Prokaryote

Cell Theory

1) Cells are the fundamental units of life. 2) All living organisms are composed of cells. 3) All cells come from preexisting cells. 4) Cells evolved from a common ancestral cell(s).

Smallest/Fundamental unit of life

The cell.

Limiting principle of cell size

As a cell gets larger, its surface-area-to-volume ratio decreases, making nutrient and waste exchange less efficient.

Effect of cell radius increase on surface area and volume

Surface area increases, but volume increases faster; surface-area-to-volume ratio decreases.

High-size limit of a cell

The cell becomes too large to exchange materials efficiently across its plasma membrane.

Low-size limit of a cell

A cell must contain the minimum machinery needed for life, including genetic material and essential cellular components.

Size ranges for prokaryotic vs. eukaryotic cells

Prokaryotic cells ≈ 1–10 µm; eukaryotic cells ≈ 5–100 µm.

Microscopy approaches

Bright-field microscopy, phase-contrast microscopy, DIC microscopy, stained bright-field microscopy, fluorescence microscopy, confocal microscopy.

Bright-field microscopy

A method where light passes directly through the specimen; unstained samples may have low contrast.

Phase-contrast microscopy

Converts light phase differences caused by cell structures into differences in brightness/contrast for visibility.

Differential interference contrast (DIC) microscopy

Uses polarized light interference to create strong contrast based on optical path length differences.

Fluorescence microscopy

A technique where fluorescent molecules emit light to visualize specific cellular structures.

Confocal microscopy

Uses fluorescence and optical sectioning to reduce out-of-focus light, allowing clearer images at different depths.

Defining structural difference between prokaryotic and eukaryotic cells

Prokaryotes lack membrane-enclosed compartments; eukaryotic cells contain membrane-bound organelles.

Domains containing prokaryotes

Bacteria and Archaea.

Major groups that are eukaryotic

Protists, plants, fungi, and animals.

Shared components of all cells

Plasma membrane, cytoplasm, DNA, and ribosomes.

Definition of unicellular

Composed of a single cell.

Three major bacterial cell shapes

Coccus (spherical), bacillus (rod-shaped), spirillum/spirochete (spiral forms).

Coccus vs. Bacillus

Coccus = spherical/round cell; Bacillus = rod-shaped cell.

Spirillum vs. Spirochete

Both are spiral-shaped; spirochetes are more flexible and have a corkscrew-like form.

Streptococcus, Staphylococcus, Streptobacillus

Streptococcus = cocci in chains; Staphylococcus = cocci in clusters; Streptobacillus = rods in chains.

Nucleoid

The region in a prokaryotic cell where its chromosome is concentrated, not membrane-bound.

Prokaryotic vs. Eukaryotic chromosome

Prokaryotic chromosomes are in the nucleoid; eukaryotic DNA is enclosed by a nuclear envelope.

Function of bacterial cell wall

Provides structural support and protects against osmotic stress.

Peptidoglycan

A bacterial cell-wall polymer made of a disaccharide-based glycan backbone cross-linked by peptides.

Repeating sugars in peptidoglycan

NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid).

Strength of peptidoglycan

Cross-linking between glycan strands creates a strong network around the cell.

Penicillin's effect on bacterial cell wall

Penicillin inhibits transpeptidase, weakening the cell wall.

Vancomycin's effect on peptidoglycan synthesis

Vancomycin binds D-Ala, blocking cross-bridge formation.

Plasma membrane function

Acts as a selective barrier, controlling transport into and out of the cell.

Glycoproteins and glycolipids location

On the extracellular side of the plasma membrane.

Bacterial flagellum composition and movement

Made largely of flagellin; rotates like a motor to produce movement.

Powering of bacterial flagellum

Powered by the proton motive force.

Fimbriae definition

Short, numerous, bristle-like protein appendages used for attachment.

Pili definition

Longer, generally less numerous protein appendages used for attachment or conjugation.

Sex pilus function

Facilitates DNA transfer between bacterial cells during conjugation.

Importance of pili and fimbriae in bacterial infection

They help bacteria adhere to host cells, promoting infectivity.

Bacterial cytoskeleton

Set of intracellular protein filaments that helps control shape, division, movement, and organization.

FtsZ

A tubulin-like protein involved in bacterial cell division.

MreB

An actin-like protein involved in maintaining cell shape and plasmid segregation.

Coupled transcription and translation in prokaryotes

Possible due to the lack of a nucleus, allowing ribosomes to translate mRNA quickly after synthesis.

Coupled transcription and translation definition

Translation can begin while the same mRNA is still being transcribed.

Coupled protein secretion in prokaryotes

Possible due to the lack of a nucleus and interaction of secretion machinery with newly synthesized proteins.

Consequence of coupled gene expression in prokaryotes

Rapid gene expression due to no separation of transcription and translation.

Defining features of Gram-positive bacteria

Thick peptidoglycan cell wall surrounding a plasma membrane; stains purple.

Defining features of Gram-negative bacteria

Plasma membrane, thin peptidoglycan layer, outer membrane with LPS; stains pink/red.

Structural difference between Gram-positive and Gram-negative

Gram-positive has thick peptidoglycan, no outer membrane; Gram-negative has thin peptidoglycan and outer membrane.

Gram stain colors of bacteria

Gram-positive stains purple; Gram-negative stains pink/red.

Peptidoglycan location in Gram-positive vs. Gram-negative

Thick outside plasma membrane in Gram-positive; thin between inner and outer membranes in Gram-negative.

LPS

Lipopolysaccharide, a component of the Gram-negative outer membrane.

Periplasmic space

Region between the inner and outer membrane of Gram-negative bacteria.

Crystal violet retention in Gram-positive bacteria

Retained due to thick peptidoglycan during decolorization; Gram-negative has thinner peptidoglycan.

Inconsistency in description of Gram-negative bacteria

Slide misstates 'thick peptidoglycan,' when it actually has a thin peptidoglycan layer.

Internal membranes of cyanobacteria origin

Resulted from invagination of the plasma membrane for increased surface area for photosynthesis.

Differences in bacterial and archaeal cell walls

Bacterial cell walls contain peptidoglycan; archaeal cell walls do not.

Bacterial vs. archaeal membrane lipids

Bacteria: ester-linked, unbranched fatty acids; Archaea: ether-linked, branched lipids.

Archaeal membrane stability in extreme environments

Ether linkages provide stability; branched lipids and tetraether lipids enhance rigidity.

Tetraether lipids in archaeal membranes

Span membrane, forming a lipid monolayer, increasing stability.

Bacterial vs. archaeal ribosomes

Bacterial ribosomes are bacteria-like; archaeal ribosomes are more eukaryotic-like.

Bacterial vs. archaeal tRNAs

Bacterial tRNAs are bacteria-like; archaeal tRNAs are eukaryotic-like.

Lipid-linkage types distinguishing Bacteria vs. Archaea

Bacteria: ester linkages; Archaea: ether linkages.

Three major domains of life

Bacteria, Archaea, Eukarya.

Endosymbiotic explanation for eukaryotic cells

Eukaryotes arose from endosymbiosis involving an archaeal host and a bacterial endosymbiont.

Ancestor of mitochondria

A Proteobacteria-like endosymbiont.

Ancestor of chloroplasts

A Cyanobacteria-like endosymbiont.

Effect of doubling cell radius on surface area and volume

Volume increases more dramatically than surface area, causing a decrease in surface-area-to-volume ratio.

Transcription and translation in prokaryotes

Possible because no nucleus/nuclear envelope separates them.

Staphylococcus-like arrangement observation

Purple spherical bacteria in grape-like clusters are Gram-positive cocci.

Observation of pink rod-shaped bacteria

Suggests Bacillus/rod shape and Gram-negative classification.

Effect of drug on peptidoglycan synthesis

Weakens cross-linking, reducing cell wall strength and inhibiting growth.

Mutation removing FtsZ effect

Most directly affects cell division.

Disruption of MreB effect

Affects maintenance of cell shape and plasmid segregation.

Loss of fimbriae effect

Reduces attachment to other cells or surfaces.

Bacterial cell structure classification

A cell with a thick peptidoglycan wall and purple stain is Gram-positive.

Gram-negative bacterial structure identification

Characterized by a thin peptidoglycan layer between inner and outer membranes.

Why would an enzyme breaking peptidoglycan damage cells?

Peptidoglycan provides strength; breaking it weakens the cell wall, compromising integrity.

Effectiveness of lysozyme against Gram-positive vs. Gram-negative

More effective against Gram-positive due to accessibility of peptidoglycan.

Why are lysozyme and enzymes useful in tears?

Contain lysozyme, degrading bacterial peptidoglycan as part of surface defenses.

Response to prokaryotic complexity statement

Prokaryotes have complex structures and functions, despite lacking membrane-bound organelles.

Targeting bacterial motility

Target the flagellum to stop motility without destroying the plasma membrane.

Selective movement into bacterial cell

The plasma membrane is responsible for selective transport.

Improving low SA:V ratio exchange

Reduce cell size or increase effective surface area.

Distinguishing Bacteria from Archaea on cell envelope

Ask if peptidoglycan is present; check lipid linkages next.

Bacterial-cell diagram structures to identify

Capsule, cytoplasm, ribosomes, nucleoid, plasma membrane, cell wall, flagellum, pili.

Difference between capsule and cell wall

Cell wall is structural; capsule is an additional coating.

Presence of flagella, capsules, pili in prokaryotes

Not all prokaryotes have these structures; they are optional.

Prokaryote literal meaning

Cells without a membrane-bound nucleus; DNA is in the nucleoid region.

Eukaryote literal meaning

Cells with a membrane-bound nucleus and organelles.

Lecture 6 outcomes checklist

Be able to state cell theory, explain cell size limits, microscopy methods, cell classifications, bacterial structures, coupled transcription/translation, and origins.