Lab 4: DNA Isolation, Structure, and Technology PDF

**Lab 4: DNA Isolation, Structure, and Technology** **OBJECTIVES** - - - - - **INTRODUCTION** *Structure* DNA (deoxyribonuleic acid) is composed of a double chain of four alternating nucleotides. Each nucleotide contains a sugar (deoxyribose), a phosphate group, and a nitrogenous bas...

**Lab 4: DNA Isolation, Structure, and Technology** **OBJECTIVES** - - - - - **INTRODUCTION** *Structure* DNA (deoxyribonuleic acid) is composed of a double chain of four alternating nucleotides. Each nucleotide contains a sugar (deoxyribose), a phosphate group, and a nitrogenous base. There are only four different nitrogenous bases in DNA: adenine, thymine, guanine, and cytosine. Figures 8.1 and 8.3 show the structures of each of these bases. These four nucleotides differ only in the nitrogenous base. Identify the sugar, phosphate group, and nitrogenous base of each nucleotide. Examine Figure 8.3 and note that the sugar of one nucleotide is bonded to the phosphate group of the next nucleotide. In this way the alternating sugar-phosphate-sugar-phosphate arrangement forms the sides of the ladder that is then twisted into a helix. The nitrogenous bases extend across the middle to bond with nitrogenous bases from the other strand, thereby forming the rungs of the ladder. Note that in DNA adenine always pairs with thymine and guanine always pairs with cytosine. *Function* DNA is the genetic material that is found in the nucleus of cells. Together with the proteins that are attached to it, this double stranded DNA makes up the chromosomes that can be seen during cell division. In nearly all cells of eukaryotic organisms, chromosomes exist in pairs called homologous chromosomes. These two chromosomes, one acquired from the male parent and one acquired from the female parent, are nearly identical in structure but may contain different genetic information for the same traits. When a nucleus contains chromosomes in homologous pairs, the cell is referred to as diploid (2n). For example, human cells contain 23 pairs of homologous chromosomes, or 46 chromosomes in a diploid cell. DNA replication (the process by which DNA is copied) takes place within the nucleus during the cell cycle stage called interphase. Each molecule of DNA (each chromosome) makes an exact copy of itself through the work of many different enzymes. The enzymes open up the double strand of DNA, the bases separate from one another and the DNA molecule unwinds or unzips. Each open strand of the DNA then serves as a template to replicate its complementary strand, following the rules of base pairing. The end result is two DNA molecules, each composed of one strand of the old DNA molecule and a newly assembled strand. Saving half of the old strand and constructing a new strand alongside is called semi-conservative replication (Figure 8.2).  ------------------------------ -------------------------------------- **Figure 8.1 DNA structure** **Figure 8.2 DNA replication model** **ACTIVITY:** Using scissors, cut out the model on figure 8.3, and place the pieces together to model a DNA molecule. Q1. What do you notice about the number of bonds between nucleotides? Q2. How does complimentary base pairing work in terms of the puzzle activity you completed here? Q3. What makes the backbone of your DNA molecule? Pre-Lab Questions: P1. What are the three sub-units of a nucleotide? P2. What is the function of DNA? P3. The shape of DNA is called P4. A nucleotide may consist of PROCEDURE --------- This experiment is a simple, effective protocol for isolating and observing DNA from plant tissue. Strawberries are a good source for extracting DNA because they are soft, making them easy to crush and break open the cell walls, where the DNA is located. Most importantly, strawberries have more DNA than any other fruit (having eight copies of each chromosome), meaning there's more DNA available to collect. ### A. Isolation of DNA from plant tissue: 1. Place 2 to 3 pieces of strawberry into a Ziploc bag. 2. Smash the contents of the bag for approximately 2 minutes. 3. Add 10 ml of lysis buffer to the bag and resume smashing the Ziploc bag for another 2 minutes. 4. Open the Ziploc bag and filter the strawberry mixture through several pieces of cheese cloth into a beaker. Pour another 5ml of lysis buffer through the cheese cloth filter. Squeeze the cheese cloth to get as much liquid as you can, leaving the solids behind. 5. Fill a test tube with the liquid strawberry extract until the test tube is about 1/3 full. 6. Tilt the test tube and slowly pour cold 70 to 95% ethanol down the side of the tube so it forms a layer on top of the DNA mixture. Keep pouring until you have the same volume of alcohol as DNA mixture Do not mix or stir. 7. After a few minutes, watch for a white layer to form above the strawberry extract layer. Congratulations! This is your DNA! Post-Lab Questions: Write a one or two-sentence summary of the purpose, methods, and results of your lab. A. Isolation of DNA from Strawberry Purpose: -- -- Materials and Methods: -- -- What do you expect to see at the end of the procedure? -- -- Why might it be important to be able to extract and amplify DNA in living organisms? What uses do you see this having in science AND in the natural world? -- -- A diagram of different colored shapes Description automatically generated Figure 8.3: Building blocks of DNA. ©bluedoor, LLC