Bacterial and Archaeal Cell Structure Overview

Bacteria

Single-celled microorganisms with diverse characteristics.

Archaea

Microorganisms similar to bacteria but genetically distinct.

Morphology

Study of the form and structure of organisms.

Coccus

Spherical-shaped bacteria.

Bacillus

Rod-shaped bacteria.

Convex

Curved outward surface texture.

Streptococci

Chain arrangement of cocci bacteria.

Staphylococci

Grape-like cluster arrangement of cocci.

Diplococci

Pair arrangement of cocci bacteria.

Tetrads

Group of four cocci bacteria.

Sarcinae

Cube-like arrangement of cocci bacteria.

Bacilli (bacillus)

Rod-shaped bacteria

Coccobacilli

Short, oval-shaped bacteria, intermediate between cocci and bacilli.

Vibrios

Comma-shaped bacteria.

Spirilla

Rigid spiral-shaped bacteria.

Spirochetes

Flexible spiral-shaped bacteria.

Pleomorphic

Bacteria with variable shapes.

Mycelium

Network of fungal filaments, not bacteria.

Surface to Volume Ratio

Measurement affecting nutrient uptake efficiency.

Cell Envelope

Outer structure including plasma membrane and cell wall.

• Plasma membrane

• Cell wall

• Layers outside the cell wall

• Capsule

• Slime layer

Plasma Membrane

Barrier enclosing cytoplasm, selectively permeable.

Cell Wall

Rigid structure providing shape and protection.

Capsule

Thick outer layer for protection and adherence.

Slime Layer

Loose, unorganized layer outside cell wall.

Membrane Proteins

Proteins that perform various functions in the membrane.

Amphipathic Lipids

Molecules with hydrophilic and hydrophobic regions.

Archaeal Membranes

Composed of unique lipids with isoprene units.

Isoprene Units

Five-carbon branched structures in archaeal lipids.

Ether Linkages

Connect glycerol in archaeal membranes, unlike esters.

Monolayer Structure

Some archaea have a single lipid layer.

Bacterial Membranes

Contain hopanoids instead of sterols for stability.

Hopanoids

Stabilize bacterial membranes, marking microdomain boundaries.

Saturation Levels

Reflect environmental conditions affecting membrane fluidity.

Macroelements

Essential elements like C, O, H, N, S, P.

Micronutrients

Trace elements required in small amounts, e.g., Zn.

Growth Factors

Organic compounds supplied by the environment for growth.

Amino acids

Building blocks essential for protein synthesis.

Purines

Nitrogenous bases in nucleic acid synthesis.

Pyrimidines

Nitrogenous bases in nucleic acid synthesis.

Vitamins

Organic compounds acting as enzyme cofactors.

Passive diffusion

Movement of particles without energy input.

Facilitated diffusion

Transport via protein channels without energy.

Active transport

Energy-requiring movement against concentration gradient.

Primary active transport

Direct use of ATP for transport.

Secondary active transport

Uses electrochemical gradients for transport.

Group translocation

Chemical modification during nutrient transport.

Siderophores

Molecules that bind ferric iron for uptake.

Peptidoglycan

Rigid polymer forming bacterial cell walls.

Gram-positive bacteria

Stain purple; thick peptidoglycan layer.

Gram-negative bacteria

Stain pink; thin peptidoglycan and outer membrane.

N-acetylglucosamine (NAG)

Sugar component in peptidoglycan structure.

N-acetylmuramic acid (NAM)

Sugar component in peptidoglycan structure.

Teichoic acids

Polymers aiding Gram-positive cell wall stability.

Lipopolysaccharide (LPS)

Complex of lipid A, core, and O antigen.

Lipid A

Endotoxin component of lipopolysaccharide.

Porin proteins

Form channels in Gram-negative outer membrane.

Periplasmic space

Area between cell wall and outer membrane.

Braun's lipoproteins

Connect outer membrane to peptidoglycan.

Gram-negative

Thinner peptidoglycan layer with larger pores.

Crystal violet

Stain lost in Gram-negative bacteria.

Alcohol treatment

Removes lipids, affecting cell wall integrity.

Archaeal cell envelopes

Lack peptidoglycan; may have S-layer.

• Lack peptidoglycan

• S-layer may be only component outside plasma membrane

• Separated from the plasma membrane by a peptidoglycan-like molecule called pseudomurein

• Some lack cell wall

Pseudomurein

Molecule separating S-layer from plasma membrane.

Cell wall protection

Lysozyme breaks NAG and NAM bonds.

Penicillin

Inhibits peptidoglycan synthesis in bacteria.

Hypotonic solution

Causes lysis if cell wall is compromised.

Isotonic solution

Allows cells to survive and grow normally.

Protoplasts

Gram-positive cells without a cell wall.

Spheroplasts

Gram-negative cells with partial cell wall.

Mycoplasma

Bacteria that never produce a cell wall.

Glycocalyx

Surface layer aiding in biofilm formation.

Capsules

Outermost layer providing protection and stability.

Slime layers

Loose polysaccharide layers aiding in adhesion.

S-layers

Protective layers maintaining shape and rigidity.

Osmotic stress

Pressure affecting cell integrity in different solutions.

Ribosomes

Sites of protein synthesis; 70S in bacteria.

Complex protein/RNA structures

• Sites of protein synthesis

• Bacterial and archaea ribosome = 70S

Ribosomal RNA

• 16S small subunit

• 23S and 5S in large subunit

Eukaryotic ribosome

• 80S

• Small subunit 40S

• Large subunit 80S

Nucleoid

Region containing bacterial DNA.

Plasmids

Small DNA molecules independent of chromosomal DNA.

Cytoskeleton

Structures aiding in cell shape and division.

Nucleoid

Region containing bacterial chromosome and proteins.

Plasmids

Extrachromosomal DNA in bacteria, replicates independently.

Cytoskeleton

Protein filaments aiding in cell shape and division.

FtsZ

Protein forming ring during bacterial cell division.

MreB

Protein maintaining shape in rod-shaped bacteria.

Motility

Movement mechanisms in bacteria, including swimming.

Chemotaxis

Movement toward attractants or away from repellents.

Bacterial Flagella

Threadlike structures enabling bacterial motility.

Monotrichous

Single flagellum at one end of the cell.

Amphitrichous

Flagella at both ends of the bacterial cell.

Lophotrichous

Cluster of flagella at one or both ends.

Peritrichous

Flagella distributed over the entire cell surface.

Flagellar Structure

Composed of filament, basal body, and hook.

Flagellar Movement

Rotational movement causing run-tumble behavior.

Archaella

Similar to flagella, involved in adhesion and motility.

Endospore

Dormant structure resistant to harsh conditions.

Activation

Prepares endospores for germination through heating.

Germination

Process where endospores detect nutrients and swell.

Outgrowth

Emergence of vegetative cell from endospore.

SASPs

Small proteins protecting DNA in endospores.

Supercoiling

DNA folding aided by nucleoid proteins.