Bacterial & Viral Structure

The structures of prokaryotes and viruses

2 categories of microbes

1.) Truly cellular

2.) Acellular

Truly Cellular

bacteria, archaea, algae, protozoa, fungi

Acellular

viruses, viroids, and prions

There are over _____ identified viruses

5000

Seawater can contain _____ million viruses per milliliter

100

Cellular microbes (microorganisms) can be divided into those that are:

1.) prokaryotic (bacteria and archaea)

2.) eukaryotic (algae, protozoa, and fungi)

The 5-Kingdom System of Classification

1.) Bacteria and archaea — Kingdom Prokaryotae

2.) Algae and protozoa — Kingdom Protista

3.) Fungi — Kingdom Fungi

4.) Plants — Kingdom Plantae

5.) Animals — Kingdom Animalia

The Three-Domain System of Classification

1.) Archaea (prokaryotic)

2.) Bacteria (prokaryotic)

3.) Eucarya (all eukaryotic organisms)

• This system is based on differences in the structure of certain ribosomal RNA (rRNA) molecules among organisms in the three domains

Taxonomy

the science of classification of living organisms

• consists of classification, nomenclature, and identification

Classification

the arrangement of organisms into taxonomic groups (known as taxa)

• (DKPCOFGS)

• Does King Philip Come Over For Good Soup 🙂

Taxonomy uses a ____ system of nomenclature

binomial

Binomial system

Each organism is given two names — Genus and the specific epithet

→ When taken together, both names constitute the species

The abbreviation of “sp.” is used to designate a single species, and _____ for more than one species

spp.

The Cell Theory

• all plants and animals are composed of 1 or more cells

• the cell is the fundamental unit of life

• all cells rise from pre-existing cells (added later by Virchow)

As science progressed, what else was added to the Cell Theory?

• all organisms have their hereditary information organized in chromosomes

• all organisms have a cell membrane which selectively allows substances in or out of the cell; in eukaryotes it is known as the plasma membrane

• All cells go through metabolism, or chemical reactions that occur in the cell to produce energy

• All cells go through protein synthesis, occurs at the ribosome

Both eukaryotic and prokaryotic cells possess a cell membrane that is _______ ________

selectively permeable

Prokaryotes have a single chromosome that is NOT enclosed by a membraneous ______

nucleus

Eukaryotic cells have multiple chromosomes and contain a “true” nucleus; a true nucleus consists of what?

• nucleoplasm

• chromosomes

• nuclear membrane

T/F Prokaryotic cells possess a complex system of membranes and membrane-bound organelles

False

Prokaryotic cells include what?

Bacteria and archaea

Prokaryotes are _____ of the size of eukaryotic cells and much simpler

1/10th

Prokaryotic cells do not have a membrane bound nucleus; they only have a _____ chromosome that is floating in the cytoplasm

single

How do prokaryotic cells reproduce?

binary fission (NOT mitosis like our cells)

Prokaryotes only have ______ bound organelles (ex. ribosomes)

non-membrane

The cytoplasm of prokaryotic cells is surrounded by what?

• cell membrane

• cell wall (usually)

• sometimes a capsule or slime layer

Prokaryotic cells have multiple external layers… from the outside inwards, these are the:

1.) Glycocalyx (two types are possible but not all have a glycocalyx!)

2.) Cell Wall

3.) Cell Membrane (most internal)

What do you call a cell membrane and the cell wall together?

cell envelope

Glycocalyx

this can either be a slime layer or a capsule

→ these vary in thickness and composition

Slime layers are less dense and are only loosely connected to the cell wall, but what is their purpose?

• protects cells from the environment

• it helps prevent phagocytosis

• BUT it can be washed away

Capsule

• when present, it is a thick gelatinous layer that is STRONGLY attached to the cell wall (unlike a slime layer)

• help make the bacteria sticky (improves adherence to host cells)

• helps prevent phagocytosis, giving the bacteria greater pathogenicity

• often made of polysaccharides, but also could be polypeptides

• Visible by negative staining

T/F The capsule is visible by negative staining

True

How is a capsule different from a slime layer?

A capsule is strongly attached to the cell wall, while a slime layer is not!

What is pathogenicity?

The ability of a microorganism to cause disease in a host

What is phagocytosis?

“Cell eating”; form of endocytosis where specialized cells engulf large particles like bacteria; it is a critical immune defense mechanism in humans to destroy pathogens

Bacterial Cell Wall

• a rigid exterior that defines the shape of bacterial cells → chemically complex

• main constituent of most bacterial cell walls is peptidoglycan (found only in bacteria)

• present in most bacteria

• provides strength to resist rupturing due to osmotic pressure

What is the main constituent of most bacterial cells walls?

peptidoglycan

Peptidoglycan

repeating framework of long glycan (sugar) chains cross-linked by short peptide (protein) fragments

T/F Gram-negative bacteria have a thinner layer of peptidoglycan

True

→ Gram-positive bacteria have a thick layer of peptidoglycan; Gram-negative bacteria have a much thinner layer

Cell Membrane

• similar in structure and function to the eukaryotic cell membrane (lipid bilayer with proteins embedded)

• selectively permeable

• many enzymes are attached to the cell membrane where metabolic reactions take place

• enzymes are present for respiration and ATP synthesis, but there are NO mitochondria

In bacterial cells, are mitochondria present?

No

Why is hand soap and other chemicals important for protection from bacteria?

Antimicrobial substances can disrupt or dissolve the cell membrane bilayer (and kill the bacteria)

Membrane proteins perform or aid in many functions, such as:

• cell wall synthesis

• energy metabolism

• DNA replication

• sensation of stimuli

• molecule transport

Gram-positive cell wall

thick peptidoglycan layer, with teichoic acid and lipoteichoic acid help forming a lattice for strength

• hard to disrupt cell wall

Gram-negative cell wall

• thin peptidoglycan layer and NO teichoic acid

• lipopolysaccharide is present

• two membranes, outer membrane separated from the cell membrane by the periplasmic space

• in this space are enzymes that break down substances to allow speedy entry of nutrients into the cell

• Porins proteins that form pore channels selectively allow small hydrophilic molecules (like sugars, amino acids, and some ions) into the periplasmic space

• large molecules cannot pass

Penicillin prevents the synthesis of the peptidoglycan chains, so where are Beta-lactamases less effective against gram negative bacteria than gram positive bacteria?

Beta-lactam antibiotics are more effective against Gram-positive bacteria because they directly target the thick, exposed peptidoglycan cell wall, which is essential for the bacteria’s survival. Gram-positive bacteria lack an outer membrane, allowing easy penetration of the drug, whereas Gram-negative bacteria have an extra outer membrane (peptidoglycan sandwiched between lipopolysaccharide layers) that acts as a barrier

What accessory to prokaryotic cells makes bacteria motile?

Flagella

Flagella

Whip-like appendages composed of threads of protein called flagellin

T/F Number and arrangement of flagella are characteristic of a particular species

True

Peritrichous bacteria

flagella over entire surface (hairy appearance)

Lophotrichous bacteria

tuft of flagella at one end

Amphitrichous bacteria

one or more flagella at both ends

Monotrichous bacteria

single polar flagellum

Flagellum structure

• varies slightly between Gram Positive and Gram Negative bacteria

• There are composed of distinct parts

• Comprised of many proteins

• 360 degree rotation

What are the three distinct parts of a flagellum structure?

1.) filament

2.) hook

3.) basal body

How does flagellum structure differ from Gram Negative and Gram Positive bacteria?

• Gram Negative bacteria have four rings to anchor the flagellum through their outer membrane (because more layers)

• Gram Positive bacteria have only two rings (inner and outer) due to the lack of an outer membrane (just peptidoglycan)

Bacterial movement: chemotaxis

bacteria use their flagella to move toward attractants or away from harmful chemicals

Positive chemotaxis

movement TOWARD beneficial chemicals (like food/nutrients)

Negative chemotaxis

movement AWAY from harmful chemicals (like toxins)

Some prokaryotes move without flagella by gliding across a solid surface, called what?

Gliding motility

Endoflagella

• Spirochetes (spiral shaped cells) contain endoflagella, which move the cell through torsion (twisting) exerted on the cell by endoflagellar rotation

• the flagella gets folded from both poles and wraps around the cell

Pili is also called what?

fimbriae

Pili

• hair-like structures, most often observed on Gram-negative bacteria

• they are composed of polymerized protein molecules called pilin

• pili are thinner than flagella, have a rigid structure, and are not associated with motility

• they enable bacteria to anchor themselves to surfaces

• some bacteria possess a sex pilus for conjugation

Pili is most commonly observed on Gram ______ bacteria

negative

Cytoplasm

• it is a semiliquid that consists of water, enzymes, waste products, nutrients, proteins, carbohydrates, and lipids → materials required for metabolic functions

• 70-80% water

• site of nearly all chemical reactions

Cytoplasmic particles

• most are ribosomes, some of which occur in clusters

Ribosome function

protein synthesis

Prokaryotic ribosomes are _____ than eukaryotic ribosomes, but their function is the same

smaller

T/F Prokaryotic chromosomes usually consists of a single, long, supercoiled, circular DNA molecule and serves as the control center of the cell

True

In bacterial cells, DNA is segregated in a dense area of the cell, which is called what?

the nucleoid region

Many bacteria contain other, nonessential pieces of DNA called what?

plasmids

Plasmids

small, circular molecules of DNA that are not part of the chromosome (extra-chromosomal)

There are 3 basic categories of bacteria based on shape:

1.) cocci (spherical)

2.) bacilli (rod-shaped)

3.) curved and spiral-shaped

Cocci variations

• Diplo means pairs (diplococci)

• Strepto means chains (streptococci)

• Staphylo means clusters (staphlococci)

• Tetrads are packets of four

• Octads are packets of eight

Bacilli variations

AKA rods

• they may be short or long, thick or thin, and pointed or with curved or blunt ends

• pairs are diplobacilli

• chains are streptobacilli

If a bacterium is able to “swim,” it is said to be ______

motile

Bacterial motility is most often associated with ______ and less often with axial filaments

flagella

Most spiral-shaped bacteria and about ___ of bacilli are motile

50%

Cocci are generally _____ (in terms of motility)

nonmotile

How can motility of bacteria be demonstrated?

by stabbing the bacteria into a tube of semisolid medium or by using the hanging-drop technique

Rickettsias, chlamydias, and mycoplasmas are bacteria, but they do not possess all the attributes of typical bacterial cells

• Rickettsias and chlamydias have a Gram-negative type of cell wall and are obligate intracellular pathogens (meaning they MUST live within a host cell; they cannot grow on artificial culture media)

Rickettsias have ______ membranes

“leaky”

Chlamydias are “energy parasites,” which means what?

They prefer to use ATP molecules produced by their host cell

mycoplasmas

• they are the smallest of the cellular microbes

• they lack a cell wall and therefore assume many shapes (i.e., pleomorphic)

• in humans, pathogenic mycoplasmas cause primary atypical pneumonia and genitourinary infections

• because they have no cell wall, they are resistant to drugs like penicillin that attack cell walls

• they produce tiny “fried egg” colonies on artificial media

What does “Archaea” mean?

ancient

Archaea

• discovered in 1977

• they are prokaryotic organisms

• genetically, archaea are more closely related to eukaryotes than they are to bacteria

• Archaea vary widely in shape; some live in extreme environments, such as extremely acidic, hot, or salty environments

• Archaea possess cell walls, but their cell walls do not contain peptidoglycan

Genetically, archaea are more closely related to what?

eukaryotes

What makes archaea cell walls different than other bacterial cells?

they do not contain peptidoglycan (in contrast, all bacterial cell walls contain peptidoglycan)

Eukaryotic microbe characteristics

Fungi

• Yeast

• Mold

Parasites

• Protozoa

• Helminths

Algae

• all algal cells consist of cytoplasm, a cell wall (usually), a cell membrane, a nucleus, plastids, ribosomes, mitochondria, and Golgi bodies

  • some have a pellicle, a stigma, and/or flagella

• algae range in size from unicellular microorganisms (ex. diatoms) to large, multicellular organisms (ex. seaweeds or kelp)

• algae produce energy by photosynthesis

  • some may use organic nutrients

• algae may be arranged in colonies or strands and are found in fresh and salt water, in wet soil, and on wet rocks

What is a pellicle?

a thin, protective film or layer that forms on surfaces

Algae produce energy by _________

photosynthesis

most algal cell walls contain ________

cellulose

Depending on their photosynthetic pigments, algae are classified as what?

• green

• brown

• golden

• red

Algae are an important source of what?

food, iodine, fertilizers, emulsifiers, and stabilizers and gelling agents for jams and culture media

Medical implications of algae

• algae of the genus Prototheca is a very rare cause of human infections (i.e., protothecosis)

• algae in several other genera secrete toxic substances called phycotoxins

Phycotoxins

• poisonous to humans, fish, and other animals

• if ingested by humans, the phycotoxins produced by the dinoflagellates that cause “red tides” can lead to a disease called paralytic shellfish poisoning

Protozoa

• non-photosynthetic, eukaryotic organisms

• most are unicellular, free-living, and found in soil and water

Why are protozoal cells more animal-like than plantlike?

• they are heterotrophic (consuming external food sources), lack rigid cell walls, and are often motile

• all protozoal cells possess a variety of eukaryotic structures/organelles

• protozoa cannot make their own food by photosynthesis; some ingest whole algae, yeasts, bacteria, and smaller protozoa as their source of nutrients

Fungi

• found virtually everywhere

• some are harmful, some are beneficial

• represent a diverse group of eukaryotic organisms that include yeasts, moulds, and fleshy fungi (ex. mushrooms)

• fungi are the “garbage disposers” of nature

• Fungi are NOT plants; they are not photosynthetic

Yeasts

• eukaryotic, unicellular organisms

• usually reproduce by budding, but occasionally by a type of spore formation

• yeasts are found in soil and water and on the skins of many fruits and vegetables