Microbial Structure Flashcards
What do eukaryotic and prokaryotic cells have in common?
Plasma membrane
Cytoplasm
DNA
Ribosomes
What characteristics are specific in eukaryotes?
True nucleus
Linear DNA
DNA organised into chromosomes
Large complex ribosomes with many types of rRNA and proteins
Cytoplasm filled with large complex collection of organelles
Mitochondria
Transcription requires formation of mRNA and movement of mRNA from nucleus to cytoplasm for translation
What characteristics are specific in prokaryotes?
No nucleus
Circular DNA
DNA naked
70S ribosome
No membrane bound organelles independent of plasma membrane
Mesosomes are used in respiration
Transcription and translation occur simultaneously
What are the structural features of bacteria?
Capsule
Pili
Flagellae
Spores
Slime
Cell wall
What is the bacterial capsule made from?
Loose polysaccharide
What is the function of the bacterial capsule?
Protects from phagocytosis
Protects cell from desiccation
What is pili made from?
Oligomeric pilin proteins
What is the function of pili?
Appendage used for bacterial conjugation
Forms tube/bridge to enable transfer of plasmids between bacteria
Characteristic of pili
Highly antigenic
What is flagellae?
Organs of locomotion
What is flagellae made out of?
Composed of flagellin protein
What are spores?
Hard, multi-layered coats making spore difficult to kill
What happens when a bacteria becomes a spore?
Metabolically inert form triggered by adverse environmental conditions
Adapted for long-term survival allowing for regrowth when conditions are desirable
Example of common diseases caused by spores?
Botulism- Clostridium botulinum
Gas gangrene-Clostridium perfringes
Tetanus- Clostridium tetani
Food poisoning- Clostridium perfringes
Anthrax- Bacillus anthracis
What is slime?
Polysaccharide material
What is the function of slime?
Protects against immune attack
Protects against eradication by antibiotics
How do you differentiate bacteria into two groups based on their cell wall?
Gram positive
Gram negative
What is the structure of a gram positive cell wall?
Thich peptidoglycan wall
Followed by a phospholipid cytoplasmic membrane
What is the structure of a gram negative cell wall?
An outer phospholipid membrane
Thin layer of peptidoglycan attached via lipoprotein
An inner phospholipid membrane
What are the four steps in gram staining?
Primary stain
Trapping agent
Decolourisation
Counterstain
What dye is used in the primary staining?
Crystal violet dye
What is used as the trapping agent?
Gram’s iodine
What is the outcome of the decolourisation step in gram staining?
Gram negative bacteria lose their lipopolysaccharide layer. This exposed the inner peptidoglycan layer, the coloured complexes are then washed away
Gram positive bacteria become dehydrated and traps the complexes in thicker peptidoglycan layer
What is used for decolourisation?
Alcohol/acetone
What is the outcome of counterstaining?
Gram negative become pink/reddish
Gram positive become purple
Summarise the structure of gram positive bacteria
2 layered wall
A thick peptidoglycan layer and a cytoplasmic membrane
Has lipoteichoic acid
Summarise the structure of gram negative bacteria
3 layers
An outer membrane
Think peptidoglycan layer inside the periplasmic space
Cytoplasmic membrane
Has Lipopolysaccharide
Describe peptidoglycan (PGN)
Polymer of sugars and amino acids
Forms a mesh-like layer outside plasma membrane
Describe lipoteichoic acid (LTA)
Complex of teichoic acid+lipids
Provides cell rigidity
Recognised by host immune cells
Describe lipopolysaccharide
Essential for function of outer membrane
Elicits potent immune and inflammatory host response
Produced endotoxins
What do outer membrane proteins do in the cell wall?
Not endotoxins but do contribute to virulence
Describe bacteria replication of genome
2 replication forks replicate DNA in a circular motion on either side of the ring
What is bacterial cell division called?
Binary fission
What is the four phases of bacterial growth?
Lag
Log/exponential
Stationary
Death
What happens in the lag phase?
Bacteria prepare for reproduction by synthesising DNA and enzymes
What does the lag phase represent?
The period of active growth ie size. not number
What happens in the log/exponential phase?
Cells divide at maximum rate
Uniform replication
What happens in the stationary phase?
The cessation of growth
Exhaustion of nutrients
What happens in the death phase?
The number of dying cells start to exceed the number of newly born cells
What is bacterial recombination?
How bacteria share DNA
What are three examples of bacterial conjugation?
Conjugation
Transformation
Transduction
What is conjugation?
Genes are transferred through the pili tube
What is transformation?
Taking up DNA from surrounding environment
What is transduction?
Exchanging of bacterial DNA through bacteriophages
What are the different areas of bacterial classification?
Gram staining
Cell shape
Atmospheric preference
Key enzymes
Fastidiousness
What essentially is a virus?
A nucleic acid enclosed in a protein shell
What are the difference viral structural components?
Nucleic acid
Capsid
Envelope
Spikes
What are the different forms of nucleic acid that can be found in a virus?
Double or single stranded
Deoxyribonucleic or ribonucleic acid
What is the capsid?
A protein coat/shell
What forms capsid?
Composed of protein subunits called capsomeres
What are capsomeres made from?
Aggregated protomeres
What are the different shapes of capsid?
Rod-like
Polyhedral
Complex
Describe the viral envelope
Amorphous structure surrounding some virus
Composed of lipid, protein and carbohydrate
Example of a virus with an envelope?
Herpes
Describe viral spikes
Glycoprotein projections arising from the envelope
What is the function of viral spikes?
May have enzymatic, adsorption or haemagglutinin activity
What is hemagglutination?
Clumping of RBC
How does a virus replicate?
Uses host’s cellular machinery
What are the 6 steps of viral replication?
Adsorption
Penetration
Replication
Assembly
Maturation
Release
What happens in the adsorption step of viral replication?
Virus binds to the host cell
What happens in the penetration step of viral replication?
Virus injects its genome into host cell via fusion, binding or ingestion
What happens in the replication step of viral replication?
Capsid digested by proteolytic enzymes
Viral genome replicated using the host’s cellular machinery
What happens in the assembly step of viral replication?
Viral components and enzymes are produced and begin to assemble
What happens in the maturation step of viral replication?
Virus fully develops
What happens in the release step of naked viruses in viral replication?
Viral enzymes break down bacterial cell wall
RNA viruses released
DNA viruses releases via autolyse or in inclusion bodies
What happens in the release step of enveloped viruses in viral replication?
Viruses migrate to either the plasma membrane or nuclear membrane
Enveloped formed around nucleocapsids by “budding” of cell membrane
No inclusion bodies
What are protozoa?
Single celled eukaryotes
How do we classify protozoa?
Sporozoa
Flagellates
Amoeba
CIliates
What are sporozoa?
Intracellular parasites
What are flagellates?
Possess tail-like structures for motility
What are amoeba?
Use temporary cell-body projections called pseudopods
What are ciliates?
They move by beating multiple hair-like structures
What protozoa leads to malaria?
Plasmodium falciparum
What protozoa leads to giardiasis?
Giardia lamblia
What protozoa leads to toxoplasmosis?
Toxoplasma gondii
What protozoa leads to cryptosporidiosis?
Cryptosporidium parvum
What are fungi?
Multinucleated eukaryotic organisms
What is the wall of fungi made from?
Thick carbohydrate containing chitin and glucans
How do fungi reproduce?
Reproduce asexually by budding and occasionally by binary fission
What are fungal infection denoted by?
Mycoses
What is candidiasis and what is it caused by?
Fungal infection
Candidiasis
What is cryptococcosis and what is it caused by?
Fungal infection
Cryptococcus neoformans
How do you treat cryptococcosis?
Amphotericin B
What causes aspergillosis?
Aspergillus flavus
How does aspergillus flavus cause aspergillosis?
Production of aflatoxins which then are inhaled
What is ringworm caused by?
Tinea corporis
Where does ringworm effect?
Scalp, skin, fingernails, toenails and feet
What are helminths?
Parasitic worms
What are the 3 main groups f helminths?
Cestoda- tapeworms
Trematoda- flukes
Nematoda- roundworms
What are the four ways helminths can be transmitted?
Intermediate host
Faecal-oral route
Active skin penetration
Injection by blood-sucking insect
What type of helminth is schistosomiasis caused by?
Fluke
What helminths cause schistosomiasis?
Schistosoma haematobium
Schistosoma mansoni
Schistosoma japonica
What type of helminth causes trichiuriasis?
Nematode
What helminth causes trichiuriasis?
Trichuris trichiuria
Example of a tapeworm
Taenia solium
