Eukaryotic cells contain multiple, linear chromosomes that are haploid or diploid and are wrapped around histone proteins. In contrast, prokaryotes typically possess a single, circular chromosome that is haploid, with bacteria lacking histones and archaea containing histones.

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Eukaryotic cells are defined by the presence of a nucleus surrounded by a complex nuclear membrane and membrane-bound organelles in the cytoplasm, which are supported and held in place by an internal cytoskeleton. These cells, which can exist as independent, single-celled microorganisms or as part of multicellular organisms (comprising protozoans, algae, fungi, plants, and animals), feature plasma membranes structured as a bilayer consisting of ester-linked, straight-chain fatty acids and sterols, and they contain multiple, linear chromosomes associated with histones.

Eukaryotic cell

Archaea are unicellular prokaryotic organisms that have distinct evolutionary histories, genetics, metabolic pathways, and structural compositions compared to bacteria. They are found in nearly every habitat, including extreme environments that are very cold, hot, basic, or acidic. While some archaea reside in the human body, none have been identified as human pathogens.

Archaea

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Eukaryotes have membrane-bound organelles, each with their own structure and function. Organelles commonly found in eukaryotes include:
- Nucleus
- Endoplasmic Reticulum
- Golgi Apparatus
- Lysosome
- Vacuole
- Mitochondria
- Chloroplast
- Peroxisomes

Organelles Commonly Found in Eukaryotes

The domain Eukarya comprises all eukaryotes, which include both unicellular and multicellular organisms such as protists, fungi, plants, and animals. The primary defining characteristic of these organisms is that their cells contain a true nucleus.

Eukarya

Comparison of Eukaryotic and Prokaryotic Chromosomes

In eukaryotic cells, the cytoskeleton is an internal network of fibers and tubes consisting of microfilaments, intermediate filaments, and microtubules. It provides structural support, anchors organelles, and serves as a transport network to move materials within the cell.

Eukaryotic Cytoskeleton

Eukaryotic cells exhibit a diverse range of shapes, including spheroid, ovoid, cuboidal, cylindrical, flat, lenticular, fusiform, discoidal, crescent, ring, stellate, and polygonal, and some can even be irregular or change their shape. These cellular morphologies are influenced by the cell's primary function, cytoskeleton organization, cytoplasm viscosity, membrane or cell wall rigidity, and external physical pressure from the environment or adjacent cells.

Eukaryotic Cell Shapes

Mitosis is a eukaryotic cell division process of asexual reproduction wherein a single parent cell divides to generate two genetically identical daughter cells.

Mitosis

The eukaryotic cell cycle is a regulated, sequential series of events involving cell growth, DNA replication, and cell division that results in the production of two clonal daughter cells.

Eukaryotic Cell Cycle

Meiosis is a eukaryotic cell division process involving two separate nuclear divisions that yields four genetically distinct gametes, each containing half the parent cell's chromosomes. This reduction in chromosome number is vital for sexual reproduction, ensuring that the resulting zygote after fertilization possesses a complete set of chromosomes.

Meiosis

The endomembrane system, unique to eukaryotic cells, is a network of membranous tubules, sacs, and flattened disks that function to synthesize cellular components and transport materials within the cell.

Endomembrane System

Eukaryotic cells that lack a cell wall, such as animal cells and certain protozoans, secrete a sticky mixture of carbohydrates and proteins into the intercellular spaces to form an extracellular matrix. This matrix provides shape maintenance and structural stability, consisting of a protein-based basement membrane, a bulky mass of proteoglycans, and strength-providing collagen fibers, all of which are linked via fibronectins to membrane-spanning integrin proteins.

Eukaryotic Extracellular Matrix

- Crenarchaeota
- Euryarchaeota
- Korarchaeota
- Nanoarchaeota
- Thaumarchaeota

Major Phylum of Archaea

Archaeal plasma membranes differ fundamentally from bacterial and eukaryotic membranes in three significant ways. First, archaeal membrane phospholipids are formed with ether linkages, rather than the ester linkages found in bacteria and eukaryotes. Second, archaeal phospholipids contain branched chains, whereas those of bacterial and eukaryotic cells are straight-chained. Finally, while some archaeal membranes form lipid bilayers similar to other domains, other archaeal plasma membranes exist as lipid monolayers.

Archaeal Plasma Membrane Structure

Archaeal cell wall structure differs from bacterial cell walls primarily because archaea do not contain peptidoglycan. Instead, they often contain a similar polymer called pseudopeptidoglycan (or pseudomurein). Alternatively, some archaea possess a layer of glycoproteins or polysaccharides that serves as the cell wall, and a few archaeal species appear to lack cell walls entirely.

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