Textbook Question
The following segment of DNA is the template strand transcribed into mRNA:
5'-...GACATGGAA...-3'
What is the sequence of mRNA created from this sequence?
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1. Introduction to Genetics
Fundamentals of Genetics
1:33 minutesProblem 25
Textbook Question
Shorter fragments of DNA (those with fewer base pairs) have a higher electrophoretic mobility than larger fragments. Thinking about electrophoresis gels as creating a matrix through which fragments must migrate, briefly explain why the size of a DNA fragment affects its electrophoretic mobility.
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Understand that electrophoresis is a technique used to separate DNA fragments based on size by applying an electric field to a gel matrix.
Recognize that the gel matrix acts like a sieve, where smaller DNA fragments can move more easily through the pores of the gel compared to larger fragments.
Consider that the electric field causes DNA fragments to migrate towards the positive electrode due to the negative charge of the DNA backbone.
Acknowledge that smaller DNA fragments experience less resistance and can navigate through the gel matrix more quickly than larger fragments, which encounter more friction and obstacles.
Conclude that the size of a DNA fragment affects its electrophoretic mobility because smaller fragments can move faster and further through the gel matrix than larger fragments.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophoresis
Electrophoresis is a laboratory technique used to separate charged particles, such as DNA fragments, based on their size and charge. In this process, an electric field is applied to a gel matrix, causing the DNA fragments to migrate towards the positive electrode. Smaller fragments move more easily through the gel's pores, resulting in faster migration compared to larger fragments, which encounter more resistance.
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Gel Matrix
The gel matrix, typically made of agarose or polyacrylamide, serves as a sieve that affects the movement of DNA fragments during electrophoresis. The size of the pores in the gel determines how easily different sized fragments can pass through. Smaller DNA fragments can navigate through these pores more efficiently, while larger fragments are hindered, leading to differences in their migration rates.
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Molecular Size and Mobility
Molecular size directly influences the mobility of DNA fragments during electrophoresis. Smaller fragments have a higher electrophoretic mobility because they can travel through the gel matrix with less friction and obstruction. In contrast, larger fragments experience greater resistance due to their size, resulting in slower movement through the gel, which is why size is a critical factor in electrophoretic separation.
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