Biology 1001A Lecture 13: bio 1001a lecture 13
Could’t you hae oegee to get
the same AA/nucleotide sequence
Could’t you hae oegee to get the sae AA/uleotide seuee?
Poteis a oege to siila futios, ut they do’t eessaily
have the same nucleotide/AA sequence
This is because natural selection acts on phenotype (protein function)
not genotype (AA/nucleotide sequence). There is no selective pressure to
change nucleotide sequence so it would look similar to another sequence
such that they would be considered homologous (convergent evolution
does’t esult i to sequences looking homologous!)
Convergence onto highly similar nucleotide sequence is rare.
Therefore, similarity between sequences are considered to be evidence of
homology because there is no force to drive convergence of nucleotide/AA
sequences
There is no reason for 2 sequences to proteins to share high identity
across their entire sequence
There would be localized regions of high similarity, but entire nucleotide
sequence would not be similar
- The functionality of a protein is not represented by its entire
sequence, but by localized regions:
o Location of cysteine amino acids (give rise disulfide (S-S)
bonding )
o Amino acids necessary for catalysis
o DNA binding domains, transcription factors, receptor binding
sites
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Could(cid:374)"t you ha(cid:448)e (cid:272)o(cid:374)(cid:448)e(cid:396)ge(cid:374)(cid:272)e to get the same aa/nucleotide sequence. P(cid:396)otei(cid:374)s (cid:272)a(cid:374) (cid:272)o(cid:374)(cid:448)e(cid:396)ge to si(cid:373)ila(cid:396) fu(cid:374)(cid:272)tio(cid:374)s, (cid:271)ut they do(cid:374)"t (cid:374)e(cid:272)essa(cid:396)ily have the same nucleotide/aa sequence. This is because natural selection acts on phenotype (protein function) not genotype (aa/nucleotide sequence). There is no selective pressure to change nucleotide sequence so it would look similar to another sequence such that they would be considered homologous (convergent evolution does(cid:374)"t (cid:396)esult i(cid:374) t(cid:449)o sequences looking homologous!) Convergence onto highly similar nucleotide sequence is rare. Therefore, similarity between sequences are considered to be evidence of homology because there is no force to drive convergence of nucleotide/aa sequences. There is no reason for 2 sequences to proteins to share high identity across their entire sequence. There would be localized regions of high similarity, but entire nucleotide sequence would not be similar.