details about structure and function of prokaryotic cells

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DEFINITION OF PROKARYOTES
 Small cells (1-5 μm)
 Hereditary material (DNA) is not enclosed within nuclear membrane
 No histones (specific basic proteins) bound to their DNA
 No membrane bound organelles (e.g. mitochondria, chloroplasts)
 It doesn’t contain distinct nucleus, chromosomes, centrioles & microtubules
 Prokaryotes may have evolved from membrane-bound organic molecules
called protobionts.
 Prokaryotes are divided into 2 domains: - Bacteria and Archea.
 Both groups consist of small, single-celled organisms, but there are differences
between them. Bacteria have peptidoglycans in their cell walls and archea do not. In
addition, bacteria have fatty acids in their plasma membrane lipids while archea
have phytanyl groups.
 Example of bacteria; E. coli and Staphylococcus aureus
 Example of archea; Salt-dwelling halophiles.

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Bacteria
 They are diverse life forms and reproduce by binary fission.
 There are three basic bacterial cell shapes: cocci, bacilli and spirilla. The cocci are
oval or spherical bacteria, the bacilli are rod-shaped and the spirilla are spirals.
 Bacteria play an important role in human disease and health. Some of these microbes,
like Staphylococcus aureus, can cause infections in people. However, other bacteria
are beneficial, such as Lactobacillus acidophilus, which helps your body break down
lactose found in dairy products.
Archaea
 Initially classified as ancient bacteria and called "archaeobacteria", archaea now have
their own domain. Many species of archaea are extremophiles and live in extreme
conditions, such as boiling hot springs or acidic water, which bacteria cannot tolerate.
 Some examples include hyperthermophiles that exist in temperatures above 176
degrees Fahrenheit (80 degrees Celsius) and halophiles that can live in salt solutions
that range from 10 to 30 percent. The cell walls in archaea offer protection and allow
them to live in extreme environments.
 Archaea have many different shapes and sizes that range from rods to spirals. Some
aspects of archaea's behavior, like reproduction, are similar to bacteria. However, other
behaviors, such as gene expression, resemble the eukaryotes.
 Methanogens are used to produce biogas and as part of sewage treatment and enzymes
from extremophiles archaea that can resist high temperatures and organic solvents are
exploited in biotechnology.
REPRODUCTION OF PROKARYOTES
 The basic types of reproduction include budding, binary fission and fragmentation.
 Some bacteria have spore formation; it is not considered reproduction because there
are no offspring formed through this process.

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 Budding – it happens when a cell makes a bud that looks like a bubble. The bud
continues to grow while it is attached to the parent cell. Eventually, the bud breaks off
from the parent cell.
 Binary fission - happens when a cell splits into two identical daughter cells.
 Fragmentation - happens when a cell breaks into small pieces or fragments, and each
piece becomes a new cell.
STRUCTURE OF PROKARYOTIC CELL
 A prokaryotic cell contains external and internal structures. Capsule, flagella, axial filaments,
Fimbriae, and Pili are present external to the cell wall, while interior of the bacterial cell
contains cytoplasm.
 The cell structure of prokaryotes can vary, but most organisms have several basic
components. Prokaryotes have a cell membrane or plasma membrane that acts like a
protective cover. They also have a rigid cell wall for added support and protection.
 Prokaryotic cells have Ribosomes, which are molecules that make proteins. Their
genetic material is in the Nucleoid, which is the region where DNA lives. Additional
rings of DNA called plasmids float around the cytoplasm. It is important to note that
prokaryotes do not have a nuclear membrane.
 In addition to these internal structures, some prokaryotic cells have
a pilus or flagellum to help them move. A pilus is a hair like external feature, while a
flagellum is a whip like external feature. Some prokaryotes like bacteria have a capsule
outside their cell walls. Nutrient storage can also vary, but many prokaryotes use
storage granules in their cytoplasm.
1) PROKARYOTIC CELL WALL
 The cell wall in prokaryotes has several purposes. It protects the cell and offers support.
In addition, it helps the cell maintain its shape and stops it from bursting. Located
outside the plasma membrane, the overall structure of the cell wall is more complicated
than the one found in plants.

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 In bacteria, the cell wall consists of peptidoglycans or murein, which is made up of
polysaccharide chains. However, the cell walls differ among gram-positive and gram-
negative bacteria.
 Gram-positive bacteria have a thick cell wall, while gram-negative bacteria have a thin
one. Since their walls are thin, gram-negative bacteria have an extra layer of
lipopolysaccharides.
 Antibiotics and other drugs can target the cell walls in bacteria without harming
humans because people do not have these types of walls in their cells. However, some
bacteria develop antibiotic resistance, and the drugs stop being effective.
 Antibiotic resistance happens when bacteria evolve, and the ones with mutations that
allow them to survive the medications are able to multiply.
2) GENETIC INFORMATION IN PROKARYOTES
 Genetic information in prokaryotes exists inside the Nucleoid. Unlike eukaryotes,
prokaryotes do not have a membrane-bound nucleus. Instead, the circular DNA
molecules live in a region of the cytoplasm. For instance, the circular bacterial
chromosome is one large loop instead of individual chromosomes.
 DNA synthesis in bacteria starts with the initiation of replication at a specific
nucleotide sequence. Then, elongation occurs to add new nucleotides. Next, termination
happens after the new chromosome forms.
3) THE PLASMA MEMBRANE
 The plasma membrane is a thin lipid bilayer (6 to 8 nanometers) that completely
surrounds the cell and separates the inside from the outside.
 Its selectively-permeable nature keeps ions, proteins, and other molecules within the cell,
preventing them from diffusing into the extracellular environment, while other molecules
may move through the membrane.
 The general structure of a cell membrane is a phospholipid bilayer composed of two
layers of lipid molecules. In archaeal cell membranes, isoprene (phytanyl) chains linked
to glycerol replace the fatty acids linked to glycerol in bacterial membranes. Some
archaeal membranes are lipid monolayer’s instead of bilayer.

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4) FLAGELLA
Flagella are whip like structures made of protein and provide motility to the cell. Prokaryotic
cells may be
 Monotrichous – Cells that have one flagellum.
 Lophotrichus – Cells that have a clump of flagella known a tuft, at one end of the cell.
 Amphitrichous – Cells that have flagella at two ends of the cell.
 Peritrichous – Cells that have flagella covering the entire cell on the surface.
5) FIMBRIAE AND PILI
 Fimbriae are proteinaceous, sticky, projected structure used by cells to attach to each other
and to objects around them, while Pili are tubules that are used to transfer DNA from one cell
to another cell. Capsule Depending on the type of bacterium, there may be an exterior
surrounding layer.
6) CYTOPLASMIC MEMBRANE
 The Cytoplasmic membrane is a membrane that provides a selective barrier between the
environment and the cell’s internal structures.
 Cytoplasm is thick. Aqueous, semitransparent, and elasticsmifluid present inside the
prokaryotic cell.
 It is about 80% water and contains primarily proteins (enzymes), carbohydrates, lipids,
inorganic ions, and many low- molecular-weight compounds. Inorganic ions are present in
much higher concentrations in cytoplasm than in most media.
7) NUCLEOID
 The cytoplasm also contains a region called the Nucleoid, which is where the DNA of the
cell is located. The prokaryotic cell consists of a chromosome that isn’t contained within a
nuclear membrane or envelope.
 The Nucleoid or bacterial chromosome comprises a closed circle of double stranded DNA,
many times the length of the cell and is highly folded and compacted.

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8) RIBOSOMES
 Ribosomes are the principle structure in a prokaryotic cell after the Nucleoid. They are
composed of a complex of protein and RNA, and are the site of protein synthesis in the cell.
The prokaryotic Ribosomes are 70S, comprised of sub units 50S and 30S (S stands for the
sydberg coefficient which is a function of their size and shape, and determined by their rate
of sedimentation in a centrifuge) such as a capsule or slime layer, made of glyocalyx
REFERENCES
 https://www.wikilectures.eu/w/Structure_and_Function_of_Prokaryotes
 https://sciencing.com/prokaryotic-cells-definition-structure-function-with-examples-
13717657.html
 https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Ge
neral_Biology_(Boundless)/22%3A_Prokaryotes%3A_Bacteria_and_Archaea/22.2%3A_
Structure_of_Prokaryotes/22.2A%3A_Basic_Structures_of_Prokaryotic_Cells
 https://lab-training.com/2015/02/04/structure-function-prokaryotic-cells/