Ch. 1 Flashcards
What are the differences between eukaryotes and prokaryotes?
- Eukaryotes have a membrane-bound nucleus and organelles
- Eukaryotes have linear DNA vs. prokaryotes have circular DNA
- Eukaryotes have multiple chromosomes while prokaryotes only have one
- Eukaryotes don’t have plasmids
- Eukaryotes have 80S ribosomes vs. prokaryotes have 70S ribosomes
What are the differences between bacteria and archaea?
- Membrane lipids of bacteria are fatty acids, esterlinked to glycerol vs. archaea are methyl-branched, isoprenoid alcohols, etherlinked to glycerol
- Archaea don’t have peptidoglycan
- Archaea have histones that resemble eukaryotic histones
- Archaeal RNA polymerase has 8-10 subunits, whereas bacterial RNA polymerase has 4 subunits, and are not sensitive to rifampin
- Some protein components of the archaeal protein synthesis machinery differ from the bacterial one
What are the similarities between archaea and eukarya?
- Have similar histones
- Similar genes/metabolic pathways
Give an overview of the structure of prokaryotes.
- Don’t have membrane-bound organelles
- Plasma membrane
- Gas vacuole
- Inclusions
- Nucleoid (like nucleus minus the membrane)
- Periplasmic space
- Cell wall
- Capsules and slime layers
- Fimbriae/pili
- Flagella
- Endospore
What is the importance of appendages on bacteria?
Motility (flagella) and adhesion (pili)
What are the two main classes of appendages?
- Flagella
- Pili
What is function of flagella?
Swimming in liquid and swarming (swimming on moist solid surfaces)
Describe the structure of flagella.
- Basal body
- Embedded in CM and surface
- 3 rings
- Motor complex rotates - Hook
- Connects basal body and filament
- Hook protein - Filament
- Made of single protein (flagellin)
- Tube shaped
- Growing tip
What is the function of fimbriae/pili?
- Help stick to surfaces
- Not usually involved in motility
- important for colonization in natural habitats
- Have adhesins at the tip –> can recognize and bind specific receptors
What is the medical significance of pili?
Attachment to host cells plays a key role in causing infection
- Ex. V. cholerae: mutants without Tcp pili don’t cause disease, therefore, pili of different types are specialized for attachment to specific receptors and can account for specificity of bacterial attachment to host and tissues
What is the glycocalyx?
All extracellular material that is external to the cell wall
- Made up of polysaccharides and/or proteins
- Surround bacteria in natural habitats
What are the 3 components of the glycocalyx?
- S layers
- Capsules (tightly integrated with cell)
- Slime layers (glycocalyx loosely associated with cell; can diffuse into medium)
What is the S layer?
Protein or glycoprotein layer found on the surface of prokaryotes
- Except mycoplasmas
- Can be lost in laboratory strains
What is the composition of the S layer?
- Repeating subunits of S layer proteins with attached carbohydrate moiety
- Form lattice structures
What are the functions of the glycocalyx?
- Adhesion and colonization - biofilm formation
- Protection from phagocytosis
- Prevention of dessication
What are the two major types of bacterial cell walls?
Gram-positive and gram-negative
What is the function of the cell wall?
To protect the cell from bursting from internal turgor pressure
Why does turgor pressure exist?
The turgor pressure exists because the bacteria generally live in environments that are more dilute than the cytoplasm
What is the main component of cell walls?
Peptidoglycan
What are the differences between gram-positive and gram-negative cell walls?
Gram-positive:
- Thick
- No OM, thicker CW
- Contains peptidoglycan, teichoic acid, lipoteichoic acid
Gram-negative:
- Structurally and chemically complex
- Outer membrane composed of LPS, phospholipid, protein, underlying peptidoglycan layer
- Periplasm between outer and inner membrane, where peptidoglycan lies
Describe peptidoglycan.
- Polymer
- Backbone: B-1,4-linked N-acetylglucosamine (NAG) and N-acetylmuramate (NAM)
- Lactyl group links the tetrapeptides
Draw the basic unit of peptidoglycan in E. coli.
Explain the cross-linking of peptidoglycan.
- Degree depends on species
- Low at growing tip of single cell
- Hydrolyzing enzymes break apart to enable growth
What do gram-positive cell walls contain?
- Peptidoglycan
- Teichoic acid
- Lipoteichoic acid
What are teichoic acids?
Polymers of glycerol or ribitol joined by phosphate groups
- Some are covalently linked to peptidoglycan
- Others are covalently connected to the plasma membrane (lipoteichoic acids)
What effect do teichoic acids have on the cell wall?
Negatively charged - help give the cell wall its negative charge
What are lipoteichoic acids?
LInear polymers of phosphodiester-linked glycerol phosphate covalently bound to lipid
What are gram-negative cell walls composed of?
- Outer membrane
- Thin peptidoglycan layer within perimplasm
What are the benefits of having a gram-negative cell wall?
More resistant to lysozyme, hydrolytic enzymes, surfactants, bile salts, and hydrophobic antibiotics
What are the functions of a gram-negative cell wall?
- Permeability barrier
- Pathogenesis/virulence
What are the components of the outer membrane?
- LPS - outer leaflet
- Phospholipids - inner leaflet
- Lipoprotein - stabilization
- OM protein A - maintain stabilization, receptor for amino acids/peptides
- Porin - channels for hydrophilic solutes
- Receptor proteins
- Other proteins
What are the 3 components of lipopolysaccharide?
- Lipid A
- Core polysaccharide
- O-antigen
Draw the structure of LPS.
What is the function of the O-antigen?
- Pathogenesis/phage recognition
- Varies with growth conditions
What is the function of lipoproteins?
Stabilizes the OM
What is the function of porins?
Size specificity
What is the function of receptors in the outer membrane?
Passage of larger molecules
What is the function of OmpA?
- Receptor for amino acids and peptides
- F-pili
Describe archaeal cell walls.
- Don’t contain peptidoglycan
- May be pseudopeptidoglycan (NAG-NAT, B-1,3 linkage, L-amino acids
- S layer (proteins)
- Polysaccharide
What is the periplasm?
Separate compartment between the cell membrane and outer membrane of gram-negative bacteria
- Gel state
What does the periplasm contain?
- Peptidoglycan
- Oligosaccharides
- Proteins (sensor proteins, enzymes, transporters, solute-binding proteins, ETC proteins, hydrolytic enzymes)
What is the cell membrane?
Selectively permeable barrier that allows particular ions and molecules to pass into/out of the cell while preventing the movement of others
What metabolic/biologic functions occur in the bacterial cell membrane?
- Solute transport
- Respiration
- Photosynthesis
- Maintenance of gradients
- ATP synthesis
- Signal transduction
- Synthesis of lipids and cell wall constituents
- Protein secretion
- Motility
Describe the bacterial cell membrane.
- Made up of phospholipids and proteins - fluid mosaic model
- Proteins may form aggregates in membranes - interact to catalyze sequential reactions
- Amphipathic (hydrophilic head, hydrophobic tails
- Mixed with water: form micelles spontaneously; bilayers form liposomes spontaneously
What are the two classes of bacterial cell membranes?
- Integral
- Hydrophoic surface
- Removed with detergents - Peripheral
- Attached by ionic interactions
- Removed with salt solutions
How do archaeal cell membranes differ from bacterial cell membranes?
- Instead of fatty acids –> long chain alcohols (isopranyl alcohol)
- Linkage to glycerol is via ether (not ester)
What is the function of archaeal cell membranes?
Ether linkage more stable to hydrolytic cleavage in acidic environments
What is the importance of phopholipid monolayers in archaeal cell membranes?
- Some archaea have polar head groups at both ends –> span the membrane
- Important for membrane stability at high temperatures
What is the cytoplasm?
Everything inside the cytoplasmic membrane
- Many metabolic processes occur here
- Lack membrane-bound organelles and compartmentalization
What is the intracytoplasmic membrane?
- Usually connected to cell membrane
- Found in methanotrophs, nitrogen fixers, nitrifiers, phototrophs
What is cytosol and what does it contain?
- LIquid portion of the cytoplasm
- Contains enzymes for metabolic pathways, DNA, ribosomes
