Introduction to the Eukaryotes of Microbiology

Eukarya

Branched off from Archaea

Unicellular and multicellular organisms

Eukaryotes

Highly diverse domain

structurally & functionally complex

Sexual and/or asexual reproduction

Larger size

Larger genome

Defined nucleus w/membrane

Membrane-bound organelles

Endosymbiosis – Origin of Eukarya

Endo: inside; symbiotic: collaboration between organisms

Endosymbiotic Theory

Mitochondria origin

Chloroplast origin

Supporting evidence – mitochondria & chloroplasts share with bacteria

Similar size

70S ribosomes 

Small, circular DNA genome; gene sequences 

Phospholipid bilayer surrounding membranes 

Ability to replicate by a binary fission-like process

Mitochondria origin

an engulfed nonphotosynthetic bacteria

Chloroplast origin

an engulfed photosynthetic bacteria

Eukaryote Kingdoms & Relevance to Microbiology

4 main branches of eukaryotes emerged from a common ancestor

Fungi

Plants

Animals

Protists

Fungi

Unicellular & multicellular 

Chitin+glucan cell wall

Produce O2 and spores

Sexually & asexually reproduce 

Can be pathogenic to humans

Protists

Most unicellular and microscopic 

Not classified as animal, plant, or fungi 

Sexually & asexually reproduce 

Photosynthetic = algae

Non-photosynthetic = protozoans 

Can be pathogenic to humans

Animals

Multicellular 

Lack cell wall 

Most use O2 

Move 

Sexually & asexually reproduce 

Can be pathogenic to humans

Plants

Most multicellular

Cellulose cell wall

Chloroplasts = photosynthetic 

Produce O2 and seeds 

Sexually & asexually reproduce 

No known human pathogens

Non-membrane Enclosed Structures

Ribosomes

Cytoskeleton

Ribosomes

Protein factories

Made of proteins + ribosomal RNA (rRNA)

80S in cytoplasm & rough ER

Free in cytoplasm

bound to ER

70S in mitochondria and chloroplasts

Cytoskeleton

Dynamic and responsive intracellular network of protein fibers

Maintain shape and mechanically resist (or allow) deformation

Membrane-bound Organelles

Unique to eukaryotes

Structural and functional compartments 

Enclosed in lipid bilayers

Nucleus 

Endomembrane System

Mitochondria 

Nucleus

Houses DNA genome within nucleoplasm

Nucleolus

Enclosed by nuclear envelope

Nuclear pores control traffic of materials

Essential role in all cellular activities and cell division, reproduction, heredity

Nucleus

Houses DNA genome within nucleoplasm

Multiple linear chromosomes 

Chromatin - complex of DNA+proteins (histones)

Nucleus

Nucleolus

dense region of rRNA biosynthesis; ribosome assembly begins

Nucleus

Essential role in all cellular activities and cell division, reproduction, heredity

Mitosis – asexual replication

Meiosis – sexual reproduction

Mitosis

Asexual replication

parent cell divides into 2 genetically identical daughter cell clones à 1 division

Meiosis

Consists of 2 cell division stages I & II

1 parent cell produces 4 genetically distinct gametes

Homologous recombination

Gametes are haploid

Each contain 1/2 chromosomes of parent (diploid)

Endomembrane System - EMS

Large cell size and volume requires cellular transport system

Series of membranous tubules, sacs, and flattened disks (cisternae) that synthesize many cell components and move materials within the cell

Composed of several organelles and connections between them

Endoplasmic Reticulum (ER)

Originate from nuclear envelope

Interconnected array of cisternae and tubules

Defined as ‘rough’ or ’smooth’

Rough ER

cisternae

Studded with ribosomes

Proteins produced, inserted into RER membrane, modified 

Bud off in vesicles – transported to Golgi apparatus for further processing, the plasma membrane, the membrane of another organelle, or out of the cell

Smooth ER

tubules

No associated ribosomes

Involved in biosynthesis of lipids, carbohydrate metabolism, and detoxification of toxic compounds

Golgi apparatus

Array of cisternae

Enzymes modify lipids and proteins transported from the ER – add carbohydrates

Produce: glycolipids, glycoproteins, or proteoglycans

Sorts and distributes final products

Transport vesicles containing products pinch off

Cell surface significance of processed products

Distinguish types of cells

Roles in cell recognition (other cells, viruses)

Serve as cell surface receptors

Vesicles

Required for survival → transport, secrete, digest, and sequester materials

Small, fluid-filled, lipid bilayer enclosed, spherical sacs

Vesicles-General Types & Function

Transport – move materials within cell

Secretory — store and traffic to cell surfaces for release

Exocytosis 

Vacuoles – typically larger than vesicles, often used for storage

Exocytosis 

process of release to cell exterior; constitutive or regulated

Lysosomes

cellular garbage disposals

Digestive enzymes + low pH = break down particles

Peroxisomes

oxidative degradation

Enzymatically degrade fats, amino acids, toxins

Mitochondria

Double membrane, 70S ribosomes, circular chromosome→ endosymbiosis

Primary function – generate energy for cell(ATP)

Carry out programmed cell death (apoptosis)

Most eukaryotic cells have mitochondria

Plasma Membrane

Phospholipid bilayer cell membrane on all cells

Peripheral and integral proteins 

Fluid-mosaic 

Selective barrier

Contain sterols (cholesterol/ergosterol)

Membrane Transport Mechanisms

Simple diffusion, facilitated diffusion, and active transport 

Unique to eukarya – endocytosis(import in) and exocytosis(export out)

Glycocalyx

Sticky, polysaccharide gel coating extracellular surface of the PM

“Face” of the cell – communicates with the extracellular world

Roles in cell protection, interactions, adhesion, associations with other macromolecules

Extracellular Matrix (ECM)

Helps maintain shape, provide structural stability, transmits signals

Produced animal and some protist cells (cells lacking cell walls)

Sticky, secreted mass of carbohydrates and proteins

Extensive, varies, distinct properties

Often the site of bacterial attachment

Cell Wall

Only in eukaryotes that lack ECM – fungi and certain protists (& plants) 

External to the plasma membrane 

Rigid, structural layer that helps maintain cell shape 

Protects against desiccation, mechanical and osmotic stress 

Made of a range of materials (vs bacteria)

Motility Structures – Cilia and Flagella

Membrane-covered hairlike structures projecting out from cell surface 

Composed of microtubules and connected to cell via basal body 

Function like oars or whips – wave-like motion

move cell through environment or move environment past cell

Cilia

numerous (1000s), shorter, coordinated movement

Flagella

less numerous (1 to a few), longer ’tail-like’

Parasites

An organism that lives on or in a host organism and obtains food from or at the expense of its host

Protozoa(unicellular endoparasite)

Helminths(multicellular, endoparasite)

Ectoparasites (multicellular)

Protista

Highly diverse group of eukaryotes – earliest evolutionary link Inhabit a wide variety of habitats, both aquatic and terrestrial

Pathogenic protists→ Parasitic protozoans “first animals” (no cell wall

Parasitic protozoans

Many have 2-phase life cycles, alternating between proliferative stages (e.g., trophozoites) and resting cysts (survive harsh conditions)

ortion of life cycle occurs within a host and has potential to cause illness

Categorized based on motility and morphology into 4 types

Parasitic protozoans

4 types

Amoeboid

Flagellated

Ciliated

Sporozoans/Apicomplexan

Helminths (worms)

Microscopic aspects of life cycle → identified by microscopic eggs and larvae

287 species of multicellular parasites can infect and live within human body

2 main categories of medical significance

Helminths (worms)

2 main categories of medical significance:

Flatworms: tapeworms(segmented) or Flukes(Non-segmented)

roundworms: nematodes

Animals – Ectoparasites of Microbiology

Some pathogenic microbes require arthropod vectors for part of life cycle (feed on blood)

Biting insects are important vectors that transmit a variety of pathogens

Fungi of Microbiology

Cell walls contain chitin; cell membranes contain ergosterols

Typically grow slower than bacteria and at lower temperature & pH

Unique and complex lifecycles involving asexual and sexual reproduction

Grow as yeast (microscopic) or mold (macroscopic) or both (dimorphic)

Mold

multicellular form with tubular filaments termed hyphae

Microscopic evaluation of hyphae and spores used for classification

Reproduce by producing large numbers of spores

Septate hyphae

walls between the cells

Nonseptate hyphae

lack separation between the cells

Mycelia

macroscopically visible intertwined mass of hyphae (fuzzy appearance)

Unicellular Fungal Characteristics

Yeast – unicellular form, 5-10X larger than bacteria

asexually by budding

Dimorphic – change between yeast and mold forms in response to environmental changes (nutrient availability or fluctuations in temperature)

Mycoses

diseases caused by fungal infection

Superficial mycoses – infect skin & nails (tinea), mouth & vagina (candida)

Invasive, systemic mycoses – widespread, involve internal organs, lethal

Eukaryotic Pathogens in Eukaryotic Hosts

Eukaryotes do NOT product peptidoglycan → target bacteria

Developing medications effective against eukaryotic cells other than human is difficult 

Medications for systemic infections with eukaryotic pathogens often have toxic side effects