Prokaryotic and Eukaryotic Cells

• How do eukaryotic cells become specialised in complex multi-cellular organisms?

  • In multicellular organisms, different cells are specialised to fulfil different functions. ​
  • This is controlled by which gene is expressed (genes that are switched on and therefore have an effect).​
  • Every somatic cell (all cell excluding the gametes) contains in its nucleus the whole genome of the organism.​
  • How the cell functions is determined by which of the many genes are expressed and which are not.
• How do eukaryotic cells become specialised in complex multi-cellular organisms?

  • The process by which a cell changes from one cell type to another is known as cell differentiation. ​
  • Stem cells can differentiate to form specialised cells. ​
  • The human embryo can give rise to more than 200 cell types of the adult human body. ​
  • Stem cells are also responsible for replacement of worn-out cells.
• Prokaryote DNA is suspended freely in the cytoplasm. ​

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  The chromosome, along with several proteins and RNA molecules, forms an irregularly shaped structure called the nucleoid. 
• Cell wall = (role) Physical barrier from substances
• Capsule - (role) Protect bacterium from other cells
• Cell membrane = (Role) Control entry and exit of chemicals
• Flagellum = (Role) Aid movement, help cells spin though fluids
• Circular DNA = (role) Possesses genes for replication 
• Plasmid = (role) Genes that aid survival of bacteria adverse conditions (produce enzymes that break down antibiotics)
• Prokaryotes have simpler structure than eukaryotes, lacking organelles such as the nucleus, ER and Golgi.
• • Many pathogenic bacteria are surrounded by a mucous-like protective layer called a capsule.
  • The capsule protects bacteria from viruses, or attack from a host organism’s immune system, by hiding antigens on the cell surface.
  • The capsule is usually composed of polysaccharides, and also contains water to protect against desiccation (drying out).
• Plasmids

  • Bacterial cells often contain several plasmids – small continuous loops of DNA. Plasmids are physically separate from chromosomal DNA and replicate independently. 
  • Many plasmids contain genes that, when expressed, make the host bacterium resistant to an antibiotic.​
  • Other plasmids contain genes that help the host to digest unusual substances or to kill other types of bacteria.
  • Plasmids are commonly used in genetic engineering to make copies of genes or large quantities of proteins or hormones. 
• Flagella and pili

  • Some prokaryotic cells feature one or more flagella. These are long helical tubes extending out of the cell wall, which rotate to provide locomotion. A tail-like structure for movement of the cell.
  • Flagella are powered by protein motors and can propel bacteria at a rate of more than 50 lengths per second. 
  • Many bacteria also feature pili. These are hollow protein structures used during bacterial conjugation – the transfer of genetic material from one bacterium to another.
• Prokaryotic Cells:

  • no nucleus
  • circular strand of DNA, no chromosomes
  • no membrane - bound organelles
  • no chloroplast
  • no endoplasmic reticulum
  • They have a cell wall that contains murein/peptidoglycan, a glycoprotein
  • They may have one or more plasmids 
  • They may have a capsule surrounding the cell
  • They may have one or more flagella
• Eukaryotic Cells:

  • distinct nucleus with an nuclear envelope
  • Linear DNA, chromosomes present - the DNA is associated with proteins called histones
  • Membrane bound organelles, mitochondria
  • chloroplast present in plants
  • endoplasmic reticulum
  • Plant cells have a cellulose cell wall while fungi have a cell wall made of chitin
  • There are no plasmids
  • There is no capsule in animal and plant cells. Fungi can form a carbohydrate capsule.
  • Flagella where present are more complex