Prokaryotic and Eukaryotic Cells

‘Pro’ means before and ‘eu’ means ‘true’ or ‘good.’ So putting all that together “Prokaryotic” means

“before a nucleus,” and “Eukaryotic” means “possessing a true nucleus.”

Differences and comparisons

Prokaryotic Cells

Prokaryotic cells have no nuclei

Prokaryotic cells are small cells

DNA is circular, without protein

Ribosomes are small (70S)

No cytoskeleton

Motility by rigid rotating flagellum

Cell division is by binary fission

Reproduction is always asexual

Huge variety of metabolic pathways

Prokaryotic Cell

Prokaryotic cells are the simplest systems that exhibit all of the signs of life. They are the smallest types of cell, averaging 2-5 um in length, which makes them just visible under the light microscope. Despite their small size, inside each cell there is the complete chemical and biochemical machinery necessary for growth, reproduction and the acquisition and utilization of energy.

Prokaryotes have a large array of abilities. Some of them live in the absence of oxygen, some live in extreme conditions of heat or cold, others at the bottom of oceans where the only source of energy is hot hydrogen sulphide bubbling up from the core of the earth.

Common Features

Energy comes in many forms, and various types of prokaryotic cells are adept at using almost all of them. In large measure the actual structure of one of these cells reflects the way in which it acquires energy, but, despite their diversity, all prokaryotic cells have the following features in common.

A Plasma Membrane

Just inside the cell wall, the plasma membrane is a selective barrier which regulates the passage

of materials to from the cell. It is through this membrane that a cell must exchange food

molecules, gases and other vital ingredients. Composed of phospholipid and

protein membranes form thin, flexible, self-sealing, highly selective barriers between the inside

of the cell and the outside world.

Binary Fission

Reproduction in prokaryotic cells is by binary fission; a process of growth, enlargement and

division. The DNA molecule of the cell is accurately duplicated and the two copies separated

from each other by movement of the cell membrane to which they are attached. The cell then

divides into two smaller but identical cells and each begins its own independent existence.

Eukaryotic Cells

Larger Cells

Often multicellular

Always have nucleus and other membrane bound

DNA is linear and associated with proteins to form chromatin

Ribosomes are large (80S) – Eukaryotic ribosomes are large and they contain 34 proteins and

two rRNA molecules. Ribosomes are also made out of nucleolus.

Ribosome is the machinery that helps build protein.

Always has a cytoskeleton

Motility by flexible waving cilia of flagella

Cell division is by mitosis or meiosis

Reproduction is asexual or sexual

Common metabolic pathways.

Eukaryotic Membranes

Eukaryotic membranes are highly modified. In addition to the protein and phospholipid layer

that acts as a selective barrier, single celled animals, for example, have special proteins

embedded in their plasma (cell) membrane that interact with molecules outside and allow the

cell to react to changing external circumstances. The plasma membrane also serves as a

'sensing organ'.

Eukaryotic Organelles

Unlike prokaryotes, eukaryotic cells compartmentalize various metabolic processes inside

membrane-bound organelles. For example, the breakdown of certain food molecules to provide

energy takes place in the mitochondrion, and photosynthesis takes place in a chloroplast.

Compartmentalization of metabolic processes makes eukaryotic cells very efficient and allows

them to increase in size.

Eukaryotic Nucleus

Within the nucleus, are the molecules of DNA, the macromolecules that carry all the genetic and hereditary information of the cell. Linear strands of DNA are entwined with histone and other proteins to form chromosomes. Normally invisible, these structures can be stained with dyes, identified, and counted during the division process. Every type of eukaryotic organism has its own unique collection of chromosomes.