Chapter 3: Introduction to Prokaryotic Cells

Approximately when did life on Earth originate as prokaryotic cells?

about 3.8 billion years ago

What are the two domains of prokaryotes>

bacteria and archaea

Prokaryote

a unicellular organism that lacks a membrane-bound nucleus and membrane-bound organelles

What is the typical diameter of most prokaryotes?

0.5-2 µm

What is the smallest bacterium?

mycoplasma

What is the largest bacterium?

thiomargarita namibiensis

Why does diffusion-based nutrient uptake limit prokaryotic cell size?

because of the surface area-to-volume ratio

Monomorphic

bacteria that maintain a single, consistent shape

Pleomorphic

bacteria that can alter their shape, enhancing survival and transmission within a host

Bacilli

rod-shaped cells

Cocci

spherical cells

Vibrio

comma-shaped cells

Coccobacilli

oviod/oval-shaped cells

Spirochetes

spiral-shaped cells with a flexible, corkscrew movement

Stella (stellate)

star-shaped cells

Diplo-

paired cells

Srepto-

chains of cells

Staphylo-

grapelike clusters of cells

Palisade

clusters of bacilli aligned side by side

How do prokaryotes reproduce?

asexually, through binary fission

What are the four steps of binary fission, in order?

1. circular DNA is replicated

2. the cell elongates

3. a septum begins forming at the midpoint

4. the septum fully partitions the cell

Fluid-mosaic model

membrane lipids and proteins move fluidly within the bilayer

What increase membrane fluidity?

warmer temperatures or higher levels of unsaturated fatty acids

What does binary fission produce?

two genetically identical daughter cells

Plasma membrane

a thin, flexible phospholipid bilayer that acts as a selective barrier between the cytoplasm and the extracellular environment

What effect do saturated fatty acids have on the membrane?

they make it more rigid

What are bacterial membranes made of?

linear fatty acid chains linked to glycerol by ester bonds, in a bilayer

What are archaeal membranes made of?

long, branched isoprenoid chains linked to glycerol by ether bonds

What can extreme-heat archaea form in their membranes?

rigid lipid monolayers

Does passive transport require ATP?

NO

Simple diffusion

direct movement of small, noncharged molecules, gases, and lipid-soluble substances down their concentration gradient

Faciliated diffusion

movement of larger or charged substances along their concentration gradient using channel or carrier proteins

Osmosis

diffusion of water across a membrane from low solute concentration to high solute concentration

Isotonic solution

solute concentrations inside and outside the cell are equal; no net water movement

Hypertonic solution

higher solute concentration outside the cell; water leaves the cell

Hypotonic solution

lower solute concentration outside the cell; water enters the cells, causing swelling

What can happen to a cell in a hypotonic solution if its cell wall is damaged?

osmotic lysis

Primary active transport

uses direct ATP hydrolysis to move substances against their concentration gradient

Secondary active transport

uses an existing ion gradient to drive transport

Symport

ion and solute move in the SAME direction

Antiport

ion and solute move in opposite directions

Group translocation

chemical modification of the transported substance, driven by high-energy substrates like phosphoenolpyruvate

What is the function of the cell wall?

provides structural rigidity and protects against osmotic stress

Peptidoglycan

the primary component of bacterial cell walls; alternating NAG and NAM sugar chains cross-linked by short peptides

What do NAG and NAM stand for?

N-acetylglucosamine and N-acetylmuramic acid

How is the peptidoglycan layer in gram-positive bacteria?

thick

How is the peptidoglycan layer in gram-negative bacteria, and where is it?

thin, within a periplasmic space

Which gram type has an outer membrane?

gram-negative

What does the gram-negative, outer membrane contain?

porins and lipopolysaccharide (LPS)

What does LPS contain?

lipid A

Which gram type contains teichoic acids?

gram-positive

What color do gram-positive and gram-negative bacteria stain?

gram-positive: purple

gram-negative: pink/red

Which gram type is highly susceptible to penicillin and anionic detergents?

gram-positive

Which gram type is highly resistant to physical drying?

gram-positive

Mycoplasma

bacteria that completely lack a cell wall; their sterol-enriched plasma membrane resists lysis

L-forms

bacteria that once had a cell wall but lost it; contribute to persistent infection and antibiotic resistance

Flagella

filaments of flagellin protein that spin like a propellor for motility

How many rings anchor flagella in gram-positive vs. gram-negative bacteria?

gram-positive: 2 rings

gram-negative: 4 rings

Monotrichous

a single flagellum

Lophotrichous

a tuft of flagella at oen pole

Amphitrichous

flagella at both poles

Peritrichous

flagella distributed over the entire cells

What movement system do flagellated bacteria use?

run and tumble

Chemotaxis

movement in response to chemicals

Phototaxis

movement in response to light

Aerotaxis

movement in response to oxygen

Periplasmic flagella

flagella in the periplasmic space of spirochetes that allow corkscrew movement

Fimbriae

short, bristle -like protein fibers that aid surface adherence and biofilm establishment

Pili

longer, less numerous protein tubes used for surface adhesion, twitching movement, and DNA transfer via conjugating

How do pili differ form fimbriae in length and number?

pili are longer and less numerous

Glycocalyx

a sticky carbohydrate layer that protects against desiccation and disinfectants

Slime layer

a loose, unorganized glycocalyx

Capsule

a well-organized, tightly bound glycocalyx that shields pathogens from immune detection

Nucleoid

the centralized region containing the single, circular, double-stranded DNA chromosome

Ribosomes

structures made of RNA and protein that carry out protein synthesis

What are the subunits of prokaryotic 70S rubosome?

a 50S large subunit and a 30S small subunit

Cytoskeleton

a filamentous protein network that gives the cell shape, coordinates division, and directs intraceullar transport

Inclusion bodies

storage granules that preserve excess nutrients

Endospores

metabolically inactive, highly resistant dormant structures formed during sporulation when conditions are harsh

What are endospores resistant to?

heat, drying, freezing, radiation, and chemicals

What happens to endospores under favorable conditions?

they germinate back into active vegetative cells

Name the key spore-forming genera?

bacillus and clostridium/clostridiodes