A2.2.5 - Prokaryote Cells Flashcards
Include these cell components: cell wall, plasma membrane, cytoplasm, naked DNA in a loop & 70S ribosomes. The type of prokaryotic cell structure required is that of Gram-positive eubacteria such as Bacillus & Staphylococcus. Students should appreciate that prokaryote cell structure varies. However, students are not required to know details of the variations such as the lack of cell walls in phytoplasmas and mycoplasmas.
A little thing to help remember what prokaryotic cells are
What does the prefix pro & suffix kary mean?
Pro: before
Kary: nucleus
No nucleus & most primitive type of cell
The prokaryote cell
What are some major characteristics of prokaryotes?
- Much smaller & simpler than ECs (many are less than 1µm in diameter)
- No nucleus
- Unicellular (no membrane-bound organelles)
Examples of PCs: bacteria & archaea
Typical cell components of Prokaryotes #1
What are the 3 main components of prokaryotes?
The 3 major characteristics of all cells
- Plasma membrane
→ Similar in composition to the membranes of eukaryotes
→ Plays a role in binary fission
→ Controls to a considerable extent the movement of materials in & out of the cell - Cytoplasm
→ Chemical reactions in the cytoplasm are not isolated from one another, ∴ reactions can be interfered. Still, prokaryotes have the most diverse metabolic reactions of all organisms - DNA: naked DNA in prokaryotes
→ 1 long, continuous thread of DNA; bacterial chromosome (in a region called nucleoid)
→ Not associated w/ histones
→ Involved w/ cell control & reproduction
Plasma membrane & cytoplasm are the same for both types of cells
Typical cell components of Prokaryotes #2
About 70S ribosomes in prokaryotes
- For protein synthesis
- Much smaller than eukaryotic ribosomes (70S < 80S)
→ Has lower mass as well - All prokaryotic ribosomes are free in the cytoplasm
- Usually ranges in diameter between 0.1~5.0µm
Ribosomes have 2 subunits
Typical cell components of Prokaryotes #3
2 additional typical components of prokaryotes
- Cell wall: Found outside of cell membrane
→ Composed of peptidoglycan (carbohydrate-protein complex)
→ Protects prokaryotes against toxins
→ Maintains shape of cell
→ Resists high osmotic pressures - Plasmid: Small circular pieces of DNA transferrable from one prokaryote to another [Horizontal gene transfer (HGT)]
→ Separate pieces from the chromosomal DNA
→ Can help the cell adapt to unusual circumstances
HGT ≠ VGT (vertical gene transfer) which occurs from reproduction
Gram-positive eubacteria
One major way of classifying bacteria
- Crystal Violet Dye
→ Gram-positive bacteria have cell walls that take on a violet/blue appearance in the presence of crsytal violet.
→ Examples of gram-positive bacteria are: bacillus & staphylococcus
Gram-negative bacteria do not react to crystal violet
Appreciation of the variation of prokaryote cell structures
What do some bacteria have an additional layer of?
- Some bacteria have an additional layer of a type of polysaccharide outside the cell wall called a capsule
→ Allows it to adhere to structures (i.e. teeth, skin, food)
Appreciation of the variation of prokaryote cell structures
What are pili & flagellum?
*Only in some bacterial cells
- Pili: hair-like growths on the outside of the cell wall
→ Allows attachment to other cells
→ Main function: Joining bacterial cells for the transfer of DNA from one cell to another (sexual reproduction) - Flagella: hair longer than pili
→ Main function: locomotion of the organism
→ Spins to propel the cell through its medium
Appreciation of the variation of prokaryote cell structures
What factors help distinguish distinct types of prokaryotes?
- Nutritional requirements
- Sources of energy
- Chemical composition
- Morphology (shape)
