Wize High School Grade 11 Biology Textbook > Cell Biology
Prokaryotic Cells & Their Structures
0:00 / 0:00
What is a Cell?
The Cell Theory states that:
- Cells are the fundamental unit of life, and that all living organisms consist of one or more cells,
- All cells arise from the division of pre-existing cells.
Structurally, cells consist of cytoplasm contained within a membrane. Cells may vary in size, shape, and (consequently) function, with differences between cell types arising from mutations (evolution) or different expression of genes.
There are two types of cells: Prokaryotic and Eukaryotic
- Prokaryotes (such as bacteria and archaea) are single-celled organisms that do not contain membrane- bound organelles; therefore, the DNA is not separated from the cytoplasm.
- Eukaryotes can be single-celled or multi-cellular organisms that contain membrane-bound organelles, including a nucleus in which DNA is stored.
0:00 / 0:00
Prokaryotic Cells
Prokaryotes are very primitive living organisms that came about before eukaryotes. Their key characteristics are:
- No nucleus
- Mostly unicellular organisms
- They have no membrane bound organelles
General Structure of Prokaryotic Cells
- Ribosomes are organelles that are responsible for producing proteins.
- The prokaryotic DNA is not protected by a nuclear membrane and is found in the cytoplasm.
- The cytoskeleton are long polymer proteins that form thin fibers.
- The cytoskeleton is responsible for: cell shape, cell division, transportation of plasmids, organization of cell interior.
- Flagella are located on the surface of the cell and allow for bacteria to move.
- Cell walls surround the plasma membrane and function to protecting the organism, giving shape and rigidity.
- Capsule enables cell attachment.
- Pili allows for exchange of genetic information with other bacteria.
- Fimbriae (not shown) can also be found and are used to attach to surfaces such as a cell the bacteria might infect.
0:00 / 0:00
Bacteria and Archaea Cell Wall Composition
Bacteria
Bacteria are the most commonly discussed organisms when talking about prokaryotes.
- They are ubiquitous (can be found everywhere) and are smaller than eukaryotic cells.
- They have a cell wall composed of a large polymer called peptidoglycan, which is made up of polysaccharides and amino acids.
- Bacterial membrane lipids have ester bonds.
Archaea
Archaea are another type of prokaryote.
- They are often extremophiles (live in extreme environments such as extremely high temperatures, salt concentration, etc.).
- Their cells walls are composed of pseudo-peptidoglycan (different from bacterial peptidoglycan).
- Their membrane lipids have ether bonds.
0:00 / 0:00
Example: Bacteria & Archaea
Archaea and bacteria are both prokaryotes. Why are they not classified together?
Practice: Parts of Prokaryotes
Which of the following are part of a prokaryotic cell?
Practice: Function of the Cell Wall
Which of the following are functions of the cell wall?
Practice: Archaea and Bacteria
Label the following statements as true or false
A. Only Archaea have plasma membranes that are lipid monolayers containing isoprene
B. One feature the differentiates Bacteria and Archaea is their shape
C. Bacteria have circular DNA, while Archaea have linear DNA
D. No Archaea are known to cause human disease.