Lecture 3

1. Microbiology
An
introduction
Presented by
D. Mona
Othman
Albureikan
Lecture (5,6)

2. Prokaryotic and Eukaryotic Cells
• Prokaryotes and eukaryotes are chemically similar.
• They both contain nucleic acids, proteins, lipids, and
carbohydrates.
• They use the same kinds of chemical reactions to metabolize
food, build proteins, and store energy.

3. Prokaryotic and Eukaryotic Cells
• Prokaryote comes from the Greek words for
prenucleus.
• Eukaryote comes from the Greek words for
true nucleus.

4. Comparing Prokaryotic and Eukaryotic Cells: An Overview
Prokaryote
• One circular chromosome, not in
a membrane
• No histones
• No organelles
• Bacteria: peptidoglycan cell
walls
• Archaea: pseudomurein cell
walls
• Binary fission
Eukaryote
• Paired chromosomes,
in nuclear membrane
• Histones
• Organelles
• Polysaccharide cell walls
• Mitotic spindle

6. Comparing Prokaryotic and Eukaryotic Cells: An Overview
Prokaryote Eukaryote
1. Their DNA is found in the cell 's
nucleus, which is separated from the
cytoplasm by a nuclear membrane,
and the DNA is found in multiple
chromosomes.
1. Their DNA is not enclosed within a
membrane and is usually a singular
circularly arranged chromosome.
(Some bacteria, such as Vibrio ch.,
have two chromosomes, and some
bacteria have a linearly arranged
chromosome.)

7. Comparing Prokaryotic and Eukaryotic Cells: An Overview
Prokaryote Eukaryote
2. Their DNA is not associated with
histones (special chromosomal
proteins found in eukaryotes); other
proteins are associated with the DNA.
2. Their DNA is consistently associated
with chromosomal proteins called
histones and with nonhistones.

8. Comparing Prokaryotic and Eukaryotic Cells: An Overview
Prokaryote Eukaryote
3. They lack membrane
enclosed organelles.
3. They have a number of
membrane-enclosed organelles,
including mitochondria,
endoplasmic retic ulum, Golgi
complex, lysosomes, and sometimes
chloroplasts.

9. Comparing Prokaryotic and Eukaryotic Cells: An Overview
Prokaryote Eukaryote
4. Their cell walls almost
always contain the complex
polysaccharide peptidoglycan.
4. Their cell walls, when present,
are chemically simple.

10. Comparing Prokaryotic and Eukaryotic Cells: An Overview
Prokaryote Eukaryote
5. They usually divide by binary
fission. During this process, the
DNA is copied, and the cell splits
into two cells. Binary fission
involves fewer structures and
processes than eukaryotic cell
division .
5. Cell division usually involves
mitosis, in which chromosomes
replicate and an identical set is
distributed into each of two
nuclei. This process is guided by
the mitotic spindle, a football -
shaped assembly of microtubules.

11. The Size, Shape, and Arrangement
of Bacterial Cells
- Most bacteria range from 0.2 to 1.0 μm in diameter
From 2 to 8 μm in length.
- Most bacteria are monomorphic; they maintain a single shape.
- Some bacteria are genetically pleomorphic., such as Rhizobium sp.
and Corynebacterium sp. which means they can have many shapes.

12. Coccus (spherical)
Bacillus (rod-shaped)
Spiral
Spirillum
Vibrio
Spirochete
Basic Shapes

13. Coccus (spherical); Arrangements
- Cocci are usually round but can be oval.
- When cocci divide to reproduce, the cells can remain attached to one another.
- Cocci that remain in pairs after dividing are called diplococci.
- Those that divide and remain attached in chain like patterns are called
streptococci.
Plane of division
Diplococci
Streptococci

14. Coccus (spherical); Arrangements
- Those that divide in two planes and remain in groups of four are
known as tetrads.
Tetrad

15. Coccus (spherical); Arrangements
- Those that divide in three planes and remain attached in cubelike groups of
eight are called sarcinae.
Sarcinae

16. Coccus (spherical); Arrangements
- Those that divide in multiple planes and form grapelike broad sheets are
called staphylococci .
- These group characteristics are helpful in identifying cocci.
Staphylococci

17. Bacillus (rod-shaped) ; Arrangements
- Bacilli divide only across their short axis, so there are fewer groupings of bacilli
than of cocci.
- Most bacilli appear as single rods .
- Scientific name: Bacillus or shape: bacillus
Single bacillus

18. Bacillus (rod-shaped) ; Arrangements
-Diplobacilli appear in pairs after division
Diplobacilli

19. Bacillus (rod-shaped) ; Arrangements
- Streptobacilli occur in chains .
Streptobacilli

20. Bacillus (rod-shaped) ; Arrangements
- Others are oval and look so much like cocci that they are called
coccobacilli .
Coccobacillus

21. Spiral bacteria ; Arrangements
- Spiral bacteria have one or more twists; they are never straight.
- Bacteria that look like curved rods are called vibrios.
Vibrio

22. Spiral bacteria ; Arrangements
-Spirillum, have a helical shape, like a corkscrew, and fairly rigid
bodies .
- The spirilla are used propeller-like external appendages called
flagella to move.
Spirillum

23. Spiral bacteria ; Arrangements
- Spirals they are helical and flexible are called spirochetes.
- Spirochetes move by means of axial filaments
Spirochete

24. In addition to the three basic shapes
- There are star-shaped cells (genus Stella).
- Rectangular, flat cells (halophilic archaea) of the genus Haloarcula .
Star-shaped bacteria Rectangular bacteria

25. In addition to the three basic shapes
-There are prokaryotes that look very much like triangles Haloarcula
japonica
- Or squares Holoquadratum walsbyi .

26. Structures External to the Cell Wall
The external structures in the prokaryotic cell wall are;
- Glycocalyx.
- Flagella.
- Axial filaments.
- Fimbriae.
- Pili.

27. 1- Glycocalyx
- Many prokaryotes secrete it on their surface.
- Glycocalyx (meaning sugar coat) that surround cells.
- It is a sticky, gelatinous polymer that is external to the cell wall.
- It composed of polysaccharide, polypeptide, or both.
- It is made inside the cell and secreted to the cell surface.
- If the substance is organized and attached to the cell wall , the glycocalyx
is described as a capsule.
-If the substance is unorganized and only loosely attached to the cell wall,
the glycocalyx is described as a slime layer.
- A glycocalyx that helps cells in a biofilm attach to their target environment
and to each other is called an extracellular polymeric substance (EPS). The
EPS protects the cells It can provide nutrients.

28. 1- Glycocalyx
- The presence of a capsule can be determined by using negative
staining.
- In certain species, capsules are important for bacterial virulence .
- Capsules often protect pathogenic bacteria from phagocytosis by
the cells of the host.
- Streptococcus pneumoniae caused pneumonia only when the cells
are protected by a polysaccharide capsule.
- Unencapsulated S. plleumoniae cells cannot cause pneumonia
- The polysaccharide capsule of Klebsiella also prevents
phagocytosis and allows the bacterium to adhere to and colonize the
respiratory tract.

29. THE EUKARYOTIC CELL 1- The Cell Wall and Glycocalyx
1. The cell walls of many algae and some fungi contain cellulose.
2. The main material of fungal cell walls is chitin.
3. Yeast cell walls consist of glucan and mannan.
4. Animal cells are surrounded by a glycocalyx (carbohydrates), which
strengthens the cell and provides a means of attaehment to other cells.
5- Some of these carbohydrates are covalently bonded to proteins
(glycoproteins) and lipids (glycolipids) in the plasma membrane that
anchor the glycocalyx to the cell.

30. 2- Flagella
- Some prokaryotic cells
have flagella (singular:
flagellum ).
-Flagella are relatively
long filamentous
appendages consisting of a
filament that contains of
the globular (roughly
spherical) protein flagellin
arranged in several chains
that intertwine and form a
helix around a attached to
a hook ( consisting of a
different protein) and basal
body , which anchors the
flagellum to the cell wall
and plasma membrane.

31. 2- Flagella

33. 2- Flagella
- Prokaryotic flagella rotate to push
the cell.
- When a bacterium moves in one
direction for a length of time, the
movement is called a "run" or "swim.“
- Random changes in direction called
"tumbles.
- "Tumbles" are caused by a reversal
of flagellar rotation
- One advantage of motility is that it
enables a bacterium to move toward a
favorable environment or away from a
particular stimulus (taxis).
- Such stimuli include chemicals
(chemotaxis) and light (phototaxis).
-Bacterial cells can alter the speed and
direction of rotation of flagella and thus
are capable of various patterns of
motility.
-Motility the ability of an organism to
move by itself.
Run
Tumble
Tumble
Run
Tumble
A bacterium running and tumbling. Notice
that the direction of flagellar rotation
(blue arrows) determines which of these
movements occurs. Gray arrows indicate
direction of movement of the microbe.

34. 2- Flagella
- Bacteria that lack flagella are referred to as atrichous .
- Flagella may be peritrichous (distributed over the entire cell)
- Polar (at one or both poles or ends of the cell).
- If polar, flagella may be monotrichous (a single flagellum at one pole)
- lophotrichous (a tuft of flagella coming from one pole).
- Amphitrichous (flagella at both poles of the cell).
Peritrichous Monotrichous and polar
Lophotrichous and polar Amphitrichous and polar

35. 2- Flagella
- Flagellar protein is an antigen.
- The flagellar protein called H antigen is useful for distinguishing a
variations species of gram negative bacteria .
- For example, there are at least 50 different H antigens for E. coli.
Those variations species identified as E. coli 0157:H7 are associated
with food borne epidemics.

36. THE EUKARYOTIC CELL 2- Flagella and Cilia
1. Flagella are few and long in relation to cell size; cilia are numerous
and short.
2. Flagella and cilia are used for motility, and cilia also move
substances along the surface of the cells.
3. Both flagella and cilia consist of an arrangement of nine pairs and
two single microtubules.
A micrograph of Euglena, containing
alga, with its flagellum.
Cilia
A micrograph of Tetrahymena,
with cilia.

37. 3- Axial Filaments
- They are structures similar to that
of flagella (endoflagellum).
- Spiral cells that move by an
endoflagellum are called spirochetes.
- One of the best-known spirochetes
is Treponema pallidum
- Axial filaments are anchored at one
end of the spirochete.
- The rotation of the filaments
produces a movement of the outer
sheath that propels the spirochetes in
a spiral motion.
- This type of movement is similar to
the way a corkscrew moves through a
cork.
- This corkscrew motion probably
enables a bacterium such as T.
pallidum to move effectively through
body fluids.
Cell wall
Axial filament
Outer sheath
A photomicrograph of the spirochete
Leptospira, showing an axial filament

38. 3- Axial Filaments
A axial filaments wrapping around part of a
spirochete for a cross section of axial filaments)

39. 4- Fimbriae and Pili
- Many gram-negative bacteria contain hairlike appendages that are
shorter, straighter, and thinner than flagella .
- They are used for attachment and transfer of DNA rather than for
motility.
- These structures, which consist of a protein called pilin arranged
helically around a central core, are divided into two types, fimbriae
and pili, having very different functions.

40. 4- Fimbriae and Pili
- Fimbriae (singular: fimbria)help cells adhere to surfaces.
- They can number anywhere from a few to several hundred per cell
- They are involved in forming biofilms
- Fimbriae can also help bacteria adhere to epithelial surfaces in the
body.

41. 4- Fimbriae and Pili
- The fimbriae of E. coli 0157 enable this bacterium to adhere to the
lining of the small intestine, where it causes a severe watery diarrhea.
- Pili (s ingular: pilus) are involved in twitching and gliding motility.
- also, involved in DNA transfer ,such pili are called conjugation (sex)
pili.
- Pili are usually longer than fimbriae and number only one or two per
cell.

42. References
• Microbiology: An Introduction Plus
MasteringMicrobiology with eText - Access Card
Package (11th Edition) Hardcover – January 2, 2012
by Gerard J. Tortora, Berdell R. Funke, Christine L.
Case.
• Some pictures from different sits.