Question 1

Which of the following best explains why SDS is used in SDS-PAGE for protein electrophoresis?

Accepted Answer

SDS solubilizes and denatures proteins, giving them a uniform negative charge so they separate based on size.

Question 2

During SDS-PAGE, which factor primarily determines the rate at which a protein migrates through the gel?

Accepted Answer

The protein's molecular size (mass)

Question 3

Why is polyacrylamide gel preferred over agarose gel for separating proteins in electrophoresis?

Accepted Answer

Polyacrylamide gels have a tighter matrix and smaller pore size, ideal for separating small protein molecules.

Question 4

A student runs an SDS-PAGE gel and observes that a protein band migrates a shorter distance than expected. What is the most likely explanation?

Accepted Answer

The protein is larger than expected.

Question 5

Which of the following best describes the principle of maximum parsimony in molecular phylogenetics?

Accepted Answer

It favors the tree that requires the fewest evolutionary changes.

Question 6

Given the following data from a standard curve in SDS-PAGE: a protein migrates 25 mm, and the standard curve equation is $$\log_{10}(M) = -0.03x + 2.0$$, where $$M is $$the molecular mass in kD and $$x is $$the migration distance in mm. What is the approximate molecular mass of the protein?

Accepted Answer

$$M \approx 89 kD$$

Question 7

Which of the following proteins would you expect to migrate the shortest distance on an SDS-PAGE gel?

Accepted Answer

Titin (3000 kD)

Question 8

In a molecular phylogenetic analysis using protein electrophoresis, which of the following would provide the strongest evidence that two fish species are closely related?

Accepted Answer

They share several protein bands at identical migration distances.

Question 9

Why is it important to use a molecular marker or size standard in each SDS-PAGE gel run?

Accepted Answer

To allow estimation of the molecular masses of unknown proteins by comparison.

Question 10

A researcher is comparing the protein profiles of five fish species using SDS-PAGE. Which step is necessary to construct a character matrix for phylogenetic analysis?

Accepted Answer

Record the presence or absence of bands at specific migration distances for each species.

Question 11

Which of the following statements about the molecular clock hypothesis is correct?

Accepted Answer

It assumes that DNA sequences diverge at a constant rate over time.

Question 12

If a protein sample is not heated before loading onto an SDS-PAGE gel, what is the most likely outcome?

Accepted Answer

Proteins may retain their tertiary or quaternary structure, affecting migration.

Question 13

Which of the following is a real-world application of protein electrophoresis in medicine?

Accepted Answer

Diagnosing genetic diseases by identifying abnormal hemoglobin variants.

Question 14

A student is analyzing a gel and finds that two fish species share all but one protein band. What is the most likely evolutionary relationship between these two species?

Accepted Answer

They are closely related, possibly recently diverged.

Question 15

Which of the following best describes the function of bromophenol blue in the sample buffer for SDS-PAGE?

Accepted Answer

It provides a visible dye to track sample migration during electrophoresis.

Question 16

If a polyacrylamide gel with a smaller pore size is used, what will be the effect on the separation of proteins?

Accepted Answer

Smaller proteins will be better resolved from each other.

Question 17

Which of the following is a key assumption of the maximum likelihood approach in molecular phylogenetics?

Accepted Answer

Specific rules about how DNA changes over time are used to find the most likely evolutionary tree.

Question 18

A researcher stains a gel with Coomassie blue after electrophoresis. What is the primary purpose of this step?

Accepted Answer

To visualize the separated protein bands.

Question 19

Which of the following best explains why a molecular phylogenetic tree should only include monophyletic groups?

Accepted Answer

Monophyletic groups include all descendants of a common ancestor, reflecting true evolutionary relationships.

L 7.1 Protein Electrophoresis and Molecular Phylogenetics in Fish

Study Guide - Practice Questions

Study Guide - Flashcards