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, “مُحب للظروف القاسية” of extreme environments and can be classified into: a)- Extreme halophilesمُحب للملوحة: live in such saline places as the Great Salt Lake and the Dead Sea. Some species require an extremely saltyشديدة الملوحة environment to grow. b)- Extreme thermophilesمُحب للحرارة live in hot environments. The optimum temperatures for most thermophiles are 60 - 80°C.
شبه نواة الريبوزومات غشاء بلازمى الجدار الخلوى الكبسولة الأسواط 2. Domain: Bacteria Bacteria occur in many shapes and sizes. Bacteria of four shapes: rod-shaped, sphere-shaped, spiral-shaped, or filamentous-shaped. الأهداب
Plasma membrane Cell Wall Capsule Ribosomes Nucleoid Cytoplasm (Cytosol) Prokaryotic Cell
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 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 تعريف bacteria, based on differences in their cell walls. A)- Gram-positive (Gram +ve) bacteria: Their cell walls have large amountsكمية 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 withGram’s stain (appear red-stained تصبغ بالأحمر) The Gram’s stain: صبغة جرام
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. • 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.
Gram Staining of Bacteria Gram +ve bacteria: have Large amount of peptidoglycan that stained violet. Gram –ve bacteria: Have small amount or no peptidoglycan stainedred. • Most Gram-negative species are pathogenic (ممرضة ) more threatening (أكثر خطورة) than gram-positive species. • Gram-negative bacteria are commonly more resistant (أكثر ممانعة) than gram-positive species to antibiotics للمضادات الحيوية.
I - the bacterial capsule • Many prokaryotes (bacteria) secrete a sticky protective layer called capsule outside the cell wall. • Capsule has the following functions وظائف: • Adhere تثبيت bacterial cells to their substratum السطح. • Increase bacterial resistance المقاومة to host defenses مناعة العائل. • Stickتلصق)) bacterialcells togetherwhen live incolonies. • Protect تحمى bacterial cell.
II - The bacterial cell wall • In all prokaryotes, the functions of the cell wall are as following: • maintains تحافظ the shape of the cell, • affords physical protection الحماية الطبيعيةتوفر • prevents the cell from bursting (إنفجار) in a hypotonic environment البيئة ذات التركيز الأسموزى المنخفض. • Most bacterial cell walls contain peptidoglycan (a polymer of modified sugars cross-linked by short polypeptides). • The walls of Archaea lack (تـفـتـقـد) peptidoglycan.
Reproduction of Bacteria التكاثر في البكتريا • Prokaryotes reproduce (تـتـكاثر) only asexually(لاجنسيا) by binary fission(الإنقسـام الثـنائي البسيط). • A single cell produces a colony of offspring.
Nutrition of Prokaryotes التغذية في بدائيات النواة • 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 (صُنٍفـَت)into four categories (أنواع)according to how they obtain energy and carbon
Nutrition of Prokaryotes التغذية فى بدائيات النواة • Phototrophs(ضوئية التغذية):Organisms that obtain energy from light. • Chemotrophs(كيميائية التغذية):Organisms that obtain energy from chemicals in their environment. • Autotrophs(ذاتية التغذية):Organisms that use CO2 as a carbon source. • Heterotrophs(متعدد التغذية):Organisms that use organic nutrients as a carbon source.
There are four major modes of nutrition • Photoautotrophs(ذاتية التغذية الضوئية): use light energy as an energy source, and CO2 as a carbon source to synthesize (تخلق) organic compounds. • Chemoautotrophsذاتية التغذية الكيميائية)):usechemical inorganic substances as an energy source, and CO2 as a carbon source. • Photoheterotrophs(متعدد التغذية الضوئية):use lightas an energy source, and organic substances as carbon sources. • Chemoheterotrophs(متعدد التغذية الكيميائية): use organic substances as a source for both energy and carbon.
Organic compounds as Carbon Source CO2 as Carbon Source Prokaryotic modes of nutrition Based on Carbon sourceand Energy source that can be used by a prokaryotic organism to synthesize organic compounds. Prokaryotes Autotrophs Heterotrophs Photo-autotroph Chemo-autotroph Photo-Heterotroph Chemo-Heterotroph - Light as energy source -CO2 as C source - Chemicals as energy source -CO2 as C source - Light as energy source -Organic compounds as C source - Chemicals as energy source - Organic compounds as C source