Lecture 3 Notes Microbiology 1 (MIB151S)

MIB151S: Structures of Prokaryotic and Eukaryotic cell (Microbiology 1)
Cape Peninsula University of Technology
Lecture 3 Notes

Microbiology 1
3.1 Overview of prokaryotic and eukaryotic cell structures
3.2 Size, shape and arrangement
3.3 Prokaryotic cell organisation
3.4 Prokaryotic cell membranes
3.5 Prokaryotic cell: the plasma membrane, internal membrane systems, cytoplasmic matrix, ribosomes and the
nucleoid
3.6 The prokaryotic cell wall
3.7 Peptidoglycan structure
3.8 Gram-positive cell walls
3.9 Gram-negative cell walls
3.10 The mechanism of Gram staining
3.11 The bacterial endospore
3.12 The eukaryotic cell: cytoplasmic matrix, microfilaments, intermediate filaments, and microtubules,
endoplasmic reticulum, Golgi apparatus, lysosomes and endocytosis, eukaryotic ribosomes, mitochondria,
chloroplasts and the nucleus
3.13 Cilia and flagella
3.14 Comparison of prokaryotic and eukaryotic cells
_______________________________________________________
Structures of Prokaryotic and Eukaryotic cells


3.1 Overview of prokaryotic and eukaryotic cell structure
 Prokaryotes can be distinguished from eukaryotes in terms of their size, cell structure
and molecular make-up;
 Prokaryotes can be divided into two major groups, i.e. Bacteria and Archaea;
 Most bacteria can be divided into two groups based on their cell wall structure – either
Gram +ve or Gram –ve;
 Some bacteria form resistant endospores in order to survive harsh environmental
conditions in a dormant state;
 When eukaryotes reproduce, genetic material is distributed between cells by the highly
organised, complex processes of mitosis and meiosis;
 Examples of eukaryotic organisms include the Protists and Fungi.


3.2 Size, Shape and Arrangement
Prokaryotes
 Different species of bacteria can be distinguished by differences in their morphological
structures, i.e. shape, arrangement and size.

1

,MIB151S: Structures of Prokaryotic and Eukaryotic cell (Microbiology 1)
Cape Peninsula University of Technology
Lecture 3 Notes

 Most commonly, bacteria have one of two shapes, cocci (s. coccus) and rod, often
called bacilli (s. bacillus).


Arrangements of cocci
Exist as individual cells
Diplococci: cocci may divide and form
pairs, e.g. Neisseria gonorrhoeae
Long chains: repeated division of cells
in one plane, e.g. Streptococci,
Enterococci, Lactococcus
Clusters: cell divides in random planes
to form irregular grape-like cluster, e.g.
Staphylococcus aureus
Tetrads: cells divide in 2 planes to
form square groups of 4 cells, e.g.
Micrococcus luteus
Cuboidal: cells divide in 3 planes to
form cubes of 8 cells, e.g. Sarcinia

Arrangements of bacilli
 Bacilli differ in their length-to-width, with coccobacilli being so short that they resemble
cocci;
 The shape of the rod’s end often varies between species – they may be flat ( Bacillus
anthracis), rounded, cigar-shaped, or bifurcated (divided into two branches or forks) ;
 Although many rods do occur singly, they may remain together after division to form
chains (Bacillus megaterium is found in long chains).
 They may form pairs, i.e., diplobacilli; form chains, streptobacilli, e.g., Bacillus subtilis;
form trichomes, which are similar to chains, with a larger area of contact between
adjacent cells (Beggiatoa, Saprospira).
 A few rod-shaped bacteria, the vibrios, are curved to form distinctive commas or
incomplete spirals.


Other forms of bacteria
 Actinomycetes (fig. a) characteristically form long multinucleate filaments or hyphae that
may branch to produce a network called a mycelium (Actinomyces, Streptomyces);

2

, MIB151S: Structures of Prokaryotic and Eukaryotic cell (Microbiology 1)
Cape Peninsula University of Technology
Lecture 3 Notes




(a) (b)




(c) (d)


 Many bacteria are shaped like long rods twisted into spirals or helices, called spirilla (fig.
b) if rigid and spirochetes when flexible;
 The oval- to pear-shaped, Hyphomicrobium (fig. c), produces a bud at the end of a long
hyphae;
 Gallionella (fig. d) produce nonliving stalks;
 Some bacteria are flat, square to rectangular boxes, e.g., Walsby’s square bacterium;
 Some bacteria are variable in shape and lack a single, characteristic form; these are called
pleomorphic even though they may, like Corynebacterium, have generally rod-like form.


Size
 Bacteria vary in size and in shape; Average size is 0.5 - 1µm in diameter. E.coli: 1.1 –
1.5µm wide x 2 - 6µm long;
 The smallest bacteria is 0.14 – 2µm in diameter;
 The largest is 600 x 80µm (Epulopiscium fishelsoni, living in the intestine of the brown
surgeonfish).




3