Chapter 3 and 4: Bacteria and Archaea cell structure

MCB 3020C

prokaryotes

bacteria and archaea

• lack a nucleus and do not have membrane-bound organelles or an endomembrane system

what is this cell shape called?

rods (bacilli)

• some short and wide that they appear to be ovals (coccobacilli)

• most rods occur singly but some for pairs or chains

what is this cell shaped called?

spheres (cocci)

• during reproduction, some cocci remain attached to each other to form pairs (diplococci), chains, clusters, square planar configurations (tetrads), or cubic configurations

describe the structure and function of the: glycocalyx

sugar coat that surrounds the cells

describe the structure and function of the: flagella

filamentous appendage to give motility

describe the structure and function of the: axial filaments

• bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell

• produces a movement for spirochetes

describe the structure and function of the: fimbriae

they allow a cell to adhere to surfaces

describe the structure and function of the: pili

longer than fimbriae and help with DNA transfer

glycocalyx

• external to the cell wall

• viscous and gelatinous

• made of polysaccharide and/or polypeptide

• two types:

  • capsule

  • slime layer

• contribute to virulence

capsule: glycocalyx

neatly organized and firmly attached

slime layer: glycocalyx

unorganized and loose = sticks along together

how does glycocalyx contribute to virulence (envade and exist inside host cells)

• capsules prevent phagocytosis

• extracellular polymeric substance helps form biofilms

flagella

• filamentous appendages external of the cell

• propel bacteria

• made of protein flagellin

• three parts:

  • filament

  • hook

  • basal body

filament of flagella

outermost region

hook of flagella

attaches to the filament

basal body of flagella

• consists of rod and pairs of rings

• anchors flagellum to the cell wall and membrane

arrangements of bacterial flagella

• peritrichous: all over

• monotrichous and polar: one

• lophotrichous and polar: multiple on one side and curve

• amphitrichous and polar: both sides and spiral

purpose of flagella

• allow bacteria to move toward or away from stimuli

• allows bacteria to rotate to run or tumble

• proteins are H antigens and distinguish among serovars

serovars

same subspecies distinguished by antigen properties

motility in prokaryotes

• responses are made to temperature, light, oxygen, osmotic pressure and gravity

• flagella rotate or create motion to help run and tumble

  • basal body is the motor that drives the flagellum powered by a proton motive force

archaeal flagella

rotate in both direction, run and tumble movement not observed

chemotaxis

directed movement of bacteria either toward a chemical attractant or away from a chemical repellent

chemotaxis in prokaryotes

• concentrations of attractant and repellents are detected by chemoreceptors in the periplasmic space or plasma membrane

• directional travel toward a chemoattractant is caused by lowering the frequency of tumbles = lengthening the runs when traveling up the gradient, but allowing tumbling to occur at normal when traveling down the gradient

  • directional travel away from chemorepellent involves similar but opposite responses

flagella and bacterial motility

run → tumble → run → tumble → tumble → run → run

axial filaments

• endoflagella

• found in spirochetes (spirals)

• anchored at one end of a cell

• rotation causes cells to move like a corkscrew

• wrapped around the outer of the spirochete

fimbriae

• hair like appendages that allow for attachment

• cells connect and allow for growth and reproduction

pili

• gliding and twitching motility

• conjugation pili involved in DNA transfer from one cell to another

fimbriae: lab relevance

• attachment of bacteria to other cells

• mostly found in gram negative

• lab strains tend to lose the feature during subculturing

fimbriae: medical relevance

• attachement to erythrocytes, causing clumping

• attachment of neisseria gonorrhoeae in the urogenital tract (cilia attach to the tract’s walls)

• bind to oligosaccharides in the endothelial cell surface receptor

  • increases host cell specificity

• inhibit oligosaccharides in vitro by attachment of bacteria with fimbriae to epithelial cells

use of cranberry juice

• a-type proanthocyanidins isolated from cranberry juice and d-mannose demonstrated an anti-adhesion activity against E. coli binding to urinary tract epithelial cells

• concentration of E.coli will affect the anti-adhesion effects along with metabolism

bacillus magaterium

collects magnetites (magnets) in high-density areas

structures of a prokaryotic cell

• cell wall

• periplasmic space

• plasma membrane

• nucleoid

• ribosomes

• inclusion bodies

• flagella

• capsules

• slime layers

cell organization of a prokaryotic cell

• morphologically simpler than eukaryotic cells

• bacteria and archaea are surrounded by a cell envelope with complex cell walls

plasma membrane

• selectively permeable barrier

• mechanical boundary of cell

• nutrient and waste transport

• location of many metabolic processes (like respiration and photosynthesis)

• detection of environmental cues for chemotaxis

gas vacuole

buoyancy for floating in aquatic environments

• not all, only aquatic envrionment

ribosomes

• protein synthesis (translation)

• complex structure with protein and rRNA

• prokaryotes are 70S with 50S and 30S subunits

inclusions

• granules of organic or inorganic material for future use:

  • carbon (glycogen and poly b-hydroxybutyrate)

  • phosphorus (polyphosphate granules)

  • wastes (sulfur globules)

  • cyanophycin granules (nitrogen in cyanobacteria)

• contains:

  • carboxysomes

  • gas vacuoles

  • magnetosomes

nucleoid

• localization of genetic material (DNA)

• irregularly shaped region where the chromosome of the prokaryote is found

• a single circular chromosome and is not membrane bound

• DNA molecule is looped and supercoiled extensively with histone like proteins

periplasmic space

• gram negative bacteria

  • hydrolytic enzymes and binding proteins for nutrient processing and uptake

• gram positive bacteria or archaeal cells

  • smaller or absent

cell wall

provides shape and protection from osmotic stress (structure)

capsules and slime layers

• known as glycocalyx = layers of polysaccharides lying outside the cell wall

• resistance to phagocytosis, desiccation, viral infection and hydrophobic toxic materials

• adhere to surfaces and gliding motility

• rare in archaea

• capsules: well organized

• slime layers: diffuse and unorganized

fimbriae and pili

• attachment to surfaces

• bacterial conjugation and transformation

• twitching and gliding motility

flagella

swimming motility

endospore

• resistant, dormant structure that enables them to survive under harsh environmental conditions

• sporulation

• transformation process from dormant endospore into active vegetative cells is a complex, multistage process:

  • preparation: activation of the endospore

  • germination: breaking of the endospore’s dormant state

  • outgrowth: emergence of the new vegetative cell

• only observed in bacteria

bacterial cell envelope

• retains the cytoplasm and separates the cell from the environment

• selective permeable barrier

• contains transport systems (nutrient uptake, waste excretion, protein secretion)

• site of metabolic processes (respiration, photosynthesis, lipid synthesis, cell wall synthesis)

fluid mosaic model

• lipid bilayers with floating proteins

• cell membranes are thin

• lipids are amphipathic

  • hydrophilic heads (face outside)

  • hydrophobic tails (face inside)

• two types of proteins:

  • peripheral (loosely associated and easily removed)

  • internal (embedded within the membrane and not easily removed)

bacterial cell walls

• rigid structure gives shape

• protects from osmotic lysis, toxins, and increases pathogenicity

• contains peptidoglycan

• alternating NAG and NAM moieties (attachment zones are where the activity is)

peptidoglycan

linear helical polysaccharide chain polymer composed of two sugar derivatives with peptide linkers

gram positive bacteria

• thick peptidoglycan with many layers and large amounts of teichoic acids

• s-layer proteins on the outer surface that aide in cell wall synthesis and virulence

• acid fast bacteria have mycolic acids in their cell walls

gram negative bacteria

• thin peptidoglycan and outer membrane

• more complex

• periplasmic space is wide and contains many different proteins

• outer membrane is composed of lipids, lipoproteins and lipopolysaccharides

techoic acids

polymers with a glycerol and phosphate backbone that span the cell wall and enhance structural stability

lipopolysaccharides

• large complex molecules composed of lipid A, core polysaccharides, and O antigen carbohydrate side chain

• stabilize the outer membrane, protect against some toxins, and cause strong host immunological responses = like an endotoxin

outside the cell wall: S-layers

• structured layers of protein or glycoprotein

• protect against ion and pH fluctuations, osmotic stress, and hydrolytic enzymes

• maintain cell shape and envelope rigidity, promote cell adhesion, and protect against host defenses

archaeal cell envelopes

• plasma membrane

• lipids have branched hydrocarbons attached to glycerol by ether links

• seen in bacteria and eukaryotes

• smaller membrane layers are due to environmental harsh conditions

archaeal cell wall

• archaea can stain Gram+ or Gram -, but their cell wall structure differs more than bacteria

• S-layer is the most common cell wall made up of protein/glycoprotein

• protein layers or chondroitin-like materials found outside s-layer

• pseudomurein between plasma membrane and s-layer

  • amino acids in its cross links

• uses N-acetyltalosaminuronic acid

bacterial flagella

• extends outward from plasma membrane and cell wall

• hollow filament, single flagellin

• hook is short, curved segment = links filament to the basal body with rings that drives rotation

• powered by proton motive force

archaeal flagella

• thinner

• more than one type of flagellin subunit

• not hollow, unique hook and basal body analogs

• powered by ATP hydrolysis

carboxysomes

microcompartments that accumulate CO2 and enzyme ribulose-1,5-biophosophate carboxylase

magnetosomes

magnetite granules that provide orientation in the earth’s magnetic field

plasmids

• small circular DNA molecules

• their own replication origins, replicate autonomously and are stably inherited

  • episomes

  • conjugative plasmids

  • resistance plasmids

episomes

plasmids that can exist either with/out being integrated into the host chromosome

conjugative plasmids (F plasmids)

episomes that usually have genes for sex pili and can transfer copies of themselves to other bacteria during conjugation

resistance plasmids (R plasmids)

• genes for resistance to various antibiotics

• R factors can be transferred to other cells even across species lines = spreading antibiotic resistance

sporulation

process is initiated when growth ceases due to a lack of nutrients or a change in the environment

properties of bacteria

• circular chromosome

• plasmids

• introns are rare

• ester linked phospholipids and hopanoids

  • some have sterols

• flagella is submicroscopic in size, composed of one protein fiber

• peptidoglycan in cell walls

• ribosome is 70S in size

• rudimentary cytoskeleton

• gas vesicles

properties of archaea

• some DNA complexed with histones

• one circular chromosome

• plasmids are very common

• introns are rare in genes

• glycerol diethers and diglycerol tetraethers

• flagella is submicroscopic in size, composed of a fiber made from multiple different flagellin proteins

• no peptidoglycan in cell walls

• ribosome is 70S in size

• rudimentary cytoskeleton

• gas vesicles

properties of eukarya

• true membrane-bound nucleus

• DNA complex with histones

• more than one chromosome, chromosomes are linear

• plasmids are rare

• introns in genes

• nucleolus

• mitochondria

• chloroplasts

• ester-linked phospholipids and sterols

• flagella microscopic in size, membrane bound, usually 20 microtubules in 9 + 2 pattern

• endoplasmic reticulum

• golgi apparatus

• no peptidoglycan in cell walls

• ribosome 80S in size

• lysosomes

• cytoskeleton

• no gas vesicles

prokaryotic cell’s size

vary in size, generally 1 to 5 um

nanobacteria’s size

0.2 um to less than 0.05 um in diameter

prokaryotes in size

up to 750 um in diameter

why smaller cells have higher surface/volume ratio?

• small size provides advantages, greater s/v ratios

  • have higher s/v ratio = better nutrient uptake and diffusion

• large size provides resistance to predation

  • have a smaller s/v ratio = increase their s/v ratio by having convoluted plasma membranes (increase in surface)