Anatomy and Physiology of Prokaryotic Cells

MicrobiologyMrs. Hieneman

Bacterial Shape and Arrangement

Streptococcus chain

Sarcinae cube

Staphylococcus aureus cluster

Spiral-shaped bacterial cell

Prokaryotic Cell Structure

Cytoplasmic Membrane

• Surrounds cytoplasm and defines boundaries of cell

• Acts as barrier, but also functions as an effective and highly discriminating conduit between cell and surroundings

• Made up of phospholipid bilayer

Figure 4.14c

Phospholipid

Figure 4.14b

Movement of Molecules through Cytoplasmic Membrane

• Several ways for molecules to move through membrane

1. Simple Diffusion2. Osmosis3. Facilitated Diffusion4. Active Transport

Simple Diffusion

• Does not require expenditure of energy• Process by which some molecules move

freely into and out of the cell• Small molecules such as carbon dioxide and

oxygen

Microbiology: An Introduction, 9eby Tortora, Funke, Case

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 4.18: The principle of osmosis - Overview.

(a) At beginning of osmotic pressure experiment

(b) At equilibrium

(c) Isotonic solution — no net movement of water

(d) Hypotonic solution — water moves into the cell and may cause the cell to burst if the wall is weak or damaged (osmotic lysis)

(e) Hypertonic solution — water moves out of the cell, causing its cytoplasm to shrink (plasmolysis)

Glass tube

Rubberstopper

Rubberband

Sucrosemolecule

Watermolecule

Cellophanesack

Cytoplasm Solute Plasma membrane

Cell wall

Water

Transport Proteins

• Transport proteins (or transporters) responsible for:

• Facilitated Diffusion• Active Transport

Microbiology: An Introduction, 9eby Tortora, Funke, Case

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 4.17: Facilitated diffusion.

Transportedsubstance

Transporterprotein

Outside

Inside

Glucose

Plasmamembrane

Cell Wall

• Composed of peptidoglycan• Comprised of alternating NAG and NAM

molecules• Attached to each NAM is four amino acid

peptide: tetrapeptide

Categories of Bacteria

• Two Major Categories:• Difference due to difference in chemical

structures of their cell walls– Gram positive: stains purple– Gram negative: stains red

Gram + Cell Wall

• Thick Layer of Peptidoglycan• Contains techoic acid: chains of ribitol-

phosphate or glycerol-phosphate to which sugars or alanine attached

• Techoic Acid sticks out above the peptidoglycan layer

Gram – Cell Wall

• More complex than Gram + cell wall• Thin layer of peptidoglycan

– Sandwiched between the cytoplasmic membrane and outer membrane

• Outside of peptidoglycan is outer membrane

Figure 4.13c

Outer Membrane

• Unlike any other membrane in nature• A lipid bilayer with the outside layer made

of lipopolysaccharides instead of phospholipids

• Also called LPS• Contains Porins

Periplasm

- Region between cytoplasmic membrane and the outer membrane

- Gel-like fluid• Filled with secreted proteins and enzymes

External Structures

• Glycocallyx• Flagella• Axial Filaments• Fimbrae and Pili

Glycocallyx

• Gel-like structure– Functions in protection and attachment– Two types- capsule and slime layer– Involved in attachment, enabling bacteria to

stick to teeth, rocks– Enables bacteria to brow as biofilm

Capsule in Acinetobacter species by gram negative staining

Filamentous Protein Appendages

• Anchored in membrane and protrude from surface

• Flagella: long structure responsible for motility

• Fimbrae and Pili: shorter, responsible for attachment

Four types of bacteria with flagella

• Montrichious- one flagella• Amphitrichous- flagella at both ends• Lophitrichous- many flagella at the end of

the cell• Peritrichous- flagella all over entire cell

Figure 4.7 - Overview

Axial Filament

• Present in Spirochetes• Attach at end of cell, spiral around,

underneath an outer sheath• Move like a corkscrew

Figure 4.10 - Overview

Fimbrae and Pili

• Shorter and surround the cell• Similar structural theme to filament of

flagella• Fimbrae- enable cell to adhere to surfaces,

including other cells• Pili- join bacterial cells in preparation for

the transfer of DNA from one cell to another

Internal Structures of Prokaryotic Cells

Cytoplasm

• Substance of cell inside the cytoplasmic membrane

• About 80% water• Thick, aqueous, semitransparent, elastic

Chromosome

• Found within a central location known as nucleoid

• Single, circular, double stranded• Consists of all DNA required by cell

Plasmids

• Some bacteria contain plasmids- small circular double-stranded DNA

• Typically cell does not require genetic information carried on plasmid

• However, it may be advantageous

Ribosomes

• Site of protein synthesis• Relative size and density of ribosomes and

their subunits expressed as distinct unit (S)• Two units of prokaryotic ribosomes: 50S +

30S= 70S• Eukaryotic ribosomes: 80S

Microbiology: An Introduction, 9eby Tortora, Funke, Case

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 4.19: The prokaryotic ribosome.

(a) Small subunit (b) Large subunit (c)

50S

50S

30S 30S

(c) Complete 70S ribosome

Inclusions

• Store excess nutrients• Examples: Polysaccharide granules-

glycogen and starch• Lipid inclusions• Metachromatic granules- inorganic

phosphate that can be used to synthesize ATP

Endospores

• Occurs in members of genera Bacillus and Clostridium

• Dormant cell produced by a process called Sporulation

• Germination- when they exit the dormant state and then become a vegetative cell

• Several species of endospore formers can cause disease