Question

1. Was there a noticeable difference between the acid treated apple piece and the untreated apple piece? Explain. Could you use vinegar instead of pineapple juice? Would you want to?
2. Obtain your bread dough and describe how it has changed since it was first made. Pull it apart and make notes about the texture, the odor, and the volume of dough. Explain the biochemistry behind this metamorphosis.
3. Why do you think that cheese is less subject to spoilage than milk?
4. Do you think that there is some population of cells in you (yourself!) that is currently undergoing mitosis?
5. What kind of circumstances would promote mitosis (e.g. a finger has been cut)?
6. Do you think that there is some population of cells in you that might never, or only very rarely, undergo mitosis at this point in your life?
7. What was the appearance of the DNA as you were spooling it?
8. What reagent (chemical compound) was used to cause the DNA to precipitate from the solution, Thus allowing it to be spooled onto the wooden applicator stick?
9. At what two wavelengths does DNA absorb? At which wavelength does it absorb the most?

Answer 1

When an apple piece is cut and exposed to the moisture and oxygen present in the air, it turns brown in colour. The discoloration is mainly due to the presence of the enzme called as polyphenol oxidase which catalyzes the conversion of polyphenols into by-products like melanin and the enzyme requires the presence of oxygen. The polypenols get released when the fruit is cut. Now, if the browning needs to be prevented, a method like adding acids like ascorbic acid proves to be very effective since they function as anti-oxidants. Vinegar too has a high acidic content and in turn, a lower pH value due to which the activity of the polyphenol oxidase enzyme is slowed down. It is preferable to use pineapple juice since they impart a sweet taste while soaking themin vinegar will only give them an acidic odour and flavour which is highly undesirable.

The dough once kneaded is set aside and allowed to rest so that it can rise and result in softness of the product. The complex sugars and carbohydrates like starch which are present in the dough undergo the process of fermetation and this process is aided by the presence of yeast and bacteria, hence carbon-dioxide will be produced and the dough rises. The lactic acid bacilli and the Saccharomyces cerevisiae are all involved in different type of fermentation processes due to which there are different conditions required for each of them to thrive and so that the flavour and texture of the final product is appropriate.

The milk is full of proteins, carbohydrates and fats which are an enriched medium for the growth of bacteria. The major protein called casein and the sugar such as lactose is extremely favourable for the growth of the bacteria. The process of fermentation results in the production of lactic acid which leads to the spoilage of milk and the curdling causes an acumulation of clumps of casein protein. This fermentation process results in the production of cheese hence, milk is more prone to spoilage rather than cheese.

Mitosis is a part of the cell cycle which is constatntly occuring in body. Hence, it can be happening right now also in the body. Since it is set into action when a cell is damaged, lost or needs repair, thus a cut finger can also trigger mitosis. The body cells are programmed to start off mitosis with which the damaged cells can be restored back to their normal role and functioning. Certain cells like the brain cells which are the neurons may never undergo mitosis and hence no cells can be renewed if damaged.

After the DNA has been spooled, it forms a viscous clump which is an opaque mass and it sticks to the rod being used for the spooling process.

The reagent which is useful in the precipitation is the ethanol since the DNA which is insoluble in the alcohol can be easily spooled out with the help of a stick.

The absorbance of DNA can vary between the wavelengths of 260 nm to 280nm. The maximum absorbance and purity of DNA is obtained at the wavelength of 260nm.