Download Prokaryotes and Eukaryotes (3 Lectures)

The Cell
Cellulae (Small room)
The Organism’s Basic Unit of Structure and Function
Types
of cells
Prokaryotic
Micro-organisms
Eukaryotic
All other forms
of life
Cell Theory
1- All organisms are composed of one or
more of cells.
2- Cell is the basic unit of life.
3- The new cell arises only from preexisting cell.
2
1). Prokaryotic and eukaryotic cells
differ in size and complexity
Similarities
• All cells are surrounded by a plasma membrane.
• The semi-fluid substance within the cell is called “cytosol”,
containing the cell organelles.
• All cells contain chromosomes which have genes in the form of DNA.
• All cells have tiny organelles called “Ribosomes” that make proteins.
1). Prokaryotic and eukaryotic cells
differ in size and complexity
Differences
• A major difference between prokaryotic and eukaryotic
cells is the location of chromosomes.
– In an eukaryotic cell, chromosomes are contained in a true nucleus ).
– In a prokaryotic cell, the DNA is concentrated in the nucleoid) without a
membrane separating it from the rest of the cell.
– In prokaryotic cell, DNA is a single strand or double strand DNA. But in
eukaryotic cell, DNA is double strand.
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.
Prokaryotes
– “Prokaryote” means “before a nucleus”
– No internal membrane-bound organelles –
just one little bag of cytoplasm
– No nucleus
– Usually single-celled (may form simple
colonies)
– May or may not require oxygen for survival.
– Earliest types of cells on Earth
– Cell type of all bacteria and Archaea
Much tougher than eukaryotes
Can survive almost anywhere – and do!
Have much greater genetic diversity than
eukaryotes
Have a cell wall surrounding the cell membrane
(different chemistry from plant cell wall)
Types of Prokaryotes
Prokaryotes
Bacteria
- Exist in most
environments
Archaea
- Exist in extreme environments
(hot and salty)
They are differing in some other structural, biochemical
and physiological characteristics
1. Domain: Archaea
•
Archaea are extremophiles, “ ‫ُمحب‬
‫ ”للظروف القاسية‬of extreme environments
and can be classified into:
a)- Extreme halophiles ‫ ُمحب 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 ‫ ُمحب للحرارة‬live
in hot environments.
•
The optimum temperatures for most
thermophiles are 60 - 80°C.
2. Domain: Bacteria
Bacteria occur in many shapes and sizes. Bacteria of four shapes: rodshaped, sphere-shaped, spiral-shaped, or filamentous-shaped.
‫األهداب‬
‫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 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.
The Gram’s stain: ‫صبغة جرام‬
• It is a tool for identifying ‫ تعريف‬bacteria, 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 (appear red-stained ‫)تصبغ باألحمر‬
Summary of 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 reddishpink under a microscope after the Gram-staining
procedure.
Summary of Gram’s stain: ‫صبغة جرام‬
• 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 (‫ ) ممرضة‬more
threatening (‫ )أكثر خطورة‬than 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:
1.
2.
3.
4.
Adhere ‫ تثبيت‬bacterial cells to their substratum ‫السطح‬.
Increase bacterial resistance ‫ المقاومة‬to host defenses ‫مناعة العائل‬.
Stick )‫ )تلصق‬bacterial cells together when live in colonies.
Protect ‫ تحمى‬bacterial cell.
II - The bacterial cell wall
•
In all prokaryotes, the functions of the cell wall are as
following:
1. maintains ‫ تحافظ‬the shape of the cell,
2. affords physical protection ‫توفر الحماية الطبيعية‬
3. prevents the cell from bursting (‫ )إنفجار‬in a hypotonic
environment ‫البيئة ذات التركيز األسموزى 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
Nutritional and metabolic diversity
All prokaryotes (and eukaryotes too) are grouped into four
(4) categories according to how they obtain energy and
carbon .
1. Photoautotrophs
- Photosynthetic  use light as the energy source
- CO2 is the carbon source
Example: Cyanobacteria; plants (eukaryotic).
2. Chemoautotrophs
- Energy from oxidation of inorganic substances (e.g. NH4,
and S)
- CO2 is the carbon source
Example: Sulfolobus, Beggiatoa (shown on slide)
3. Photoheterotrophs
- Light as energy source
- Organic compounds are source of carbon
4. Chemoheterotrophs
- Organic compounds are energy source and source
of carbon (this includes humans)
Examples: Many prokaryotes; animals (eukaryotic);
fungi (eukaryotic)
binary fission in bacteria
• Cell division
involves inward
growth of the
plasma
membrane,
dividing the parent
cell into two
daughter cells,
each with a
complete genome.
B- Eukaryotic Cell
26
• In eukaryote cells, the chromosomes are
contained within a membranous nuclear
envelope.
• The region between the nucleus and the
plasma membrane is the cytoplasm.
– All the material within the plasma membrane of
a prokaryotic cell is cytoplasm.
• Within the cytoplasm of a eukaryotic cell is
a variety of membrane-bounded organelles
of specialized form and function.
– These membrane-bounded organelles are
absent in prokaryotes.
• Eukaryotic cells are generally much bigger
than prokaryotic cells.
• The logistics of carrying out metabolism set
limits on cell size.
– At the lower limit, the smallest bacteria,
mycoplasmas, are between 0.1 to 1.0 micron.
– Most bacteria are 1-10 microns in diameter.
– Eukaryotic cells are typically 10-100 microns in
diameter.
Internal membranes compartmentalize the
functions of a eukaryotic cell
•
An eukaryotic cell has internal membranes, which partition the cell into
compartments .
•
These membranes also participate in metabolism as many enzymes are
built into membranes.
•
The general structure of a biological membrane is a double layer of
phospholipids and diverse proteins.
•
Each type of membrane has a unique combination of lipids and proteins
for its specific functions.
– For example, those in the membranes of mitochondria function in
cellular respiration.
B- Eukaryotic Cell
Eu: True
Karyon: Nucleus
Animal Cell
Plant Cell
What are the functions of cell organelles ?
Compare between Animal and Plant cell?
Euokaryotes: Euo = true karyot = •
nucleus . Plant and animals have
real nucleus, surrounded with
nuclear membrane.
-The Bacteria and the virus’s have •
no real nucleus they contain
nucleiod region (no nuclear
membrane) were the very simple
genetic material (DNA or
chromosome)
-The prokaryotic cells (bacteria and •
viruses) also have a very simples
cell structure cell wall, cell
membrane, cytoplasm, ribosome’s
and nucleiod area for a very simple
genetic material (DNA or RNA) and
cilia or flagella.
The euokayotic cells have a very •
complex structure and many cell
organelles (Look at the book page 112. 6th ed.)
Fig. 7.8
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
‫المادة الوراثية‬
‫النواة‬
‫الشبكة اإلندوبالزمية‬
‫نوية‬
‫الجدار النووى‬
‫سوط حركى‬
‫جسم مركزى‬
‫ريبوسوم‬
‫حهاز جولـﭽـى‬
‫غشاء بالزمى‬
‫حلمات دقيقة‬
‫ميتوكوندريا‬
‫جسم ُمحلل‬
‫‪33‬‬
‫الهيكل الخلوى‬
‫فجوة مركزية‬
‫بالستيدة خضراء‬
‫الجدار الخلوى‬
‫ثقوب بينية‬
‫‪34‬‬
Cytokinesis in animal cell:
• Cytokinesis, division of
the cytoplasm, typically
follows mitosis.
• In animals, the first sign
of cytokinesis
(cleavage)
is the appearance of a
cleavage furrow in the
cell surface near the old
metaphase plate.
• Cytokinesis in plants, which have cell walls,
involves a completely different mechanism.
• During telophase, vesicles
from the Golgi coalesce at
the metaphase plate,
forming a cell plate.
– The plate enlarges until its
membranes fuse with the
plasma membrane at the
perimeter, with the contents
of the vesicles forming new
wall material in between.
Prokaryotic vs. eukaryotic gene
structure
prokaryotes:
polycistronic
transcripts
eukaryotes:
monocistronic
transcripts
37