Unlocking DNA: A Guide to Gel Electrophoresis

Biology Grades High School 6:59 Video
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Lesson Description

Explore the principles and applications of gel electrophoresis in separating DNA and protein fragments by size. Learn about agarose and SDS-PAGE techniques.

Video Resource

Gel electrophoresis | Chemical processes | MCAT | Khan Academy

khanacademymedicine

Duration: 6:59
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Key Concepts

  • Gel Electrophoresis: Separating molecules by size using an electric field.
  • Agarose Gel: Used for separating large DNA fragments.
  • SDS-PAGE: Used for separating small DNA fragments and proteins.

Learning Objectives

  • Explain the principles of gel electrophoresis and its applications in separating DNA and protein fragments.
  • Differentiate between agarose gel electrophoresis and SDS-PAGE, understanding their respective uses.
  • Interpret gel electrophoresis results to determine the size of DNA fragments.

Educator Instructions

  • Introduction (5 mins)
    Begin with a brief overview of the central dogma of molecular biology (DNA -> RNA -> Protein). Introduce the concept of DNA and protein separation techniques, highlighting the importance of gel electrophoresis in molecular biology research.
  • Video Presentation (10 mins)
    Play the Khan Academy video on gel electrophoresis. Instruct students to take notes on the key steps and concepts presented.
  • Discussion and Q&A (10 mins)
    Facilitate a class discussion based on the video content. Clarify any misconceptions and address student questions regarding the procedure and concepts.
  • Activity: Interpreting Gel Results (15 mins)
    Present students with sample gel electrophoresis results and guide them through the process of determining the size of unknown DNA fragments using a DNA ladder.
  • Wrap-up and Review (5 mins)
    Summarize the key concepts covered in the lesson. Assign a follow-up activity, such as reading a related article or completing a worksheet.

Interactive Exercises

  • Gel Electrophoresis Simulation
    Use an online gel electrophoresis simulation to allow students to virtually perform the experiment and manipulate variables such as voltage and gel type.
  • Fragment Analysis Worksheet
    Provide students with a worksheet containing different gel electrophoresis results for them to analyze and determine the sizes of the DNA fragments.

Discussion Questions

  • Why is an electrical field necessary for gel electrophoresis?
  • How does the pore size of the gel affect the separation of DNA fragments?
  • What is the purpose of the DNA ladder in gel electrophoresis?

Skills Developed

  • Critical Thinking
  • Data Interpretation
  • Scientific Reasoning

Multiple Choice Questions

Question 1:

What is the primary purpose of gel electrophoresis?

Correct Answer: To separate DNA and protein fragments by size

Question 2:

Which electrode does DNA migrate towards during gel electrophoresis?

Correct Answer: Anode (positive)

Question 3:

What is the purpose of a DNA ladder in gel electrophoresis?

Correct Answer: To provide a size standard for comparison

Question 4:

Which type of gel is best suited for separating large DNA fragments?

Correct Answer: Agarose gel

Question 5:

What does SDS do in SDS-PAGE?

Correct Answer: It denatures proteins and gives them a uniform negative charge

Question 6:

What property of DNA allows it to be separated by gel electrophoresis?

Correct Answer: Its negative charge

Question 7:

If a DNA fragment travels further on the gel, is it larger or smaller than a fragment that travels less far?

Correct Answer: Smaller

Question 8:

In gel electrophoresis, what provides the medium through which molecules move?

Correct Answer: The gel

Question 9:

Why is a dye mixed with the DNA sample before loading it into the gel?

Correct Answer: To visualize the DNA movement during electrophoresis

Question 10:

What is the purpose of the buffer solution used in gel electrophoresis?

Correct Answer: To conduct electricity and maintain pH

Fill in the Blank Questions

Question 1:

Gel electrophoresis separates DNA and protein fragments based on their ____.

Correct Answer: size

Question 2:

Agarose gel is typically used for separating ____ DNA fragments.

Correct Answer: large

Question 3:

The positively charged electrode in gel electrophoresis is called the ____.

Correct Answer: anode

Question 4:

DNA has a negatively charged backbone due to the presence of ____ groups.

Correct Answer: phosphate

Question 5:

SDS-PAGE is commonly used for separating ____ and small DNA fragments.

Correct Answer: proteins

Question 6:

The DNA ____ is used as a standard to determine the sizes of unknown DNA fragments.

Correct Answer: ladder

Question 7:

____ is a chemical agent that denatures proteins in SDS-PAGE.

Correct Answer: SDS

Question 8:

During electrophoresis, DNA fragments migrate towards the ____ electrode.

Correct Answer: positive

Question 9:

The substance used to make the gel in SDS-PAGE is called ____.

Correct Answer: polyacrylamide

Question 10:

A ____ is needed to power the electrical field in gel electrophoresis.

Correct Answer: battery

Educational Standards

B.LS1.1:[Standard] Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. B.LS3.1:[Standard] Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring. B.LS4.1:[Standard] Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.

Teaching Materials

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