PROKARYOTIC
CELLS
By Tibor Cemicky
2 Main Types of Cells
Prokaryotic Cells = Primitive Cells
Eukaryotic Cells = much more complex
Animal / Plant Cells
What are Prokaryotic
Cells?
• Cells that lack a membrane-bound nucleus are called
prokaryotes (from the Greek meaning before nuclei)
• All Bacteria, Achaea and Cyanobacteria are prokaryotic
organisms
Archaea:
Haladaptatus
Cyanobacteria:
Fischerella
Bacteria:
Streptococcus
Structure of a Prokaryotic
Cell
• Capsule: Secretion of sticky substances
that form protective layer outside of the cell
wall. Enables the organisms to adhere to
their substrate and provide additional
protection
•Cell Wall: Protects the cell from outer
damage or bursting if internal pressure of
the cell is high
• Plasma Membrane: Controls entry and
exit of substances in or out of the cell
(diffusion)
• Nucleoid: Region where the circular
chromosome (DNA) is located
•Ribosomes: Only ‘organelles’ in a
prokaryotic cell - Produce protein
• Cytoplasm: Contains enzymes that
catalyze (speed up) the chemical reaction of
metabolism
• Pili: Protects cell wall, can be used to pull
cells together or attach to surfaces
• Flagellum: used for locomotion
(movement)
Prokaryotic Cell vs.
Eukaryotic Cells
Prokaryotic Cells
Eukaryotic cells
small cells
larger cells
always unicellular
often multicellular
no nucleus or any membrane-bound
organelles
always have nucleus and other
membrane-bound organelles
DNA is circular, without proteins
DNA is linear and associated with
proteins to form chromatin
ribosomes are small (70S)
ribosomes are large (80S)
no cytoskeleton (controversial)
always has a cytoskeleton
cell division is by binary fission
cell division is by mitosis or meiosis
reproduction is always asexual
reproduction is asexual or sexual
Reproduction
ALL prokaryotic organism reproduce by binary fission
Binary fission is the form of asexual reproduction and
cell division. It is the division of a cell into two parts
and each has the potential to grow to the size of the
original cell.
Binary Fission
Process:
1. DNA of the cell is replicated
2. Each circular strand of DNA then
attaches to the plasma membrane
3. The cell elongates, causing the two
chromosomes to separate
4. The plasma membrane then grows
inward and splits the cell into two
daughter cells
5. These 2 cells than both grow to the
size of the parent cell
...(Show a video)
Genetic Recombination
Although Prokaryotes do not reproduce sexualy genetic
recombination still occurs through these 3 proceses:
•Conjugation: A cell with DNA called F factor is able to replicate and inject
a copy if it's DNA to another cell (without F factor) through a tube called a
sex pilus. F factor may exist as a plasmid (independent DNA chromosome)
or become integrated into the chromosome. If it is integrated into the
chromosome, it may also transfer part of the chromosome.The DNA that is
transferred is used to replace similar genes in the recipient cell.
•Transformation: occurs when a bacterium (plural of bacteria) picks up
fragments of DNA released by dead bacteria or secreted by live bacteria.
•Transduction: occurs when viruses carry portions of bacterial DNA from
one cell to another.
Classification of
Prokaryotes
• Bacteria: (differ in shape)
– Round cells are called cocci
– Rod-shaped cells are bacilli
– Rigid, spiral-shaped cells are spirilla
cocci
bacilli
spirilla
Classification of
Prokaryotes
• Archaea: (differ in environment)
– Methanogens are found in anaerobic environments (without
oxygen) such as marshes and in the intestinal tracts of animals.
They produce methane as a result of cellular respiration.
– Halophiles are found in environments with high salt concentration
such as the great salt lake or soil with a high salt concentration.
– Thermophiles live in hot environments such as hot springs and
hydrothermal vents.
Classification of Prokaryotes
• Cyanobacteria: (differ in shape)
Unicellular:
- Gloeocapsa. Gloeocapsa is
a unicellular cyanobacteria.
The gelatinous material
surrounding each cell
causes the cells to stick
together.
Filamentous:
- Oscillatoria cyanobacteria
Prokaryotes - Organic Food
2 Types of Prokaryotic Organisms (food source):
Autotrophs: They make their own food through
photosynthesis or using energy from inorganic
chemicals
Heterotrophs: Heterotrophic prokaryotes feed on
organic matter by secreting enzymes and
absorbing the digested material.
Prokaryotes - Autotrophs
2 Types of Autotrophs:
Photosynthetic Prokaryotes: Prokaryotes
that make organic food using energy from
sunlight are photosynthetic
Chemosynthetic Prokaryotes: Prokaryotes
that make organic food by oxidizing highenergy inorganic compounds (hydrogen gas,
ammonia, nitrites, and sulfides)
Prokaryotes - Heterotrophs
3 Types of Heterotrophs:
–
Saprotrophic prokaryotes: They feed on nutrients that are tied
up in the bodies of dead organisms.
–
Parasites: are prokaryotic organisms that live in close
association with another species and benefits at its expense.
Normally, the larger organism is not killed.
–
Mutualistic prokaryotes: They live in close association with
another specie and both benefit as a result of the association.
(For example, some nitrogen-fixing bacteria live on the roots of
plants. They convert atmospheric nitrogen (N2) to a form that is
usable by plants. In return plants provide the bacteria with
carbohydrates.)