# 1.2: Cellular Organization – Prokaryotic and Eukaryotic Cells

Learning Objectives

1. Briefly describe why, in terms of differences in cell size, a eukaryotic cell is structurally more complex and compartmentalized than a cell that is prokaryotic.
2. When given a description, determine whether a cell is prokaryotic or eukaryotic and explain why.
3. Briefly state why viruses are not considered as prokaryotic nor eukaryotic.

According to the cell theory, the cell is the basic unit of life. All life organisms are composed of one or more cells. Based on the organization of their cellular structures, all living cells can be divided into two groups : prokaryotic and eukaryotic ( besides spelled prokaryotic and eukaryotic ). Animals, plants, fungi, protozoans, and algae all possess eukaryotic cell types. lone bacteria have prokaryotic cell types .
Figure $$\PageIndex{1}$$: Bacteria on a Human Epithelial Cell from the Mouth. The bacteria are the small dark purple dots and dashes on the light blue cell. The oval purple mass in the center is the nucleus of the epithelial cell.
prokaryotic cells are broadly much smaller and more elementary than eukaryotic ( Figure \ ( \PageIndex { 1 } \ ) ). prokaryotic cells are, in fact, able to be structurally more simple because of their humble size. The smaller a cell, the greater is its surface-to-volume proportion ( the surface area of a cell compared to its bulk ) .
The airfoil area of a spherical object can be calculated using the follow formula :

\ [ S = 4\, \pi\, r^2\ ]
The bulk of a spherical object can be calculated using the formula :
\ [ V = \dfrac { 4 } { 3 } \, \pi\, r^3 \ ]
For exemplar, a ball-shaped cell 1 micron ( µm ) in diameter – the median size of a coccus-shaped bacteria – has a surface-to-volume ratio of approximately 6:1, while a spherical cellular telephone having a diameter of 20 µm has a surface-to-volume proportion of approximately 0.3:1 .
A large surface-to-volume ratio, as seen in smaller prokaryotic cells, means that nutrients can easily and quickly reach any contribution of the cells interior. however, in the larger eukaryotic cell, the circumscribed surface area when compared to its book means nutrients can not quickly diffuse to all interior parts of the cell. That is why eukaryotic cells require a assortment of specialize internal organelles to carry out metamorphosis, provide energy, and transport chemicals throughout the cell. Both, however, must carry out the same life processes. Some features distinguishing prokaryotic and eukaryotic cells are shown in Table \ ( \PageIndex { 1 } \ ). All of these features will be discussed in detail late in Unit 1 .
Table $$\PageIndex{1}$$: Eukaryotic Versus Prokaryotic Cells

## Nuclear Body

eukaryotic cell
a. The nuclear body is bounded by a nuclear membrane having pores connecting it with the endoplasmic reticulum ( see Figure \ ( \PageIndex { 2 } \ ) and Figure \ ( \PageIndex { 3 } \ ) ).
barn. It contains one or more pair, linear chromosomes composed of deoxyribonucleic acid ( DNA ) associated with histone proteins ).
c. A nucleolus is award. Ribosomal RNA ( rRNA ) is transcribed and assembled in the nucleolus.
d. The nuclear consistency is called a core .

An electron micrograph of a cell nucleus, showing the darkly stained nucleolus. ( public Domain ; US National Institute of General Medical Sciences/National Institutes of Health )
prokaryotic cell
a. The nuclear body is not bounded by a nuclear membrane ( see Figure \ ( \PageIndex { 4 } \ ) ).
b. It normally contains one circular chromosome composed of deoxyribonucleic acidic ( DNA ) associated with histone-like proteins.
c. There is no nucleolus.
d. The nuclear consistency is called a nucleoid .

## Cell Division

eukaryotic cell
a. The nucleus divides by mitosis.
b. Haploid ( 1N ) sex cells in diploid or 2N organisms are produced through meiosis .
For More data : revue of Mitosis from Unit 7

prokaryotic cell
a. The cell normally divides by binary fission. There is no mitosis.
b. Prokaryotic cells are haploid. meiosis is not needed .

## Cytoplasmic Membrane – also known as a cell membrane or plasma membrane

eukaryotic cellular telephone
a. The cytoplasmic membrane ( see Figure \ ( \PageIndex { 2 } \ ) and Figure \ ( \PageIndex { 3 } \ ) ) is a fluid phospholipid bilayer ( see Figure \ ( \PageIndex { 5 } \ ) ) containing sterols ( see Figure \ ( \PageIndex { 6 } \ ) ).
barn. The membrane is capable of endocytosis ( phagocytosis and pinocytosis ) and exocytosis .
prokaryotic cell
a. The cytoplasmic membrane ( Figure \ ( \PageIndex { 4 } \ ) ) is a fluid phospholipid bilayer ( Figure \ ( \PageIndex { 5 } \ ) ) that normally lacking sterols. Bacteria by and large contain sterol-like molecules called hopanoids ( Figure \ ( \PageIndex { 7 } \ ) ) .
Figure $$\PageIndex{4}$$: Prokaryotic Cell (Bacillus megaterium)
Figure $$\PageIndex{5}$$: Diagram of a Cytoplasmic Membrane
Figure $$\PageIndex{7}$$: Sterol-like hopanoids are found in the cytoplasmic membrane of many bacteria.
b.The membrane is incapable of endocytosis and exocytosis .

## Cell Wall

eukaryotic cell
a. Plant cells, alga, and fungi have cellular telephone walls, normally composed of cellulose or chitin. Eukaryotic cell walls are never composed of peptidoglycan ( see Figure \ ( \PageIndex { 3 } \ ) ).
b. Animal cells and protozoans lack cell walls ( see Figure \ ( \PageIndex { 2 } \ ) ) .
prokaryotic cell
a. With few exceptions, members of the domain Bacteria have cell walls composed of peptidoglycan ( see Figure \ ( \PageIndex { 4 } \ ) ).
b-complex vitamin. Members of the world Archae have cell walls composed of protein, a complex carbohydrate, or alone molecules resembling but not the lapp as peptidoglycan .

## Representative Organisms

• eukaryotic cell: The domain Eukarya: animals, plants, algae, protozoans, and fungi (yeasts, molds, mushrooms).
• prokaryotic cell: The domain Bacteria and the domain Archae.

Since viruses are acellular- they contain no cellular organelles, can not grow and divide, and carry out no independent metabolism – they are considered neither prokaryotic nor eukaryotic. Because viruses are not cells and have no cellular organelles, they can merely replicate and assemble inside a populate host cell. They turn the host cell into a factory for manufacturing viral parts and viral enzymes and assembling the viral components .
Viruses, which possess both survive and inanimate characteristics, will be discussed in Unit 4. recently, viruses have been declared as living entities based on the large number of protein folds encoded by viral genomes that are shared with the genomes of cells. This indicates that viruses likely arose from multiple ancient cells.

## Summary

1. There are two basic types of cells in nature: prokaryotic and eukaryotic.
2. Prokaryotic cells are structurally simpler than eukaryotic cells.
3. The smaller a cell, the greater its surface to volume ratio.
4. The smaller the surface to volume ratio, the more structurally complex (compartmentalized) a cell needs to be in order to carry out life functions.
5. There are fundamental differences between prokaryotic and eukaryotic cells.
6. Bacteria are prokaryotic cells; fungi, protozoa, algae, plants, and animals are composed of eukaryotic cells.
7. Viruses are not cells so they are neither prokaryotic nor eukaryotic. They can replicate only inside a living cell.