Lecture Quiz #1 Flashcards
Bacteria are ________, whereas fungi, protozoa, parasites are _________.
prokaryotes; eukaryotes
What structures and organelles do bacteria have?
- Bacteria do not have internal membrane-bound organelles
- Bacteria have no sophisticated internal structures: no nuclear membrane, no mitochondria, no Golgi, no endoplasmic reticulum
List and describe the 6 common shapes of bacteria
Cocci: round Coccobacilli: two cocci attached to each other Curved: horseshoe shaped Diplococci: two cocci next to each other Bacilli: rod-shaped Spiral: wavy-shaped
Define morphology
The form and structure of an organism or group of identical organisms
What do you need to know about a bacteria cell to identify its morphology?
What stage of growth a bacteria is in
Patterns of groups of identical bacteria are reflective of what?
cell division/ binary fission
Define pleomorphic
Each cell of a species has a slightly different shape when it divides
Describe aggregation properties
- Determined by the orientation of the cell division plane to the axis of the cell and the tendency of progeny cells to adhere to one another
- Can be characteristic of a species
What functions do structures from the cytoplasmic (inner) membrane and outward perform?
1) Protection from the external environment (includes host defense)
2) Permeability barrier for selective transport of nutrients and information
3) Control over physical location (ex: through flagella)
What does an environment primarily see first about a bacteria? Why?
Structures, because they are both external and unique (or foreign)
What do bacterial structures allow for humans to do?
Structures are often important antigens, so they can be used as vaccine targets and in diagnostics and epidemiology
Bacterial structures and their composition often reflect what?
Adaptations to the environment
Cell surface _______ can be targets for antibiotics
Cell surface _______ can be a barrier to antibiotics
structures; properties
What do bacterial cells use external structures for?
1) Cell surface structures often used to attach to and invade host cells and “sense” their environment to appropriately express virulence factors
2) Certain structures are not necessarily essential for viability, but are often important in pathogenesis as virulence factors
True or false: Structures are not expressed at all times and may be lost during continuous culture in laboratory media
True
Define peptidoglycan (murein)
One of the key components of bacteria that makes up cell wall and is the basis for a Gram stain reaction
The cell membrane of a bacteria is called the _______ membrane
cytosolic
List the 4 characteristics of peptidoglycan
1) Key contributor in overall shape of bacteria
2) Crucial for osmotic stability
3) Unique structure found only in bacteria
4) Makes a good target for antimicrobial agents (since it’s unique to bacteria and crucial to their survival)
Define lipopolysaccharide
An endotoxic structure found in the outer membrane (of the cytosolic membrane) of gram-negative bacteria.
How can you tell lipoteichoic acid and teichoic acid apart?
Lipoteichoic acid has a connection down to the cell membrane, whereas teichoic acid is only on the surface of the cell wall.
Lipoteichoic acids and teichoic acids are only found in gram-_______ bacteria
positive
Describe the characteristics of a gram-negative cell envelope
1) Inner membrane: symmetrical bilayer of phospholipids
2) Periplasm: sandwiched between IM and OM / gel-like matrix
3) Outer membrane: asymmetrical bilayer of lipids; serves as a selective permeability barrier that is virtually impermeable to hydrophilic solutes
4) Phospholipids in the inner leaflet and LPS in outer leaflet
How does the difference between gram-positive and gram-negative bacteria affect treatment plans for patients?
Since gram-negative bacteria’s outer membranes are virtually impenetrable to hydrophilic solutes, it affects which antibiotics are used in treatment
Define porins
Channel-forming proteins for the purpose of allowing
influx of nutrients and extrusion of waste products
True or false: The fluid mosaic model applies to the lipid bilayer of bacteria
True
Define a phospholipid
Has a head group and long hydrophobic fatty acid chains
Describe the importance of phospholipids to bacteria
- There’s a lot of diversity in just phospholipids; there are numerous fatty acids that can make up the fatty acid chains.
- Can vary in saturation (triple bonds, double bonds, single bonds, etc), length, cis/trans bond confirmations, isomerase, branched fatty acids, anteiso, and modification with OH groups
- Aids in membrane homeostasis (particularly with environmental changes like pH, salinity, oxygen, pressure, temperature, etc)
If a bacteria needed to change an element of itself to avoid lyseing due to environmental changes, what element would that be?
The fatty acids of phospholipids
Define a cell wall and describe where they can and can’t be found
- Defined as a semirigid structure surrounding the cytoplasmic membrane enabling the cell to resist bursting from osmotic pressure
- Found only in true Eubacteria, not found in Mycoplasmas
True or false: the cell membranes of bacteria are porous
True, so nutrients/ metabolites can actively diffuse to the plasma membrane
What is the main component of a bacteria’s cell wall?
Peptidoglycan (murein)
Describe what peptidoglycan (murein) is composed of
- Consist of a polymer of sugars and amino acids that forms a mesh-like layer located outside the cytoplasmic membrane
- Carbohydrate portion consists of alternating residues of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
- A peptide chain (3-5 amino acids) is attached to N-acetylmuramic acid
- Contains cross-linking bridges
How does the peptidoglycan of bacterial cell walls undergo degredation?
Undergoes degradation and remodeling through autolysins that introduce controlled breaks for growth/division
Describe the importance of peptidoglycans for immune response
- Peptidoglycan is conserved microbial structure that is immunogenic; recognized by the Nod proteins (innate immune response)
- Bacteria incorporate D-amino acids (unlike humans’ L-amino acids), so we know to attack it
Peptidases only recognize the ______ of amino acid residues
L-isomers
Are the peptides found in peptidoglycan produced ribosomally or enzymatically?
Enzymatically
There are _______ layers of peptidoglycan in Gram-positive organisms and _______ layers of peptidoglycan in Gram-negatives
20-40; 1-2
What increases the structural integrity of bacterial cell walls?
Peptidoglycan subunits are cross-linked between the peptides
Describe the difference in the cross-linkage of peptidoglycan subunits in Gram-positive and Gram-negative cells
Gram negative: DAP to D-Ala via direct attachment
Gram positive: Glycine linker (D-Ala to L-Lys)
Describe how lysozymes damage bacterial cells, and where lysozymes are found
- An enzyme that damages the cell wall of bacteria by catalyzing hydrolysis of the 1,4-beta-linkages between NAG and NAM residues in peptidoglycan
- Defense of the innate immune response: lysozyme is present in various secretions including tears, saliva, and mucus.
Describe Transpeptidation/ Carboxypeptidase reactions
- Penicillin-binding proteins (PBPs) are the targets for penicillin and other β-lactam antibiotics
- Penicillin and related β-lactam antibiotics resembles the ‘transition state’ conformation of the D-Ala-D-Ala substrate when bound to these enzymes.
- Basically they make bacteria divert their resources so they can’t make peptidoglycan (as fast), so our body can catch up and kill the bacteria
Describe how the rigid cell wall of bacteria grows
- Peptidoglycan is constantly being synthesized and degraded.
- Autolysins (murein hydrolases) are used to aid in cell wall growth
- A group of enzymes that exist in all bacteria contains peptidoglycan and can break down the peptidoglycan chains in small sections to allow for growth and cell divisions
- Like lysozymes, they cleave the β-1,4 linkages in the glycan chain
- The process must be regulated as to not allow osmotic rupture of the cell
Describe teichoic and lipoteichoic acids
- Defined as polymers of chemically modified ribose or glycerol
- Only found in Gram-positive bacteria and are connected by phosphate groups (ester linkage)
- May be covalently modified with sugars, choline, or D-alanine groups that serve as antigenic determinants
Teichoic and lipoteichoic acids are only found in Gram-________ bacteria
positive