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Structure and function of bacterial cells

47 important questions on Structure and function of bacterial cells

What is the primary subunit of a protein and where are they found in bacterial cell?

Amino acids
found in:

flagella
pilli
cell walls
cytoplasmic membranes
ribosomes
cytoplasm

What is the primary subunit of polysaccharides and where are they found in the bacterial cell?

Sugars (carbohydrates)
found in:

capsules
inclusions (storage)
cell walls

What is the primary subunit of nucleic acids (DNA/RNA) and where can they be found?

Nucleotides
found in:

DNA -> nucleoid (chromosome), plasmids
rRNA -> ribosomes (in mRNA) and cytoplasm in tRNA

How is the flagellar filament rotated?

By a motor apparatus in the plasma membrane allowing the cell to swim in fluid environements

Of which three distinct proteins consist the flagellar apparatus?

- System of rings embedded in the cell envelope
- Hook-like structure near the cell surface
- Flagellar fillament

What is the difference between flagella of prokaryotic cells and those of eukaryotic cells?

Prokaryotic cells are thinner and lack the '9+2' arrangement of microtubules

How does the system of rings work?

The innermost rings (M+S) are located in the plasma membrane, comprise the motor appartus
The outermost rings (P+L) are located in the periplasm, and function as bushings to support the rod where it is joined to the hook of the filament on the surface
As the M ring turns, powered y an influx of protons, the rotary motion is transferred to the filament which turns to propel the bacterium

Of what 3 components does the flagella consist?

Basal body (system of rings in cell envelope) - 4 ring shaped proteins in cell envelope. Inner rings are associated with the plasma membrane and are the powerhouse for activation. Outer rings are support rings
hook-like structure near the cell surface
flagellar filament

How can flagella be distributed?

Variously; But they are basically:

polar (one or more flagella arising from one or both poles of the cell)
Peritrichous (distributed over the entire cell surface)

Flagellar distribution is a genetically distinct trait

What organisms have flagella?

All spiral and curved bacteria have flagella
hardly any cocci have flagella (adaptation to dry environment)

How was it proved that flagella were organelles of bacterial motility?

By shearing them off and observing that the cells could no longer swim although they remained viable

What is the difference between polar and peritrichous flagellae?

Polar: one or more flagella arising from one or both poles of the cell
peritrichous: lateral flagellae distributed over the entire cell surface

Where do the flagellar filaments grow?

At its tip (by the deposition of new protein subunits) and not at its base

Name the 4 ways of moving in response to environmental stimuli:

Chemotaxis = bacterium can smell and sense the presence of chemicals and moves towards them or away
phototaxis (light)
aerotaxis (oxygen)
magento taxis

What are the techniques to demonstrate bacterial motility?

- Flagellar strains outline flagella and show their pattern of distribution
- Motility test medium: If cloudiness due to bacterial growth can be observed away from the line of inoculation, it is evidence that bacterial were able to swim through the medium
- Direct microscopic observation of living bacteria in a wet amount

True motility is confirmed by observing the bacterium swim from one side of the microscope field to the other side

What are fimbirae and pili?

Interchangeable terms used to designate shot, hair-like protein structures on the surface of prokaryotic cells (mostly gram-negative)

What do fimbriae and pili mean?

They mean the same -> short, hair-like structures on surface of prokaryotic cells.
composed of protein
have nothing to do with the movement of bacteria
are often involved in adherence to surfaces

In what do fimbriae differ from flagella?

They are shorter and stiffer and slightly smaller in diameter

What is the cell envelope?

A descriptive term for the several layers of material that envelope or enclose the protoplasm of the cell (plasma membrane, cell wall, capsule)

What is a capsule?

Discrete detectable layer of polysaccharides deposited outside the cell wall

What is a slime layer or biofilm?

A less discrete structure or matrix which embeds the cells

Properties of gram positive cell envelope:

Wall is a thick layer external to the plasma membrane, composed of peptidoglycan (murein)

What is a glycocalyx?

A type of capsule fount in bacteria with a thin layer of tangled polysaccharide fibers which occurs on the surface of cells growing in nature

Properties of gram negative cell envelope:

Thin and multi layered, consits of thin peptidoglycan layer between plasmamembrane and phospholipid-liposaccharide (LPS) outer membrane
LPS attaches peptidoglycan sheet to outer membrane

What are capsules containing possibly too?

Amino sugars or peptide

What do capsules perform?

- Mediate adherence of cells to surfaces
- Protect bacterial cells from engulfment by predatory protozoa or phagocytes or from attack by antimicrobial agents of plants or animal origin

What is a biofilm?

This is constructed when bacteria may attach to the surface, produce slime, divide and produce microcolonies within the slime layers

It becomes an enriched and protected environment for themselves and other bacteria

Examples of gram positive and gram negative bacteria are:

Positive:

bacillus
streptococcus

Negative:

acetobacter
E. Coli
pseudomonas

What is the cell wall?

An essential structure that protects the cell protoplast from mechanical damage and from osmotic rupture or lysis

Name 7 characteristics of cell walls:

Essential structure for viability
contains Murein at outside of cell wall (porous material)
protects against mechanical damage and osmotic rupture or lysis
one of the most important sites for attack by antibiotics
provide ligands for adherence and receptor sites for drugs or viruses
cause symptoms of disease in animals
provide for immunological distinction and variation

What are gram-negative bacteria?

The cell wall is relatively thin and composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane interspersed with lipopolysaccharide (Toxic to animals)

Of what does the backbone of murein (peptidoglycan) consist?

The backbone of peptidoglycan (or murein) consists of repeating subunits of 2 sugars (N-acetylglucosamine and N-acetylmuramic acid)

Properties and function of lysoszyme:

It can cleave the glycan backbone from peptidoglycan molecules
lyses bacterial cells as defense against pathogens
gram-pos are more sensitive to lysozyme than gram-neg bacteria -> because gram negative bacteria have peptidoglycan in outer membrane

Properties of staphylococcus aureus:

Gram positive bacteria
gram positive bacteria are more sensitive to penicillin, because peptigoglycan is not protected by an outer membrane and peptidoglycan is more abundand in gram positive bacteria

What are teichoic acids?

Linear polymers of polyglycerol or polyribitol with substitutions of of phosphates and amino acids and sugars
they are anchored to the plasma membrane (LTA)

What is the role of teichoic acids in streptococci?

Teichoic acids play a role in the adherence of bacteria to tissue surfaces

What does LPS or endotoxin activate in animals?

Lipid A is toxic to animals
LPS/endotoxin activates:

macrophages to produce pyrogens (bacterial endotoxins)
complement cascade -> inflammation
blood factors, resulting in intravascular coagulation (stolling) and haemorrhage (bloeding)

Name two proteins in the outer membrane of E. Coli

Braun lipoprotein: attached to peptidoglycan sheet at one end and inserted into hydrophobic inside of the membrane
porins: form pores through lipid bilayer

ompC and ompF allow passage o hydrophilic molecules
ompA: takes up specific ions and in a receptor for F pilus and is an attachement site for bacterial viruses
omp = outer membrane protein

What are S-layers and what are their functions?

S-layer proteins are the outermost component of the cell envelope. It allows binding of molecules and particles.
Functions:

Protection of bacteria
contribution to virulence by protection of bacteria
functions as adhesin -> many of the cell associated proteins adhesins are components of the S-layer

What are cell wall-less forms and name examples:

Some bacteria can live without cell wall -> mycoplasmas
they have sterol-like molecules in their membranes
example: mycolplasma pneumoniae -> penicillin does not have an effect, because there is no cell wall synthesis

spheroplasts/protoplasts -> pathogenic bacteria can revert to cell wall-less forms under pressure of antibiotic therapy

Consistence of bacterial membranes:

40% phospholipid. (Polar hydrophilic glycerol head attached to two nonpolar hydrophobic fatty avid tails -> form bilayer in aqueous environment)
60% protein. (Within the bilayer there are structural and enzymatic proteins, responsible for most membrane functions)

What are the 9 functions of the plasma membrane in prokaryotes?

Osmotic or permeability barrier
location of transport systems for specific solutes (nutrients and ions)
energy generation, involving respiratory and photosynthetic electron transport systems
membrane lipid synthesis
murein synthesis (peptidoglycan)
assembly (samenkomen) and secretion of extracytoplasmic protein
coordination of DNA replication and segregation (scheiding) with septum formation (new cell wall between dividing cells) and cell division
chemotaxis (movement as a result of concentrations of substances)
location of specialized enzyme system

What are the two types of active transport of bacteria?

Ion driven transport (IDT) -> used for accumulation of ions and amino acids
binding-protein dependent transport system (BPDT) -> used for sugars and amino acids

What systems are present in the periplasm?

Enzymes for assembly of cell wall and membrane components
degradative and detoxifying enzymes
secretion systems
sensing proteins for chemotaxis and signal transduction

What are the 3 main groups of molecules in the cytoplasm?

Macromolecules (proteins, mRNA, tRNA)
small molecules (energy sources, metabolites, vitamins)
inorganic ions and cofactors

What are the properties of nucleoids in prokaryotes?

One large circular molecule of DNA, free in the cytoplasm (no nucleus), but anchored by proteins
sometimes prokaryotes possess plasmids (small extrachromosomal pieces of DNA)
The cell chromosome determines all properties and functions of the bacterium
an exact copy of the nucleoid (DNA) is made during growth for reproduction
prokaryotes do not have mitosis and meiosis, coordination of reproduction is in the membrane

What are the properties of ribosomes in prokaryotic cells?

Ribosomes are composed of proteins and RNA
prokaryotic ribosomes are smaller than eukaryotic ribosomes
involved in translation process (protein synthesis)
eukaryotic ribosomes contain ssrRNA, closely related to bacterial ribosomal RNA

The question on the page originate from the summary of the following study material:

Microbial disease mechanisms

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