BIOL 226 Lecture Notes - Lecture 7: Pilipili, Crystal Violet, Gram-Negative Bacteria
3 May 2018
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Department
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Biol 226- CH27
Prokaryotes
prokaryotes inhibit earth 3.5 billion years ago
biomass of Prokaryotes 10x or more than all the Eukaryotes combined
Prokaryotic Shape
Prokaryotic cells have a variety of shapes
-Spheres (cocci)
-Rods (bacilli)
-Spirals
Most prokaryotic cells are 0.5-5 um
- Smaller than eukaryotic cells (10-100 um)
Cell wall
Maintain cell shape
Protect cell
in hypertonic cells lose water and shrink away from their wall inhibit cell reproduction salt
can be used to prevent bacteria from rapidly multiplying
contain peptidoglycan (composed of modified sugar cross-linked by polypeptide)
archaeal cell also contains polysaccharides and protein but lack peptidoglycan
Grain stain
Samples are first stained with crystal violet dye and iodinethen rinsed in alcohol stained
with a red dye such as safranin
i) Gram positive
Simpler walls
large amount of peptidoglycan
thick
ii) Gram negative
have less peptidoglycan and are structurally more complex, with an outer membrane
that contains lipopolysaccharides (carbohydrates bonded to lipids).
More pathogenic
Why is it more pathogenic?
(a) Lipid portion of the lipopolysaccharides in the walls of many gram-negative bacteria
are toxic causing fever and shock
(b) the outer membrane of a gram- negative bacterium helps protect it from the body’s
defenses.
(c) Gram-negative bacteria also tend to be more resistant than gram-positive species to
antibiotics because the outer membrane impedes entry of the drugs.
Capsule:
Dense and well-defined Sticky layer of polysaccharide or protein over cell wall
It is a slime layer if it is less well organized
Enable prokaryote to adhere to their substrate or other individual colony
In Some protect against dehydration
Fimbriae
Hair like appendages that will help bacteria stick to one another or the substrate
Shorter and more than pili
Pili
Appendages that pull 2 cells together prior to DNA transfer (sex pili)
Endospore
Ability of some prokaryotes to withstand harsh environment contribution to their success
Taxis
Direct movement towards or away from a stimulus
The flagella of prokaryotes are also very different in their molecular composition and their
mechanism of propulsion
However, some prokaryotic cells do have specialized membranes that perform metabolic
functions --> infolding of the plasma membrane
genome consists of a circular chromosome with many fewer proteins than found in the linear
chromosomes of eukaryotes
prokaryotes lack in a membrane-bounded nucleus
Nucleoid
a region of cytoplasm that appears lighter than the surrounding cytoplasm in electron
micrographs.
Prokaryotic DNA
Structurally different genome
Less DNA
One single circular
Plasmids
In addition to its single chromosome, a typical prokaryotic cell may also have much smaller
rings of independently replicating DNA molecules
Small rings of independently replicating chromosomes
How antibiotic works?
prokaryotic ribosomes are slightly smaller than eukaryotic ribosomes and differ in their protein
and RNA content.
Binary fusion
A single prokaryote divides into 2 cells and so on
Under optimal condition the can divide every 1-3hr
Some reproduce every 20min at 20ﾟ
reproduction in prokaryotes draws attention to three key features of their biology:
i) They are small
ii) they reproduce by binary fission
iii) they have short generation times
In sexually reproducing species, the generation of a novel allele by a new mutation is rare for any
particular gene.
most of the genetic variation in sexual populations results from the way existing alleles are
arranged in new combinations during meiosis and fertilization
in prokaryotes this variation can result from prokaryotes’ rapid reproduction and mutation.
Diversity In prokaryotes;
i) Mutation: main source of variation in prokaryotes
ii) Genetic recombination
Genetic recombination
Document Summary
Prokaryotes inhibit earth 3. 5 billion years ago. Biomass of prokaryotes 10x or more than all the eukaryotes combined. Prokaryotic cells have a variety of shapes. In hypertonic cells lose water and shrink away from their wall inhibit cell reproduction salt can be used to prevent bacteria from rapidly multiplying. Contain peptidoglycan (composed of modified sugar cross-linked by polypeptide) Archaeal cell also contains polysaccharides and protein but lack peptidoglycan. Samples are first stained with crystal violet dye and iodine then rinsed in alcohol stained with a red dye such as safranin: gram positive. Have less peptidoglycan and are structurally more complex, with an outer membrane that contains lipopolysaccharides (carbohydrates bonded to lipids). Dense and well-defined sticky layer of polysaccharide or protein over cell wall. It is a slime layer if it is less well organized. Enable prokaryote to adhere to their substrate or other individual colony. Hair like appendages that will help bacteria stick to one another or the substrate.
