The DNA with the code for chymosin is isolated from calf cells. A copy of this DNA is inserted into yeast cells in a small ring of DNA known as a plasmid. Plasmids replicate independently from chromosomes. The plasmid is copied within the
yeast cells. Yeast cells are cultivated in large fermentation vats like those used for brewing. Chymosin identical to the
animal protein is then made by the yeast.
Lab Activity: Separate Skim Milk and Whole Milk into Curds and Whey
Materials:
Whole Milk 2 Saucepans or Crockpots
Skim Milk Vinegar or Lemon Juice
Candy thermometer (only if you have already have one) 4 Cups or mugs
Coffee Filters or Paper Towels or Nylon hosiery or Cheesecloth Liquid measuring cup & spoons
Method:
1. Warm the whole milk and skim milk separately in saucepans or crockpots. You only need to heat it to between 85 to
105 degrees Farenheit , so DON’T BOIL THE MILK! If you have a candy thermometer, you can get an exact temperature. Otherwise, this is around body temperature, so if you stick your finger in the milk, it won’t feel warm OR cold.
2. Transfer identical volumes of the warm skim and whole milk (such as 1 cup each) to 2 cups or mugs.
3. Add 2 Tablespoons of vinegar or lemon juice to each of your cups of milk.
4. Wait about 10 minutes. By now, you should see the milk completely separating into fluffy white curds and pale
yellowish-green whey. If you don’t see this, add another Tablespoon of vinegar until you see this.
5. Put a paper towel folded into a funnel shape, a coffee filter, a cheesecloth, or an old pair of nylon hosiery over 2 other cups or mugs. This will filter the curds out and allow the whey to soak through. Do this separately for the skim and whole milk. Remove as much of the whey from the curds as you can.
6. Compare the size of the curd from the whole versus the skim milk . Take a
picture of your experiment set up and the curds you produced and submit it with your answers to the questions.
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