Structure and Function of prokaryotes Flashcards
Three main shapes of bacteria
COCCUS- close to a perfect sphere
ROD shape - a very short( almost like a sphere) or very long ( bacillus)
SPIRILLIUM- a rod that has a gentle twist on it, a small length with a little twist or SPIROCHETE ( long with a more extreme twist ) -
What is the form of budding and appendaged bacteria
Very strange bacteria that has two forms on it-> stalk and budding cells at the same time
Stalk cells - swim
Budding cells- divide
Shape mostly depends on
The cell wall
What is the exception fro the rule that all cells have only one genome
Filamentous bacteria, because the cell divide , but the cell wall does not separate, forming one cell with multiple genome
What is the role of the cell wall
To withstand the intracellular osmotic pressure and is responsible for the shape and rigidity of the bacteria
Explain the procedure of the gram staining
We start off with two different types of bacteria
We do not know what they are
1) Flood the cells with crystal-violet, the stain that will turn all the bacteria purple
2) Adding of iodone solution, this will link the the crystal-violet together, forming a large molecule
3) To decolorize with alcohol, by adding ethanol, from one of the cells the crystals will b washed off, but not from others. The one that stay purple are grain positive
4) To the other ones we add a counter stain to make them visible-> gram negative
Why shapes of bacteria are usually gram positive and gram negative
Coccus-> gram positive-> appear purple
Rods->negative-> appear any other color,except purple
The difference in cell wall structure between gram-positive and gram-negative bacteria
Ethanol is very dehydrating, and cause petidoglycan contract and become even more dense and trap the pigment - the crystals
In the negative they do not have a thick layer peptidoglycan and the pigment washes away. the bacteria has a thin layer of petidoglycan above cytoplasmic membrane and then one more layer- outer membrane
Gram positive have a thick petidoglycan layer above the cytoplasmic membrane
What is the other name for peptidoglycan
Murein
2 sugars in peptidoglycan
N-acetylglucosamine(NAG)
N-acetylmuramic acid( NAM)
NAG and NAM in peptidoglycan are connected by
Beta 1,4 linkage
Subunits of petidoglycan
NAG and NAM
Short peptide side chain hanging from NAM
What is particular about peptidoglycan in bacteria
1) It has D- amino acids, which is usually not found in living organisms
2) NAM and DAP ( diaminopimelic acid) has never been found in Archea and Eukarya
What is the sequence of polymeric sugar backbone
NAG-NAM-NAG-NAM
How does lysozyme function
It damages the B bond between the sugars -> damage to petidoglycan layer->protection against bacterial pathogens
Where is lysozyme excreted?
In tears, saliva and other body fluids
How does peptidoglycan provide rigidity
Polymerization of the sugar backbone-> strength in X direction
The cross-linkage between AA-> rigidity in Y direction
What is the difference in connection between AA in peptidoglycan in Gram positive and gram negative bacteria
Gram negative, one AA will directly link with another AA
In gram positive, the connection is made through a connection( interbridge-repeting units of glycine)
How is cross-linking between AA called
Transpeptidation
How much percent of the cell wall is peptidoglycan in the wall of gram positive bacteria
Up to 90%
In gram -positive bacteria Peptidoglycan has
Wall-associated proteins Teichoic acid(TA) Lipoteichoic acid (LTA)
How are wall-associated proteins attached to the peptidoglycan layer?
Covalently attached to the peptidoglycan by an enzyme called sortase
The composition of TA/LTA
Glycerol-phosphate (3C) OR ribitol-phosphate (5C), decorated with AA and sugars
TA/LTA are ____ bonded to the peptidoglycan
covalently
What is the charge of the surface in gram positive bacteria
Negatively charged, because of the presence of negative charges on the phosphate groups
Structure of LTA
from 2 carbons- long, non-polar, hydrophobic FA that are connected to each other with the ester linkage
From the third one a long chain of repeated units of phosphate and carbon
How does LTA connected to cytoplasmic membrane
LPA extends all the way through peptidoglycan and has FA on the bottom, to allow to imbed in the cytoplasmic membrane
Surface proteins of gram negative bacteria should have
Hydrophobic domain to allow the anchoring in the outer membrane
The outer membrane is decorated with ____
Lipopolysaccharides
What percentage of the cell wall is peptidoglycan in gram-negative bacteria
5-10%
What is the cell wall in gram-negative bacteria
Periplasm, peptidoglycan, outer membrane
What is the function of periplasm
The periplasm contains a high concentration of proteins involved in nutrient acquisition, extracellular enzymatic reactions, sensing, etc.
What is the other name for periplasm and why
It is so dense that it is sometimes called a protein gel
What is the other name for outer membrane
LPS layer
The function of LPS layer
Helps to protect the bacteria against a variety of substances, including antibiotics, and against the host defense system
The structure of LPS in gram negative bacteria
Lipid A, that consists of 6 FA ,which is in the membrane, and N-acetylglucosamine +phosphate
KDO(2-keto-deoxyoctonate) that connects Lipid A to the core polysaccharide
Core polysaccharides and O-specific polysaccharides
What is the antigen in LPS layer
O-specific polysaccharide that consists of repeating sequence of 2-4 monosaccharides, the way to recognize different strains in one species
What is the danger of Lipid A
Toxic to many animals. Can result in inflammation and vascular problems(septic shock) that can result in death. Plays the major role in parthenogenesis of Gram-negative bacterial pathogens
What is the difference between Archea’s cell wall and bacterial cell wall
Archea does not have peptidoglycan and no outer-membrane
Cell walls of Archea usually consist of
polysaccharides, and/or/ glycoproteins
What do Archea have instead of peptidoglycan
Pseudopeptidoglycan or pseudomyelin
What does Pseudopeptidoglycan have
It contains of NAG and N-acetylalosaminuronic acid instead of NAM and has only L-AA
Why archea are insensitive to lysozyme
The linkage between two sugars in the backbone is beta 1,3 linkage that the lysozyme cannot break
Some species of Archea have cell walls that are composed of ___
Heteropolysaccharides
The great majority of cell walls in Archea species consists of ____ and\or
proteins and glycoproteins
What is the other name for the cell wall in Archeal species
Paracrystalline surface or S-layers
Is the S layer is specific only to archea?
No, you can find them in some species of bacteria.
Then S-layer will form an additional layer on top of peptidoglycan (Gram-positive) or on the top of the outer membrane ( Gram-negative)
What is the difference between capsule and slime layer?
Capsules are more firmly attached, slime is more diffused
The composition of capsule layer
In bacteria- heteroplysaccharides
In some gram-negative bacteria - homopolysaccharides
How the capsule is attached in bacteria
Covalently bound to the outer membrane or to the peptidoglycan
Why the capsule is important virulence determinant?
The capsule protects against host defense system
What other two surface appendages that batceria and archea can have on the surface?
Flagella and fimbriae
What is the difference between flagella and fimbriae
Flagella are used for locomotion, they are longer (15-20 micrometers)
Fimbriae are primary involved in surface attachement, they are short (less than 4 micrometers)
Fimbria are assembled from the base, flagella-from the top
The outer part of flagella consist of
The protein- flagellin
