Cell Biology: Plasma Membrane and Cytoplasm

### Plasma Membrane

• The outer boundary of the cell, enclosing all of its contents
• Controls the entry and exit of substances
• Can pump substances in, even if the concentration outside the cell is very low
• Very effective at preventing entry of unwanted or even toxic substances
• Allows a cell to maintain concentrations of substances that are very different from those in the surrounding environment
• The permeability of the plasma membrane relies on a structure based on lipids
• Lysis is the bursting of the plasma membrane, which can be caused by excess pressure, viruses, or even the cell itself (autolysis)
• Lysis always leads to the death of the cell, showing that the plasma membrane is a vital structure

Cytoplasm

• The main component of water
• Dissolved or suspended in this water are enzymes, which catalyse hundreds or even thousands of chemical reactions

DNA

• Genes, made of DNA, contain the information needed for a cell to carry out all its functions
• Many genes hold the instructions for making a protein
• Some proteins are structural, therefore needed for growth and repair
• Others act as enzymes, without which many biochemical reactions would occur too slowly to support life

Prokaryote Cell Structure

• The first organisms to evolve on Earth and possess the simplest cell structure
• Mostly small in size and found almost everywhere
• Cytoplasm is not divided into compartments by membranes (it is one uninterrupted chamber)
• Structurally simpler than eukaryotic cells
• Bacteria are prokaryotic
• Prokaryotic cells do not have a nucleus
• Include these cell components: cell wall, plasma membrane, cytoplasm, naked DNA in a loop, and 70S ribosomes

Gram-Positive Eubacteria

• The type of prokaryotic cell structure required involves Gram-positive eubacteria such as Bacillus and Staphylococcus
• Prokaryote cell structure varies, for example, the lack of cell walls in phytoplasmas and mycoplasmas