In this exercise, you will compare the amino acid sequence from the aphid to the amino acid sequences of the other species to identify how similar they are. as a first step, you will compare the aphid sequence (acyrthosiphon) to a bacterial sequence (pantoea).

the sequences below show the first 60 amino acids of one polypeptide, using the one-letter abbreviations for the amino acids. an underscore indicates a gap inserted in a sequence to optimize its alignment with the corresponding sequence in arabidopsis.
acyrthosiphon (aphid) ikgsgv ggtrls kkgfqvevye
pantoea (bacterium) krtfvigagf gglalairlq aagiattvle
acyrthosiphon (aphid) knsynggrcs ihr_hnghrf dqgpsl__yl
pantoea (bacterium) qhdkpggray vwq_dqgftf dagptv__it

at how many positions are the amino acids the same between the two species?

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!

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