Prokaryotic and Eukaryotic Cells

Prokaryotic and Eukaryotic cells

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Prokaryotes lack DNA with a bound membrane, eukaryotes on the other hand, have a nucleus (containing DNA) surrounded by a nuclear envelope. Prokaryotes have circular DNA found freely in the cytoplasm. Prokaryotes also lack endoplasmic reticulum and have smaller ribosomes. It is thought that eukaryotes have evolved from simpler prokaryotes.

The structure of a generalised prokaryotic cell is shown below:

All bacterial cells have the following features:

1. No true nucleus- the genetic information is not contained within a membrane bound organelle
2. Have circular DNA called plasmids
3. The cell wall is not composed of cellulose- Made up of peptidoglycan
4. Have the smaller ribosomes (70s ribosomes)
5. Cells reproduce via binary fission (asexual reproduction)
6. There is no membrane bound organelles e.g. nucleus, mitochondria, chloroplasts etc.

Using an electron microscope, the ultrastructure of the cell can be seen. The ultrastructure of a typical animal cell is shown below:

Key words

Cytoplasm:  Where chemical reactions occur

                       Where substances dissolve

Ribosome: Provides a site for protein synthesis

                   70s ribosomes

Cell membrane: Acts as a partially permeable membrane barrier to control what goes in and out of the cell

Droplets of lipids or glycogen: Used as a store of energy

Flagellum: Allows movement and rotation of cell but not found in all Prokaryotic cells

Mesosome: Folding of cell membrane, this increases the surface area for respiration

Cell wall: Made up of peptidoglycan (murein)

                  Prevents cell bursting when turgid

                  Provides a shape, rigidity and protection for the cell

Pili: Allows transfer of DNA between cells

       Helps with adhering to surfaces

Capsule: Provides protection

                Prevents dehydration of cell

                Allows the cell to adhere to surfaces

Plasmids: Double stranded, circular loops od DNA formed from the main DNA of the cell

Circular/ coiled DNA: The DNA is not found associated with histone proteins and so doesn’t form chromosomes, so it isn’t linear.