Microscopes and the biology of microbes- Lecture 2 Flashcards
What are the major parts of a light microscope?
- Light source
- Incident light
- Light beam
- Specimen
- Transmitted light
(look at diagram)
What is the magnification for a light microscope?
1000x
What do light microscopes need?
stains to provide contrast - simple and negative stain
What are simples stains?
Basic dyes that absorb light- methylene blue
malachite green
crystal violet
safranin
What is a con of light microscopy?
It gives limited information on bacteria cell structure - only on size, shape and organisation
What is cell shape?
Cell shape is rarely definitive but is constant within a species
What is a spherical bacterial shape?
Spherical = coccus
Cells in a regular chain- Streptococcus mutans
Irregular clumps-
Staphylococcus aureus
What is cylindrical bacterial shape?
Cylindrical = rod (bacillus)
Cells without recognized grouping-
Escherichia coli
Cells in chains with spores- Bacillus anthracis
What are simple stains?
They are Basic (+) dyes only, like Carbol Fuschin, Malachite Green, Crystal Violet and they bind to (almost) all bacteria, irrespective of composition
What are differential stains?
Combinations of dyes and other treatments with different binding patterns and are related to cell envelope composition- e.g
Gram Stain
What is an electron microscopes magnification and wavelength?
up to x 100,000 and the wavelength is 1,000 times shorter than light
What can electron microscopes measure?
- Size
- Shape
- Organisation
- Internal structure
What are needed for electron microscopes?
Stains to provide contrast
What can heavy metals do in microscopes?
They can deflect electrons
What metal ions can do this?
Molybdenium, Uranium, Tungsten, Lead and Gold
What is a scanning electron microscope?
It produces images of a sample by scanning it with a focused beam of electrons. The signals result from interactions of the electron beam with atoms at or near the surface of the sample
What is a transmission electron microscope?
A beam of electrons is transmitted through an ultra-thin specimen, interacting with the specimen as it passes through.
What is the highest magnification of a light microscope?
1,000
What is the resolution of a light microscope?
0.2 um
what is the lens on a light microscope?
glass
what is the contrast on a light microscope?
Differential light absorption
What is the highest magnification of an electron microscope?
100,000
What is the resolution on an electron microscope?
0.5nm
What is the lens on an electron microscope?
electromagnet
what is the contrast on an electron microscope?
electron scattering
What are the important sub-groups of bacteria?
Gram positive and gram negative
What are prokaryotes?
A simple internal organisation with NO MEMBRANE BOUND NUCLEUS, No mitochondria, No Golgi or Endoplasmic Reticulum
What are the 2 types of prokaryotes?
Bacteria and Arhaea
What are bacteria?
they have many impacts on humans
and Pathogens and Partners are the
most intensively studied group
What are archaea?
Environmental organisms (?) with a separate Domain of Life and are inhabitants of harsh environments
What are the key parts of a bacterial cell?
- Cytoplasm
- Cell envelope, which consists of the
plasma membrane, cell wall and outer membrane
(only on Gram negative) - Surface appendages, which is variable between species
What is the role of the cytoplasm in the bacterial cell?
Protein synthesis
DNA replication
RNA transcription
(Most) metabolic reactions
What does the bacterial cell not have?
a nucleus, tightly wound DNA, mitochondria, golgi and ER and limited storage
What is the plasma membrane in the bacterial cell?
It is a lipid bilayer (7nm thick)
Composed of:
Phospholipids and proteins in an asymmetrical distribution
What is the organisation of the bacterial cell envelope?
Organisation fits Fluid Mosaic Model of membrane structure
What does every cell have?
A plasma membrane
What are the functions of the bacterial cell envelope plasma memebrane?
1.compartmentalisation
2. energy generation
(electron transport
ATP production)
3. nutrient transport
4. DNA replication
Why is the plasma membrane very active?
It is very metabolically active as there is a high ratio of protein:lipid
What is another name for the bacterial cell envelope cell wall?
Peptidoglycan- this is a heteropolysaccharide
with sugar chains cross-linked by peptide chains.
What is the cell wall like in gram positive?
30-60 nm thick and makes up 60-90% of cell envelope
What is the cell wall like in gram negative?
2-3 nm thick and makes up 10-15% of cell envelope
What is the bacterial outer membrane called and what is it?
The lipid bilayer (7nm thick) and is composed of:
Phospholipids,
Lipopolysaccharide that are Highly antigenic and toxic and
Lipid A and Proteins
(asymmetric distribution
transport and structure)
Fluid Mosaic Model
What is flagella?
Organelles of motility and non-covalent polymers of proteins.
What does flagella consist of?
A Filament, hook and Basal bodies with rods and rings. It has a characteristic size and distribution for each organism. Filament is helical and has a characteristic wavelength
What are alternatives of flagellar motility and how do they work?
Twitching and gliding motility and they work for bacteria moving across a solid surface
What does flagellar motility work for?
works best for bacterial moving through a liquid
What is Pili?
Hair-like appendages on cell surface. They are 2-40 nm in diameter, up to 12 microns in length, can be straight or curved, evenly distributed or present in bundles and can be found on gram-negative and gram positive species but not a universal property
What does the expression of pili depend on
growth temperature, pH and nutrient avliabilty
How does pili work?
it binds bacteria to surfaces and is the
first step in infection- e.g
Neisseria gonorrhoeae:
Pilus-mediated binding to genital epithelial cells
The first step in the sexually transmitted disease called gonorrhoea
What are capsules and biofilm?
They are cell-surface polymers of carbohydrate secreted by some bacteria. They are made of sugars, aminosugars, sugar alcohols, DNA, short peptides and some lipid structures
What is the size of Escherichia coli?
1.0-2.0 micrometers long and a radius of 0.5 micrometers
What is the size of Treponema pallidum?
6 to 15 μm in length and 0.2 μm in diameter
What is the size of Thiomargarita namibiensis?
750 microm
What is the process of the gram stain?
Crystal violet renders cells purple in color. Cells are then treated with ethanol, which decolorizes gram-negative cells but not gram-positive cells. Finally, cells are counterstained with a different-colored stain, typically the red stain safranin. As a result, gram-positive and gram-negative cells can be distinguished microscopically by their different colors
What are the final colours of gram stains? why is this caused?
gram-positive bacteria appear purple-violet and gram- negative bacteria appear pink. This is caused by differences in the cell wall structure
What are some bacterial phospholipids?
Phosphatidylglycerol (PG)
Phosphatidylserine (PS)
Phosphatidylinositol (PI)
What is the role and chemical composition of teichoic acids?
Found in Gram-positive bacteria CW and are made of polyglycerol phosphate . Involved in regulation of cell morphology as well as in cell division.
What is the role and chemical compition of lipoteichoic acids?
It is important cell wall polymer found in gram-positive bacteria and are polymers of alternating units of a polyhydroxy alkane, joined to form phosphodiester units
What is the role and chemical composition of Teichuronic acids?
It is a long chain polysaccharide composed of almost a hundred disaccharide repeating units. TUA plays an important role in protecting the microbe and interacting with the host cells.
what is Mycoplasma pneumoniae?
an ‘atypical’ bacterium that causes lung infection
What are endospores?
They are made in the process of endosporulation and they are highly differentiated cells that are extremely resistant to heat, harsh chemicals, and radiation. Endospores function as survival structures and enable the organism to endure unfavorable growth conditions, e.g extreme temps
what acid do endospores contain?
dipicolinic acid, which accumulates in the core.
How do bacteria move?
Flagella propel bacteria through the body
What are extracellular carbohydrate capsules?
They protect bacterial cells from external aggressions such as antibiotics or desiccation
