Prokariates

2. A prokaryote is a single-celled organism that lacks a membrane-
bound nucleus (karyon), mitochondria, or any other membrane-
bound organelle. The word prokaryote comes from the Greek πρό (pro)
"before" and καρυόν (karyon) "nut orkernel". Prokaryotes can be divided into
two domains, Archaea and Bacteria, with the remainder of species, called
eukaryotes, in the third domain Eukaryota.
In the prokaryotes all the intracellular water-soluble components
(proteins, DNA and metabolites) are located together in
thecytoplasm enclosed by the cell membrane, rather than in separate cellular
compartments.
Bacteria, however, do possess protein-based bacterial microcompartments, which
are thought to act as primitive organelles enclosed in protein shells

3. Some prokaryotes, such as cyanobacteria may form large colonies. Others, such
as myxobacteria, have multicellular stages in their life cycles.
Molecular studies have provided insight into the evolution and interrelationships
of the three domains of biological species. Eukaryotes are organisms,
including humans, whose cells have a well defined membrane-bound nucleus
(containingchromosomal DNA) and organelles.
The division between prokaryotes and eukaryotes reflects the existence of two
very different levels of cellular organization. Distinctive types of
prokaryotesinclude extremophiles and methanogens; these are common in
some extreme environments.

4. Prokaryotic cell structure
• Flagellum (only in some types of prokaryotes)[which?]
• Long, whip-like protrusion that aids cellular locomotion.
• Cell membrane
• Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.
• Cell wall (except genera Mycoplasma and Thermoplasma)
• Outer covering of most cells that protects the bacterial cell and gives it shape.
• Cytoplasm
• A gel-like substance composed mainly of water that also contains enzymes, salts, cell
components, and various organic molecules.
• Ribosome
• Cell structures responsible for protein production.
• Nucleoid
• Area of the cytoplasm that contains the single bacterial DNA molecule.
• Glycocalyx (only in some types of prokaryotes)
• A glycoprotein-polysaccharide covering that surrounds the cell membranes.
• Inclusions

5. .Morphology of prokaryotic cells
Prokaryotic cells have various shapes; the four
basic shapes of bacteria are:
➢Cocci – spherical
➢Bacilli – rod-shaped
➢Spirochaete – spiral-shaped
➢Vibrio – comma-shaped
➢The archaeon Haloquadratum has flat square-
shaped cells.

6. Reproduction
• Bacteria and archaea reproduce through asexual reproduction, usually
by binary fission. Genetic exchange and recombination still occur, but this
is a form of horizontal gene transfer and is not a replicative process, simply
involving the transference of DNA between two cells, as in bacterial
conjugation

7. DNA transfer
• DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has
been mainly studied in bacteria. In bacteria, gene transfer occurs by three processes.
• These are (1) bacterial virus (bacteriophage)-mediated transduction, (2) plasmid-
mediated conjugation, and (3) natural transformation. Transduction of bacterial genes by
bacteriophage appears to reflect an occasional error during intracellular assembly of virus
particles, rather than an adaptation of the host bacteria.
• The transfer of bacterial DNA is under the control of the bacteriophage’s genes rather than
bacterial genes. Conjugation in the well-studied E. coli system is controlled by plasmid
genes, and is an adaptation for distributing copies of a plasmid from one bacterial host to
another.
• Infrequently during this process, a plasmid may integrate into the host bacterial
chromosome, and subsequently transfer part of the host bacterial DNA to another
bacterium. Plasmid mediated transfer of host bacterial DNA (conjugation) also appears to
be an accidental process rather than a bacterial adaptation.

8. • Natural bacterial transformation involves the transfer of DNA from one
bacterium to another through the intervening medium. Unlike transduction and
conjugation, transformation is clearly a bacterial adaptation for DNA transfer,
because it depends on numerous bacterial gene products that specifically
interact to perform this complex process.
• For a bacterium to bind, take up and recombine donor DNA into its own
chromosome, it must first enter a special physiological state called competence.
About 40 genes are required inBacillus subtilis for the development of
competence.
• The length of DNA transferred during B. subtilis transformation can be as
much as a third to the whole chromosome. Transformation is a common mode
of DNA transfer, and 67 prokaryotic species are thus far known to be naturally
competent for transformation.

9. • Among archaea, Halobacterium volcanii forms cytoplasmic bridges
between cells that appear to be used for transfer of DNA from one cell
to another. Another archaeon, Sulfolobus solfataricus, transfers DNA
between cells by direct contact.
found that exposure of S. solfataricus to DNA damaging agents induces
cellular aggregation, and suggested that cellular aggregation may
enhance DNA transfer among cells to provide increased repair of
damaged DNA via homologous recombination.
• prokaryotes are considered strictly unicellular, most can form stable
aggregate chotomous prokaryote-eukaryote distinction points out that
the word "prokaryote" is based on what these organisms are not (they
are not eukaryotic), rather than what they are (either archaea or
bacteria)]

10. STRUCTURES IN ALL EUKARYOTIC
CELLS
Eukaryotic Cell Structure and Function
• A cell is defined as eukaryotic if it has
a membrane-bound nucleus. Any organism
composed of eukaryotic cells is also
considered aeukaryotic organism.

12. Here are some examples of eukaryotes:
• Animals
• Plants
• Fungi (mushrooms, etc.)
• Protists (algae, plankton, etc.)
Most plants, animals, and fungi are composed of
many cells and are, for that reason, aptly classified
as multicellular, while most protists consist of a single
cell and are classified as unicellular. Funny how that
works.

13. All eukaryotic cells have
• A nucleus
• Genetic material
• A plasma membrane
• Ribosomes
• Cytoplasm, including the cytoskeleton

14. Most eukaryotic cells also have other membrane-bound
internal structures called organelles.
Organelles include
• Mitochondria
• Golgi bodies
• Lysosomes
• Endoplasmic reticulum
• Vesicles

15. There are a few major differences between animal, plant, fungal, and protist an
cells, Here they are:
All plant cells have
• A cell wall made of cellulose
• A large central vacuole
• Chloroplasts
Some animal and protistan cells have
• Flagella, Cilia
All animal cells have
• Centrioles
All fungal cells have
• A cell wall made of chitin.
• Also, quiteshort.
• StructuresFound in All EukaryoticCells
• The Nucleus and Eukaryotic Genetic Material
• The nucleusin the cell is analogous to the brain in the body. It is a control
center for a cell.
Presenting, the nucleus:

17. • The nucleus stores all the information the cell needs to grow, reproduce, and
function. This information is contained in long but thin molecules of
deoxyribonucleic acid, or DNA. One of the functions of the nucleus is to
protect the cell’s DNA from damage, but that is not all that it does. The nucleus
is basically a large membranous sac. Like your face.
The nucleus also contains a small round body called a nucleolus that holds
nucleic acids and proteins. The nuclear membrane has pores through which
the contents of the nucleus communicate with the rest of the cell. The nuclear
membrane tightly controls what gets into the nucleus and what gets out. This
regulation of communication by the nuclear membrane has a great effect on
what a cell looks like and what it does.

18. • Chromosomes are also located in the nucleus and are basically organized
structures of DNA and proteins. In eukaryotes, the chromosomal DNA is
packaged and organized into a condensed structure called chromatin.
Chromosomes are single pieces of DNA along with genes, proteins, and
nucleotides, and chromatin is a condensed package of chromosomes that
basically allows all the necessary DNA to fit inside the nucleus.
• We will dive deeper into the world of chromosomes in another section, but just
know that eukaryotic and prokaryotic cells each have genomes, which is what
we call the entire set of an organism's genetic and hereditary information.
Genomes are entirely encoded in either the DNA or the RNA. In the case of
eukaryotes, multiple linear pieces of DNA comprise its genome.

19. In eukaryotic organisms, the DNA inside the nucleus is also closely associated
with large protein complexes called histones. Along with the nuclear
membrane, histones help control which messages get sent from the DNA to
the rest of the cell. The information stored in DNA gets transferred to the rest
of the cell by a very elegant process—a process so common and so important
to life on Earth that it is called the central dogma of biology.
In eukaryotic cells, the first stage of this process takes place in the nucleus and
consists of specific portions of the DNA, called genes, being copied, or
transcribed, into small strands of ribonucleic acid, or RNA. RNA containing a
copy, or transcript, of DNA is called messenger RNA, or mRNA. These mRNA
molecules are then physically transported out of the nucleus through the
pores (holes) in the nuclear membrane and into the cytoplasm where they are
eventually translated into proteins by ribosomes.

20. DNA RNA → Protein
Most eukaryotic cells have a nucleus throughout their entire life cycles, but there
are a few notable exceptions. Human red blood cells (the good ol' RBCs), for
example, get rid of their nuclei as they mature. Rebels without a cause. Or
actually, with a cause, because, with their nuclei removed, red blood cells have
more space to carry oxygen throughout the body.
• Eukaryotic Plasma Membrane
• The plasma membrane in eukaryotic cells is responsible for controlling what
gets into and out of the cell. A series of proteins stuck in the membrane help the
cell communicate with the surrounding environment. Among other things, this
communication can include
• Sending and receiving chemical signals from other eukaryotic cells

21. • Interacting with the cells of prokaryotic organisms during the process of
infection.
• Keep in mind that the plasma membrane is universal to all cells, prokaryotic
and eukaryotic. Because this cellular component is so important and so
common, it is addressed in greater detail further on in the In Depth section.
Eukaryotic Ribosomes
• Ribsomes are small cellular machines made of proteins and ribosomal RNA. All
cells, both eukaryotic and prokaryotic, have ribosomes.

23. • Eukaryotic ribosomes are larger and have a slightly different shape and
composition than those found in prokaryotic cells. Eukaryotic ribosomes, for
instance, have about twice the amount of ribosomal RNA (rRNA) and one
third more ribosomal proteins (~83 vs. 53) than prokaryotic ribosomes have.
• Despite these differences, the function of the eukaryotic ribosome is
virtually identical to the prokaryotic version.
• This is a remarkable example of what we call evolutionary unity. Ribosomes
translate mRNA into protein, or the last step in the central dogma of biology
described earlier. It all comes together…

24. Eukaryotic Cytoplasm and Cytoskeleton
• The cytoplasm in eukaryotic cells is a gel-like, yet fluid, substance in
which all of the other cellular components are suspended, including
all of the organelles.
• The underlying structure and function of the cytoplasm, and of the
cell itself, is largely determined by the cytoskeleton, a protein
framework along which particles in the cell, including proteins,
ribosomes, and organelles, move around.