Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Prokaryotes
Content:
Structure of prokaryotes……………………………………………………………………………………(2 – 5)
Cell wall ( gram positive and negative)………………………………………………………………
...
(9 – 12)

1

Prokaryote structure
Overview of prokaryotes (bacteria and archaea)
...


•

Prokaryotic cells are much smaller than eukaryotic cells, have no nucleus, and lack
organelles
...
Many also have a capsule or slime
layer made of polysaccharide
...
Flagella and
some pili are used for locomotion, fimbriae help the cell stick to a surface, and sex
pili are used for DNA exchange
...
They may also have
smaller pieces of circular DNA called plasmids
...
(Eukarya, the third,

contains all eukaryotes, including animals, plants, and fungi
...


Fossils show that prokaryotes were already here on Earth 3
...
53, point, 5 billion years
ago, and scientists think that prokaryotic ancestors gave rise to all of the life forms
present on Earth today^{2,3}2,3start superscript, 2, comma, 3, end superscript

2

The capsule
Many prokaryotes have a sticky outermost layer called the capsule, which is usually made
of polysaccharides (sugar polymers)
...
In the case of disease-causing
prokaryotes that have colonized the body of a host organism, the capsule or slime layer
may also protect against the host’s immune system
...

This structure maintains the cell’s shape, protects the cell interior, and prevents the cell
from bursting when it takes up water
...
The basic building block of the plasma
membrane is the phospholipid
...

Appendages
Prokaryotic cells often have appendages (protrusions from the cell surface) that allow the
cell to stick to surfaces, move around, or transfer DNA to other cells
...
are used for adhesion—that is, they help cells stick to
objects and surfaces in their environment
...
For instance, a sex pilus holds two bacterial cells together and allows DNA to be
transferred between them in a process called conjugation
...

The most common appendages used for getting around, however,
are flagella (singular: flagellum)
...


3

Chromosome and plasmids
Most prokaryotes have a single circular chromosome, and thus a single copy of their genetic
material
...
Instead, the
chromosome of a prokaryote is found in a part of the cytoplasm called a nucleoid
...
They also may contain small rings of double-stranded extrachromosomal DNA called plasmids
...
Plasmids carry a
small number of non-essential genes and are copied independently of the chromosome
inside the cell
...

For instance, some plasmids carry genes that make bacteria resistant to antibiotics
...
) When the plasmids carrying R genes are exchanged in a
population, they can quickly make the population resistant to antibiotic drugs
...

Spores
Some bacteria produce spores, which are an inactive (dormant) form
...
When conditions are favorable, each spore germinates into an active
bacterium
...
Having said that though, it is
also important to note that most bacteria (about 90%) have a cell wall and they typically
have one of two types: a gram positive cell wall or a gram negative cell wall
...

Gram Positive Cell walls
The cell walls of gram positive bacteria are composed predominantly of peptidoglycan
...

Gram-positive bacteria are classified by the color they turn after a chemical called Gram
stain is applied to them
...
Other bacteria stain red
...
Gram-positive and gramnegative bacteria stain differently because their cell walls are different
...

5

All bacteria may be classified as one of three basic shapes: spheres (cocci), rods (bacilli), and
spirals or helixes (spirochetes)
...

Some Gram-positive bacteria cause disease
...
These bacteria, called resident flora, do not usually cause disease
...
(This is because the thick
peptidoglycan layer in the bacterial cell wall)
• Cytoplasmic lipid membrane
• Thick peptidoglycan layer
• Teichoic acids and lipoids are present, forming lipoteichoic acids, which serve as
chelating agents, and also for certain types of adherence
...

• A much smaller volume of periplasm than that in gram-negative bacteria
...
Also, only some
species are flagellates, and when they do have flagella, have only two basal body rings to
support them, whereas gram-negative have four
...

The presence of inner and outer cell membranes defines a new compartment in these
cells: the periplasmic space or the periplasmic compartment
...

Gram-negative bacteria are enclosed in a protective capsule
...
Under the capsule,
gram-negative bacteria have an outer membrane that protects them against certain
antibiotics, such as penicillin
...
Endotoxins contribute to the severity of symptoms during infections with
gram-negative bacteria
...
Gram-negative
bacteria are resistant to multiple drugs and are increasingly resistant to most available
antibiotics
...

An inner cell membrane is present (cytoplasmic)
A thin peptidoglycan layer is present (this is much thicker in gram-positive bacteria)
Has outer membrane containing lipopolysaccharides
And phospholipids in the inner leaflet
...
The outer leaflet of this membrane contains
lipopolysaccharide (LPS), whose lipid A portion acts as an endotoxin
...

This leads to inflammation and can cause a toxic reaction, resulting in fever, an
increased respiratory rate, and low blood pressure
...

The outer membrane protects the bacteria from several antibiotics, dyes, and detergents
that would normally damage either the inner membrane or the cell wall (made of
peptidoglycan)
...

Three domains of life on Earth
Bacteria and archea (prokaryotes)
Eukarya (eukaryotes)
The fossil record indicates that the first living organisms were prokaryotes (Bacteria and
Archaea), and eukaryotes arose a billion years later
...
In this way they are different
from eukaryotes, which include both unicellular and multicellular organisms
Archaea and bacterial cells lack organelles or other internal membrane-bound
structures
...

Archaea and Bacteria generally have a single circular chromosome– a piece of
circular, double-stranded DNA located in an area of the cell called the nucleoid
...


9

• Archaea and Bacteria reproduce through fission, a process where an individual cell
reproduces its single chromosome and splits in two
...

• Almost all prokaryotes have a cell wall, a protective structure that allows them to
survive in extreme conditions, which is located outside of their plasma membrane
...


Importance of microorganisms for human health
1
...
They protect us from pathogens, help us digest our food, and produce some of
our vitamins and other nutrients
...

Scientists are also discovering that the absence of certain key microbes from our intestinal
tract may set us up for a variety of problems
...

There are intriguing findings that suggest that the absence of these microbes is an
important contributor to the development of allergies and some autoimmune disorders
...
A particularly fascinating example of our normal flora relates to our digestive
systems
...

Obviously, trying to treat this problem with antibiotics only makes it worse
...


10

Prokaryotes play a critical role in biogeochemical cycling of nitrogen, carbon, phosphorus,
and other nutrients
...

Nitrogen is a very important element to living things, because it is part of nucleotides and
amino acids that are the building blocks of nucleic acids and proteins, respectively
...

However, eukaryotes cannot use atmospheric, gaseous nitrogen to synthesize
macromolecules
...
Abiotic nitrogen fixation occurs as a result
of lightning or by industrial processes
...
(filamentous bacteria interacting with actinorhizal plants
such as alder, bayberry, and sweet fern)
...

11

Prokaryotes are also essential in microbial bioremediation, the use of prokaryotes (or
microbial metabolism) to remove pollutants, such as agricultural chemicals (pesticides,
fertilizers) that leach from soil into groundwater and the subsurface, and certain toxic
metals and oxides, such as selenium and arsenic compounds
...

To clean up these spills, additional inorganic nutrients that help bacteria to grow are added
to the area, and the growth of bacteria breaks down the excess hydrocarbons
...

Which organelle's function is likely to be impaired by this mutation?
A
...

C
...


Chloroplasts
Mitochondria
Ribosomes
Plasma membrane

What is the main function of cytoplasm in a cell?
A
...
Regulating the transport of molecules into and out of the cell
C
...
Packaging and sending out proteins and lipids
Which of the following choices correctly describes the composition of the cell membrane?
•

Contains lipids and cholesterol

•

Contains only proteins

•

Contains only lipids

•

Contains lipids and proteins

Which of the following choices correctly describes the composition of a ribosome?
A
...

C
...


Contains RNA, proteins, and lipids
Contains RNA and lipids
Contains RNA and proteins
Contains only RNA

13



---