CELL BIOLOGY LAB (PCB 3023L)
MIDTERM EXAM QUESTIONS AND
ANSWERS GRADED A+ 2026
Standard curve - ANS graph or curve generated from a series of samples of known
concentration
What's the purpose of a standard curve? - ANS To determine the concentration of an
unknown sample using the known concentrations of a stock solution
colorimetric assay - ANS used to determine the concentration of colored compounds in a
solution
What was used in lab 1 to measure the absorbances of the standard solutions? -
ANS Coomassie Brilliant Blue G-250
Colors of Coomassie Dye - ANS Red = highly protonated (acidic)
Green= slightly protonated (neutral)
Blue= unprotonated (basic)
In acidic environment (low pH), most of the dye will exist in the red form due to an excess of H+
ions in solution
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, Which form of the Coomassie Dye binds to proteins? - ANS Blue (unprotonated)
How does the blue Coomassie Dye bind to the proteins? - ANS By noncovalent interactions
(with arginine) , Van der Waals forces and hydrophobic interactions with aromatic amino acid
side chains
T/F In the acidic environment of the Coommassie Plus reagent, a small percentage of dye exists
in the blue form - ANS True
What will happen to the color of the reagent as more protein is added and why? - ANS As
more protein is added, the color turns from a reddish-brown color (doubly protonated) to a blue
color (unprotonated)
-More blue color and higher absorbances will be read at 595 nm
-When more proteins are added, they bind to to the blue form, which generates more blue dye-
protein complexes
Wavelengths of Coomassie Reagents - ANS Red = 470 nm
Green = 650 nm
Blue = 595 nm
*Absorbance readings at 595 nm will therefore serve to reflect protein concentrations in the
solution*
Why is an acidic environment used for the Coomassie Reagent? - ANS In the absence of
proteins, a low pH results in the red form dye, which can give a negative reading.
The amount of blue dye in an acidic environment is proportional to the amount of proteins
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
MIDTERM EXAM QUESTIONS AND
ANSWERS GRADED A+ 2026
Standard curve - ANS graph or curve generated from a series of samples of known
concentration
What's the purpose of a standard curve? - ANS To determine the concentration of an
unknown sample using the known concentrations of a stock solution
colorimetric assay - ANS used to determine the concentration of colored compounds in a
solution
What was used in lab 1 to measure the absorbances of the standard solutions? -
ANS Coomassie Brilliant Blue G-250
Colors of Coomassie Dye - ANS Red = highly protonated (acidic)
Green= slightly protonated (neutral)
Blue= unprotonated (basic)
In acidic environment (low pH), most of the dye will exist in the red form due to an excess of H+
ions in solution
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, Which form of the Coomassie Dye binds to proteins? - ANS Blue (unprotonated)
How does the blue Coomassie Dye bind to the proteins? - ANS By noncovalent interactions
(with arginine) , Van der Waals forces and hydrophobic interactions with aromatic amino acid
side chains
T/F In the acidic environment of the Coommassie Plus reagent, a small percentage of dye exists
in the blue form - ANS True
What will happen to the color of the reagent as more protein is added and why? - ANS As
more protein is added, the color turns from a reddish-brown color (doubly protonated) to a blue
color (unprotonated)
-More blue color and higher absorbances will be read at 595 nm
-When more proteins are added, they bind to to the blue form, which generates more blue dye-
protein complexes
Wavelengths of Coomassie Reagents - ANS Red = 470 nm
Green = 650 nm
Blue = 595 nm
*Absorbance readings at 595 nm will therefore serve to reflect protein concentrations in the
solution*
Why is an acidic environment used for the Coomassie Reagent? - ANS In the absence of
proteins, a low pH results in the red form dye, which can give a negative reading.
The amount of blue dye in an acidic environment is proportional to the amount of proteins
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
