Structure and Function of prokaryotes Flashcards by Valeriya Boyarkina

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 ) -

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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

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Shape mostly depends on

The cell wall

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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

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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

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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

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Why shapes of bacteria are usually gram positive and gram negative

Coccus-> gram positive-> appear purple

Rods->negative-> appear any other color,except purple

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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

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What is the other name for peptidoglycan

Murein

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2 sugars in peptidoglycan

N-acetylglucosamine(NAG)

N-acetylmuramic acid( NAM)

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NAG and NAM in peptidoglycan are connected by

Beta 1,4 linkage

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Subunits of petidoglycan

NAG and NAM

Short peptide side chain hanging from NAM

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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

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What is the sequence of polymeric sugar backbone

NAG-NAM-NAG-NAM

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How does lysozyme function

It damages the B bond between the sugars -> damage to petidoglycan layer->protection against bacterial pathogens

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Where is lysozyme excreted?

In tears, saliva and other body fluids

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How does peptidoglycan provide rigidity

Polymerization of the sugar backbone-> strength in X direction
The cross-linkage between AA-> rigidity in Y direction

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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)

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How is cross-linking between AA called

Transpeptidation

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How much percent of the cell wall is peptidoglycan in the wall of gram positive bacteria

Up to 90%

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In gram -positive bacteria Peptidoglycan has

Wall-associated proteins
Teichoic acid(TA)
Lipoteichoic acid (LTA)

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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