Chapter 4: Functional Anatomy of Prokaryotic and Eukaryotic Cells 🦠🧬

Prokaryotic Cell

A cell that lacks a true nucleus and membrane-bound organelles

- circular DNA is located in the nucleoid region

- divide by binary fission

Eukaryotic Cell

A cell that contains a true nucleus with linear DNA

- surrounded by a membrane and membrane-bound organelles

- divide by mitosis

Pleomorphic

Having many different shapes.

What are the three basic bacterial shapes?

Coccus (spherical), bacillus (rod-shaped), and spiral.

Coccus

A spherical bacterial cell.

Bacillus

A rod-shaped bacterial cell.

Spiral Bacterium

A bacterium with a curved or spiral shape.

Vibrio

A comma-shaped curved bacterium.

Spirillum

A rigid spiral-shaped bacterium.

Spirochete

A flexible spiral-shaped bacterium that moves using axial filaments.

Diplococci

Cocci arranged in pairs.

Streptococci

Cocci arranged in chains.

Staphylococci

Cocci arranged in grape-like clusters.

Tetrads

Groups of four cocci.

Sarcinae

Cube-like groups of eight cocci.

What are some unusual bacterial shapes?

Star-shaped and rectangular bacteria.

Glycocalyx

A sticky, gelatinous external coating outside the cell wall made of polysaccharides and/or polypeptides.

Capsule

A well-organized glycocalyx firmly attached to the cell wall.

Slime Layer

A loose, unorganized glycocalyx that is easily removed.

What are the functions of the glycocalyx?

Protection, attachment to surfaces, biofilm formation, and increased virulence.

How does a capsule increase virulence?

It helps bacteria avoid phagocytosis by immune cells.

Flagellum

A long, filamentous appendage that propels bacteria.

What are the three parts of a bacterial flagellum?

- Filament: the long outer portion of a flagellum composed of flagellin protein

- Hook: the structure that connects the filament to the basal body

- Basal body: the anchoring structure that attaches the flagellum to the cell wall and plasma membrane

Chemotaxis

Movement of a bacterium toward beneficial chemicals (positive) or away from harmful chemicals (negative).

Axial Filament (Endoflagellum)

A flagellar structure found in spirochetes that wraps around the cell and produces corkscrew-like movement.

Fimbriae

Short, hairlike appendages used primarily for attachment to surfaces.

Pilus (Pili)

Longer, fewer appendages used for DNA transfer during conjugation and for certain types of motility.

What is the difference between fimbriae and pili?

Fimbriae are mainly for attachment, while pili function in DNA transfer and motility.

Cell Wall

A rigid structure outside the plasma membrane that prevents osmotic lysis and provides shape and protection.

Peptidoglycan

The major component of bacterial cell walls consisting of alternating NAG and NAM molecules linked by peptides.

Gram-Positive Cell Wall

A cell wall with a thick peptidoglycan layer and teichoic acids.

Teichoic Acids

Molecules found only in gram-positive cell walls that help strengthen the wall and distinguish gram-positive bacteria.

How does a gram-positive bacterium appear after Gram staining?

Purple.

Why do gram-positive bacteria remain purple during Gram staining?

Alcohol dehydrates the thick peptidoglycan layer, trapping crystal violet-iodine complexes.

Characteristics of Gram-Positive Bacteria

- thick peptidoglycan

- teichoic acids

- highly susceptible to penicillin

- sensitive to lysozyme

Gram-Negative Cell Wall

A cell wall with a thin peptidoglycan layer, outer membrane, and periplasmic space.

Outer Membrane

An additional membrane outside the peptidoglycan layer containing lipopolysaccharide (LPS).

Lipopolysaccharide (LPS)

Molecule found in gram-negative outer membranes that contains endotoxin and helps identify bacteria.

How does a gram-negative bacterium appear after Gram staining?

Pink or red.

Why do gram-negative bacteria lose the crystal violet stain?

Alcohol dissolves the outer membrane and allows crystal violet-iodine complexes to wash out.

Characteristics of Gram-Negative Bacteria

- thin peptidoglycan layer

- outer membrane containing LPS

- produces endotoxin

- has lower susceptibility to penicillin

Compare gram-positive and gram-negative cell walls

Gram-positive bacteria have thick peptidoglycan and teichoic acids, while gram-negative bacteria have thin peptidoglycan, an outer membrane, LPS, and a periplasmic space.

Which type of bacteria contains endotoxin?

Gram-negative bacteria.

Which type is more susceptible to penicillin?

Gram-positive bacteria.

Which type contains teichoic acids?

Gram-positive bacteria.

Acid-Fast Cell Wall

A cell wall containing waxy mycolic acid that resists ordinary staining methods.

Mycolic Acid

A waxy lipid found in acid-fast bacterial cell walls.

Which bacteria are acid-fast?

Mycobacterium and Nocardia.

Mycoplasmas

Bacteria that completely lack a cell wall.

How do Mycoplasmas maintain cell structure without a cell wall?

Sterols in the plasma membrane provide support.

Archaea Cell Walls

Cell walls that contain pseudomurein or may be absent entirely.

Pseudomurein

A cell wall material in archaea that lacks NAM and D-amino acids.

Lysozyme

An enzyme that breaks the bonds between NAG and NAM in peptidoglycan.

What effect does lysozyme have on bacterial cell walls?

It hydrolyzes peptidoglycan and weakens the cell wall.

Penicillin

An antibiotic that prevents formation of peptide cross-bridges in peptidoglycan.

What effect does penicillin have on bacterial cell walls?

It prevents proper peptidoglycan cross-linking and cell wall synthesis.

Protoplast

A gram-positive cell that has completely lost its cell wall.

Spheroplast

A gram-negative cell that has lost most of its cell wall; but the outer membrane remains

L Forms

Cell wall-deficient bacteria that survive and grow as irregularly shaped cells.

Why are protoplasts and spheroplasts fragile?

Without a cell wall, they are highly susceptible to osmotic lysis.

Plasma Membrane

A selectively permeable phospholipid bilayer surrounding the cytoplasm.

Simple Diffusion

Movement of molecules directly through the membrane from high concentration to low concentration.

Facilitated Diffusion

Passive movement through membrane transport proteins from high concentration to low concentration.

Osmosis

Diffusion of water across a selectively permeable membrane.

Active Transport (Detailed)

Transport requiring a carrier protein and energy (ATP) to move substances against their concentration gradient.

Comparison of Transport Methods

- Simple diffusion moves molecules directly through the membrane

- Facilitated diffusion uses transport proteins

- Osmosis is water movement

- Active transport requires energy and moves substances against the gradient

Isotonic Solution

A solution with equal solute concentration inside and outside the cell, causing no net water movement.

Hypotonic Solution

A solution with lower solute concentration outside the cell, causing water to enter the cell.

Hypertonic Solution

A solution with higher solute concentration outside the cell, causing water to leave the cell.

Plasmolysis

Shrinkage of the cytoplasm due to water loss in a hypertonic environment.

Osmotic Lysis

Bursting of a cell due to excessive water entering the cell.

Ribosomes

Structures responsible for protein synthesis.

Where are ribosomes located?

Free in the cytoplasm of prokaryotic and eukaryotic cells and attached to rough ER in eukaryotes.

What are prokaryotic ribosomes composed of?

A 50S large subunit and a 30S small subunit, forming a 70S ribosome.

Endospore

A dormant, highly resistant structure formed inside certain bacteria when conditions become unfavorable.

What is the function of an endospore?

Survival during harsh environmental conditions.

Which genus commonly produce endospores?

Bacillus and Clostridium.

Sporulation

The process of endospore formation.

Germination

The return of an endospore to an active vegetative cell.

Why are endospores difficult to destroy?

They resist heat, drying, chemicals, and radiation.

Nucleus

Membrane-bound organelle that contains the cell's DNA.

Endoplasmic Reticulum (ER)

Membrane network involved in protein and lipid synthesis

- Rough ER: covered with ribosomes that synthesizes proteins

- Smooth ER: synthesizes lipids and detoxifies chemicals

Golgi Complex

Organelle that modifies, packages, and distributes proteins and lipids.

Lysosomes

Organelles containing digestive enzymes that break down cellular materials.

Mitochondria

Organelles that generate ATP through cellular respiration.

Chloroplasts

Photosynthetic organelles found in plants and algae that convert light energy into chemical energy.