Example of palindromic sequence mcat1/17/2024 ![]() As a result, you can assume that every strand of DNA and RNA has a constant and equal distribution of charge or an equal charge density. Importantly, each phosphate group carries a negative charge, so DNA and RNA will always be negative and will always be attracted to the positive charge. How does charge affect gel migration for nucleic acids? You might know that in the structure of DNA and RNA, each nucleoside or subunit (A, C, G, T, or U) is joined to the next using a link that contains a phosphate group. If you add up all of these charges, you get a net charge that’ll tell you 1) how quickly the protein will move and 2) in which direction. Acidic side chains are negatively charged when deprotonated, while basic side chains are positively charged when protonated. On the other hand, protein 1 will travel the slowest.Īs we saw above, the total charge does vary for proteins, and this variation of charge is dependent on the protein’s side chains. Which protein will travel towards the positively charged anode more quickly? Protein 3 will travel towards the positive end of the gel faster than Proteins 1 and 2 because it is more highly charged and experiences greater attraction to the positive side. Let’s say we start with 3 proteins of equal size. While molecules are usually separated by just size, you need to remember that charge can also be a factor. If you stop the race at any point by turning off the electric field, your proteins will stop moving. (Think of walking through waist-deep water versus knee-deep water!) If you start the race by turning on the electric field, all the proteins will move towards the finish line, but the smallest will get there first. However, the proteins are in the Jell-O, so if one protein is really big, it’ll move more slowly than the smaller proteins. When you turn on the electric field, all 5 proteins will move towards the positively charged side of the electric field. Let’s look at size first: pretend each of our 5 proteins has the same net negative charge. Polyacrylamide just refers to the type of gel that is used!)Īll gel electrophoresis experiments work by taking advantage of three properties: size, charge, and shape. (Note: many gel electrophoresis experiments are referred to with the acronym PAGE, or polyacrylamide gel electrophoresis. The molecules will travel through the Jell-O, and you can think of the system as a molecule swim meet through a Jell-O pool. You then apply an electric field across the gel using a negatively charged side ( cathode) and a positively charged side ( anode). If the 5 proteins each have a different size (or different amino acids), you can separate them with gel electrophoresis.ĭuring an experiment, you begin by placing your mixture on the gel, which you can think of as a large sheet of Jell-O. Let’s say you have a test tube containing 5 different proteins, but you only want one of them. Normally, these components are strands of DNA, RNA, or different proteins. Gel electrophoresis is an experiment used to separate different components of a mixture based on their size and charge. Part 2: Gel electrophoresis a) Basic principles (Suggested reading: MCAT Biochemistry: Everything You Need to Know) We’ll focus on the details that will help you ace these questions from an MCAT perspective, and we’ll finish with some sample questions to help you assess your proficiency. We’re going to go into many of the techniques that may show up on your MCAT, including chromatography, molecular cloning, DNA sequencing, PCR, Blotting, ELISA, and gel electrophoresis. ![]() By understanding these techniques, you’ll put yourself in the position to answer the diverse array of questions you may be asked on the exam. Remember, the MCAT test-writers develop passages by adapting scientific articles and asking you questions. This is a long guide, but it’ll help you with the complex biochemistry techniques that the MCAT will throw at you. In many cases, it’s also easy to feel like you need to learn everything about an experimental technique to master these questions on the MCAT, but we’ll show you exactly what you need to know! One of the most difficult parts about learning these techniques is that they’re often presented at a very complex level, but we’ll provide concise and clear explanations in this guide. This is a high-yield topic, and a knowledge of the experimental techniques we will discuss will help you when you take your MCAT. Welcome to our guide on experimental techniques in biochemistry. Part 1: Introduction to biochemistry lab techniques
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