W19 Microbiology Flashcards
How do prokaryotes divide?
Most bacteria/prokaryotes divides by Binary Fission
Some by budding
What are the 4 sequential phases of Bacterial population growth?
Lag phase
Exponential or Log
Stationary
Death phases
What is a microorganism?
Microorganisms (or microbes) are organisms that are too small to be seen with the unaided eye so require a microscope
What are the Major groups of microbes? (5)
- Bacteria
- Fungi (yeasts and moulds)
- Parasites (protozoa, helminths, ectoparasites)
- Microalgae
- Viruses and prions
Which are the smallest and biggest of the following microorganisms?
Viruses, Bacteria, Yeasts, Protozoa, Prions, Moulds
Moulds > Protozoa > Yeasts > Bacteria > Viruses > Prions
What are the types of microorganism diversity?
Cellular = formed by cell(s)
- A single cell (monocellular) – e.g. bacteria
- More cells (pluricellular) – e.g. moulds
-Consist of Prokaryotic (e.g. bacteria) or
- Eukaryotic cells (protozoa, yeasts, moulds)
Acellular = without a cellular structure (e.g. viruses and prions)
What are the 3 domains?
What are the differences based on?
Bacteria, Archaea, Eukarya
Classification mainly based on differences in the
sequences of nucleotides of ribosomal RNAs (rRNA)
What are the features of Viruses?
- Acellular (do not have a cellular structure)
- Small infectious particles consist of nucleic acids surrounded by a protective coat of protein(s)
- Coat may be enclosed in a lipid envelope
- They do not divide
- They need to infect a cell to replicate their particles
What are prions?
What are they made up of?
Simpler infectious particles made up of only proteins (no nucleic acids)
What are the Impact of Microbes on the Environment and Human Activities? (6)
organic?
produce?
synthesis?
generation?
Fix?
O2?
- Organic waste decomposition (e.g. sewage)
- Production of food (e.g. cheese, bread, beer by fermentation)
- Drugs/enzymes synthesis (e.g. penicillin, insulin,
etc.) - Digestion and molecule generation (e.g. vitamins, etc)
5.Nitrogen fixation (converting atmospheric N2 to ammonia, NH3) - Oxygen generation (photosynthesis)
How can microbiota be helpful? (3)
prevent?
produce?
break down?
- Prevent growth of pathogens
- Produce growth factors (e.g. vitamins B and K)
- Breaking down toxic molecules, boosting the immune system and antimicrobial chemicals
Do microbes cause disease?
Microbes are present in and on the human body
>100 trillions microorganisms harboured per person (≈10X higher human cells)
But Less than 1% of microbes cause diseases (pathogens)
Majority of microbes are helpful and not harmful
What are the different types of bacteria called? (for info)
Coccus
Bacillus
Vibrio
Coccobacillus
Spirillum
Spirochete
What are the different arrangements of bacteria called? (for info)
Pairs
Clusters
Chains
Tetrads
How are bacteria named?
Genus and Species
Name is italicised and genus is capitalised
e.g. Escherichia coli becomes E. coli
Bacteria and Archaea are what type of cell?
What features do they have?
Prokaryotes
- Without a nucleus
- Without membrane-bound organelles
(such as mitochondria, lysosomes, etc)
- Simple organisation
What is the plasma membrane structure of bacteria?
What is the function?
Phospholipid bilayer
Composition:
* 40% lipids (mainly phospholipids), 60% proteins
* Lacking sterols (cholesterol of human cells)
* Contain sterol-like molecules (hopanoids)
* Fluid-mosaic model like eukaryotes
=Serves as a selectively permeable barrier:
Controls movements of molecules across the cells
What are mesosomes?
Functions?
Plasma membrane infoldings
Site for DNA replication and cellular respiration
Bacteria cell wall:
What are the functions?
Why is it important?
What is the composition?
Functions
* Maintain bacterial cell integrity and shape
* Prevents the cell from bursting when water flows into the cell by osmosis
* Can contribute to pathogenicity (ability to cause disease)
Evidence of importance
* Only a few bacteria do not posses cell walls (e.g. mycoplasma)
* Target of many antibiotics (anti-bacterial drugs)
Composition
* Structural difference between these two groups
(Gram+ and Gram-)
What is the composition of peptidoglycan/murein?
What ate the 2 monosaccharides it consists of?
- A rigid multi-layered network made up of linear chains
- Each chain is a polymer of a repeating identical disaccharide unit
(made up of the following 2 monosaccharides) in long rows: - N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
A tetrapeptide chain of 4/5 amino acids is linked to NAM
* Chains are linked by peptide cross bridges between tetrapeptide side chains of NAMs
* Archea do not posses peptidoglycan
How can you distinguish between gram +/-
What are the results for gram positive ?
What are the results for gram negative ?
Gram staining:
* Gram-positive (cells are stained BLUE/PURPLE due to the crystal violet-iodine complex – the primary stain/mordant)
- Alcohol dehydrates peptidoglycan (thick layer) forming crystals inside and the dye is retained
Principles:
* Gram-negative (cells stain RED/PINK as the counterstain – e.g. safranin)
- Alcohol dissolves the outer membrane and leaves holes in peptidoglycan
- Crystal violet-iodine complex washes out; cells are colourless
- Safranin (pink) added to stain cells
What is the process of gram staining?
What are the steps? (4)
- Distinguishing groups of bacteria
according to their cell wall structure
- Primary staining with Crystal violet
- Mordant application- Iodine Treatment
- Decolorisation
- Counterstaining with Safranin
What are the features of gram+?
Consists of a thick structure (several layers) of peptidoglycan, separated from the plasma membrane by a thin periplasmic space.
* Also contains teichoic acids, made up of an alcohol and a phosphate group (negative charge)
- Bind to and regulate movement of cations into cell
- Regulate cell growth and prevent cell lysis
- Linked also to the cell membrane
What are the features of Gram -ve bacteria?
Composition?
- Cell wall is thinner, more complex and more susceptible to mechanical breakage
Consists of:
- A thin peptidoglycan layer
- Periplasmic space, containing degradative
enzymes and lipoproteins
- Outer membrane (the most external)
What is the outer membrane composition in gram negative bacteria?
- Consists of:
- Phospholipid bilayer
- Lipopolysaccharides (LPS): acting as antigen and endotoxin
- Porins: membrane pores that allow
the passage of molecules - Lipoproteins
Main differences in the cell wall of Gram+ and -bacteria
Gram +ve
- THICK peptidoglycan
- Teichoic acids
Gram -ve
- THIN peptidoglycan
- Outer membrane (containing LPS, lipoproteins, porins)
- Periplasmic space
What are the functions of the Outer membrane in Gram- bacteria?
- Evade phagocytosis and immune system
- Permeability barrier to antibiotics
(penicillin), digestive enzymes, etc
What are the functions of the glycocalyx?
- Confer pathogenicity (only capsule)
- Prevent phagocytosis by host phagocytes
- Avoid desiccation by preventing water loss
- Aid in attachment to solid surfaces
What are.
Nucleoids?
Plasmids?
Ribosomes?
-Nucleoid: central region containing circular DNA (up to 3500 genes).
- Plasmids: small, nonessential, circular DNA (5-100 genes; e.g., antibiotic resistance, production of toxins, digest antibiotics). They replicate independently.
- Ribosomes: bacterial ribosomes are termed 70S ribosomes (50S + 30S), which distinguish them from the 80S of eukaryotic cells. Selective antibiotic target.
What are flagella?
structure?
function?
- Hairlike filamentous appendages external to the cell
- Propel bacteria (process requiring ATP) toward or away from stimuli, detected by chemoreceptors
- May also be a sensory organelle
(detecting chemicals, temperature, etc)
What is the composition of bacterial flagella? (3)
- Three parts, made of protein flagellin:
- Filament: outermost region
- Hook: attaches to the filament
- Basal body: consists of rod and pairs of rings; anchors flagellum to the cell wall and membrane
What are fimbriae?
What are they involved in?
- Thin hairlike appendages that allow for attachment
- Some types are involved in a twitching motility (how bacteria move along surfaces)
What are sex pili?
*Hair-like tubular structure
* Conjugation pili involved in DNA transfer from
one cell to another
How do Flagella and bacteria move?
- Flagella rotate to “run” or “tumble”
- Direction of flagella determines the movements
What occurs in the lag phase of bacterial population growth?
Lag phase
- Little or no cell division occurs
- Intense metabolic activity. Individual cells increase in size
What occurs in the log/ exponential phase of bacterial population growth?
- Rapid and constant population growth (exponential manner)
- Number of cells produced > Number of cells dying
What occurs in the stationary phase of bacterial population growth?
- Population size begins to stabilize
- Number of cells produced = Number of cells dying
What occurs in the death phase of bacterial population growth?
- Population size begins to decrease
- Number of cells produced < Number of cells dying
What is the generation time?
What does t stand for?
Time required for a bacteria to complete the cell cycle
* E. coli divides every 20 minutes.
* Most bacteria divide every 1 to 3 hours.
* Some bacteria (M. tubercolosis) require over 24 hours to divide.
Some bacteria stain gram-positive and others stain gram-negative because of differences in the structure of their;
a) Plasma membrane
b) Cell wall
c) Capsule
d) Flagella
e) Ribosomes
Cell wall
Which ONE of the following molecules is only contained in the cell wall of Gram +?
a) Porins
b) Lipopolysaccharides (LPS)
c) Sterols
d) Teichoic acids
e) Cellulose
Teichoic acids
Which ONE of the following about the bacterial scientific name is correct?
a) It must be written in bold
b) Includes the Domain
c) All bacteria belong to the same Genus
d) It has been introduced to honour the discoverer
e) It is made of Genus and species
It is made of Genus and species
What are inclusion bodies?
Granules as reserve deposits of nutrients in the form of high molecular weight polymers. E.g. glycogen, polymeric phosphates, etc.
What are Biofilms?
Where are they found?
- Microbial communities
- Form slime or hydrogels that adhere to surfaces
- Bacteria communicate cell-to-cell
- Share nutrients
- Shelter bacteria from harmful environmental factors or microbicides
Biofilms are ubiquitous in nature. They are also found in the digestive system, dental plaque and involved in infections. Also found in sewage treatment systems.
What are the physical reqiurements for bacterial growth?
pH
Osmotic pressure
Temperature
What are chemical requirements for bacterial growth?
Oxygen
Organic growth factors
Ions, Trace elements
Carbon source
Nitrogen, Sulphur and Phosphate