A)- Prokaryotes

What are 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, “ ُم�حبالقاسية of extreme ”للظروف

environments and can be classified into:

a)- Extreme halophiles للملوحة : ُم�حب live in such saline places as the

Great Salt Lake and the Dead Sea.

Some species require an extremely salty الملوحة environment to شديدةgrow.

b)- Extreme thermophiles للحرارة live ُم�حبin hot environments.

The optimum temperatures for most thermophiles are 60 - 80°C.

بالزمى غشاء

الخلوى الجدار

شبه نواةالريبوزومات

الكبساألسواولة

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Bacteria occur in many shapes and sizes. Bacteria of four shapes: rod-shaped, sphere-shaped, spiral-shaped, or filamentous-shaped.

2. Domain: Bacteria

األهداب

Prokaryotic Cell

CapsuleCell WallPlasma membrane

Cytoplasm (Cytosol)

NucleoidRibosomes

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.

Shapes of Bacteria

It is a tool for identifying تعريف bacteria, based on differences in their cell walls.

A)- Gram-positive (Gram +ve) bacteria:

Their cell walls have large amounts كبيرة of peptidoglycans كميةthat react with Gram’s stain (appear violet-stained بنفسجيا .(تُـصبغ

The Gram’s stain: جرام صبغة

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 باألحمر (تصبغ

The Gram’s stain: جرام صبغة

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 reddish-pink under a microscope after the Gram-staining procedure.

Summary of Gram’s stain: جرام صبغة

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 (ُممرضة ) more threatening ( خطورة .than gram-positive species (أكثر

Gram-negative bacteria are commonly more resistant ( ُممانعة (أكثرthan gram-positive species to antibiotics الحيوية .للمضادات

Summary of Gram’s stain: جرام صبغة

Many prokaryotes (bacteria) secrete a sticky protective layer called capsule outside the cell wall.

Capsule has the following functions وظائف:

1. Adhere تثبيت bacterial cells to their substratum السطح.

2. Increase bacterial resistance المقاوُمة to host defenses ُمناعة .العائل

3. Stickتلصق) ) bacterial cells together when live in colonies.

4. Protect تحمى bacterial cell.

I - the bacterial capsule

In all prokaryotes, the functions of the cell wall are as

following:

1. maintains تحافظ the shape of the cell,

2. affords physical protection الطبيعية توفر الحماية

3. prevents the cell from bursting (إنفجار) in a hypotonic

environment ذات المنخفض التركيزالبيئة األسموزى .

Most bacterial cell walls contain peptidoglycan

(a polymer of modified sugars cross-linked by short

polypeptides).

The walls of Archaea lack (تـفـتـقـد) peptidoglycan.

II - The bacterial cell wall

Structural Characteristics of a Bacterial Cell

Prokaryotes reproduce (تـتـكاثر) only asexually ( جنسيا ال ) by binary fission ( الثـنائ البسيط ياإلنقسـام ).

A single cell produces a colony of offspring.

Reproduction of Bacteria

البكتريا في التكاثر

Nutrition of Prokaryotes بدائيات النواةيالتغذية ف

• Prokaryotes are grouped (فَـتS into four (ص�ن

categories (أنواع) according to how they

obtain energy and carbon

Nutrition refers to how an organism obtains energy and a carbon source from the environment to build the organic molecules of its cells.

Phototrophs ( التغذية Organisms that obtain energy from :(ضوئية

light.

Chemotrophs ( التغذية Organisms that obtain energy :(كيميائية

from chemicals in their environment.

Autotrophs ( التغذية Organisms that use CO2 as a carbon :(ذاتية

source.

Heterotrophs ( التغذية Organisms that use organic :(متعدد

nutrients as a carbon source.

Nutrition of Prokaryotes التغذية فى بدائيات النواة

Photoautotrophs ( الضوئية التغذية :(ذاتية use light energy as an energy source, and CO2 as a carbon source to synthesize (تخلق) organic compounds.

Chemoautotrophs الكيميائية التغذية :((ذاتية use chemical inorganic substances as an energy source, and CO2 as a carbon source.

Photoheterotrophs ( الضوئية التغذية :(ُمتعدد use light as an energy source, and organic substances as carbon sources.

Chemoheterotrophs ( الكيميائية التغذية :(ُمتعدد use organic substances as a source for both energy and carbon.

There are four major modes of nutrition

Prokaryotic modes of nutritionBased on Carbon source and Energy source that can be used

by a prokaryotic organism to synthesize organic compounds.

Autotrophs Heterotrophs

Photo-autotroph

Chemo-autotroph

Chemo-Heterotroph

Photo-Heterotroph

CO2 as Carbon SourceOrganic compounds as

Carbon Source

- Light as energy source

-CO2 as C source

- Light as energy source

-CO2 as C source

- Chemicals as energy source

-CO2 as C source

- Chemicals as energy source

-CO2 as C source

- Light as energy source

-Organic compounds as C source

- Light as energy source

-Organic compounds as C source

- Chemicals as energy source

- Organic compounds as C source

- Chemicals as energy source

- Organic compounds as C source

Prokaryotes

Quiz1

19

Prof. Ashraf M. Ahmed

aalii@ksu.edu.sa

College of Science, Zoology Department

General Animal Biology (Zoo-145)General Animal Biology (Zoo-145)