Download What are Prokaryotes?

Zoology 145 course
General Animal Biology
For Premedical Student
Zoology Department
Lecture 5: Prokaryotic Cell
(Bacteria and Archaea)
1436-1437H
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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
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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.
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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
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Thank you
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