Microbial Structure Flashcards
What are the genetic differences between eukaryotes and prokaryotes?
Eukaryotes: Have a true nucleus bound by double membrane Linear DNA DNA organised into chromosomes 80s ribosomes
Prokaryotes: Do not have a nucleus: nucleoid instead but no physical boundary Circular DNA DNA naked (plasmids present however) 70s ribosomes
What are the structural differences between eukaryotes and prokaryotes?
Eukaryotes:
Cytoplasm filled with organelles
Mitochondria are energy centres
Transcription requires formation of mRNA and movement of mRNA from nucleus to cytoplasm for translation
Prokaryotes:
No membrane bound organelle
Mesosomes used in aerobic respiration
Transcription and translation occur simultaneously
What are the main structural components of bacteria ?
Capsule Cell Wall Pili Flagellae Spores Slime
What is the capsule made of ? What is its function ?
Loose polysaccharide structure.
Protects cells from phagocytosis and dessication
What is pili made of ? What is its function ?
Made of oligomertic pilin proteins
Functions as appendage for bacterial conjugation (tube for transfer of plasmids between bacteria)
What is the role of fimbriae ?
Attachment of bacteria onto cell (thanks to lectins which recognize oligosaccharides on host cell)
What is the the flagellum made of ? What is its function ?
Made up of flagellin protein.
Function is locomotion thanks to rotary engine at anchor point on inner cell membrane.
What are the different types of flagella ?
Monotrichous - having a single flagellum
Amphitrichous - having flagella at each end.
Peritrichous - having a uniform distribution of flagella over the body surface
Lophotrichous - having two or more flagella at one end
What are spores ? What feature makes them hard to kill ?
Highly resistant, dormant structures triggered formed in response to adverse environmental conditions. Allows regrowth under suitable conditions.
Hard multilayered coats.
What are examples of diseases caused by sporing bacteria ?
Botulism due to clostridum botulinum
Tetanus due to clostridum tetani
What is slime made of ? What is its function ?
Slime is made by polysaccharide material.
Protects against immune attack and antibiotics, secreted by some bacteria growing in biofilm.
What are the distinctive features of gram positive bacteria ?
- 2 layers (Peptidoglycan (PGN) layer in the cell wall + cytoplasmic membrane)
- lipoteichoic acid (LPA) is the key protein
What are the distinctive features of gram negative bacteria ?
- 3 layers (outer membrane phospholipid membrane + thin PGN layer + cytoplasmic membrane)
- lipopolysaccharide (LPS) is the key protein
What are the steps of gram staining ?
- Primary stain (CRYSTAL VIOLET DYE)= stains all bacteria purple
- Trapping agent (Gram’s iodine)= Forms CVI complex in cell wall
- Decolorisation (alcohol/acetone)= interacts with lipids in the cell wall.
Gram (-) loses outer LPS layer which exposes thin inner PGN. COLORS WASHED AWAY.
Gram (+) becomes dehydrated and traps complexes in thicker PGN layer of cell wall. STAYS PURPLE. - Counterstain (safranin):
Turns Gram (-) pink/reddish
Gram (+) stays purple
What is PGN made up of ?
Sugars and AAs
Sugar component = alternating residues of N-acetylglucosamine and N-acetylmuramic acid
What is lipoteichoic acid (LPA) made up of ? What is its role ? How does LPA of bacteria help the immune system?
Teichoic acid and lipds.
Provides cell rigidity.
Recognised by host immune cells.
What are the functions of LPS ?
Function in outer membrane
Elicits potent immune and inflammatory response
Produces endotoxins (toxins inside the cells, released when cell disintegrates)
What are examples of outer membrane proteins ?
Lipoproteins and porins.
How do bacteria replicate ?
By asexual binary fission. Replication starts at origin of circular DNA —> 2 replication forks split from origin —>
The 2 replication forks meet at the bottom (bidirectional replication)
What are the 4 phases of bacterial Replication ?
1) Lag phase: period of active growth (in size, not number), prepare for reproduction.
2) Log phase: Cell divides at maximum rate, uniform replication
3) Stationary phase: cessation of growth due to accumulation of inhibitory end products or O2 unavailability, number of cells dying = number of new cells
4) Death phase: Number dying cells exceeds number of newly born cells
What is conjugation ?
One bacterium connects to other through pilus.
Geners transferred from one to other.
What is transformation ?
Bacteria taking up DNA from their environment.
What is transduction ?
Exchanging of bacterial DNA between bacteria through bacteriophages (virus infecting the bacteria)
What are the shapes for bacteria ?
cocci (spherical), bacilli (helical), coccobaccili, spiral (helical rod)
What are the possible atmospheric preferences for bacteria ?
Aerobic
Anaerobic
Microaerophillic (needs a little bit of O2)
What are the components of viral stucture ?
Nucleic acid (ss DNA, ds DNA, ss RNA, ds RNA)
Capsid
Envelope (optional)
Spike (optional)
What is the function of the capsid ? What are its components ? What are the possible shapes for capsids?
Shell for the virus. Composed of capsomeres.
Possible shapes: rod-like, polyhedral, complex
What is the function of spikes ? What are its components ?
Attachment to cells + enzymatic/adsorption/haemagluttinin activity
Glycoproteins (highly antigenic)
How does viral replication occur ? What are the steps to it ?
Uses host cell’s machinery to replicate.
- Adsorption (virus binds host cell, very specific)
- Penetration (virus injects genome into cell by fusion or binding or ingestion)
- Replication (Capsid digested bt enzymes and viral genome replicates)
- Assembly (viral components and enzymes are produced and begin to assemble)
- Maturation (virus fully develops)
- Release of naked viruses
- Release of envelopped viruses
How does release of naked virus take place ?
- Where ? Takes place at site of nucleic acid replication
- How ? Viral enzymes break down bacterial cell wall
- Who ? RNA viruses released as they are produced
- Who ? DNA viruses expelled from host cell as the cell autolyse in inclusion bodies
How does release of enveloped virus take place ?
- Where ? Virus migrates to enter plasma membrane or nuclear membrane
- How ? Envelopes form around nucleocapsids by budding of cell membrane
- Slow continuous release of mature viral particles WITHOUT inclusion bodies
How many cells do protozoa have ?
Unicellular
What are the types of protozoa that exist ? What is the distinctive characteristic of each kind ?
- Sporozoa (intracellular parasite)
- Flagellates (have flagellae for movement)
- Amoeba (have pseudopds for movement and feeding)
- Ciliates (have cilia for movement)
What is an example of protozoal infections ?
Malaria, Giardiasis
What is the normal microbiota ?
Bacteria and fungi that live in our bodies.
What are the structural features of fungi ?
Unicellular or multicellular
Chitin and glucans cell wall
How do fungi reproduce ?
Asexually by budding (sometimes by binary fission)
What is the other name for fungal infections ?
Mycoses
What are examples of fungal infections ?
Ringworms (tinea corporis and tinea pedis), candidiasis (due to Candida Albicans)
What are the main Helminths groups (parasitic worms) ?
Tapeworms (Cestoda)
Roundworms (Nematoda)
Flukes (trematoda)
Which part of the body do helminths usually infect ?
The intestine
How are helminths transmitted ?
- Via intermediate host (like pork)
- Injection by blood-sucking insect
- Fecal oral route
- Active skin penetration
What are examples of infections by helminths ?
Tapeworm due to Taenia Solium (has scolex for attachment). Large intestine.
Schistosmoiasis (=bilharzia) due to flukes. Affects urinary system and intestines.
