Chapter 4. Characteristics of Prokaryotic and Eukaryotic Cells

Assignment: Black Chapter 4

·         All living cells can be defined as prokaryotic (without a nucleus) or eukaryotic (with a nucleus).

·         Both cell types are surrounded by a cell membrane.

·         Both cell types may or may not have a cell wall.

·         Eukaryotic cells have extensive organization and partition as opposed to prokaryotes.

·         Prokaryotes are unicellular organisms.

·         Prokaryotes include two small groups of organisms: the archaebacteria and the large group of true bacteria or eubacteria.

·         Eukaryotes may be unicellular or multicellular and include all animals, plants, algae, fungi and protists.

·         Prokaryotes are generally small - in the range of 0.5 to 2.0 mm.  Eukaryotic cells are generally larger.  For example, a red blood cell is about 7.5 mm in diameter.  However, there are exceptions.  Cyanobacteria may be 60 mm long.

·         Table 4.1 - illustrates many of the similarities and differences between pro- and eukaryotes.

·         Shapes of bacteria - Figure 4.1

·         Arrangements of bacteria Figure 4.2

·         Structure of a prokaryote - Figure 4.3

·         Capsule or slime layer - can contribute to pathogenicity and escape from immune surveillance

·         Cell wall - peptidoglycan or murein is the major component of cell wall.  Structure is illustrated in Figure 4.4. (sugars + peptides).

·         Teichoic acid consisting of glycerol, phosphates and ribitol is found in polymers in gram-positives.

·         Outer membrane - found primarily in Gram negatives - lipopolysaccharide (LPS) is a major component - also called endotoxin - lipid A is a major component of LPS and can cause the toxic events of fever and blood vessel dilation observed in Gram-negative infections.

·         Periplasmic space - a gap between the cell membrane and the cell wall - particularly evident in Gram negative bacteria.

·         Comparison of cell walls of Gram negative, positive and acid-fast - Table 4.2, Figure 4.6.

·         Figure 4.7 structure of membrane - a - basic phospholipid molecule, b - the fluid mosaic model of membrane structure.

·         Different properties of the cell membrane.

·         Movement of substances across membranes

·         A living cell - any type, prokaryote or eukaryote is a living entity.  It is a dynamic organism.  It must take in nutrients, expel wastes, secrete products of metabolism

·         Cells are separated from the environment by a membrane.

·         Substances can move across membranes by passive or active processes.

·         Passive processes

·         In passive processes, substances move down a concentration gradient from a higher concentration to a lower concentration.  Passive processes include simple diffusion, facilitated diffusion and osmosis.

·         Simple diffusion Figure 4.28 - movement of particles or molecules from a higher concentration to a lower concentration.  Substances can move across membranes by simple diffusion through pores in the membranes.

·         Facilitated diffusion - Figure 4.29 - transmembrane carrier proteins participate in the movement of substances across the membranes.

·         Osmosis the diffusion of water from an area of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration) Figure 4.30.

·         The effects of tonicity (hyper, hypo, iso) on osmosis -Figure 4.31 - the point is the effect of tonicity on living cells.

·         Active processes

·         Active transport is the process of transporting molecules from a region of lower concentration to a region of higher concentration.  Active transport is mediated by specific transport molecules in the membrane of the cell.  The results of active transport are to move a molecule into a region of higher concentration and keep it there.  An example is active transport of glucose into a cell.  The energy is supplied by phosphoenolpyruvate - a high energy compound.  The glucose is modified once inside the cell as a part of metabolism.  Thus there is no real concentration gradient to deal with.  Figure 4.32.

·         Figure 4.11 - Clostridia and Bacillus species produce endospores as a means of survival.

·         Figure 4.12 flagella structure - important for movement and useful in diagnosing particular infections - monotrichous, peritrichous, amphitrichous etc.

·         Associated with flagella is the phenomenon of chemotaxis - cells have the capability of responding to chemical attractants - Figure 4.14.

·         Pili are formed on certain bacterial cells and are important for bacteriophage attachment, conjugation bridges for gene transfer (transfer of antibiotic resistance e.g.) - Figure 4.16.

·         Structure of a eukaryotic cell - Figure 4.18.

·         Describe components of cell and compare to components of prokaryotic cell.  Relate importance of differences between prokaryotic pathogens and eukaryotic victims and similarities of eukaryotic pathogens and victims relative to treatment of disease.

·         Note the organelles and specific partitioning resulting in specialization of compartmentalization

·         Structure of nucleus - Figure 4.19.

·         Structure of mitochondrion - Figure 4.21 - note similarity to bacterial cells - important in energy generation.

·         Structure of chloroplast - Figure 4.22.

·         Movement of substances across membranes

·         Some substances (more complex molecules and substances) are transported into eukaryotic cells by endocytosis.  The cell membrane pokes in and the substance is surrounded by the membrane to form a vesicle.  The vesicle pinches off the membrane and enters the cell.  Exocytosis is the reverse to secrete substances.  Figure 4.33.  Phagocytosis is a special case of endocytosis where a cell engulfs (eats) a substance or particle.