Biochemistry Lab Midterm

What is the unit for concentration commonly used in biochemistry?

Molarity (M), which is moles of solute per liter of solution (mol/L).

What is the unit for enzyme activity?

Enzyme units (U), which is the amount of enzyme that catalyzes the transformation of 1 micromole of substrate per minute.

What is the unit for mass commonly used in molecular biology?

Micrograms (µg) or milligrams (mg).

What is the unit for volume used for small-scale liquid handling?

Microliters (µL), milliliters (mL), and liters (L).

What is the unit for molecular weight?

Daltons (Da) or kilodaltons (kDa). 1 Da = 1 atomic mass unit.

What does the Ka value represent?

measures the strength of an acid in solution, representing how much an acid dissociates into its ions.

What does a high Ka value indicate?

indicates a strong acid, meaning it dissociates more in water.

What does the pKa value represent?

the negative logarithm of the Ka value: pKa=−log⁡(Ka) It measures how easily an acid gives up a proton. The lower the pKa, the stronger the acid.

How are Ka and pKa related?

pKa is inversely related to Ka. A lower pKa means a higher Ka, which means the acid is stronger and dissociates more in solution.

What does a low pKa value indicate?

indicates a stronger acid.

At what point in a titration is pH equal to pKa?

at the half-equivalence point of a titration, where half of the acid has been deprotonated.

What is the formula for calculating dilution factor?

Dilution factor = Vf/Vi

How do you calculate the new concentration after dilution?

New concentration = Concentration(i)/DF

What is a 1:10 dilution?

1 part solute to 9 parts solvent, resulting in a 10-fold decrease in concentration.

If 5 mL of a 2 M solution is diluted to a total volume of 50 mL, what is the final concentration?

Final concentration = 2M/10 = 0.2M

What does a micropipette measure?

Micropipettes measure very small volumes of liquid, typically in microliters (µL).

How do you read a P200 pipettor set to 150 µL?

top digit=1 middle=5 bottom=0

What is the volume range for a P20 micropipettor?

can measure volumes from 2 µL to 20 µL.

How should you hold a pipettor while aspirating liquid?

Hold the pipettor vertically to avoid drawing air bubbles into the tip while aspirating liquid.

What should you always do after using a micropipettor?

Always change the tip between samples to avoid contamination.

What is the pI (isoelectric point) of a protein?

the pH at which the protein carries no net charge, meaning it does not migrate in an electric field.

How do you calculate the pI of a simple amino acid?

pI=pKa1+pKa2/2, where pKa1 and pKa2 are the pKa values of the carboxyl and amino groups.

How do you calculate the pI for amino acids with ionizable side chains?

find the average of the two pKa values that are closest to the neutral form of the amino acid.

What is a buffer?

a solution that resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base, or a weak base and its conjugate acid.

How does a buffer maintain pH?

by neutralizing added acids (H⁺) with the conjugate base or added bases (OH⁻) with the weak acid, minimizing the change in pH.

What is the Henderson-Hasselbalch equation used for?

used to calculate the pH of a buffer system: pH=pKa+log([A]/[HA])

What is the effective buffering range of a buffer?

within ±1 pH unit of its pKa.

What is a common biological buffer?

Tris buffer is commonly used in biological experiments to maintain stable pH, especially in electrophoresis.

What is the Henderson-Hasselbalch equation?

pH=pKa+log([A]/[HA])

This equation relates pH, pKa, and the ratio of conjugate base ([A⁻]) to acid ([HA]).

How do you calculate the ratio of conjugate base to acid from pH and pKa?

[A]/[HA]=10^(pH-pKa)

If pH = pKa, what is the ratio of conjugate base to acid?

[A−]/[HA]=1[A⁻]/[HA] = 1[A−]:1[HA], meaning equal amounts of acid and conjugate base are present.

How do you calculate pKa from pH and the acid-base ratio?

Rearrange the Henderson-Hasselbalch equation:
pKa=pH-log([A]/[HA])

What happens when the pH is lower than the pKa

the acid form ([HA]) predominates.

What is the equation for a weak acid dissociation?

HA⇌H++A− Ka=[H+][A]/[HA]

What is the equation for a weak base?

B+H+⇌BH+ Kb=[BH+]/[B][H+]

What is the equation for % saturation in protein purification?

%Saturation=[Solvent Component] [Desired concentration]/[Solvent capacity] * 100

What is the second % saturation equation used in protein purification?

%saturation= mass of solute/total mass *100

What protein was purified using ammonium sulfate precipitation?

Typically large, soluble proteins are purified by ammonium sulfate precipitation to separate based on solubility.

What is salting out in protein precipitation?

a method where high concentrations of salt (e.g., ammonium sulfate) are added to precipitate proteins by reducing their solubility.

What role does pH play in protein precipitation?

Adjusting pH near the protein's pI can cause it to precipitate because the protein has no net charge and becomes less soluble.

How do you calculate % saturation?

%saturation= (Solute/solvent) * 100

What does a titration curve for an amino acid show?

shows the change in pH as a strong acid or base is added, indicating pKa values and the isoelectric point (pI).

What does the flat region on a titration curve represent?

The flat region corresponds to the buffer region, where the amino acid resists changes in pH (near its pKa values).

What is the significance of the equivalence point on a titration curve?

where the amino acid has fully reacted with the titrant, often where it carries no net charge (at its pI).