There are two types of cells known as the bacteria and human
cells. Bacteria cells are also known as the prokaryotic cells and human cells
are as well known as eukaryotic cells. Prokaryotes are unicellular organisms and
do not contain a nucleus or other membrane-bound organelles. Prokaryotes consist of two groups and these include the eubacteria
and the archaea. However, eukaryotic cells can be unicellular or multicellular
and do contain a nucleus and membrane-bound organelles. Eukaryotes consist of protists,
fungi, animals and plants. Prokaryotes generally range in size about 0.5 – 2.0 mm in diameter and often have either one of these three shapes: cocci
which is a spherical shape, bacilli which are
known as rod-like shape and spirilla which is also known as helically coiled.
Firstly, the main difference between the two cells is that prokaryotic cells do not have a
nucleus. Whereas, eukaryotic cells do have a nucleus. The nucleus is seen to be
the largest organelle in the Eukaryotic cell with the size of about 6mm.
The nucleus contains genetic material as DNA which is also known
as deoxyribonucleic acid. It also manages
with the activities of the other organelles within the cell. The nucleus is
bounded by two different membranes known as the inner and the outer nucleus
membranes. The other characteristics of the nucleus include the nucleolus which
is a dark area within the nucleus and this is quite important in cell division;
the area becomes denser and darker during rRNA synthesis. The nucleus also
includes a nucleus envelope which is a double membrane that is surrounded by pores and these allow communication to take
place between the nucleus and the cytoplasm; linked to the endoplasmic reticulum. The nucleus consists of
chromatin which are DNA proteins that have a thread-like appearance when the
cell is not going through the mitosis or meiosis process. Similarly, the
nucleus involves chromosomes that have genetic information of a cell; made when
chromatin transforms into shorter and denser coils.
Eukaryotic cells are larger in size than prokaryotic cells –
usually with a diameter of about 10-100mm,
related to the diameter of 0.2-2mm
of prokaryotes. A prokaryotic cell has a greater surface area to volume ratio
and this is beneficial as it enables it to have a simpler internal structure, as
molecules can simply and rapidly be transported to all of the parts of the cell
by diffusion. However, this cannot be done in a eukaryotic cell as it needs
more complex organelles to make and transport the molecules.
A prokaryotic cell consists of a bacterial cell wall.
However, eukaryotic cells do not have a bacterial cell wall. Instead, a
eukaryotic cell consists of plant cell wall. In order to protect the cell from
getting mechanical damage and osmotic pressure, almost all of the prokaryotes
are surrounded by a rigid thick cell wall
about the size of 3-25 nm. The cell wall is made up of proteins, peptidoglycan
and a complex of oligosaccharides. A peptidoglycan is a polymer of amino acids
and sugars that often make up the cell wall of bacteria. An Oligosaccharide is
a type of saccharide polymer comprising a small number (about 3 to 10) of
monosaccharides which are simple sugars. Whereas, the cell wall surrounding the
plant cell in eukaryotic cells consists of polysaccharide cellulose, with a
rod-like polysaccharide appearance. These cellulose molecules are combined
together by hydrogen bonding into packages of fibres and these fibres are often
cross-linked together by other polysaccharides. Another polymer known as the
lignin which is in wood provides the cell
wall with supplementary rigidity and strength.
Prokaryotic and eukaryotic cells both have DNA in common.
However, the methods and roles of the DNA in each cell is different. For
example, the DNA in prokaryotic cells are circular, without proteins. However,
the DNA in eukaryotic cells is linear and
connected with proteins to produce chromatin.
Prokaryotic cells have bacterial
flagella. Whereas, eukaryotic cells do not have flagella.
On the other hand, prokaryote and eukaryote cells both have
plasma membranes. The plasma membrane which is also called the cell membrane is
the cells outermost surface and this part of the cell often splits the cell
from the external environment and keeping the right ionic structure and osmotic
density of the cytosol. Like the other membranes, the plasma membrane is
selectively permeable to certain molecules due to the existence of specific
proteins in the membrane. Also, the plasma membrane is involved in
communicating with other cells, in particular
through the binding of ligands (tiny particles such as neurotransmitters or
hormones) to receptor proteins on its surface. The plasma membrane is also involved in the discharge and
internalisation of proteins and other macromolecules.