cell with their labelled parts."/>
Figure 1.2 Schematic structure of prokaryotic and eukaryotic cells. (a) Bacterial cell, (b) plant mesophyll cell, and (c) animal cell.
Nucleotide sequences from 16S rRNA, amino acid sequences of cytoskeleton proteins, and characteristics of the cell structure were used to reconstruct this phylogenetic tree. Prokaryotes are divided into Bacteria and Archaea. Archaea form a sister group with eukaryotes; they share important characteristics (Tables 1.1 and 1.2). Many monophyletic groups can be recognized within the eukaryotes (diplomonads/trichomonads, Euglenozoa, Alveolata, Stramenopilata [heterokonts], red algae and green algae/plants, fungi and animals; see Tables 6.3–6.5 for details).
Table 1.1 Comparison of important biochemical and molecular characteristics of the three domains of life.
| Character | Prokaryotes | Eukaryotes | |
|---|---|---|---|
| Archaea | Bacteria | ||
| Organization | Unicellular | Unicellular | Unicellular or multicellular |
| Cytology | |||
| Internal membranes | Rare | Rare | Always (Table 1.2) |
| Compartments | Only cytoplasm | Only cytoplasm | Several (Table 1.2) |
| Organelles | No | No | Mitochondria; plastids |
| Ribosomes | 70S | 70S | 80S (mt, cp: 70S) |
| Membrane lipids | Ether lipids | Ester lipids, hopanoids | Ester lipids, sterols |
| Cell wall | Pseudopeptidoglycan, polysaccharides, glycoproteins | Murein (peptidoglycan), polysaccharides, proteins | PL: polysaccharides, cellulose F: chitin A: no |
| Cytoskeleton | FtsZ and MreB protein | FtsZ and MreB protein | Tubulin, actin, intermediary filaments |
| Cell division | Binary fission | Binary fission | Mitosis |
| Genetics | |||
| Nuclear structure | Nucleoid | Nucleoid | Membrane‐enclosed nucleus with chromosomes |
| Recombination | Similar to conjugation | Conjugation | Meiosis, syngamy |
| Chromosome | Circular, single | Circular, single | Linear, several |
| Introns | Rare | Rare | Frequent |
| Noncoding DNA | Rare | Rare | Frequent |
| Operon | Yes | Yes | No |
| Extrachromosomal | DNA plasmids (linear) | Plasmids (circular) | mtDNA, cpDNA, plasmids in fungi |
| Transcription/translation | Concomitantly | Concomitantly | Transcription in nucleus, translation in cytoplasm |
| Promotor structure | TATA box | −35 and −10 sequences | TATA box |
| RNA polymerases | Several (8–12 subunits) | 1 (4 subunits) | 3 (with 12–14 subunits) |
| Transcription factors | Yes | No (sigma factor) | Yes |
| Initiator tRNA | Methionyl‐tRNA | N‐Formylmethionyl‐tRNA | Methionyl‐tRNA |
| Cap structure of mRNA polyadenylation | No | No | Yes |
PL, plants; F, fungi; A, animals; mt, mitochondria; cp, plastid.
Table 1.2 Compartments of animal and plant cells and their main functions.
| Compartment | Occurrence | Functions | |
|---|---|---|---|
| Nucleus | A | P | Harbors chromosomes, site of replication, transcription, and assembly of ribosomal subunits |
| Endoplasmic reticulum (ER) | |||
| Rough ER | A | P | Posttranslational modification of proteins |
| Smooth ER | A | P | Synthesis of lipids and lipophilic substances |
| Golgi apparatus |
|