Introduction to Prokaryotes Flashcards
(85 cards)
1
Q
Prokaryote Definition
A
Cellular organisms with no true nucleus
2
Q
Prokaryotic Shape
A
- Cocci (spherical):
- Streptococci: Chains
- Staphylococci: Grape like clusters
- Bacili (rods):
- Coccobacili: Very short rods
- Vibrios: Resemble rods, comma shaped
- Spirilla: Rigid helices
- Spirochetes: Flexible helices
- Filamentous
3
Q
Common features in all prokaryotes
A
- Cell envelope = plasma membrane plus all layers outside of it (cell wall etc. )
- Cytoplasm (no organelles, no ER, no GA)
- External structures (fimbriae, flagella, some bacteria have a capsule)
4
Q
Structure of Polar membrane lipids
A
- Polar & hydrophilic head (phosphate group and glycerol mol)
- Long, non polar, hydrophobic fatty acid chain tail
- Lipid composition of membrane phospholipids changes with environmental temp to maintain membrane fluidity.
5
Q
Bacterial membrane proteins
A
Integral Proteins:
- 70-80% of total membrane proteins - Amphipathic, embedded in membrane - carry out important functions
Peripheral Proteins:
- 20-30% of total membrane proteins - Loosely connected to membrane, easy to remove
6
Q
Hopanoids
A
Sterol-like molecules found only in bacterial membranes
7
Q
Peptidoglycan
A
- Also called Murein
- Rigid structure that lies just outside the bacterial cell membrane (Makes up the cell wall)
8
Q
Gram-Positive Bacteria
A
- Stain purple
- thick layer of peptidoglycan (20-80nm)
9
Q
Gram-Negative Bacteria
A
- Stains pink or red
- Thin peptidoglycan layer (2-7nm) plus an outer membrane
10
Q
Functions of the bacterial cell wall
A
- Maintains shape of the bacterium
- Help protect cell from osmotic lysis
- Helps protect from toxic molecules
- May contribute to pathogenicity in pathogenic bacteria
11
Q
Peptidoglycan Structure
A
- Mesh-like polymer of identical subunits forming long strands
o Forms a helical spiral with some peptides facing vertically and some facing horizontally. - Each subunit consists of:
o 2 sugars: N-acetylglucosamine (NAG)
& N-acetylmuramic acid (NAM)
o Alternating D- and L- amino acids - Side-chain of peptide always ONLY added to NAM unit and not NAG
- Strands have a helical shape and short peptides extend from glycan backbone at right angles to each other.
o Means that each peptidoglycan strands can be cross-linked to peptidoglycan strands above it, below it and the either side of it. - Chains are cross-linked by peptides for strength:
o Direct crosslinking – amino of 1 to amino of another
o Interbridges may form (bridge made of short peptide chain between the short peptidoglycan peptides)
o Various structures occur (determined by the amino acids used in the cross-linking peptides)
12
Q
Transpeptidation
A
o Bond formed between adjacent peptide chains, catalysed by enzyme transpeptidase.
- Enzyme removes C5 (terminal C) during reaction. - Antibiotics like penicillin interfere with transpeptidation (inactivate transpeptidase), which makes the peptidoglycan mesh around a bacterial cell weaker so it is more susceptible to death by lysis.
13
Q
Peptidoglycan as a drug target
A
o Penicillin’s and cephalosporins and glycopeptides only kill growing cells (because all of these antibiotics target peptidoglycan synthesis).
o Peptidoglycan is an important target for beta-lactam antibiotics and glycopeptide antibiotics.
14
Q
Peptidoglycan as an enzyme target
A
o Lysozyme hydrolyses the B(1-4) glycosidic bonds in glycan chains of peptidoglycan.
o This hydrolysis makes bacteria susceptible to lysis by osmotic effects.
o Lysozyme is an antimicrobial enzyme produced by humans and animals, present in human secretions like tears, saliva etc.
o Lysozyme is most effective against Gram-positive pathogens like Streptococcus.
15
Q
Gram-Negative Cell Walls Structure
A
- Thin layer of peptidoglycan surrounded by an outer membrane
- More complex than gram-positive cell walls
- Outer membrane composed of lipids, lipoproteins and lipopolysaccharides
- No techoic acids
- Harder to treat gram-negative infections because of double membrane and periplasmic space (space between outer Membrane and peptidoglycan)
- Many enzymes present in the periplasmic space. Space constitutes 20-40% of cell volume
16
Q
Gram-Negative Outer Membrane Permeability
A
- More permeable than plasma membrane due to porin proteins and transporter proteins
- Porin proteins form channels through which small mols can pass
17
Q
Gram- Positive Cell Wall Structure
A
- Composed primarily of thick layer of peptidoglycan
- May contain large amounts of techoic acids (Neg charge):
- Helps maintain structure of cell envelope
- Protects from environmental substances (like antibiotics and host defence molecules)
- May help pathogens bind to host tissues in initiating infection
- Some gram+ bacteria have layer of proteins on surface of peptidoglycan
- Periplasmic space between plasma membrane and cell wall, very few proteins, smaller than in Gram-.
18
Q
Techoic Acid Structure
A
- Polymers of glycerol or ribitol linked by phosphate groups
- ONLY in Gram+ bacteria
- Amino Acids or sugars attached to glycerol/ribitol units
- Techoic acids contribute to negative charge of Gram+ cells
19
Q
Lipopolysaccharides (LPs)
A
- In the Gram negative bacterial cell wall
- Consist of 3 parts:
- Lipid A - anchors polysaccharide in outer membrane
- Core polysaccharide
- O-side chain - O antigen; varies between bacterial strains
- Lipid A embedded in outer membrane; Core polysaccharide and O-side chain extend out from the cell
20
Q
Importance of Lipopolysaccharides
A
- Contribute to negative charge on cell surface
- Help stabilise outer membrane structure
- May contribute to attachment to surfaces and biofilm formation
- Creates a permeability barrier
- Protection from host defences
- Lipid A part of LPS can act as an endotoxin
21
Q
Exoenzymes
A
Enzymes secreted by Gram+ bacteria
Aid in degradation of polymeric nutrients
22
Q
S Layers
A
- Regularly structured layers of protein or glycoprotein that self-assembles in bacterial cell walls.
- In Gram- bacteria the S layer adheres to the outer membrane
- In Gram+ bacteria it is associated with the peptidoglycan surface
23
Q
S Layer Function
A
- Protects from ion & pH fluctuations, osmotic stress, enzymes and predation
- Maintains shape and rigidity
- Promotes adhesion to surfaces
- Protects from host defences
- Potential use in nanotechnology (because of its spontaneous association)
24
Q
Main groups of Archaea
A
- Methanogens (Produce methane)
- Halophiles (salt loving)
- Thermophiles (Heat loving)
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Archaeal Cell envelope differences to Prokaryotes
- S-layer may be only component outside plasma membrane
- Some archaea lack a cell wall
- Capsules and slime layers are rare
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Archaeal Cell Walls
- Lack peptidoglycan
- Most common cell wall is an S-layer
- May have protein sheath external to S-layer
- S-layer may be outside the membrane and separated by a psuedomurein
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Pseudomurein subunit composition
- Peptidoglycan-like molecule
- L-amino acids rather than D-amino acids
- NAG & NAT (N-acetyltalosaminouronic) not NAM
- B(1-3)glycosidic bonds not B(1-4)glycosidic bonds
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Archaeal Membranes
- Have distinctive membrane lipids (different from BOTH bacteria and eukaryotes)
o Branched-chain hydrocarbons bonded to glycerol by ETHER bonds, not fatty acids linked by ESTER bonds.
- Contain diglycerol tetraether
- May also have polar lipids: phospholipids, sulpholipids and glycolipids
- Can mix diethers, tetraethers and other lipids to give membranes of differing rigidity and thickness.
- Some have monolayer structure instead of a bilayer structure (unique to archaea)
29
What makes the archaeal membrane different to that of bacteria and eukaryote?
1. Some have monolayer structure instead of a bilayer structure
2. Contains diglycerol tetraether
3. Has distinctive membrane lipids (different from BOTH bacteria and eukaryotes)
o Branched-chain hydrocarbons bonded to glycerol by ETHER bonds, not fatty acids linked by ESTER bonds.
30
What are 6 similarities between Archaeal and Bacterial Molecular Biology?
1. Pyrococcus exhibits bidirectional DNA replication from a single origin (like bacteria)
2. Archaeal mRNA similar to bacterial mRNA
o Polycistronic mRNAs (RNA from operon) are produced and NO evidence for mRNA splicing – very bacterial like.
3. Archaeal promoter similar to those in bacteria
4. Ribosomes are 70S (Like bacteria) BUT shape is variable and can be different from bacteria and eukaryote.
5. Archaeal small-subunit rRNA is 16S like bacteria
6. Both have single circular chromosome per cell
31
What are 5 similarities between Archaeal and Eukaryote Molecular Biology?
1. EF-2 (elongation factor) sensitive to Diptheria toxin (inhibits protein synthesis)
2. Archaeal DNA replication proteins similar to those in eukaryotes
3. Archaeal RNA polymerase also similar to that in eukaryotes: INSENSITIVE to rifampicin and streptolydigin (which inhibit bacterial transcription)
4. Protein synthesis is sensitive to anisomycin, resistant to kanamycin and chloramphenicol.
5. Most aspects of archaeal DNA, RNA and protein synthesis resemble those in eukaryotes
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Common Properties to All Archaea
1. Cell Walls
2. Membrane Lipids
3. Transcription & Translation machinery
4. Coenzymes
5. Mechanism of autotrophic CO2 fixation
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Are Archaea more closely related to Eukaryotes or Bacteria?
Eukaryotes
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What are 8 Cellular Structures common to all Prokaryotes? (Bacteria & Archaea)
1. Protoplast
2. Cytoplasm
3. Cytoskeleton
4. Nucleoid
5. Plasmids
6. Pili
7. Fimbriae
8. Flagella
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What is Protoplast?
The Plasma membrane and everything within it
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What is the Cytoplasm?
The material bounded by the plasma membrane
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What is the Nucleoid?
- Irregularly shaped region in bacteria and archaea
- Not membrane bound (there are a few exceptions)
- Location of the chromosome and associated proteins
- Usually 1 chromosome (closed circular double-stranded DNA mol)
- Supercoiling and nucleotide proteins (different to histones) probably aid in folding
38
What are plasmids?
- Extrachromosomal DNA
- Exist and replicate independently of the chromosome
- Contains only a few non-essential genes which confer selective advantages to the host
- May exist in many copies in a cell
- Are inherited stably during cell division
39
What are fimbriae?
- Short thin, hair-like appendages made of protein that extend beyond the cell envelope
- Mediate attachment to surfaces
- Some are required fro motility or DNA uptake
40
What are Sex Pili?
- Similar to fimbrae except longer, thicker and less numerous
- Genes for formation found in plasmids
- Used in Horizontal Gene transfer
41
What are Flagella?
- Threadlike, locomotory appendages extending outward from plasma membrane and cell wall
- Function in: Motility & swarming behaviour, Attachment to surfaces, May be virulence factors in pathogenic bacteria
42
Bacterial patterns of flagellation
- Varies in terms of where they are in the cell
- Monotrichous polar flagellation: single strand right at end of rod-shaped cell
- Lophotricous flagellation: Polar 'tuft' of flagellation (>1 strand)
- Petrichous flagellation: looks like hair, has flagella along whole length of cell.
43
What is a refractive index?
Measure of how greatly a substance slows the velocity of light
44
What is the focal length?
Distance between the centre of the lens to the focal point in a microscope.
45
What is microscope resolution?
The ability of a lens to separate small objects that are close together
46
Types of fixation of species in preparation for microscopy
1. Heat fixation: preserved overall morphology but not internal structures; used with bacteria & archaea
2. Chemical fixation: used with larger, more delicate organisms; protects fine cellular substructure and morphology
47
What is differential staining?
- Divides microorganisms into groups based on their staining properties (e.g. gram stain)
- Used to detect presence or absence of structures
48
Mechanism of Gram Stain
- Results of the stain are due to differences in the nature of the cell wall
- Shrinkage of pores of thick peptidoglycan layer of Gram+ cells prevents loss of crystal violet during decolourization step
- Thinner peptidoglycan layer & larger pores of Gram- cells does not prevent loss of crystal violet.
49
What is the purpose of a simple stain?
- To determine size, shape and arrangement of cells.
50
What are the 3 reproduction strategies employed by Bacteria and Archaea?
1. Binary Fission
2. Budding
3. Filamentous Growth
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Are Bacteria and Archaea haploid or diploid?
Haploid
52
Is Prokaryotic reproduction asexual, sexual, or both?
Asexual
53
How does Binary Fission occur?
- A parent cell prepares for division by enlarging its cell wall, cell membrane and overall volume.
- Genome is replicated and 2 chromosomes move to opp ends of cell
- Septum begins to grow inward as chromosomes move toward opposite ends of the cell. Other cytoplasmic components are distributed to the 2 developing cells
- Septum synthesized completely through cell centre, and cell membrane patches itself so that there are 2 separate cell chambers.
- Daughter cells are divided. Some species separate completely, while others remain attached, forming chanson, doublets or other cellular arrangements.
54
What is the growth curve?
- Graph of the increase in cell number in population versus time
- Usually plotted as log of number of cells vs time
- Has 4 phases: lag, exponential, stationary, death
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Microbial Growth: Lag phase
- cells are synthesising new components
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Microbial Growth: Exponential (log) phase
- Rate of growth and division is constant and maximal
| - Cells exhibit balanced growth
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Microbial Growth: Stationary phase
- Closed-system population growth eventually ceases, and total number of viable cells remains constant
- Either active cells stop reproducing OR reproductive rate is balanced by cell death rate
- Possible reasons for the Stationary Phase:
a. Nutrient limitation
b. Limited oxygen availability
c. Toxic waste accumulation
d. Critical population density reached
58
Microbial Growth: Unbalanced growth
- Rates of synthesis of cell components vary relative to each other
- Occurs under a variety of conditions:
1. Change in nutrient levels (Shift up = poor to rich medium; Shift down = rich to poor medium)
2. Change in environmental conditions (pH, Temp etc.)
59
Ways to get a direct measurement of cell numbers
1. Direct cell count
2. Viable counting methods (spread-and-pour plate technique)
3. Measurement of cell mass
a. Dry weight (time consuming and not very sensitive)
b. Quantity of particular cell component (e.g. protein, DNA etc. ) - only useful if amount of substance in each cell is constant
c. Turbidimetric methods (based on light scattering by cells) - Often expressed as the optical density at a particular wavelength
60
What are autotrophs?
Use carbon dioxide as their sole or principal Carbon source
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What are prototrophs?
Require the same nutrients as most of the NATURALLY OCCURRING members of its species
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What are auxotrophs?
Prototrophs that have mutated and are no longe able to synthesise a molecule necessary for growth and reproduction
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What are growth factors?
- Essential cell components that the cell cannot synthesis
- All are organic compounds
- Must be supplied by the environment if the cell is the survive and reproduce
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What are the 3 classes of growth factors?
1. Amino acids (for protein synthesis)
2. Purine and pyrimidines (for nucleic acid synthesis)
3. Vitamins (function as enzyme cofactors)
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What are 3 common culture media components?
1. Peptones: protein hydrolysates prepared by partial digestion of various protein sources
2. Extracts: Aqeuous extracts, usually of beef or yeast
3. Agar: Sulphated polysaccharide used to solidify liquid media (most organisms cannot degrade it)
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Chemical and Physical types of culture media
1. Defined medium
| 2. Complex Medium
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What is a defined medium?
(synthetic medium) all component and their concentrations are known
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What is a minimal medium?
Special kind of defined medium containing minimal nutrients required for growth
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What is a complex medium?
Contains some ingredient of unknown composition and/or concentration
e.g. you might know it will give amino acids, but not which ones
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What are the 4 functional types of media?
1. General purpose
2. Enriched media
3. Selective media
4. Differential media
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What is a general purpose media?
Supports the growth of many types of microorganisms
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What is an enriched media?
- General purpose media supplemented by blood or other special nutrients
- Blood agar is used in medical microbiology
- Chocolate agar is a kind of blood agar. Blood cells are lysed by heating to 56 deg C before being added to agar.
o Alpha-haemolysis: blood cells aren’t lysed, but blood under colonies go green.
o Beta-haemolysis: produces haemolyses that go into agar under cells and hydrolyses blood creating an opaque ring around colony.
o Gama-haemolysis: non-haemolytic.
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What is a selective media?
- Favour the growth of some microorganisms and inhibit the growth of others
- MacConkey agar selects for Gram-negative bacteria by inhibiting the growth of Gram-positive bacteria.
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What is Differential Media?
- Distinguish between different groups of microorganisms based on their biological characteristics.
- Blood agar allows differentiation between haemolytic and non-haemolytic bacteria. Blood agar is both enriched and differential mediums.
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Influence of Temperature on Microbial growth
- Microbes cannot regulate their internal temp
- Enzymes have an optimal temp at which they function optimally
- High temps may inhibit enzymes functioning and be lethal to the cell
- 3 cardinal temperatures (minimal, maximal, optimal (always closer to maximal than minimal temperature)).
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What is an aerobe?
Microbe that grows in the presence of atmospheric O2 which is 20%
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What is an Obligate aerobe?
Microbe that requires O2
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What is an Anaerobe?
Microbe that grows in the absence of O2
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What is an Obligate Anaerobe?
Microbe that grows only in the absence of O2, usually killed by the presence of O2
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What is a Microaerophile?
Microbe that requires 2-10% O2
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What is a facultative anaerobe?
Aerobic but can switch to anaerobic if necessary
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What is a Aerotolerant anaerobe?
Grows with or without O2. They are ANAEROBES that aren't killed by O2
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Why can aerobes survive/thrive in O2 when anaerobes can't?
Aerobes produce protective enzymes (Catalase, Peroxidase, Superoxidase dismutase â)
84
What is numerical aperture?
The ability of a lens to gather light
85
What does the Abbe equation tell us?
The minimum resolvable distance between 2 objects is inversely proportional to the numerical aperture
