Functional Anatomy of Prokaryotic and Eukaryotic Cells

Objectives:

12. Describe the plasma membrane.

  • What is the fluid mosaic model?
  • 13. List three functions of the plasma membrane in prokaryotic cells. How are the functions of chloroplasts, mitochondria, and the nucleus in eukaryotic cells carried out in prokaryotic cells?

    14. Differentiate between passive and active transport mechanisms.

    15. List and describe three types of passive transport mechanisms used by prokaryotic cells.

    16. Define:

  • Omosis
  • Osmotic pressure
  • 17. Describe what will occur when a cell is placed in a (an):

  • Hypertonic solution
  • Hypotonic solution
  • Isotonic solution
  • 18. List and describe two types of active transport mechanisms used by prokaryotic cells. What is the difference between transporter proteins used in active transport and transporter proteins used in passive transport? What is group translocation?

    19. Define, identify and give the function of the following:

  • Chromatophores or thylakoids
  • Mesosomes
  • Cytoplasm
  • Nuclear area or nucleoid
  • Ribosome
  • Inclusions
  • Carboxysomes
  • Gas vacuoles
  • Endospores
  • 20. Give the function of endospores and list the genera in which endospores are generally produced.

    Structures Internal To The Cell Wall

    The Plasma (Cytoplasmic) Membrane

    The plasma membrane encloses the cytoplasm and is a phospholipid bilayer with peripheral and integral proteins (the fluid mosaic model).

    The plasma membrane is selectively permeable.

    Plasma membranes carry enzymes for metabolic reactions, such as nutrient breakdown, energy production, DNA replication and photosynthesis in prokaryotes. These reactions take place in mitochondria, the nucleus, and chloroplasts in eukaryotic cells.

     

    Chromatophores

    Infoldings of the plasma membrane that contain pigments involved in photosynthesis.

     

    Mesosomes, irregular infoldings of the plasma membrane, are artifacts, not true cell structures.

    Plasma membranes can be destroyed by alcohols and polymyxins.

    The Movement Of Materials Across Membranes

    Movement across the membrane may be by passive processes, in which materials move from areas of higher to lower concentration, and no energy is expended by the cell.

     

    In simple diffusion, molecules and ions move until equilibrium is reached.

    In facilitated diffusion, substances are transported by transporter proteins across membranes from areas of high to low concentration.

    Osmosis is the movement of water from areas of high to low concentration across a selectively semi permeable membrane until equilibrium is reached.

     

     

    In active transport, materials move from areas of low to high concentration by transporter proteins, and the cell must expend energy.

    In group translocation, energy is expended to modify chemicals and transport them across the membrane. Once inside the cell the chemical modification prevents the transported substance from moving out of the cell. Example: glucose is converted to glucose-6- phosphate as it passes into the cell. This traps it and allows the movement of more glucose into the cell even when extracellular concentrations may be low.

    Cytoplasm

    Cytoplasm is the fluid component inside the plasma membrane.

    The cytoplasm is mostly water, which inorganic and organic molecules, DNA, ribosomes, and inclusions.

    The Nuclear Area

    The nuclear area contains the DNA of the bacterial chromosome.

    Bacteria can also contain plasmids, which are circular, extra-chromosomal DNA molecules.

    Ribosomes

    The cytoplasm of a prokaryote contains numerous 70s ribosomes; ribosomes consist of rRNA and protein.

    Protein synthesis occurs at ribosomes; it can be inhibited by certain antibiotics. The difference between prokaryotic (70s) and eukaryotic (80s) ribosomes allows antibiotics to selectively target the prokaryotic ribosomes while sparing eukaryotic ribosomes.

     

    Inclusions

    Inclusions are reserve deposits found in prokaryotic and eukaryotic cells.

    Among the inclusions found in bacteria are metachromatic granules (inorganic phosphate), polysaccharide granules (usually glycogen or starch), lipid inclusions, sulfur granules, carboxysomes (ribulose 1,5-diphosphate carboxylase), magnetosomes (Fe3O4), and gas vacuoles.

    Magnetosomes

    Endospores

    Endospores are resting structures formed by some bacteria for survival during adverse environmental conditions.

    The process of endospore formation is called sporulation; the return of an endospore to its vegetative state is called germination.  Two genera that commonly form endospores are Bacillus and Clostridium.