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kupik [55]
4 years ago
11

In a famous experiment, Matthew Meselson and Franklin Stahl grew E. coli cells in a medium containing only the "heavy" isotope o

f nitrogen, 15 N . These cells were then transferred to a medium with the "light" isotope of nitrogen, 14 N . The results of the experiment supported the hypothesis of semiconservative replication, which was proposed by Watson and Crick. Heavy DNA ( 15 N DNA), hybrid DNA, and light DNA ( 14 N DNA) can be separated by centrifugation. If cells containing 15 N DNA are transferred to a medium with only 14 N NH 4 Cl as a nitrogen source, what percent of daughter molecules are composed of hybrid DNA after 3 generations?
Biology
1 answer:
Alex777 [14]4 years ago
4 0

Answer:

3rd generation = 2 Hybrid DNA molecules + 6 Light DNA

In Percentage 2÷8 × 100 = 25%

25% of the DNA are hybrid

Explanation:

Semi conservative model proposed by Watson and Crick states that one strand of the DNA comes from parent DNA which act as a template for the other newly formed strand.

First generation:

If cells containing 15 N DNA are transferred to a medium with only 14 N then in initial first generation two parent strands becomes separated and act as template for newly synthesized strands. this means that in first generation both DNA molecules are hybrid, one strand of 15 N DNA and other strand of 14 N DNA

Ist generation = 2 Hybrid DNA molecules

Second generation:

In Second generation these two hybrid molecules become unzip. Two strands are 15N and two strands are 14N. All these 4 strands act as template and 4 new strands are synthesized. The molecules of Hybrid DNA is still 2 with 2 molecules of Light DNA.

2nd generation = 2 Hybrid DNA molecules + 2 Light DNA

Third generation:

In Third generation these two hybrid molecules and two light DNA molecules become unzip. Two strands are of 15N and six strands are of 14N. All these 8 strands act as template and 8 new strands are synthesized. The molecules of Hybrid DNA is still 2 with 6 molecules of Light DNA.

3rd generation = 2 Hybrid DNA molecules + 6 Light DNA

In Percentage 2÷8 × 100 = 25%

25% of the DNA are hybrid

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C-14 half-life is the time it takes for half of the isotope mass to decay into its daughter form. Line graphs are the best way to represent data about half-lives and the amount of isotope (gr).

<h3>What is Carbon 14?</h3>

Carbon 14, also known as radiocarbon, is a radioactive carbon isotope.

Isotopes are the atoms of the same element -carbon- that vary in neutrons and, hence, in their massic number. They are alternative forms of the same element.

The radioactive C14 nucleus contains 6 protons and 8 neutrons and has a half-life of 5730 years.

The term <u>half-life</u> is a reference. It means that an organism that has been dead for 5730 years has half the C14 amount or concentration than the same organism had when it was alive.

In other words, the half-life is the time it takes for half the mass of this isotope to become its daughter form.

Knowing the half-life of an element is useful to determine the age of the dead matter.

C14 is used in radiocarbon dating techniques or methods to estimate the age of fossils. This is a reliable technique used for dating organic samples that are less than 50,000 years old.

An easy way of representing the change in mass of the isotope through the years is to make a line graph, which is easy to interpret and compare the information.

In this example, our line graph must represent the number of half-lives related to the amount of parent isotope in grams.

The table details the years and the amount of isotope. So, by kowing the half-life of C-14, we can get how many half-lives there are.

5,700 years ---------- 1 half-life

11,400 years--------- X = 2 half-lives ⇒ (5700 x 2) or (11,400/5,700)

17,100 years -------- X = 3 half-lives ⇒ (5700 x 3) or (17,100/5,700)

22,800 years ------ X = 4 half-lives ⇒ (5700 x 4) or (22.800/5,700)

28,500 years ------ X = 5 half-lives ⇒ (5700 x 5) or (28,500/5,700)

34,200 years ------ X = 6 half-lives ⇒ (5700 x 6) or (32,200/5,700)

39,900 years ------ X = 7 half-lives ⇒ (5700 x 7) or (39,900/5,700)

45,600 years ------ X = 8 half-lives ⇒ (5700 x 8) or (45,600/5,700)

51,300 years ------- X = 9 half-lives ⇒ (5700 x 9) or (51,300/5,700)

Now, we can make a new table,

<u>Number of half-lives       Carbon-14 (g) </u>

                0 ..............................10,000

                 1 ...............................5,000

                 2................................2,500

                 3 ................................1,250

                 4 ................................  625

                 5 ................................  312

                 6 ................................  156

                 7 .................................   78

                 8 .................................   39

<u>                  9 .................................   20         </u>

<u />

Finally, we can make the line graph using the data of this new table. You will find it in the attached files.

In conclusion, the best graph you can make is a line graph, and if they ask you to graph the number of half-lives and give you the number of years, you can just make the conversion using the half-life of the isotope.

You can learn more about isotopic half-life at

brainly.com/question/12341489

brainly.com/question/4702752

brainly.com/question/14508944

brainly.com/question/13462855

brainly.com/question/16930674

#SPJ1  

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