Structure and Function of Bacterial cells Flashcards
What are the three regions of a bacteria?
Surface Appendages
Cell envelope
Cytoplasmic region
What makes up the surface appendage region of bacteria?
Either flagella and pili (fimbriae) are attached to cell surfaces
What does the cell envelope consist of?
Capsule (glycocalyx)
Outer membrane (only in gram negative cells)
Cell wall
Cytoplasmic membrane
What is the capsule also called?
Glycocalyx
What part of the cell envelope is only found in gram negative cells?
Outer membrane
What is found in the cytoplasmic region of a bacteria?
3
Chromosome (DNA)
Ribosomes
Inclusions
What are pili also called?
Fimbriae
What is the function of flagella?
Motility
What is the function of pili?
Adherence
What type of bacteria are flagella found on?
2
On both gram + and - bacteria
On many bacilli but not many cocci
What are the three parts of a flagellum?
Filament
Hook
Basal body
What is a filament?
A region of the bacterial flagella which is composed of flagellin (protein)
What protein is found in the filament of a flagellum?
Flagellin
What is the hook of a flagellum?
2
The wider region at the base of the filament
It connects the filament to the motor portion of the flagellum
What is the basal body of a flagellum?
3
The motor of a flagellum
It is anchored in cytoplasmic membrane and the cell wall
Consists of four ring shaped proteins stacked around a central rod
What is it called when a bacteria has a single flagellum?
Monotrichous
What is it called when a bacteria has flagella all over its surface?
Peritrichous
What is it called when a bacteria has a tuft of flagella at one end?
Lophotrichous
What is it called when a bacteria has a tuft of flagellum at either end?
Amphitrichous
How do flagella move?
4
By rotation like a propeller
This causes the bacteria to move in pulses along a line and tumble
A counterclockwise rotation leads to lines
A clockwise rotation leads to a tumbling motion
What are the benefits of being motile to a bacteria?
2
Motility serves to keep bacteria in an optimum environment via taxis
Motility assists in bacterial pathogenesis - move through mucous layer - attach to epithelial cells of the mucous membranes
What is taxis?
Motile response to an environmental stimulus
How does the flagella move when the bacteria is moving towards a gradient with favourable stimulus or away from an unfavourable one?
(2)
The frequency of tumbles is low
Trying to get to the favourable area quickly
How do the flagella move when the bacteria is moving towards an unfavourable stimulus or away from a favourable stimulus?
(2)
The frequency of tumbles increases
Allows the cell to reorient itself and move towards a more suitable environment
What are pili?
3
Thin filamentous protein structures
They extend from the surface of the bacterial cell
They have a shaft composed of pilin (protein)
On what type of bacteria are pili found?
Found on nearly all gram-negative bacteria but not many gram positive bacteria
What protein is found in the shaft of pili?
Pilin
What are the two main types of pili?
Short attachment pili
Long conjugation pili
What are short attachment pili also called?
Fimbriae
Write a note on fimbriae.
4
These are organelles of adhesion
They allow bacteria to colonize environmental surfaces or cells and resist flushing
There is an adhesive tip structure at the end of the shaft
These tips have a shape corresponding to specific glycolipid or glycoprotein receptors on a host cell
What is the function of fimbriae?
2
They allow bacteria to colonize environmental surfaces or cells
They allow bacteria to resist flushing
What is found at the end of the shaft on fimbriae ?
An adhesive tip
What is the role of the adhesive tips on fimbriae?
Their shape corresponds to specific glycolipid or glycoprotein receptors on a host cell
Why are fimbriae needed?
Since both the bacteria cell and the host cell have negative charges
How do fimbriae work?
They enable bacteria to bind to host cells without getting very close (avoid electrostatic repulsion)
What are long conjugation pili also called?
2
F pili
sex pili
What is the function of long conjugation pili?
They are important in conjugation
What is conjungation?
The transfer of genetic material between bacteria through direct cell-to cell contact
What is spread through conjugation?
This genetic transfer facilitates the spread of virulence and antimicrobial resistance genes to other bacterial cells
What is the overall role of the glycocalyx?
Protection and adherence
What is the overall role of the outer membrane in gram negative bacteria?
Structure and permeability
What is the overall role of the cell wall?
Shape and protection
What is the overall role of the cytoplasmic membrane?
Transport
What is the glycocalyx?
A viscous covering of fibres outside of the cell wall
When is the glycocalyx called a capsule?
If it appears as an extensive tightly bound accumulation of gelatinous material adhering to the cell wall
When is the glycocalyx called a slime layer?
If it appears unorganized and more loosely attached
What are the three functions of the glycocalyx?
Protection
Immune evasion
Formation of a biofilm
Explain the protection function of the glycocalyx.
Shields bacteria from drying out, chemicals and environmental stresses
Explain the immune evasion function of the glycocalyx.
Capsulated bacteria are difficult to detect by phagocytic cells
e.g. meningitis
What is biofilm?
A common secreted adhesive matrix
What is special about the bacteria in a biofilm?
Biofilm allows bacteria to communicate with one another through quorum sensing
The bacteria live a community
What are the advantages of biofilm?
4
Bacteria are better able to adhere and resist flushing
Bacteria are better able to resist phagocytosis
Bacteria better at trapping nutrients
Bacteria better able to resist antibiotic attacks
Give four examples of places where biofilm can form.
Catheters/IVs - indwelling lines
Medical implants
Medical devices - endoscope channels
Water supply systems
Give three examples of bacteria that form biofilm.
Pseudomonas
Enterobacterales
Staphylococcus
What are the two main functions of the cell wall?
Allow the cell to withstand internal pressure - prevent lysis
Give shape and rigidity to the cell
What does the cell wall contain?
A tough mesh of polysaccharide and peptidoglycan (tight-knit complex)
What is peptidoglycan also called?
Murein
What does peptidoglycan do?
Gives strength and rigidity to the cell
Describe the structure of peptidoglycan.
3
A polymer consisting of interlocking chains of identical monomers
Each monomer consists of two joined amino sugars (G and M) with a pentapeptide coming off M
Long sugar chains are joined together by cross links between the peptides off each M
Why is peptidoglycan a vulnerability for bacteria?
Peptidoglycan is unique to bacteria
Cell wall antibiotics (penicillin) prevent bacteria from forming peptidoglycan
How do gram negative cells make up for their lower amounts of peptidoglycan?
They have an outer membrane outside the cell wall
Where is the layer of peptidoglycan located in the gram negative bacteria?
Located in the periplasm which is surrounded by the outer membrane
What is the periplasmic space?
2
The space either side of the peptidoglycan layer
It is between the cell membrane and the outer membrane
What does the outer membrane consist of?
2
Consists of a lipid bilayer
Additional polysaccharide
What forms the lipopolysaccharide layer (LPS) in gram negative bacteria?
Lipid A from the outer membrane and a polysaccharide
What are the three main functions of the outer membrane?
Structure
Permeability - it is semi-permeable
Pathogenicity
How does the outer membrane add to pathogenicity?
2
The toxicity of the lipopolysaccharide layer
This LPS acts as an endotoxin and is released when the bacteria lyse
What is the cytoplasmic membrane also known as?
2
The cell membrane
The plasma membrane
What is the cytoplasmic membrane?
A thin inner layer that surrounds the bacterial cell constituents
What is the main function of the cell membrane?
It is the barrier separating the cytoplasm from the environment
What happens if the cell membrane is broken?
2
The integrity of the cell is destroyed
The cytoplasm will leak out and the cell will die
Explain the permeability function of the cell membrane.
4
The cytoplasmic membrane is a highly selective permeability barrier
This allows the cell to take in specific metabolites and excrete waste material
It is a phospholipid bilayer (40%) with proteins (60%) suspended at the surface and spanning layers
Materials move across by passive diffusion or active transport using carrier proteins
Explain the structure of a phospholipid bilayer.
2
The fatty acids point inward to form a hydrophobic environment
The hydrophilic components remain exposed to the aqueous environment
Explain the role of the proteins that make up part of the cytoplasmic membrane.
Some of these function as selective transport proteins across the membrane
Others function as enzymes during chemical reactions
What is the cytoplasmic membrane referred to as due to its ever changing nature?
A fluid mosaic
What is the cytoplasm in terms of bacteria?
Everything enclosed by the cytoplasmic membrane
What is the cytoplasm composed of?
80% water
What is the cytosol?
The liquid component of the cytoplasm
What is the liquid component of the cytoplasm?
The cytosol
What does the cytoplasm contain?
6
Nucleic acids (DNA and RNA)
Enzymes
Amino acids
Carbohydrates
Lipids
Inorganic ions
What two types of metabolic reactions take place in the cytoplasm?
Catabolic reactions
Anabolic reactions
What do catabolic reactions do in bacterial cells?
They break down molecules in order to obtain building block molecules for more complex cellular molecules
What do anabolic reactions do in bacterial cells?
They synthesize cellular molecules
What governs all living process of all cells?
Genes
What is a gene?
A segment of DNA that encodes a protein
In what form is the genome present in bacteria?
The genome is encoded on one long single double-stranded molecule called a chromosome
What is a chromosome also known as?
A bacterial nucleoid
What does the bacterial chromosome do?
Its the genetic control centre of the cell which determines all the properties and functions of the bacterium
Why are most prokaryotes haploid?
As they usually only have one single chromosome
What are plasmids?
They are tiny loops of DNA suspended in the cytoplasm
What are ribosomes?
2
Small dense structures that assemble proteins
They act by translating genetic information into proteins
What are inclusions also called?
Granules
What type of bacteria produce endospores?
Gram positive bacteria
What is an endospore?
A resistant, dormant survival form of the organism
List the four main parts of an endospore.
Exosporium
Spore coat
Cortex
Core
What is the exosporium?
The outermost layer of an endospore
Where is the spore coat found?
Between the exosporium and the cortex
Where is the cortex found?
Between the spore coat and the core
What does the core of an endospore contain?
3
A chromosome
Ribosomes
Cellular essentials
What are endospores resistant to?
High temperatures
Most disinfectant
Antibiotics
Physical agents e.g. radiation, boiling and drying
