Chapter 27 & 28

Prokaryotes & Protists

Ch. 27 ~ Prokaryotes Overview: They’re (Almost) Everywhere! Most prokaryotes are microscopic

But what they lack in size they more than make up for in numbers

The number of prokaryotes in a single handful of fertile soil Is greater than the number of people who have ever

lived

Prokaryotes thrive almost everywhere Including places too acidic, too salty, too cold, or too

hot for most other organisms

Figure 27.1

27.1 ~ Structural, functional, and genetic adaptations contribute to prokaryotic success

Most prokaryotes are unicellular Although some species form colonies

Prokaryotic cells have a variety of shapes The three most common of which are spheres

(cocci), rods (bacilli), and spirals

1 m 2 m 5 m(a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral

Cell-Surface Structures One of the most important features of nearly all

prokaryotic cells Is their cell wall, which maintains cell shape,

provides physical protection, and prevents the cell from bursting in a hypotonic environment

Using a technique called the Gram stain Scientists can classify many bacterial species

into two groups based on cell wall composition, Gram-positive and Gram-negative

(a) Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye,which masks the added red dye.

(b) Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between theplasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added.

Figure 27.3a, b

PeptidoglycanlayerCell wall

Plasma membrane

Protein

Gram-positivebacteria

20 m

Outermembrane

Peptidoglycanlayer

Plasma membrane

Cell wall

Lipopolysaccharide

Protein

Gram-negativebacteria

The cell wall of many prokaryotes Is covered by a capsule, a sticky layer of

polysaccharide or protein

200 nm

Capsule

Figure 27.4

Some prokaryotes have fimbriae and pili Which allow them to stick to their substrate or other

individuals in a colony

200 nm

Fimbriae

Figure 27.5

Motility Most motile bacteria propel themselves by

flagella Which are structurally and functionally different from

eukaryotic flagellaFlagellum

Filament

HookCell wall

Plasmamembrane

Basal apparatus

50 nm

Figure 27.6

Internal and Genomic Organization Prokaryotic cells

Usually lack complex compartmentalization Some prokaryotes

Do have specialized membranes that perform metabolic functions

(a) Aerobic prokaryote (b) Photosynthetic prokaryote

0.2 m 1 m

Respiratorymembrane

Thylakoidmembranes

Figure 27.7a, b

The typical prokaryotic genome Is a ring of DNA that is not surrounded by a

membrane and that is located in a nucleoid region

Figure 27.81 m

Chromosome

Some species of bacteria Also have smaller rings of DNA called plasmids Draw a prokaryotic cell and label the DNA and plasmids

Prokaryotes reproduce quickly by binary fission And can divide every 1–3 hours Many prokaryotes form endospores

Which can remain viable in harsh conditions for centuries

Endospore

0.3 mFigure

27.9

27.2 A great diversity of nutritional and metabolic

adaptations have evolved in prokaryotes Examples of all four models of nutrition are

found among prokaryotes: List Energy source & Carbon source:

Photoautotrophy Chemoautotrophy Photoheterotrophy Chemoheterotrophy

Major nutritional modes in prokaryotes

Table 27.1

27.3 Molecular systematics is illuminating

prokaryotic phylogeny Until the late 20th century

Systematists based prokaryotic taxonomy on phenotypic criteria

Applying molecular systematics to the investigation of prokaryotic phylogeny Has produced dramatic results

A tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematics

Figure 27.12

Domain BacteriaDomainArchaea

DomainEukarya

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Proteobacteria

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Sp i

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Ko r

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Eu r

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Cre

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Universal ancestor

Bacteria

Diverse nutritional types Are scattered among the major groups of bacteria

The two largest groups are The proteobacteria and the Gram-positive bacteria

Chlamydias, spirochetes, Gram-positive bacteria, and cyanobacteria

Chlamydia (arrows) inside an animal cell (colorized TEM)

Leptospira, a spirochete (colorized TEM)

Streptomyces, the source of many antibiotics (colorized SEM)

Two species of Oscillatoria, filamentous cyanobacteria (LM)

Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM)

2.5

m

5

m5

m

50

m

1

m

Figure 27.13

Archaea

Archaea share certain traits with bacteria And other traits

with eukaryotes

Table 27.2

Some archaea live in extreme environments Extreme thermophiles thrive in very hot

environments Extreme halophiles live in high saline

environmentsColorful “salt-loving” archae live in these ponds near San Fransisco. Used for commercial salt production.

MethanogensLive in swamps and marshes and produce methane as a waste product

27.4 Prokaryotes play crucial roles in the biosphere Chemical Recycling Prokaryotes play a major role in the continual

recycling of chemical elements between the living and nonliving components of the environment in ecosystems

Chemoheterotrophic prokaryotes function as decomposers Breaking down corpses, dead vegetation, and waste products

Nitrogen-fixing prokaryotes Add usable nitrogen to the environment

Symbiotic Relationships Many prokaryotes -

Live with other organisms in symbiotic relationships such as mutualism and commensalism

Figure 27.15

27.5 Prokaryotes have both harmful and beneficial

impacts on humans Some prokaryotes are human pathogens

But many others have positive interactions with humans Prokaryotes cause about half of all human diseases

Lyme disease is an example

5 µm

Figure 27.16

Prokaryotes in Research and Technology Experiments using prokaryotes have led to important

advances in DNA technology Prokaryotes are the principal agents in bioremediation

The use of organisms to remove pollutants from the environment

Prokaryotes are also major tools in Mining, the synthesis of vitamins, production of

antibiotics, hormones, and other products

Ch. 28 ~ Protists 28.1: Protists are an extremely diverse

assortment of eukaryotes Protists are more diverse than all other

eukaryotes And are no longer classified in a single kingdom

Most protists are unicellular, colonial or multicellular

Protists, the most nutritionally diverse of all eukaryotes, include Photoautotrophs, which contain chloroplasts Heterotrophs, which absorb organic molecules or

ingest larger food particles Mixotrophs, which combine photosynthesis and

heterotrophic nutrition

There is now considerable evidence that much of protist diversity has its origins in endosymbiosis

Cladogram of Protists:

28.3: Euglenozoans have flagella with a unique internal structure

Euglenozoa is a diverse clade that includes Predatory heterotrophs, photosynthetic autotrophs,

and pathogenic parasites

Dinoflagellates Are a diverse group of aquatic photoautotrophs and heterotrophs Are abundant components of both marine and freshwater phytoplankton

Ciliates, a large varied group of protists Are named for their use of cilia to move and feed Have large macronuclei and small micronuclei

Conjugation – Two cells exchange haploid micronuclei (similar to prokaryotic conjugation).

**Produces genetic variation

28.5 Hairy and smooth flagella1. Diatom – Surrounded by a two part glass like wall and are a major component of phytoplankton.

Phytoplankton account for half of the photosynthetic activity on earth – responsible for much of the oxygen

in our atmosphere.

2. Golden Algae – Have two flagella and their color results from carotenoids.

3. Brown Algae – multicellular mostly marine protists, commercially used; seaweeds

28.6 Threadlike pseudopodia Pseudopodia extend and help to injest

microorganisms.

28.7 ~ Amoebozoans

Lobed shaped pseudopodia*Entamoebas – parasites of vertebrates and cause amebic dysentry in humans.

*Slime molds – extend their pseudopodia through decomposing material, engulfing food by phagocytosis.

28.8 ~ Red & Green Algae are the closest relatives of land plants.