Prokaryote Structure Flashcards
All cells have the following in common:
Cytoplasmic membrane
Cytoplasm
Ribosomes
DNA chromosome
Viruses are…
Not considered cells• Composed, as a minimum, of protein coat and nucleic acid genome• No metabolic abilities of their own, some carry enzymes• Rely completely on biosynthetic machinery of infected cell• Infect nearly all types of cells• Smallest virus is 10 nm in diameter
Prokaryotic cells generally have a what kind of chromosome?
Single, circular DNA molecule: chromosome
DNA aggregates to form the
nucleoid region (not confined by membrane)
Prokaryotes also may have small amounts of extra-chromosomal DNA called
Plasmids
Coccus (pl. cocci):
spherical or ovoid
Rod:
cylindrical shape, aka bacillus (pl. bacilli)
Spirilla:
spiral shape
Size range for prokaryotes:
0.2 μm to > 700 μm in diameter
Size range for eukaryotic cells
10 to > 200 μm in diameter
Examples of large prokaryotes
sturgeon gut inhabitant
sulfur oxidizing chemolithotroph
There are advantages to being small:
Small cells contain more surface area relative to cell volume than large cells (i.e., higher S/V)
- support greater nutrient exchange per unit cell volume
- tend to grow faster than larger cells
Lower Limits of Cell Size
Cellular organisms < 0.15 μm in diameter are unlikely
Open oceans tend to contain small cells 0.2–0.4 μm dia. (maximize nutrient exchange
Many of these small cells also have small genomes (under 500,000 bp)
minimal existence
Intracellular pathogens also small with minimal genomes
ex:Prochlorococcus marinus
Cytoplasmic membrane: thin structure that surrounds the cell
6–8 nm thick
Vital barrier that separates cytoplasm from environment
Highly selective permeable barrier; enables concentration of specific metabolites and excretion of waste products
The Cytoplasmic Membrane in Bacteria
General structure is phospholipid bilayer
Contain both hydrophobic and hydrophilic components
Fatty acids point inward to form hydrophobic environment; hydrophilic portions remain exposed to external environment or the cytoplasm
What are key building blocks of membrane phospholipids in Bacteria and Archaea
Fatty acids(Bacteria and eukaryotes) and isoprene(Archaea)
? help stabilize membrane by forming ionic bonds with negative charges on the phospholipids
Mg and Ca
Phospholipids are amphipathic
The head region ? The tail region is ?
Head: contains highly polar covalent bonds
•Consists of glycerol, a phosphate, and a charged group(varies)
hydrophillic
Tail: hydrophobic: contains highly polar covalent bonds •Consists of a glycerol, a phosphate, and a charged group(varies)
Membrane-Strengthening Agents are
Sterols and Hopanoids
Sterols
Rigid, planar lipids found in eukaryotic membranes• Strengthen and stabilize membranes
Cholesterol
Hopanoids
Structurally similar to sterols• Present in membranes of many Bacteria
Archaeal Membranes have ? linkages
Ether
Bacteria and Eukarya that have ? linkages in phospholipids
Ester
Archaeal lipids lack ? , have isoprenes instead
fatty acids
diglycerol tetraethers is a
lipid monolayer and does not separate easily due to heat easily
Three major classes of transport systems in prokaryotes
Simple transport
Group translocation
ABC system
Simple transport uses
PMF
Group translocation uses
chemical modification driven by phosphoenolpyruvate
ABC system uses
ATP
The Phosphotransferase System in E. coli
AKA how E.coli eats sugar
Type of group translocation: substance transported is chemically modified during transport across the membrane
•Moves glucose, fructose, and mannose
•Five proteins required
•Energy derived from phosphoenolpyruvate (PEP!
)•The phosphoryl group on PEP is eventually transferred to the sugar after it passes through 4 proteins
•The resulting compound is larger and won’t easily move back across the membrane leading to a concentration gradient of sugar
ABC (ATP-Binding Cassette) Systems
200 different systems identified in prokaryotes
• Often involved in uptake of organic compounds (e.g., sugars, amino acids), inorganic nutrients (e.g., sulfate, phosphate), and trace metals
•Typically display high substrate specificity andaffinity
•Contain periplasmic binding proteins
Gram Negative Cell wall
at least 2 layers of cell wall
Gram + cell wall
thicker but only a single molecule type
Rigid layer that provides strength to cell wall in Bacteria
Peptidogylcan
Gram-Positive Cell Walls
Can contain up to 90% peptidoglycan
Common to have teichoic acidsembedded in their cell wall
•Teichoic acids impart negative charge to wall, help attract cations
•Lipoteichoicacids: teichoic acids covalently bound to membrane lipids
See diagram
Name Prokaryotes that Lack Cell Walls
Mycoplasmas
•Group of pathogenic bacteria
•Have cholesterol in membrane like Eukaryotes
The Outer Membrane of Gram-Negative Bacteria has what?
Total cell wall contains ~10% peptidoglycan
•Most of cell wall composed of outer membrane(aka Lipopolysaccharide[LPS] layer)
LPS consists of core polysaccharide and O-polysaccharide
LPS replaces most of the phospholipids in outer half of outer membrane
Endotoxin: the toxic component of LPS, attributed to lipid A
Porins:
channels for movement of hydrophilic low molecular-weight substances
Periplasm:
space located between cytoplasmic and outer membranes
• ~15 nm wide
• Contents have gel-like consistency
• Houses many proteins (hydrolytic, binding, chemoreceptors)
What are bacteria are responsible for differences in the Gram stain reaction?
Structural differences between cell walls of gram-positive and gram-negative
? dehydrates the peptidoglycan
Alcohol
Become impermeable to the crystal violet
gram +
cells are washed free of crystal violet
gram -
Cell Walls of Archaea
No peptidoglycan
•Typically no outer membrane
•Somehave Pseudomurein:
•Found in cell walls of certain methanogenic Archaea
•Polysaccharide similar to peptidoglycan
•Composed of N-acetylglucosamine and N-acetylalosaminuronic acid
S-Layers:
found in other Archaea
• “Paracrystalline surface layer”
• Most common cell wall type among Archaea
• Consist of protein or glycoprotein
Cell Surface Layers: Capsules and Slime Layers
Polysaccharide layers
•Assist in attachment to surfaces
•Aid in evasion of immune system
•Resist dessication
•Capsule tighter matrix, often bonded to cell wall
•Slime layer loose, less connected to cell
Pili
Filamentous protein structures
• Typically longer than fimbriae
• Assist in surface attachment
•Facilitate genetic exchange between cells (conjugation)
• Pili involved in twitching motility and colonization in Vibrio cholerae
Fimbriae
Filamentous protein structures
• Enable organisms to stick to surfaces or form pellicles
Endospores
Highly differentiated cells resistant to heat, harsh chemicals, and radiation
• “Dormant” stage of bacterial life cycle
• Ideal for dispersal via wind, water, or animal gut
• Only present in some gram-positivebacteria
• Most studied in Clostridium and Bacillusspecies
Endospore Structure
•Resistant to dyes
•Special stains like malachite green
•Characteristic component is dipicolinic acid •
Also enriched in Ca2+
•Dehydrated core, gives high heat tolerance
•Small acid soluble proteins complex with DNA; stabilize, condense and protect
Flagella:
structure that assists in swimming • Different arrangements: peritrichous, polar, lophotrichous • Helical in shape • Filament composed of flagellin • Move by rotation
flagellated cells move more rapidly and typically spin around
polarly
What type of flagellated cells move slowly in a straight line
Peritrichously
Taxis
directed movement in response to chemical or physical gradients
Nutrients
Supply of monomers (or precursors of) required by cells for growth
Macronutrients
Nutrients required in large amounts
Essential elements
CHNOPS Se
Autotrophs
Heterotrophs
inorganic
organic
