Assume that a culture of e. coli was grown for approximately 50 generations in 15n (provided in the medium in the ammonium ion), which is a heavy isotope of nitrogen (14n). you extract the dna from the culture, and it has a density of 1.723 gm/cm3 (water = 1.00 gm/cm3). from the literature, you determine that dna containing only the common form of nitrogen, 14n, has a density of 1.700 gm/cm3. bacteria from the 15n culture were washed in buffer and transferred to 14n medium for one generation immediately after which the dna was extracted and its density determined.
(a) what would be the expected density of the extracted dna?
(b) after you heat the extracted dna until it completely denatures (95oc for 15 minutes), what would you expect the density of the dna in the denatured extract to be? for the purposes of this question, assume that dna has the same density regardless of whether it is single- or double-stranded.
(c) assuming that the molar percentage of adenine in the extracted dna was 20%, what would be the expected molar percentages of the other nitrogenous bases in this dna?
(d) assume that a fraction of the extracted dna was digested to completion with the enzyme snake venom diesterase. this enzyme cleaves between the phosphate and the 3' carbon. present a "simplified" diagram that would illustrate the structure of the predominant resulting molecule.

question#1

ans:

cell is the basic unit of organization of all living things. cells are often called the building block of life and it is the smallest unit of life. the study of cell is called cell biology. cell consists of cytoplasm enclosed within membrane, which contain bio-molecules such as proteins and nucleic acid.

two third of cell is water, which means that two-third of your whole body is water. the rest is the mixture of molecules, mainly proteins, lipids and carbohydrates.

question#2

ans:

organ:

an organ is a group of tissues specialized to form a functional unit. an example is the heart in animals.

organ system:

an organ system is a group of several organs whose functions are synchronized to release an effective action in a living organism. an example is digestive system.

question#3

different systems perform different function at tissue level. for example, the respiratory system facilitates breathing. in the alveoli tissue of the lungs, the exchange of oxygen and carbon dioxide molecules between the air and the bloodstream occurs by passive transport, so that oxygen is taken in and carbon dioxide and water are removed. different systems of the body carry out different functions. for example, your digestive system is responsible for taking in and processing food, while your respiratory system working with your circulatory system is responsible for taking up oxygen and getting rid of carbon dioxide.

question#4

different systems perform different function at tissue level. for example, the respiratory system facilitates breathing. in the alveoli tissue of the lungs, the exchange of oxygen and carbon dioxide molecules between the air and the bloodstream occurs by passive transport, so that oxygen is taken in and carbon dioxide and water are removed. different systems of the body carry out different functions. for example, your digestive system is responsible for taking in and processing food, while your respiratory system—working with your circulatory system is responsible for taking up oxygen and getting rid of carbon dioxide.

question#5

our body works because of the interactions that happen between organs and organ systems.  

for example:  

the heart to regulate blood flow throughout the body. the blood carries oxygen and nutrients to the cells and carries carbon dioxide and waste away from the cells. body systems work together in maintaining a constant internal environment. when this balance is disrupted, the body systems may not function properly, and human health can suffer.   you start to feel bad.