resin containing sulfonate (-SO3) groups flow down the column at different rates because of two factors that influence their movement: (1) Ionic attraction between the sulfonate groups and positively charged functional groups on the amino acids, and (2) Hydrophobic interactions between amino acid side chains and the hydrophobic backbone of the polystyrene resin. For each pair of amino acids listed, which will be elute first from a cation exchange column by a buffer at pH 7.0?
- (A) Asp (B) Lys
- (A) Arg (B) Met
- (A) Glu (B) Val
- (A) Gly (B) Leu
- (A) Ser (B) Ala
(A)(B)(A)(A)(A)
The isoelectric point (pI) of a peptide is the pH at which the peptide does not migrate in an electric field. Since the peptide is zwitterionic, there are the same number of positive charges as negative charges on the peptide population The pI can be estimated fairly accurately (within 0.1 or 0.2 pH units) from the pK values of all the proton dissociable groups in the peptide. Using pK values from the table provided, estimate the pI value of the following hexapeptide.
Ala-His-Glu-Lys-Leu-Arg
9.25
Which amino acid sequence will form a more stable a-helix?
LKAENDEAARAMSEA
Where are B-turns most likely to occur?
7 and 19
If this sequence is part of a larger globular protein, an interior salt bridge might form between residues:
9 and 28
Where are disulfide bonds most likely to occur?
13 and 24
B-sheets are the main secondary structure in the following regions:
Pink and blue
Which region is most likely to constitute a domain (i.e most likely to be stable on its own):
Yellow
Which of the following explains why all individual amino acids are soluble in water but not all peptides are soluble?
Individual amino acids are zwitterions at physiological pHs
Study Notes
Storing Glucose
- To minimize osmotic pressure on a cell, 1000 glucose units of fuel should be stored as polysaccharides.
pH Concentration
- In an aqueous solution of pH 6, the concentration of [OH-] is 10^(-8) M.
Aqueous Solutions pH
- The aqueous solution with the lowest pH is HCl.
- The aqueous solution with the highest pH is NaOH.
Solubility
- Ethanol is more soluble in water than ethane because of its hydroxyl group, allowing it to form hydrogen bonds with water.
Poison Ivy and Oak
- The components of poison ivy and poison oak that produce the characteristic itchy rash are catechols substituted with long chain alkyl groups.
- To treat the affected area, wash with soap and water and apply calamine lotion or hydrocortisone cream.
Aspirin Absorption
- Aspirin is a weak acid with a pKa of 3.5.
- Aspirin is absorbed into the blood through the cells lining the stomach and small intestine.
- The rate of absorption is determined by the polarity of the molecule: charged and highly polar molecules pass slowly, whereas neutral hydrophobic ones pass rapidly.
- More aspirin is absorbed into the bloodstream from the stomach than the small intestine.
Amino Acids
- The amino acid ... is ...
- The amino acid ... is ...
- The amino acid ... is ...
- The amino acid ... is ...
Protein Purity
- The best method to determine the purity of a protein is through gel electrophoresis.
Protein Structure
- When different folded polypeptides interact noncovalently to form a multisubunit protein, this is an example of quaternary structure.
- A disulfide bond in a protein is a covalent bond between two cysteine residues.
Cation Exchange Resin
- Amino acids placed on a cation exchange resin containing sulfonate (-SO3) groups flow down the column at different rates due to ionic attraction and hydrophobic interactions.
- The elution order from a cation exchange column by a buffer at pH 7.0 is:
-
- Lys, then Asp
-
- Arg, then Met
-
- Glu, then Val
-
- Leu, then Gly
-
- Ala, then Ser
-
Isoelectric Point (pI)
- The isoelectric point (pI) of a peptide is the pH at which the peptide does not migrate in an electric field.
- The pI of a peptide can be estimated from the pK values of all the proton dissociable groups in the peptide.
- The pI of the hexapeptide Ala-His-Glu-Lys-Leu-Arg is approximately 8.5.
Amino Acid Sequence and Structure
- The amino acid sequence that will form a more stable α-helix is ...
- β-turns are most likely to occur at the protein surface.
- An interior salt bridge might form between residues with opposite charges in the sequence.
- Disulfide bonds are most likely to occur between cysteine residues near the protein surface.
- β-sheets are the main secondary structure in the protein's core region.
- A domain is a region that is most likely to be stable on its own, with hydrophobic residues buried and hydrophilic residues exposed.
Peptide Solubility
- All individual amino acids are soluble in water because they have polar and hydrophilic groups.
- Not all peptides are soluble in water because they can have nonpolar and hydrophobic regions.
Test your knowledge on the optimal storage of fuel in cells to minimize osmotic pressure. Learn about the most efficient way to store 1000 glucose units as fuel within a cell.
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