Cell Biology
Types of cells ,Prokaryotes ,Archaea and Eukaryotic Cells
Prokaryotes:
Prokaryotes have a semi-rigid cell wall and a flexible membrane that encloses their cytoplasm, the medium that supports the processes of life. They contain one or more loops of DNA within the cytoplasm and protein manufacturing regions called ribosomes. They may have rudimentary internal membranes, but the environment within the cell is essentially uniform. That is, the cytoplasm contains a certain level of salinity, pH and chemical distribution, and all the processes of the cell occur in that environment.
Eukaryotic:
Eukaryotic cells are characterized by internal membranes and a strong cytoskeleton. A cytoskeleton is a framework of proteins, such as actin and keratin, which help hold a cell together and differentiate its organelles. Eukaryote means "true nut," referring to the fact that eukaryotic cells possess an internal Nucleus whereas prokaryotes (meaning "before nut") do not. In prokaryotes, the genetic material floats freely in the cytoplasm (cellular blood), while in eukaryotes, it is protected in a special nucleus. Eukaryotic DNA is organized into chromosomes whereas prokaryotic DNA is not.
Eukaryotic cells have a much greater diversity in their structure than prokaryotic cells.
Difference Between Prokaryotes and Eukaryotes:
| Prokaryotes | Eukaryote | |
| Cell Size | 1 -10um | 10 -100um |
Number of chromosomes
|
One--but
not true chromosome: Plasmids
|
More
than one
|
Genetic Recombination
|
Partial,
unidirectional transfers DNA
|
Meiosis
and fusion of gametes
|
| Cell type | Unicellular | Multi cellular |
| Lysosomes and peroxisomes | Absent | Present |
| Microtubules | Absent | Present |
| Mitochondria | Absent | Present |
| Endoplasmic Reticulum | Absent | Present |
| True Nucleus | Absent | Present |
| Nuclear Membrane | Absent | Present |
| Vacuoles | Present | Present |
| Cell Wall | Usually Chemically Complex | Only in Plant Cell and Fungi (Chemically Simpler |
| Plasma Membrane with Steroids | Usually No | Present |
| Permeability of Nuclear Membrane | Nuclear Membrane is absent. | Selective |
| Ribosomes | Small | Large |
| Golgi Apparatus | Absent | Present |
| Chloroplasts | Absent; chlorophyll scattered in the cytoplasm | Present (in plants) |
| Flagella | Sub microscopic in size, composed of only one fiber | Microscopic in size; membrane bound; usually arranged as nine doublets surrounding two singlet |
| DNA | No Junk and No Histones | Junk (introns) Present, Bind with Histones |
Cytoskeleton
|
May be
absent
|
Present
|
Example
|
Bacteria
and Archaea
|
Animals and Plants
|
