Prokaryotic Cells

Bacteria

Classification of Bacteria We classify, or name, bacteria based on 3

main factors… Size Shape Arrangement

We only study a handful of all bacteria within health science!

Bacterial Size Surface-to-Volume

Ratio: The ratio of total surface space compared to the total volume of a given cell. The smaller the cell, the

larger the surface-to-volume ratio.

A larger surface-to-volume ratio helps with quicker nutrient absorption.

Also allows absorbed nutrients to reach cellular organelles faster!

Bacterial Shapes The shape of a bacteria is the basic shape

of an individual bacteria cell, not the colony.

5 shapes: Cocci Bacilli Vibrios Spirochetes Spirillum

Bacterial Shapes Cocci: Spherical in shape.

Bacterial Shapes Bacilli: Rod-like.

Bacterial Shapes Vibrios: Comma-shaped.

Bacterial Shapes Spirochetes: Corkscrew-shaped.

Bacterial Shapes Spirillum: Rigid & wavy-shaped.

Bacterial Arrangements Bacterial Arrangements: Groups of bacterial

cells that have divided without complete separation of the cell walls.

Cocci can divide in many different planes to create.. Diplo- Strepto- Staphylo- Tetrad- Sarcina-

Bacilli can only divide on one plane, so produce cells that are connected end-to-end or side-by-side.

Bacterial Arrangements Diplo-: Pairs of

bacterial cells. Strepto-: Chains of

bacterial cells. Staphylo-: Grapelike

clusters. Tetrad-: Cocci in

squares of 4. Sarcina-: Cocci in

squares of 8.

Bacterial Arrangements

Internal Structures Cytoplasm: A

semifluid substance that makes up the majority of the interior of a bacterium.

Internal Structures Ribosome: A cellular

organelle responsible for translating RNA & synthesizing protein. Prokaryotic ribosomes are

only 70S. Eukaryotic ribosomes are

80S. Difference in ribosome

sizes aids in chemotherapeutic drugs differentiating between prokaryotic & eukaryotic cells.

Streptomycin & Erythromycin target 70S ribosomes specifically to disrupt protein synthesis & cause cell death only to bacteria.

Internal Structures Nuclear Region aka

Nucleoid: The central region in the bacterial cell where DNA is located. Bacteria do not have a

defined membrane-bound nucleus.

DNA consists of one or more chromosomes, either circular or linear.

Internal Structures Plasmids: Smaller

circular DNA molecules containing genes that supplement the chromosomal material. Often the site where

antibiotic resistant genes are located.

Internal Structures Inclusions: “Extras” that

are not a normal cellular structure. Granules: Small bodies of

densely compacted substances that have not been dissolved in the cytoplasm & without a membrane.

Vesicles: Membrane-bound particles occasionally found that typically play very specialized roles.

Ex. Gas-filled vesicles in cyanobacteria help control their depth in the water.

External Structures Flagella: Long, thin helical

appendages that allow motility (movement).

Only 1/10 the thickness of eukaryotic flagella.

About half of known bacteria species are motile.

Basal Region: The point where the flagella attaches to the cell membrane.

Consists of a hook-like structure and a complex basal body.

Basal body consists of a central rod or shaft surrounded by a set of rings.

Gram positive bacteria have one ring in the cell membrane and one in the cell wall.

Gram negative bacteria have a pair of rings in the cell wall.

External Structures Movement aided by Flagellum:

Chemotaxis: Movement toward or away from a chemical substance in the bacteria’s environment.

Phototaxis: Movement toward or away from light in the bacteria’s environment.

External Structures Pilli: Tiny hollow projections

not involved in movement. Conjugation Pilli: Pilli

designed to attach two bacterial cells together to facilitate the movement of genetic material. Only found in certain groups of bacteria.

Conjugation allows bacteria to pass on antibiotic resistant genes to each other!

Attachment Pilli: Pilli designed to help the bacteria attach to surfaces.

Contributes to pathogenicity of bacterial species since it can aid in attachment to water & air (transfer) and the surface of cells (virulence).

Other Structures Endospore: A small, compact, tough,

structure produced by some bacteria as a means of preserving their genetic material. NOT a form of reproduction. Produced when the bacteria’s environment

becomes unfavorable or too harsh for survival. Can remain dormant but viable for thousands

of years. Will germinate (develop) into functional cells

once environmental conditions improve. Most often found in soil & water.

Glycocalyx Glycocalyx: External structure of

polysaccharides or polypeptides outside the cell membrane.

Capsule: Glycocalyx layer that helps protect the bacterium & keep it from being phagocytized.

Considered a virulence factor. Slime Layer: Glycocalyx layer

that is thinner & less tightly bound to the cell wall.

Prevents the cell from drying out. Helps to trap nutrients near the

cell. Can help cells stick together. Can help bacteria adhere to

objects in the environment. Plaque on teeth is the slime layer

of Streptoccus mutans and a few anaerobes (Fusobacterium & Actinobacteria).

Cell Walls Cell Wall: The structure

that allows us to characterize bacteria into different groups. Not found in eukaryotic

cells, so typically targeted by antibiotics.

Two Important Rolls: Maintains the

characteristic shape of a bacterial cell – would be spherical without it.

Prevents the cell from lysing (bursting) when osmosis triggers fluid to flow into the cell.

Cell Wall Peptidoglycan:

Covalently-linked polymer that surrounds the cell. Resembles a chain-link

fence or net. Provides support to the

cell. Does not play a major role

in regulating entry of materials into the cell.

The most important component of the bacterial cell wall.

Cell Membrane Cell Membrane: The

boundary between the interior of the cell & the environment. Made up of a lipid bilayer

interspersed with proteins. Some proteins act as

carriers, pores, or channels.

Material exchange for the cell occurs through these proteins constantly.

Material exchange for the cell occurs selectively through the lipid bilayer.

Cell Membrane The primary membrane

accessible to the interior of the cell to carry out specialized tasks.

Eukaryotic cells have multiple membrane-bound organelles for this.

Proteins in the cell wall aid in specialized task, including…

DNA replication Respiration Cell wall component synthesis

Some proteins are located on the outer surface of the cell membrane.

Includes the proteins that identify the bacteria as a particular organism.

Internal Membrane Systems

Internal membrane Systems: Found in some bacteria, mostly those with photosynthetic capabilities. Chromatophores: A

system of membranes derived from the cell membrane that makes photosynthetic reactions possible.

Differentiating Bacteria Differentiating bacterial species depends

on the cell walls. Bacteria are named after the staining

properties and tests used to “see” them under microscopes.

The different “classes” of bacteria respond in noticeably different ways to these tests.

Gram Positive Bacteria Gram Positive Bacteria:

Bacteria that turn purple during a Gram stain.

Very thick peptidoglycan cell wall up to 40 layers thick, with little space between the cell wall & cell membrane.

60-90% peptidoglycan. Tiechoic Acid: A unique form of

acid in the cell wall that helps set Gram+ bacteria apart.

Periplasm: Fluid located within the network of the cell wall where digestive enzymes are located.

Enzymes destroy substances that are potentially harmful to the bacteria.

Also contains transport proteins to aid in transporting metabolites & nutrients into the cytoplasm.

Gram Negative Bacteria Gram Negative Bacteria: Bacteria that

turn red during a Gram stain. A bacterial cell with a different external

system structure than Gram Positive. Cell wall is thinner than in Gram+ and more

complex. 10-20% peptidoglycan. The rest is made up of polysaccharides,

proteins, & lipids. Outer Membrane: Forms the outermost

layer on the cell wall, attached to the peptidoglyccan in the cell wall by a layer of small lipoprotein molecules.

Does not control the movement of substances through the cell wall but can control the transport of certain proteins.

Endotoxin: A base of lipopolysaccharides within the outer membrane that is released when the bacterial cell is killed.

This causes fever, vasodilation, & a drop in blood pressure.

Antibiotics given too late in an infection can cause massive release of endotoxins & potentially death.

Periplasmic Space: Space between the cell wall & membrane – takes on the same tasks as the periplasm in G+.

Gram Positive vs Gram Negative Bacteria

Acid-Fast Bacteria Acid-Fast Bacteria aka

Mycobacteria: Bacteria that does not Gram stain, so is visualized using the Ziehl-Neelsen Acid-Fast Stain.

Cell wall is thick, similar to Gram+ bacteria. Has less peptidoglycan. 60% of cell wall is

composed of lipids. Image: A = Non Acid-Fast

bacteria, B = Acid-Fast Bacteria

Mycoplasma Mycoplasma: Bacterium

with no cell wall. Protected from osmostic

swelling & lysing by a strong cell membrane.

Cell membrane contains sterols, which provide rigidity – more common in Eukaryotic cells.

More resistant to antibiotic treatment since antibiotics typically attack the cell wall.

Binary Fission Binary Fission: The method

of asexual reproduction used by most prokaryotic cells.

DNA of the mother cell replicates & joins into circular pairs.

The circular pairs attach to the cell membrane/plasma membrane.

The cell elongates, forcing the paired chromosomes separate.

The cell membrane invaginates (pinches inward toward the middle).

When the cell membrane has completed invaginating, the cell splits off into two identical daughter cells.

It is fairly common for one of the daughter cells to not be identical to the mother cell – this causes the high mutation rate of bacteria.

Bacterial Growth Phases We grow bacteria in nutrient-rich medium

(typically broth or agar) in order to watch them grow!

Standard Bacterial Growth Curve: The rate through which bacteria go through the 4 phases of bacterial growth. Lag Phase Log Phase Stationary Phase Decline Phase

Some bacteria complete this in a few days, some can take years to complete!

Bacterial Growth Phases Lag Phase: The initial

phase where the bacterium is adapting to the environment, particularly if it was previously in a poor environment and is now in an optimal environment. Can last one hour to

several days, depending on previous environment & the need for adaptation.

Bacteria are not currently dividing but are gearing up for it.

Cells increase in size & produce large amounts of ATP energy to prepare.

Bacterial Growth Phases Log Phase: Bacteria have

adapted to the environment and population growth begins. Growth occurs at a

logarithmic rate – this means an exponential and rapid rate of growth.

Generation Time: The genetically determined, rapid rate at which bacteria reproduces.

The generation time is the amount of time it takes for the bacterial population to double.

Bacterial Growth Phases Stationary Phase: The

bacteria have stopped exponential growth and is simply being maintained.

The larger the number of organisms, the faster nutrients are used up & metabolic wastes build up in the environment.

Living space becomes scarce. The growth curve levels off. New cells are produced at the

same rate as the death of old cells.

The colony does not grow or decline, it remains at a constant rate.

Chemostat: A device used to constantly refresh the medium a bacterial culture is being grown in – prevents stationary phase from occurring.

Bacterial Growth Phases Decline Phase: The

phase at which the bacterial colony begins to die off. Environmental conditions

become increasingly less favorable.

Toxic waste products build up.

Nutrients dwindle. Cells loose their ability to

divide & finally die off. The number of cells

decrease at a rapid logarithmic rate.

Bacterial Environments Bacteria are found in nearly every environment

on earth. They can be found in places where no other living

organism can survive. This is due to…

Small size Easily dispersed Occupy very little space Need only small quantities of nutrients Very diverse in nutritional requirements

Live mostly in water. Can adapt to conditions we would find

unpleasant.

Important Environmental Factors

Bacterial Growth Rates can be affected by several environmental factors… pH Temperature Oxygen Content Moisture Hydrostatic Pressure Osmotic Pressure Nutritional Factors

pH pH: The measure of the acidity or

alkalinity of a substance. Optimum pH: The pH level at which a

bacteria grows best. Neutrophile: Any bacterium whose optimum

pH is neutral, or 5.4-8.0. Acidophile: Any bacterium whose optimum

pH is acidic, or 1.0-5.4. Alkaliphile: Any bacterium whose optimum

pH is alkaline, or 7.0-11.5.

Temperature Temperature: The measure of warmth or

coolness of a substance or the environment itself.

Optimal Temperature: The temperature at which a bacteria grows best. Mesophile: Any bacterium that grows best at

a “warm” temperatures – 25-40°C/77-104°F. Most common type – includes most human

pathogens! Psychrophile: Any bacterium that grows best

at “cold” temperatures – 15-20°C/59-68°F. Thermophile: Any bacterium that grows best

at “hot” temperatures – 50-60°C/122-140°F.

Oxygen Oxygen: A gaseous element common to

many metabolic processes of living things. Aerobe: A bacterium that requires oxygen

for metabolic functions. Anaerobe: A bacterium that does not

require oxygen for metabolic processes.

Oxygen Obligate Aerobe: A bacterium that MUST have

free oxygen present for aerobic respiration – cannot perform anaerobic respiration.

Obligate Anaerobe: A bacterium that cannot tolerate any oxygen in the environment – they use a different molecule for respiration.

Aerotolerant Anaerobe: A bacterium that can survive in the presence of oxygen but do not use it for metabolism.

Microaerophile: A bacterium that grows best in the presence of small amounts of oxygen.

Facultative Anaerobe: A bacterium that carries on aerobic metabolism when oxygen is present but shifts to anaerobic metabolism if oxygen is absent.

Moisture Moisture: Any liquid required for survival

or produced as a metabolic byproduct. Actively metabolizing bacteria typically

require a water-based environment to survive.

Most bacterium can survive a few hours without moisture.

Only spore-forming bacteria can exist in a dormant state in a dry environment.

Hydrostatic Pressure Hydrostatic Pressure: The pressure

exerted by standing water. The deeper the water, the higher the

hydrostatic pressure. Some bacteria MUST have high hydrostatic

pressure. Ex. Those that live at the bottom of the ocean

must have this high pressure for their membranes and enzymes to function properly.

Osmotic Pressure Osmotic Pressure: The

pressure exerted within a solution containing dissolved substances (solutes) within a liquid (solvent).

Osmosis: The diffusion of water through a selectively permeable membrane from the area of higher water concentration to the area of lower water concentration. The higher solvent (water)

concentration area has a low solute concentration.

The higher solute concentration has a low solvent concentration.

Osmotic Pressure Tonicity: The ability of a solution to affect the fluid volume

and the pressure in a cell. If a solute cannot pass through a plasma membrane, but

remains more concentrated on one side of the membrane than on the other, it triggers osmosis.

Hypotonic Solution: Area surrounding a cell has a lower concentration of nonpermeating solutes than the intracellular fluid. Cells absorb water, swell, and lyse (burst).

Hypertonic Solution: Area surrounding cell has a higher concentration of nonpermeating solutes than the intracellular fluid. Plasmolysis: The shrinking of a cell in as hypertonic solution

due to water loss. Isotonic Solution: The area surrounding the cell has the

same total concentration of nonpermeating solutes as the intracellular fluid. Cells will neither loose nor gain water molecules & do not

change size or shape.

Osmotic Pressure Halophile: A bacterium specifically

designed to require moderate to large quantities of sodium chloride (“salt”) in their environment. These guys love hypertonic solutions!

Nutritional Factors All bacteria have basic nutritional needs for the

elements & molecules that serve as their building blocks for metabolism & cell structure.

Nutritional Complexity: The number of nutrients a microbe must have to grow. Determined by the kind & number of its enzymes. Number of enzymes varies by microbe. The lower the number of enzymes, the more nutrients

the bacteria will have to find in their environment. The higher the number of enzymes, the simpler their

nutritional needs are since less nutrients will need to be absorbed from the environment.

The absence of a single enzyme can leave a bacterium incapable of synthesizing needed elements.

Fastidious Microbes: Bacteria that have specific nutritional needs. These may be very difficult to grow in the laboratory.

Nutritional Factors Carbon: Carbon-based molecules act as a source of energy

for living organisms – required for ATP production. Ex. Sugar, Carbon Dioxide

Nitrogen: Needed to synthesize proteins that do the work of the cell, including enzymes. Important component of the amino acids that act as the base

for proteins. Sulfur & Phosphorus: Needed to make some proteins.

Phosphorus is required for ATP, DNA & RNA. Trace Elements: Tiny amounts of certain elements serve

as cofactors for cellular processes. Includes copper, iron, zinc, & cobalt.

Vitamins: An organic substance that an organism requires in small amounts, typically to be used as a coenzyme (to help another enzyme function). Some bacteria possess enzymes that allow them to produce

their own vitamins from other substance. Most bacteria have to track these down in the environment.