Prokaryotic and Eukaryotic Cells: An overview
All living things are composed of cells. Cells are living, growing, reproducing, responding and
- Cells can be categorized as either prokaryotic or eukaryotic
- Scientist categorize organisms onto groups called taxa ex for prokaryote’s taxa’s would be
Domain Achaea and Domain Bacteria
- Distinctive feature of prokaryotic is that they can make proteins simultaneously to reading the
genetic code because the typical prokaryotic does not have a membrane covering its genetic
material. Meaning they do not have nucleus.
- Eukaryotic have a membrane surrounding their DNA and have more organelles than the
- Cells of algae, protozoa, fungi, animals and plants are all prokaryotes
- External Structures of Bacteria Cells
Many cells have special external features that enable them to respond to other cells or their
environment. In bacteria these features include glycocalyces, flagella, fimbriae and pili
- Some cells have a sticky substance that surrounds the outside of the cell, this is called glycocalyx
which means “sugar cup”.
- These chemicals are produced in the inside and extruded on the outside
- When the glycocalyx of a bacterium is composed of organic chemicals firmly attached to the
cells surface the glycocalyx is called a capsule.
- When there is a loose, water-soluble glycocalyx it is called a slime layer, they are often sticky
allowing it to attach to things ex in your teeth, sticking to your teeth and causing decay
- They protect the bacteria from drying out
- Because these capsules are chemically alike to the ones in our body our defensive cells overlook
them ex streptococcus pneumonaie and Klebsiella pneumonia found in the respiratory tract
Cells mobility may enable it to flee or go towards certain environments; the organelle responsible for
this is the flagella
- Bacteria Flagella are composed of three parts, a long thin filament, a hook and a basal body
about 20nm extending out of the cells environment.
- It is composed of many identical sphere like molecules of a protein called flagellin 62
- No membrane covers the flagella
- The filament inserts into a curved structure, the hook which is made out of different protein, the
basal body which is also made out of diff proteins it anchors the filament and hook to the cell
wall and cytoplasmic membrane by means of a rod and 2 integral proteins for gram(+) and four
- Together the hook, rod, and rings allow the filament to rotate at a 360 degree angle.
- Flagella that covers the surface of the cells is called peritrichous, polar flagella are at the ends ex
(63) Some have tufts of polar flagella- meaning a lot are located in one area.
- Some spiral shaped bacteria called spirochetes have flagella at both ends that spiral tightly
around the cell instead of protruding outside of the cell these flagella are called endoflagella
form an axial filament and wrap itself around the cell between its cytoplasmic membrane and
- It moves as if it was a corkscrew, some scientist believe their shapes allow them to invade
human tissue Treponema palladium agent of syphilis Function
- They rotate at about 360 degrees, The flow of hydrogen ions or of sodium ions through the
cytoplasmic membrane near the basal body powers the rotation, propelling it at 60 cell lengths
a sec equ to a car going 670 miles per hour.
- They move with a series of “runs” and “tumbles”
- Counter clockwise flagellar rotation produces runs - moves forward, If more than one flagellum
is present the flagella and rotate together as a bundle, Tumbles are abrupt, random changes in
direction caused by clockwise flagellar rotation
- Responses to stimuli is called taxis, light phototaxis and chemicals chemotaxis
Fimbriae and Pilli
- Bacteria use fimbriae –sticky, bristle like projections to attach to things in its environment, may
be hundreds per cell they are shorter than flagella.
- Ex. Neisseria gonorrhoea causes gonorrhoea able to colonize in the mucous membrane of the
- They use fimbriae to move across a something or toward another bacterium they use a method
similar to pulling a rope. Its fimbriae attach, then the bacterium retracts pulling itself closer to
- Fimbriae play an important role in biofilms, slimy masses of microbes adhering to something by
means of fimbriae and glycocalyces.
- Some fimbriae act as electrical wires conducting electrical signals within the biofilms.
- 99% of all bacteria in nature are found in biofilms - Biofilms form plaque on teeth, slime on rocks bunch of microbes attached to a surface
- Special type of fimbria is a pilus also called conjugation pilus, they are longer than fimbriae
typically a few pili are on the bacteria and that’s if they have them
- Conjugation pili mediate the transfer of DNA from one cell to the other via a process called
Bacterial Cell Wall
The cells of most prokaryotic are surrounded by a cell wall that provides structure and shape to the cell
and helps in assistance or resistance. On most note that animal cells do not have cell walls so it helps in
the treatment of bacteria cells,
- Cocci can appear singly or in chains ex streptococci or in cuboidal packets
- Rod-shaped cells called Bacilli appear singly or in chains
Bacterial cells are composed of peptidoglycan a complex polysaccharide; it in turn is made up of sugar
molecules called N-acetylglucosamine (NAD) and N-acetylmuramic acid (NAM)- structurally similar to
- Millions of these two sugars are in a chain alternating this is the glycan part of the peptidoglycan
, they are attached to other chains by crossbridges of four amino acids (tetrapeptides), this is
the “peptido” part
- Depending on the bacterium the tetrapeptides could be linked together or by short connecting
chains of other amino acids.
- These peptidoglycan’s surround the whole cell, they must continually insert these chains if it is
to grow and divide
Gram –Positive Bacterial Cell Walls Gram-positive bacterial have thick layer of peptidoglycan that contains a chemical called teichoic acid.
Some are linked to lipids forming lipoteichoic acids that anchor the peptidoglycan to the cytoplasmic
- Teichoic acids have a neg charge giving the surface of the gram positive a ng charge- may play a
role in the passage of ions