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.
Prokaryotic and eukaryotic cells differ in
size and complexity
• All cells are surrounded by a plasma
membrane.
• The semifluid substance within the membrane
is the cytosol, containing the organelles.
• All cells contain chromosomes which have
genes in the form of DNA.
• All cells also have ribosomes, tiny organelles
that make proteins using the instructions
contained in genes.
• A major difference between prokaryotic and
eukaryotic cells is the location of
chromosomes.
• In an eukaryotic cell, chromosomes are
contained in a membrane-enclosed organelle,
the nucleus.
• In a prokaryotic cell, the DNA is concentrated
in the nucleoid without a membrane
separating it from the rest of the cell.
(A)- Prokaryotes
Micro-organisms
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
Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other
membrane-enclosed organelles of the eukaryotic cell.
• 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.
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.
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
16
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
‫‪20‬‬
‫الهيكل الخلوى‬
‫فجوة مركزية‬
‫بالستيدة خضراء‬
‫الجدار الخلوى‬
‫ثقوب بينية‬
‫‪21‬‬
Prokaryotic vs. eukaryotic gene
structure
prokaryotes:
polycistronic
transcripts
eukaryotes:
monocistronic
transcripts
22
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)