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Zoology 145 course General Animal Biology For Premedical Student Zoology Department Lecture 5: Prokaryotic Cell (Bacteria and Archaea) 1436-1437H 1 A)- Prokaryotes Objectives •What are Prokaryotes? •Domain: Archaea •Domain: Bacteria •Prokaryotic Cell •Shapes of Bacteria •The Gram’s stain. •Cell-Surface Structures •Major Nutritional Modes 3 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, of extreme environments and can be classified into: a)- Extreme halophiles: • live in such saline places as the Great Salt Lake and the Dead Sea. • Some species require an extremely salty environment to grow. b)- Extreme thermophiles live 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. 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 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 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 • It is a tool for identifying bacteria, based on differences in their cell walls. • A)- Gram-positive (Gram +ve) bacteria: • Their cell walls have large amounts of peptidoglycans that react with Gram’s stain (appear violet-stained). The Gram’s stain • 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) The Gram’s stain • 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 stained red. Most Gram-negative species are pathogenic more threatening than gram-positive species. Gram-negative bacteria are commonly more resistant than grampositive species to antibiotics. I - the bacterial capsule • • Many prokaryotes (bacteria) secrete a sticky protective layer called capsule outside the cell wall. Capsule has the following functions: 1. 2. 3. 4. Adhere bacterial cells to their substratum. Increase bacterial resistance to host defenses. Stick bacterial cells together when live in colonies. Protect bacterial cell. II - The bacterial cell wall • In all prokaryotes, the functions of the cell wall are as following: 1. maintains the shape of the cell, 2. affords physical protection 3. prevents the cell from bursting in a hypotonic environment. • Most bacterial cell walls contain peptidoglycan (a polymer of modified sugars cross-linked by short polypeptides). • The walls of Archaea lack peptidoglycan. Structural Characteristics of a Bacterial Cell Reproduction of Bacteria Prokaryotes reproduce only asexually by binary fission. A single cell produces a colony of offspring. Nutrition of Prokaryotes 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 into four categories according to how they obtain energy and carbon Nutrition of Prokaryotes Phototrophs: Chemotrophs: Organisms that obtain energy from light. Organisms that obtain energy from chemicals in their environment. Autotrophs: Heterotrophs: source. Organisms that use CO2 as a carbon source. Organisms that use organic nutrients as a carbon There are four major modes of nutrition Photoautotrophs : use light energy as an energy source, and CO2 as a carbon source to synthesize organic compounds. Chemoautotrophs: use chemical inorganic substances as an energy source, and CO2 as a carbon source. Photoheterotrophs: use light as an energy source, and organic substances as carbon sources. Chemoheterotrophs: use organic substances as a source for both energy and carbon. 20 Prokaryotic modes of nutrition Based on Carbon source and Energy source that can be used by a prokaryotic organism to synthesize organic compounds. Prokaryotes Autotrophs CO2 as Carbon Source Heterotrophs Organic compounds as Carbon Source Photoautotroph Chemoautotroph PhotoHeterotroph - 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 ChemoHeterotroph Reference 22 Thank you 23