Microbial Structure Flashcards
Describe the differences between Eukaryotes and prokaryotes with respects to genetic material
Eukaryotic:
Nucleus bound with double membrane, linear DNA, DNA organised into chromosomes and large complex ribosomes
Prokaryotic:
No nucleus, has a nucleoid which has no physical boundary, circular DNA which is present in plasmids and has 70S ribosomes.
Describe the difference in structures between eukaryotes and prokaryotes
Eukaryotes:
Cytoplasm filled with large organelles, mitochondria with cristae are ‘energy centres’ and transcription requires formation of mRNA and then movement of mRNA to cytoplasm for translation.
Prokaryotes:
No membrane bound organelles, mesosomes are used in aerobic respiration and transcription and translation occur simultaneously.
Name the structural components of bacteria
Capsule, Pili (fimbriae), flagella, spores, slime and a cell wall.
Describe the basic structure of the capsule and how protects the bactrium
It is made of a loose polysaccharide and protects baterium from phagocytosis and desiccation (removal of moisture)
Describe the structure and features of pili/fimbriae
KEY- NOT on all bacteria. Pilus and fimbria for singular. They are composed of oligomeric proteins, used for bacterial conjugation (transfer of plasmids between cells), highly antigenic (triggers a quick immune response), facilitates attachment. and contains lectins which are easily recognisable by the body.
Describe the structure and features of flagella
Flagellum is singular term. They can be singular or a bacteria cell can have multiple. The are composed of flagellin protein and are thick helical hollow tubes. They facilitate movement and are driven by a rotary engine at the anchor point on the inner cell membrane.
Give two examples of bacterium with flagellum
Vibrio cholerae and Escherichia coli
Describe some of the features of spores
Metabolically inert, has a hard, multi-layered coats making them very resistant.
Describe the features of slime
It’s made from a polysaccharide material and is secreted by bacteria growing in biofilms. It protects them against the immune system and antibiotics.
What groups can bacterium be separated into due to staining?
Gram positive and Gram negative. These are based on the properties on the cell walls.
What makes a cell wall Gram positive?
The thick peptidoglycan layer. Only 2 layers
What makes a cell wall Gram negative?
The presence of lipopolysaccharides in the phospholipid layer. It contains 3 layers
Describe the steps in Gram staining
Primary stain - use of a crystal violet dye that stains all cells purple.
Trapping agent - the use of Gram’s iodine which forms a CVI complex in the cell wall.
Decolourisation- use of alcohol or acetone which interacts with lipids. Gram negative loses the outer LPS layer exposing the inner PGN layer so the colour is washed away. Gram positive becomes dehydrated and traps the complexes in the thick PGN layer.
Counterstain - use of safranin which stains Gram negative pink and Gram positive purple.
Name some of the bacteria cell wall components
Peptidoglycan (PGN) Lipoteichoic acid (recognised by immune cells) Lipopolysaccharide (LPS) in Gram negative, essental for function. Outer membrane proteins (OMPs)
Explain bacterial replication
They reproduce asexually (by binary fission) has circular DNA which is self replicating; it replicatees in two directions with replicating forks splitting from the origin and meeting at the bottom.
what are the four growth phases of bacteria and explain them.
Lag phase - Cells grow in size
Log phase - Cells divide at maximum rate
Stationary phase - Exhaustion of nutrients, oxygen and accumulation of inhibitory end products. No. cells reproducing = No. dying
Death phase - Number of cells dying starts to exceed the number born.
Name the three ways of bacterial recombination
Conjugation - Bacterium connect through pilus and genes are transferred.
Transformation - bacteria take up DNA from environment
Transduction - exchange of DNA through bacteriophages (virus that infects bacteria cells)
What are the basic classifications of Bacteria?
Gram staining, cell shape, atmospheric preference, key enzymes and fastidiousness
Name the three different shapes of bacteria
Cocci - spherical
Bacilli - rod shaped
Spiral - helical rod
Name a Gram positive cocci
staphylococcus aureus
Name a Gram negative Bacilli
Haemophilus influenzae
Name the viral structural components
Nucleic acid, capsid, envelope and spikes
Describe some of the features of a caspid coat
It is a protein shell composed of protein subunits called capsomeres. Can have a variety of different shapes; rod-like, polyhedral and complex.
Name some of the features of the viral envelope
amorphous structure that surrounds SOME viruses. It’s composed of lipids, proteins and carbohydrates.
Name some of the features of viral spikes
They are glycoprotein projections arising from the envelope, highly antigenic meaning they trigger a quick immune response and the may have an enzymatic, adsorption or haemagglutin (causing haemogglutination -the clumping of red blood cells) activity.
Name the six steps of viral replication
Adsorption, penetration, replication, assembly, maturation and release.
Describe absorption (step 1)
virus binds to host cell
Describe penetration (step 2)
Virus injects its genome into host cell, occurs by fusion, binding and ingestion.
Describe Replication (step 3)
Caspid digested by proteolytic enzymes and the viral genome replicates using host cell machinery
Describe Assembly and maturation (step 4 & 5)
Viral components and enzymes are produced and begin to assemble.
In maturation the virus fully develops
Describe release of naked viruses (step 6)
It occurs at the site of nucleic acid replication, the viral enzymes break down the cell wall.
RNA viruses are released as they are produced. DNA viruses are expelled from host cell as cell autolyse and in inclusion bodies.
Describe the release of enveloped viruses (step 6)
Viruses migrate to either plasma or nuclear membrane. Envelopes formed around nucleocapsids by budding of cell membrane. Slow continuous release, no inclusion bodies.
What are the classifications of protozoas?
Sporozoa - intracellular parasites
Flagellates - possess tail-like structures for movement
Aomeba - uses temporary cell-body projections
Ciliates - move by beating cilia.
Name some common protozoal infections
Malaria, Giardiasis, Toxoplasmosis and cryptosporidiosis.
Describe some of the features of fungi
Multinucleate or multicellular organisms. usually grow as thread-like filaments (hyphae), Reproduce asexually by budding and occasionally binary fission.
What are fungal infection called?
Mycoses.
Name some common fungal infections
Candidiasis, cryptococcosis, aspergillosis and ringworm.
What are the three types of helminths found in humans?
Cestoda - tapeworms
Trematoda - flukes
Nematoda - roundworm
Name some examples of helminths
Schistosomiasis, Trichuriasis, tapeworm
