Animal cells are eukaryotic. Every animal, from sponges to humans, is built from eukaryotic cells, meaning each cell contains a true nucleus enclosed by a membrane and a collection of specialized internal compartments called organelles. Prokaryotic cells, found in bacteria and archaea, lack these features entirely.
What Makes a Cell Eukaryotic
The word “eukaryotic” comes from Greek roots meaning “true kernel,” referring to the nucleus. In animal cells, DNA is housed inside a membrane-wrapped nucleus, organized into multiple linear chromosomes. Those chromosomes are wound around small spool-like protein complexes called histones, which compact the DNA tightly enough to fit inside the nucleus while keeping it accessible when the cell needs to read specific genes.
Prokaryotic cells take a fundamentally different approach. They have no nucleus at all. Instead, their genetic material sits in an open region of the cell called the nucleoid, and it typically consists of a single circular chromosome. There are no histone-wrapped packaging systems and no nuclear membrane separating DNA from the rest of the cell.
Size Difference Between the Two
A typical animal cell measures 10 to 20 micrometers in diameter, roughly one-fifth the size of the smallest speck visible to the naked eye. Prokaryotic cells are dramatically smaller, usually 1 to 10 micrometers. That size gap isn’t random. Eukaryotic cells need more internal space to house their organelles, and the larger volume allows for more complex chemistry happening in parallel across different compartments.
Organelles That Define Animal Cells
The hallmark of eukaryotic cells is membrane-bound organelles, each performing a distinct job. Animal cells contain a rich set of these compartments:
- Nucleus: stores DNA and coordinates protein production
- Mitochondria: generate the cell’s energy supply (ATP) using a unique double-membrane structure
- Endoplasmic reticulum: comes in two forms, one studded with ribosomes for building proteins and a smooth version for assembling fats
- Golgi apparatus: sorts and packages proteins and lipids for delivery to other parts of the cell or export outside it
- Lysosomes: sacs filled with digestive enzymes that break down captured food, worn-out cell parts, and debris
- Peroxisomes: neutralize toxic byproducts of normal cell metabolism, including hydrogen peroxide
Prokaryotic cells have none of these. They carry out all their functions in the open cytoplasm, without internal membranes dividing labor into separate rooms. Even ribosomes, the protein-building machines found in both cell types, differ in size. Animal cells use larger 80S ribosomes (assembled from a 40S and a 60S subunit), while prokaryotes use smaller 70S ribosomes. This size difference is actually the reason certain antibiotics can target bacteria without harming your own cells.
The Cell Membrane
Both prokaryotic and eukaryotic cells have an outer plasma membrane, but animal cell membranes contain cholesterol, a feature that is essentially absent in most bacteria. Cholesterol changes how the membrane behaves: it makes the membrane less permeable to oxygen and other small molecules, gives it structural flexibility, and plays a direct role in cell signaling. Some disease-causing bacteria, like the one responsible for Lyme disease, actually steal cholesterol from their animal hosts to strengthen their own membranes, but they cannot produce it themselves.
Internal Skeleton
Animal cells maintain their shape and move materials around using a cytoskeleton, an internal network of protein filaments. Three types make up this scaffolding: actin filaments, intermediate filaments, and microtubules. Together they support the cell’s structure, help it divide, and transport organelles from place to place. Prokaryotic cells have some simple structural proteins, but nothing approaching this level of organized architecture.
How Animal Cells Divide
Cell division highlights another major difference. Animal cells reproduce through mitosis, a carefully choreographed process where chromosomes are duplicated, lined up along a spindle structure, and pulled apart into two identical sets before the cell splits in two. Specialized structures called centrioles help organize that spindle.
Prokaryotes skip all of this. They divide by binary fission, a faster and simpler process. The single circular chromosome copies itself, the two copies migrate to opposite ends of the cell, and a ring of proteins pinches the cell in half. No spindle, no centrioles, no nuclear envelope to dissolve and reform.
How Animal Cells Differ From Other Eukaryotes
Plants and fungi are also eukaryotic, so the distinction between animal cells and prokaryotes is clear-cut. But animal cells also have features that set them apart from other eukaryotes. Plant cells use a large central vacuole for storage and structural support; animal cells rely instead on multiple smaller lysosomes. Plant and fungal cells lack centrioles entirely. Animal cells also contain motor proteins called dyneins that plants do not have, and they possess specialized organelles like melanosomes (which produce the pigment melanin in skin cells) and acrosomes (enzyme-packed compartments in sperm cells that help penetrate an egg during fertilization).
Animal cells also lack two structures commonly associated with other kingdoms: a rigid cell wall (found in plants, fungi, and most prokaryotes) and chloroplasts (the organelles that carry out photosynthesis in plants). The absence of a cell wall is what gives animal cells their flexible, often irregular shapes compared to the boxy geometry of plant cells.