Download Prokaryotes

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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Bacteria occur in many shapes and sizes. Bacteria of four shapes: rodshaped, sphere-shaped, spiral-shaped, or filamentous-shaped.
‫األهداب‬
‫شبه نواة‬
‫الريبوزومات‬
‫غشاء بالزمى‬
‫الجدار الخلوى‬
‫الكبسولة‬
‫األسواط‬
Plasma
membrane
Ribosomes
Nucleoid
Cell Wall
Cytoplasm
(Cytosol)
Capsule
 Bacteria occur in many shapes and sizes. Most bacteria have one of
three basic shapes: rod-shaped, sphere-shaped, or spiral-shaped.
 Spiral shaped bacteria in the form of spirilla (singular, spirillum) or
vibrio (comma like).
 Sphere-shaped bacteria are called cocci (singular, coccus). An
example of cocci is Micrococcus luteus. Cocci are single or
aggregate cells in different shapes.
 Rod-shaped bacteria are called bacilli (singular, bacillus). An
example of bacilli is Escherichia coli. Bacilli are single or aggregate
cells in different shapes also.

It is a tool for identifying ‫ تعريف‬bacteria, based on differences in
their cell walls.

A)- Gram-positive (Gram +ve) bacteria:

Their cell walls have large amounts ‫ كمية كبيرة‬of peptidoglycans
that react with Gram’s stain (appear violet-stained ‫)تـُصبغ بنفسجيا‬.

B)- Gram-negative (Gram -ve) bacteria:

their cell walls have no or small amount of
peptidoglycan. So, do not react or very weakly react with
Gram’s stain (appear red-stained ‫)تصبغ باألحمر‬
 Gram Stain
 Most species of bacteria are classified into two categories
based on the structure of their cell walls as determined by
a technique called the Gram stain.
 Gram-positive bacteria have a thick layer of
peptidoglycan in their cell wall, and they appear violet
under a microscope after the Gram-staining procedure.
 Gram-negative bacteria have a thin layer of
peptidoglycan in their cell wall, and they appear reddishpink under a microscope after the Gram-staining
procedure.

Gram +ve bacteria: have Large amount of peptidoglycan
that stained violet.

Gram –ve bacteria: Have small amount or no peptidoglycan
stained red.

Most Gram-negative species are pathogenic (‫ ) ممرضة‬more
threatening (‫ )أكثر خطورة‬than gram-positive species.

Gram-negative bacteria are commonly more resistant (‫)أكثر ممانعة‬
than gram-positive species to antibiotics ‫للمضادات الحياتية‬.


Many prokaryotes (bacteria)
secrete a sticky
protective layer called
capsule outside
the cell wall.
Capsule has the
following functions ‫وظائف‬:
1.
2.
3.
4.
Adhere ‫ تثبيت‬bacterial cells to their substratum ‫السطح‬.
Increase bacterial resistance ‫ المقاومة‬to host defenses ‫مناعة العائل‬.
Stick )‫ )تلصق‬bacterial cells together when live in colonies.
Protect ‫ تحمى‬bacterial cell.

In all prokaryotes, the functions of the cell wall are as
following:
1.
maintains ‫ تحافظ‬the shape of the cell,
2.
affords physical protection ‫توفر الحماية الطبيعية‬
3.
prevents the cell from bursting (‫ )إنفجار‬in a hypotonic
environment ‫البيئة ذات التركيز األسموزى المنخفض‬.

Most bacterial cell walls contain peptidoglycan
(a polymer of modified sugars cross-linked by short polypeptides).

The walls of Archaea lack (‫ )تـفـتـقـد‬peptidoglycan.
‫التكاثر في البكتريا‬


Prokaryotes reproduce (‫)تـتـكاثر‬
only asexually (‫ )ال جنسيا‬by
binary fission (‫)اإلنقسـام الثـنائي البسيط‬.
A single cell produces a
colony of offspring.

Nutrition refers to how an organism obtains
energy and a carbon source from the environment
to build the organic molecules of its cells.
• Prokaryotes are grouped (‫صنٍفـَت‬
ُ ) into four
categories (‫ )أنواع‬according to how they obtain
energy and carbon

Phototrophs (‫)ضوئية التغذية‬:

Chemotrophs (‫)كيميائية التغذية‬:
Organisms that obtain energy from light.
Organisms that obtain energy from
chemicals in their environment.

Autotrophs (‫)ذاتية التغذية‬:

Heterotrophs (‫)متعدد التغذية‬:
a carbon source.
Organisms that use CO2 as a carbon source.
Organisms that use organic nutrients as

Photoautotrophs (‫)ذاتية التغذية الضوئية‬:
use light energy as an energy source, and CO2 as a carbon source to
synthesize (‫ )تخلق‬organic compounds.

Chemoautotrophs )‫)ذاتية التغذية الكيميائية‬:
use chemical inorganic substances as an energy source, and CO2 as a carbon
source.

Photoheterotrophs (‫)متعدد التغذية الضوئية‬:
use light as an energy source, and organic substances as carbon sources.

Chemoheterotrophs (‫)متعدد التغذية الكيميائية‬:
use organic substances as a source for both energy and carbon.