The nucleus has chromosomes inside it that contain genes made of deoxyribonucleic acid (DNA) and these genes control all of the cells activity. The nucleus in eukaryotic cells is separated from the cytoplasm by a nuclear envelope. The nucleus divides by mitosis. The DNA inside the nucleus is packaged in a highly organized way. It consists of a basic unit called a nucleosome, which is a bead like structure 11nm in diameter that consists of 146 pairs of DNA wrapped around eight histone molecules. Theses nucleosome threads form large coil loops that are held together by special proteins. These loops interact to form condensed chromatin seen in chromosomes during mitosis.
The mitochondrion is another very important organelle; it produces ATP, which the cell uses as a source of energy.
Ribosomes are present in some eukaryotic cells but are not in the above diagram. They are seen as small black spheres. Theses ribosomes assemble amino acids to make proteins.
Lymsosomes contain powerful protein-digesting enzymes. These organelles are used to digest protein.
The Rough and smooth endoplasmic reticulum have many small functions but in general they speed up the distribution of substances through the cytoplasm.
The outer plasma membrane separates the cell from its surroundings and controls the movement into and out of the cell.
The Golgi body/apparatus has the job of storing and chemically modifying substances in the cell. These substances are later secreted using the vesicles.
As explained the eukaryotic cell has many organelles inside it, each doing a job that helps keeps the overall cell functioning.
Prokaryotic cells have a very different ultra structure compared with that of a eukaryotic. See diagram below;
Picture from
As mentioned earlier the only prokaryotic cell is bacterium. It consists of a cytoplasmic membrane surrounded by a peptidogycan cell wall. The cytoplasm does not contain most of the cell organelles as it does in the eukaryotic cell. The only organelle present is the ribosome. These ribosomes are of a slightly smaller size than they are in the eukaryotic cell but they have the exact same function.
Most noticeably, there is no nucleus in a prokaryotic cell all the genetic information is not surrounded by a nuclear envelope it is free flowing in the cytoplasm.
The bacteria nucleoid does not divide by mitosis instead the cytoplasmic membrane plays a role in DNA separation during bacterial replication. Since bacteria are haploid that is they have only one chromosome they reproduce asexually, there is no meiosis process in bacterium. This completely contrasts with a eukaryotic cell.
The prokaryotic cell is surrounded by flagella; these are made of protein and play the part of propelling the cell along.
The size of the two cells are different also. The eukaryotic is much bigger than the prokaryotic. The respective units of size with respect to cells are micrometres and nanometres. To see the ultra structure of both cells an electron microscope must be used.
In conclusion the ultra structures of these two cells differ tremendously, the eukaryotic cell has many more organelles inside it and has more functions. Where as the prokaryotic cell is smaller and has less organelles and no nucleus. The cells differ also in the way the reproduce.
