"Critical thinking question" for Chapter 4
Student name: Dilnaz Kairzhanova
Student ID: 20240968
Question: Several lines of evidence support the hypothesis that mitochondria and
chloroplasts evolved from parasitic prokaryotic cells living in the cytoplasm of primitive
eukaryotic cells. What types of evidence would you look for to support or refute this
hypothesis?
Interestingly, compared to other organelles, mitochondria and chloroplasts contain
their own DNA and ribosomes (see Figures 1 and 2), which then interact to synthesize
proteins (Simon & Dickey, 2019). Their genetic systems are very different from the genome
of the eukaryotic cell they reside in. Firstly, according to Simon and Dickey (2019), every
mitochondrion and chloroplast may have only one circular DNA chromosome. Also, they
reproduce themselves by dividing into two parts. This is done by replication of their DNA
and transmission of the genes to ribosomes at each division. These characteristics of
mitochondrial and chromosomal genetic systems resemble those of prokaryotic cells.
Moreover, if we pay attention to the very structures of these organelles, we can notice many
similarities, too. For example, the presence of a double membrane in both organelles is
similar to those of bacterial cells. Moreover, the size of the mitochondrion and chloroplast is
nearly the same as the size of the tiny prokaryotic cell (Cooper, 2000). Thus, since
mitochondria and chloroplasts are similar to prokaryotic cells both physiologically and
biochemically, there is a basis for this hypothesis of organelle evolution. Also, this hypothesis
can be reasoned by the fact that even if prokaryotic cells lived in the host organism by
symbiosis, over time they could become interdependent on the host and turn into its
organelles.
Figure 1. Inner structure of mitochondrion (Rogers, 2024)
Figure 2. Inner structure of chloroplast (Bashir, 2023)
References
Bashir, R. (2023, February 10). Chloroplast - Its structure and function - Microbial notes.
https://microbialnotes.com/chloroplast#google_vignette
Cooper, G. M. (2000). The origin and evolution of cells. The Cell - NCBI Bookshelf.
https://www.ncbi.nlm.nih.gov/books/NBK9841/
Rogers, K. (2024, August 23). Mitochondrion Structure [Schematic]. Encyclopedia
Britannica.
https://cdn.britannica.com/89/22489-050-EB3B8C59/membrane-mitochondrion-crista
e-structures-Proteins-majority-components.jpg
Simon, E. J., & Dickey, J. L. (2019). Campbell Essential Biology, Global Edition. Pearson
UK.