The earliest life, prokaryotes, appeared approximately 3.5 billion years ago. Common prokaryotes include bacteria, cyanobacteria, mycoplasma and chlamydia. They lack a true nucleus and all their circular DNA is concentrated in a central region called the nucleoid.
Eukaryotes evolved from prokaryotes and appeared about 1.8 billion years ago. The biggest difference between them is that eukaryotes have a nucleus enclosed by a membrane and various organelles that compartmentalize different types of chemical reactions in a small region to prevent interference. Common examples of eukaryotes include animals, plants, fungi and protists.
Although they both have cytoplasm, phospholipid cell membrane and genetic material DNA, there are still many differences.
Nucleus and chromosomes
Prokaryotes: All their circular DNA are concentrated in a non-membrane enveloped region called nucleoid. They also have independent replicable circular DNA molecules called plasmids. Transcription and translation occur simultaneously in the cytoplasm to allow the rapid reproduction. For example, E. coli can divide every 20 minutes. Eukaryotes: Linear DNA is surrounded by a double membrane to form a bounded region called the nucleus. DNA containing histones coil to become chromosomes during mitosis. Eukaryotes transcribe mRNA from DNA in the nucleus. Then the mRNA passes through the nuclear pore into the cytoplasm where proteins are synthesized by ribosomes. Eukaryotes do not have plasmids.
Prokaryotes: They only have ribosomes, and lack other organelles. Their ribosomes are different from those of eukaryotes in terms of protein and RNA, and are smaller in size. Eukaryotes: Eukaryotes have various organelles enclosed by membranes, such as mitochondria, chloroplasts, Golgi apparatus, endoplasmic reticulum, centrioles, lysosomes, vacuoles, etc. These organelles segregate different chemical reactions in a isolated room to prevent interference with each other.
Prokaryotes: The cell wall of prokaryotes is composed of peptidoglycan which provides defense against external attacks and dehydration. Some bacteria also have a polysaccharide capsule outside the cell wall, which enhances their defense and helps them adhere to surfaces. Eukaryotes: The cell wall is made of cellulose or chitin.
Prokaryotes: They do not have a cytoskeleton that allows their bodies to undergo large deformations. Most prokaryotes are symmetrical in shape and cannot engulf large material, but can absorb some large molecules. Eukaryotes: The cytoskeleton in the cytoplasm provides support to eukaryotic cells and allows them to undergo various shape changes. Eukaryotes can directly engulf and ingest organisms that only slightly smaller than themselves.
Prokaryotes: Their simple structures nake them in size, mostly ranging from 0.5 to 5 μm. Eukaryotes: Due to their cytoskeleton and more complex structure, eukaryotes are generally much larger than prokaryotes, ranging from 10 to 100 μm.