Transcript Lecture 5 (1)

A)- Prokaryotes
A)- Prokaryotes
 It includes two Major Domains: Archaea and Bacteria
 Prokaryotes are single-celled organisms that do not
have a membrane-bound nucleus, and can live in
nearly every environment on Earth.
 Although tiny, prokaryotes differ greatly in their genetic
traits, their modes of nutrition, however, their habitats
are similar.
 Based on genetic differences, prokaryotes are
grouped in two domains: Domain Archaea and
Domain Bacteria.
1. Domain: Archaea

Archaea are extremophiles, “ ‫مُحب‬
‫ ”للظروف القاسية‬of extreme environments
and can be classified into:
a)- Extreme halophiles ‫مُحب للملوحة‬:
 live in such saline places as the
Great Salt Lake and the Dead Sea.

Some species require an extremely
salty ‫ شديدة الملوحة‬environment to grow.
b)- Extreme thermophiles ‫ مُحب للحرارة‬live
in hot environments.

The optimum temperatures for most
thermophiles are 60 - 80°C.
2. Domain: Bacteria
Bacteria occur in many shapes and sizes. Most bacteria have one of
three basic shapes: rod-shaped, sphere-shaped, or spiral-shaped.
‫شبه نواة‬
‫الريبوزومات‬
‫غشاء بالزمى‬
‫الجدار الخلوى‬
‫الكبسولة‬
‫األسواط‬
Prokaryotic Cell
Plasma
membrane
Ribosomes
Nucleoid
Cell Wall
Cytoplasm
(Cytosol)
Capsule
Shapes of Bacteria


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 are called spirilla (singular, spirillum).

Sphere-shaped bacteria are called cocci (singular, coccus). An
example of cocci is Micrococcus luteus. Cocci that form chains similar
to a string of beads are called streptococci.

Rod-shaped bacteria are called bacilli (singular, bacillus). An example
of bacilli is Escherichia coli.
The Gram’s stain: ‫صبغة جرام‬

It is a tool for identifying ‫ تعريف‬specific bacteria, 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.
The Gram’s stain: ‫صبغة جرام‬

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 (do not appear stained ‫)ال تظهر الصبغة‬
The Gram’s stain: ‫صبغة جرام‬

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.
1. Gram-positive bacteria have a thick layer of
peptidoglycan in their cell wall, and they appear purple
under a microscope after the Gram-staining procedure.
2. 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 Staining of Bacteria

Gram +ve bacteria: have Large amount of peptidoglycan
that stained violet (most of them are non-pathogenic ‫)غير ممرضة‬.

Gram –ve bacteria: Have small amount or no peptidoglycan
(no staining) (most of them are pathogenic ‫)ممرضة‬.

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.
I - the bacterial capsule


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 ‫ تثبيت‬bacteria cells to their substratum ‫السطح‬.
Increase bacteria resistance ‫ المقاومة‬to host defenses ‫مناعة العائل‬.
Stick (‫ )تلصق‬bacterial cells together when live as colonies.
Protect ‫ تحمى‬bacterial cell.
II - The bacterial cell wall

In all prokaryotes, the functions of the cell wall are as
following:
1.
maintains ‫ تحافط‬the shape of the cell,
2.
affords physical protection ‫توفر الحماية الطبيعية‬
3.
prevents the cell from bursting (‫ )إنفجار‬in a hypotonic
environment ‫البيئة ذات التركيز األسموزي المنخفض‬.

Most bacterial cell walls contain peptidoglycan
(a polymer of modified sugars cross-linked by short polypeptides).

The walls of Archaea lack (‫ )تـفـتـقـد‬peptidoglycan.
Structural Characteristics of a Bacterial Cell
Reproduction of Bacteria
‫التكاثر في البكتريا‬


Prokaryotes reproduce (‫ )تـتـكاثر‬only asexually (‫)ال جنسيا‬
by binary fission (‫)اإلنقسـام الثـنائي البسيط‬.
A single cell produce a colony of offspring.
Nutrition of Prokaryotes
‫التغذية في األحياء الدقيقة‬

Nutrition refers to how an organism obtains
energy and a carbon source from the environment
to build the organic molecules of its cells.
ُ ) into four
• Prokaryotes are grouped (‫صنٍفـَت‬
categories (‫ )أنواع‬according to how they obtain
energy and carbon
Nutrition of Prokaryotes
‫التغذية فى األحياء الدقيقة‬

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
There are four major modes of nutrition

Photoautotrophs (‫)ذاتية التغذية الضوئية‬:
use light energy as energy source, and CO2 as carbon source to synthesis
(‫ )تخلق‬organic compounds.

Chemoautotrophs )‫)ذاتية التغذية الكيميائية‬:
use chemical inorganic substances as energy source, and CO2 as a carbon
source.

Photoheterotrophs (‫)متعدد التغذية الضوئية‬:
use light as energy source, and organic substances as carbon source.

Chemoheterotrophs (‫)متعدد التغذية الكيميائية‬:
use organic substances as a source for both energy and carbon.
Prokaryotic modes of nutrition
Based on Carbon source and Energy source that can be used
by a prokaryote organism to synthesize organic compounds.
Prokaryotes
Autotrophs
CO2 as Carbon Source
Photoautotroph
Chemoautotroph
Heterotrophs
Organic compounds as
Carbon Source
PhotoHeterotroph
ChemoHeterotroph
- Light as energy
source
- Chemicals as
energy source
- Light as
energy source
- Chemicals as
energy source
-CO2 as C source
-CO2 as C source
-Organic
compounds as
C source
- Organic
compounds as C
source