L.11 Cytochrome C Comparison Lab

PROTEINS AND EVOLUTION

Genes are made of DNA and are inherited from parent to offspring. Some DNA sequences code for mRNA which, in turn, codes for the amino acid sequence of proteins. Over time, random mutations in the DNA sequence occur. As a result, the amino acid sequence of Cytochrome C also changes. Cells without usable Cytochrome C are unlikely to survive. The cytochrome C is a small protein found loosely associated with the inner membrane of the mitochondrion. It is found in eucariotic cells and has an hemeprotein. It is essential to the electrone transport chain and it is involved in using energy in the cell (ATP).

The purpose of this practice is to compare the relatedness between organisms by examining the amino acid sequence in the protein.

METHOD

First, we compared the amino acid sequence of Cytochrome C in various organisms:
-horse, donkey, whale (mammals)
-penguin, chicken (birds)
-snake (reptile)
-moth (insect)
-wheat (plant)
-yeast (fungi)

1- We marked the amino acids which were different.
2-Then we counted and recorded the total number of differences.
3- We shared the data with the rest of the class to complete Table 1.


After that, we made a cladogram (branching tree)
1- The two most closely related species had the fewest differences in amino acid sequence. We placed the two most closely related species on the two shortest branches of the tree.
2-Then we placed the next two closest species on the next shortest branches.
3- And we continued until all the species had been placed.

RESULTS AND OBSERVATIONS

CONCLUSIONS

There are 0 differences between chickens and turkeys in their Cytochrome C amino acid sequence.

We think that the horse and the zebra have 1 or 2 differences, like the donkey and zebra.
To make this prediction we used this information: if they can reproduce and if the offspring will be fertile or not, we compared organs, compared embrios...

More closely related organisms have more similar Cytochrome C because evolutionarily, it hasn't been that long since they separated. If the species are close, it means that less time has passed since they separated (there are less accumulated mutations). They have a common ancestor.

Other data, including genes, suggests that fungi are more closely related to animals than plants. But Cytochrome C data suggests that fungi, plants and animals are equally distantly related because if there are more than 40 genes, there are too many mutations to see it clearly.