How DNA Makes Us Unique

Transcription

1 What your DNA says about you? Standards SC.7.L.16.1 Understand and explain that every organism requires a set of instructions that specifies its traits, that this hereditary information (DNA) contains genes located in the chromosomes of each cell, and that heredity is the passage of these instructions from one generation to another. SC.912.L.16.3 :Describe the basic process of DNA replication and how it relates to the transmission and conservation of the genetic information. Objectives Recognize that diversity can be genetic. Explore the complementary base pairing structure of DNA Visualize DNA How DNA Makes Us Unique Our sequence of DNA says a lot about us. Codes in our DNA make up our genes; these are regions on our DNA that determine what our phenotypic traits will be. Phenotypic traits are things that we can see, such as someone s hair or eye color. Phenotypic traits are inherited, that means that your genes are passed to you by your mother and father. Are you a taster or non- taster for PTC? The taste of PTC is bitter, most of the time it is easy to tell if you are a taster or non- taster simply by the fact that if you taste anything, even if it is faint, then you are a taster. Are you a taster or non- taster for Thiourea? The taste of Thiourea is bitter, most of the time it is easy to tell if you are a taster or non- taster simply by the fact that if you taste anything, even if it is faint, then you are a taster. Write down what you tasted for Sodium Benzoate. Did you taste sweet, sour, salty, bitter or were you a non- taster? Very subjective. Could be used as a discussion to compare different tastes. The ability to taste these chemicals are based on your genes!

2 Extracting DNA A single strand of DNA is tiny; only 2 nanometers across! However, much of DNA is coiled inside of the nucleus in order to fit it all inside of a small cell. Using a few ingredients (which you can probably find in your kitchen) you can extract the DNA from a sample of your cheek cells that will be large enough for you to see. Materials: Cup of water 8% sodium chloride solution 10% SDS solution 0.1 EDTA solution 95% Ethyl Alcohol Test Tube Eppendorf tube Procedure: 1. Vigorously swish water in your cup around your mouth for at least 1-2 mins. Make sure to do it this amount of time- the longer you swish, the more cells you will get. 2. Spit it back into your cup. Take a test tube and put 1 ml (20 drops) of 8% sodium chloride solution into it. 3. Pour your mouth water into the test tube until it is half full. Put the cap on and gently mix by inverting the tube a few times. Not too hard, we don t want to create bubbles. The NaCl solution causes the cell wall of the cheek cells to break apart. Why do you think this is necessary to isolate the DNA? The salt helps to precipitate the DNA by increasing the ionic strength of the solution. 1. Add 1 ml (20 drops) of 10% SDS solution and 1 ml of 0.1 EDTA solution to your test tube. 2. Put cap back on and let sit for 5 minutes 3. Tilt your test tube to a 45 degree angle. VERY gently pour 5 ml (100 drops) 95% ethyl alcohol down the side of the tube so it creates a layer on top of the water layer from your mouth. Why do you think we re adding alcohol? The alcohol does not mix with the water and DNA is not soluble in the alcohol. The DNA will float into the alcohol layer but the proteins and lipids in the sample will not. 4. Return to upright position and let sit for 1 minute.

3 5. You should see DNA floating in the alcohol layer. What appearance does the DNA have? Color? The DNA will be white and look like long thin strands. Most of the time the DNA will start clumping together so it will look like a white stringy clump. 6. Fill an Eppendorf tube with 1 ml of ethyl alcohol. You can use a wooden skewer to wrap the DNA and lift it out of the test tube and into your vial. DNA is made out of nucleotides; which contain a sugar, a phosphate, and a base that makes up the DNA code. Adenine (A), Cytosine (C), Guanine (G), and Thymine (T) are the four bases used and they follow the rules of complementary base pairing, rules that govern how DNA is created. Adenine in one DNA strand must connect to Guanine in the second strand. Similarly, Cytosine connects to Thymine. Try this practice sequence: A G C T T A G C T A A T G C C C T G G T A C T C G A A T C G A T T A C G G G A C C A T G

4 DNA Bracelet Now that you know how DNA is organized you can make your own DNA structure bracelet. This bracelet is made out of two string with complementary base pairing. On the table are some different DNA sequences for various organisms. This DNA sequence is one string of your bracelet, you will have to come up with the complementary base pair in order to make the second one! Hint: You can write down your sequence below and use it to figure out the complementary base pair in your booklet. Then you can follow it to make the bracelet. Sequence: These will vary depending on what they pick. The website where you can find all of the DNA sequences is bracelets. This will have a link for instructions which will include full instructions and the sequences. Base pairs: Bracelet: A- Green T- Red G- Yellow C- Blue Tie two strings together. String the given DNA sequence of your desired organism onto one string. Now you can string your complementary base pairs onto the other string. When done, tie a knot at the other end of the string. You can then tie the two ends together to make a bracelet!

5 You can do this experiment at home! All you have to do is substitute The 8% sodium chloride solution for a drop or two of detergent SDS solution and EDTA solution together can be switched out for a pinch of meat tenderizer (pineapple juice works as well!). You could also try different foods as well to compare DNA, these foods work really well: Banana, strawberries, kiwi fruit, onion, liver and beef thymus. You will need to squish up the food and then drain all the liquid out and use the liquid instead of cheek cell water. What happened? DNA is usually very small, but if you get a large amount of it together then it s natural clumping nature will make it into a mass big enough to see! The first step was to collect the cells; our cells come off rather easily; every time we touch something our skin cells fall off. So the swishing of the liquid was enough to break off the cells from your cheek. The detergent was necessary because of the nature of cells, the outer membrane of cells are made out of lipids which are fatty molecules that repel water. Detergents are used for cleaning because they are able break apart these fatty molecules from each other. This released the inside of the cell, containing the DNA, for us. DNA is tightly wound in the nucleus of cells so that all of the DNA that you have will fit into such a small space. One strand of DNA stretched out would be up to 2 or 3 meters long. Since we want to see the DNA we want it to be as stretched out as possible. DNA is held together by proteins to make sure it doesn t unravel, enzymes break down these proteins allowing the DNA to unwind. The alcohol is used because DNA is not soluble in it. That way the DNA precipitates (clumps together) out into the alcohol layer while leaving behind the lipids and proteins.