I-2 Comparison of pro- and eukaryotic cells

Prokaryotes are those organisms which have no nucleus. And, eukaryotes have nuclei on the other hand. Aside from this, there are some different points between these two groups, for example in terms of size, chromosomes, mitochondria, and so on.

Included kingdoms

Eukaryotes include alga, fungi, protozoa, plants, and animals, while prokaryotes include bacteria and archaea. This way of grouping organisms is called kingdoms, which is the first classification after the domain. 

Size

Generally, eukaryotic cells are larger than prokaryotic cells. Most of the eukaryotic cells are larger than 5 μm, while most of the prokaryotic cells are between 0.5 and 20 μm in size. 

Chromosome

Chromosome number means the number of sets of chromosomes. For example, human beings have 2 sets of chromosomes. When a cell has only one set of chromosomes, then we call it haploid, when a cell has two sets of chromosomes, then we call it diploid. All prokaryotes are composed of haploid cells, and all eukaryotes are composed of diploid cells or polyploid cells which have more than two sets of chromosomes.

Mitochondria

Mitochondria is one of the organelles whose origin is hypothesized by endosymbiotic theory. This theory advocates that the common ancestor of eukaryotes once ingested (endocytosed) an energy-producing prokaryote, and then the prokaryote began to live in the cells of eukaryotes, which then turned into mitochondria. Since the common ancestor of eukaryotes got mitochondria, it’s natural to say that prokaryotes do not have mitochondria.

Ribosome

The eukaryotic and prokaryotic ribosomes are different in size, composition, and function. The size of the ribosomes is measured by a unit, Svedverg unit, which indicates the sedimentation time of the substance during centrifugation. 

The prokaryotic ribosomes are composed of a 50S larger subunit and a 30S smaller subunit, altogether they form a 70S ribosome.

On the other hand, the prokaryotic ribosomes are composed of a 60S larger subunit and a 40S smaller subunit, which altogether form an 80S ribosome.

Plasma membrane

The composition of the plasma membranes is also different between the two. Both of the membranes are composed of a phospholipid bilayer in most cases. The fluidity of the phospholipid bilayer has to be regulated by other substances, which are hopanoids in prokaryotes, and sterols in eukaryotes.

Cell wall

The cell wall is a structure that surrounds the cell membrane and protects or sustains the structure of the cell. The term “cell wall” is not defined by its composition, but rather by its function, meaning the composition of the cell wall varies from organism to organism.

Reproduction

Eukaryotes can reproduce themselves either in sexual or asexual ways, while prokaryotes reproduce through binary fission which is an asexual reproduction.

Respiration

Respiration, specifically “cellular respiration”, means a process of consuming oxygen to produce energy. Oxygen is used as a terminal electron acceptor during energy metabolisms, so we can say the place of respiration is the place of the electron transport chain. The place of ETC in eukaryotes is the inner membrane of the mitochondria, but that of prokaryotes is the cytoplasmic membrane. As you know, prokaryotes do not have mitochondria, and mitochondria itself is developed from prokaryotes. According to this, it is natural to think that prokaryotes can manage ETC in their plasma membrane.