Microbial Structure Flashcards
Features of Eukaryotes (DNA)
Have a true nucleus (bound by a membrane)
Linear DNA
DNA organised into chromosomes; complexed with proteins
Large complex ribosomes with many types of rRNA & proteins
Features of Prokaryotes (DNA)
No nucleus; has a nucleoid; no physical boundary
Circular DNA (plasmids)
DNA nuceloid-associated proteins that help pack DNA into nucleotid, plasmids present
Features of Eukaryotes (membrane bound organelles)
Cytoplasm filled with large complex collection of organelles
Mitochondria with cristae are power plants of the cell.
Plants also have chloroplasts for photosynthesis.
Transcription and translation are physically separated.
Features of Prokaryotes (membrane bound organelles)
No membrane bound organelles independent of the plasma membrane.
Transcription and Translation occur simultaneously.
What type of cells are bacterial cells ?
Prokaryotic cells
What layers are bacterial cells surrounded by ?
Collectively called the cell envelope.
Consists of the capsule (glycocalyx, cell wall, plasma membrane)
Main components of bacterial cells
Glycocalyx
Cell Wall
Plasma Membrane
Nucleoid
Ribosome
Plamsid
Outer structure of bacterial cells
Pilus / Finbriae
Flagellum
Function of the glycocalyx capsule
Acts as a shield and protects the bacteria against phagocytosis and helps the bacteria to adhere to surfaces.
Structure of the glycocalyx capsule
Tightly organised polysaccharide layer that excludes small particles.
Structure of glycocalyx slime
More easily deformed polysaccharide layer, less tightly organised and doesn’t exclude small particles.
Loosely attached to cell surface and so can be easily lost
Function of glyocoalyx - slime
Protects cell from immune response
Can prevent access to antibodies
Function of Pili
Hair like structures that allows them to attach to other cells.
Forms a bridge to enable the transfer of plasmids between bacteria.
What are fimbriae ?
Shorter hair like structures on the external surface of bacterial cells.
Flagella
Long, whip-like protrusions that allow the bacteria to move.
What are flagella composed of ?
Flagellin protein
What are spores ?
Metabolically inert form of bacteria, triggered by adverse environmental conditions.
What is an advantage of spores ?
They are adapted for long-term survival, allowing regrowth under suitable conditions.
They have hard, multi-layered coats, making them difficult to kill.
What are round shaped bacteria called ?
Cocci
What are rod shaped bacteria called ?
Bacilli
What are spiral shaped bacteria called ?
Spirilla
What are oddly shaped bacteria called ?
Pleomorphic
What is the function of gram staining bacterial cells ?
Divides species into 2 groups, gram +/-
This is based on chemical and physical properties of the cell walls.
Cytoplasm
Gel-like substance, composed mainly of water that also contains cell components, enzymes and various organic molecules.
Plasma membrane function
Most important layer as it encloses the cytoplasm.
Also involved in respiration, photosynthesis and synthesis of lipids and cell wall components.
Ribosomes
Site of protein synthesis
Nucleoid
Contains the cell’s chromosomes
Chromosomes
Contain the genes needed to provide instructions for protein synthesis in the cell.
Plasmids
Contain extrachromosomal DNA
Plasmids often contain genes that confer a selective advantage to the bacterium such as resistance to antibiotics.
What are the main functions of the cell wall ?
Prevents the cell from rupturing.
Confers shape and rigidity to cels.
Helps differentiate whether bacteria are gram + or -
Gram + cell wall
Have a single THICK layer of peptidoglycan, above the plasma membrane.
This allows them to retain the staining dye.
Gram - cell wall
Have a thinner layer of peptidoglycan sandwiched between the surface membrane and the plasma membrane.
These cannot retain the dye.
Peptidoglycan function
PGN - forms a mesh like layer outside the plasma membrane
Peptidoglycan Composition
Polymer of sugars and amino acids
Lipoteichoic Acid type of gram cell wall
Gram + bacteria
Function of Lipoteichoic Acid
Provides cell rigidity
Composition of Lipoteichoic Acid
Complex of teichoic acids + lipids
Lipopolysaccharide type of gram cell wall
Gram - bacteria
Function of Lipopolysaccharide
Elicits potent immune and inflammatory host responses
Produces endotoxins
Steps in gram staining
Primary Stain
Trapping Agent
Decolourisation
Counter stain
Primary Stain function
Stains all the bacterial cells PURPLE
(crystal violet dye)
Trapping Agent function
Forms crystal violet iodine (CVI) complexes in the cell wall (larger than CV so not to be easily washed out of the peptidoglycan (PGN) layer)
Decolorisation (with alcohol) function
Interacts with lipids in the cell wall
Gram negative: loses outer LPS layer; exposes thin inner PGN layer; coloured complexes mainly wash away
Gram positive: becomes dehydrated and traps the complexes in thicker PGN layer of cell wall
Counterstain results
Gram -ve : Pink/Reddish
Gram +ve : Purple
Why do Gram + cells stain Purple ?
Gram positive: becomes dehydrated and traps the complexes in thicker PGN layer of cell wall
Why do Gram - cells stain red ?
Gram negative: loses outer LPS layer; exposes thin inner PGN layer; coloured complexes mainly wash away
How do bacterial cells replicate ?
By Binary fission.
1 cell reproduces to give 2 daughter cells
Steps in Bacterial Replication
Prokaryotic parent cell initiates replication
A copy of the cell’s DNA is created
Cell elongates and cross wall forms
Cross wall forms completely and daughter cells separate.
Where is the genetic information found in bacterial cells ?
Circular DNA
- distributed equally between daughter cells
Bacterial Replication of GENOME stages
Circular DNA replication starts at the Origin.
The replisome binds and initiates synthesis.
Bi-directional replication (opposite directions)
Replication ends at the terminus of replication, releasing 2 chromosome copies.
What are the phases in bacterial GROWTH ?
Lag phase
Log phase
Stationary phase
Death phase
What happens in the lag phase of bacterial growth ?
Period of active growth
Bacteria prepare for replication
What happens in the log phase of bacterial growth?
Cells divide at maximum rate
Uniform replication
Graph line is almost straight
What happens in the stationary phase of bacterial growth?
Exhaustion of nutrients
Cessation of growth
Number of cells dying balances the number of new cells.
What happens in the death phase of bacterial growth ?
Number of cells dying exceeds the number of newly born cells.
How are genes transferred ?
Horizontal Gene Transfer
Stages in Horizontal gene transfer
Transformation
Transduction
Conjugation
Outer membrane synthesis
What is transformation in horizontal gene transfer ?
Bacteria take up DNA from their environment.
What is transduction in horizontal gene transfer ?
Bacteriophages (bacterial viruses) move genes from one cell to another
What is conjugation in horizontal gene transfer ?
One bacterium connects itself to another through the pilus.
Bacteria directly transfer genes to another.
What are some ways to identify bacteria ?
Morphology - coccus, bacillus, spiral…
Arrangement - single, chain, clusters…
Gram Stain
Atmospheric preference
Key enzymes
Fastidiousness
Gram + coccus arrangement
Cluster, grape like
Staphylococcus Aureus
Gram - coccus arrangement
2 attached bugs
Neisseria Meningitidis
Gram + bacillus arrangement
Single rods
Listeria Monocytogenes
Gram - bacillus arrangement
Single rods
Esterichia Coli
Structural components of viral cells
Nucleic acid
Capsid
Envelope
Spikes (antigens)
What does it mean that viruses are intracellular obligate parasites ?
Only contains the parts needed to enter and control a host cell.
How is genetic material stored in viruses ?
DNA or RNA
Capsid
Protective protein coat
Shapes of capsids
Icosahedral
Helical
Complex
Spikes
Highly antigenic
Viral Life Cycle
Viral antigens attach to host cell
Viral DNA is inserted into the host cell
Viral DNA is replicated by host cell enzymes
New viral particles are assembled and packaged into new virions
They are released from the cell
What type of cells are fungi ?
Eukaryotic cells - multicellular
Structure of Fungi
Same structure as eukaryotic cells
Contains a bud with a vesicle, ribosomes and septum
What is the body of a fungus called ?
Thallus
What is hyphae ?
Long branched filaments in mould
What is the cell wall made of in fungi ?
Thick carbohydrate wall containing CHITIN and glucans.
How do fungi replicate ?
Asexually by BUDDING, and occasionally by binary fission.
Conidia
Ending in the name of fungal types
Mycoses
Fungal Infection
What type of cells are protozoa ?
Single celled eukaryotes
How are protozoa classified ?
Based on motility
Sporozoa
Non-motile, INTRAcellular parasites
Flagellates
Possess tail-like structures for motility
Ameoba
Use temporary cell-body projections
Ciliates
Move by beating cilia
What are protozoa and helminths ?
Parasites
PARASITES
Diplomonads and parabasalids location
Live in the intestinal tract (ANOXIA)
Features of diplomonads
Diplomonads are defined by the presence of a nonfunctional, mitochrondrial-remnant organelle called a mitosome.
Features of parabasalids
Parabasalids are characterized by a semi-functional mitochondria referred to as a hydrogenosome
Protozoa disease example
Malaria
Kinetoplastid
Kinetoplastids are a group of flagellated protozoans that are distinguished by the presence of a DNA-containing region, known as a “kinetoplast,” in their single large mitochondrion.
How to characterise alveolata ?
BY the presence of alveoli
What are the 2 kinds of nuclei that ciliates possess ?
Macronucleus
Micronucleus
Function of macronucleus (parasites)
Regulates basic cellular function
Function of micronucleus
Controls sexual reproduction
Helminths
Term used for all parasitic worms
Cestoda
Tapeworms
Trematoda
Flukes
Nematoda
Roundworms
Schistosomiasis
Urinary and Intestinal infections
FLATWORM
Trichiuriasis
Intestinal infections
ROUNDWORM (Human whipworm)
Tapeworm
Acquired from ingesting worms or eggs in undercooked pork
Reside in large intestine
What is a scolex ?
The anterior end of a tapeworm, bearing suckers and hooks for attachment.
Name the types of gram + bacteria
Bacillus
Clostridium
Staph
Strep
Name the types of gram - bacteria
Coli
Pylori
Neisseria
