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The Origin and Evolution of Microbial Life: Prokaryotes and Protists
Chapter 16 The Origin and Evolution of Microbial Life: Prokaryotes and Protists
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How Ancient Bacteria Changed the World
How Ancient Bacteria Changed the World Mounds of rock found near the Bahamas Contain photosynthetic prokaryotes
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Fossilized mats 2.5 billion years old mark a time when photosynthetic prokaryotes
Were producing enough O2 to make the atmosphere aerobic Layers of a bacterial mat
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EARLY EARTH AND THE ORIGIN OF LIFE
16.1 Life began on a young Earth Planet Earth formed some 4.6 billion years ago
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The early atmosphere probably contained
H2O, CO, CO2, N2, and some CH4 Volcanic activity, lightning, and UV radiation were intense Figure 16.1A
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Fossilized prokaryotes called stromatolites
Date back 3.5 billion years Figure 16.1B
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A clock analogy tracks the origin of the Earth to the present day
And shows some major events in the history of Earth and its life Paleozoic Meso- zoic Ceno- zoic Humans Land plants Animals Multicellular eukaryotes Single-celled eukaryotes Origin of solar system and Earth 1 2 4 3 Proterozoic eon Archaean eon Billions of years ago Atmospheric oxygen Prokaryotes Figure 16.1C
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16.2 How did life originate? Organic molecules
May have been formed abiotically in the conditions on early Earth
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TALKING ABOUT SCIENCE 16.3 Stanley Miller’s experiments showed that organic molecules could have arisen on a lifeless earth Figure 16.3A
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Simulations of such conditions
Have produced amino acids, sugars, lipids, and the nitrogenous bases found in DNA and RNA Cooled water containing organic molecules Cold water Condenser Sample for chemical analysis H2O “Sea” Water vapor “Atmosphere” Electrode CH4 NH3 H2 Figure 16.3B
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16.4 The first polymers may have formed on hot rocks or clay
Organic polymers such as proteins and nucleic acids May have polymerized on hot rocks
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16.5 The first genetic material and enzymes may both have been RNA
The first genes may have been RNA molecules That catalyzed their own replication G A C U 1 2 Formation of short RNA polymers: simple “genes” Assembly of a complementary RNA chain, the first step in replication of the original “gene” Monomers Figure 16.5
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16.6 Membrane-enclosed molecular cooperatives may have preceded the first cells
RNA might have acted as templates for the formation of polypeptides Which in turn assisted in RNA replication Self-replication of RNA Self-replicating RNA acts as template on which poly- peptide forms. Polypeptide acts as primitive enzyme that aids RNA replication. RNA Polypeptide Figure 16.6A
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Membranes may have separated various aggregates of self-replicating molecules
Which could be acted on by natural selection LM 650 Membrane Polypeptide RNA Figure 16.6B, C
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PROKARYOTES 16.7 Prokaryotes have inhabited Earth for billions of years Prokaryotes are the oldest life-forms And remain the most numerous and widespread organisms Colorized SEM 650 Figure 16.7
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More bacteria inhabit a handful of soil than the total number of people who have ever lived!
Bacteria grow in extreme conditions (unsuitable for eukaryotes) Too Cold Too Hot Too salty Too acidic Too alkaline Bacteria have high genetic diversity Most prokaryotic cells have diameters in the range of 1 – 5 μm
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‘Infamous’ Bacteria Bubonic Plague Tuberculosis Cholera Yesinia pestis
Mycobacterium tuberculosis Cholera Vibrio cholerae
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Not all bacteria is bad Bacteria in our intestines provide us with important vitamins There are approximately 100 trillion bacteria living inside each human. Ideally, the body should have at least 85% good bacteria for optimal health. Proper digestion of food *Absorption of nutrients *Production of vitamins *Elimination of toxins. *Prevention from allergies, since good bacteria allow the body to distinguish between harmful substances and healthy ones.
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Not all bacteria is bad cont.,
Bacteria in our mouth protect us against some harmful fungi candida fungus - thrush Bacteria that decompose dead organism (detritovoures)
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16.8 Bacteria and archaea are the two main branches of prokaryotic evolution:
Domains Bacteria and Archaea Are distinguished on the basis of nucleotide sequences and other molecular and cellular features
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Differences between Bacteria and Archaea
Archaea have characteristics that resemble prokaryotes (bacteria) and eukaryotes. One theory is that present day archaea and eukaryotes evolved from a common ancestor. Table 16.8
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Other differences between bacteria and archaea
Domain Bacteria: Cell wall Provides shape and protection peptidoglycan Plasma membrane Archaea: Do not contain peptidoglycan Lipid structure of the plasmid membrane is different.
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16.9 Prokaryotes come in a variety of shapes
Prokaryotes may be shaped as Spheres (cocci) Rods (bacilli) Most bacillus occur singly Some in pairs or diplobacilli or chains streptobacilli Curves or spirals Syphilis - spirochete Colorized SEM 12,000 Colorized SEM 9,000 Colorized SEM 3,000 Figure 16.9A–C
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The arrangement of the bacteria lends to its name
Staphylo Clusters staphylococcus Strepto Chains Streptococcus streptobacilli
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16.10 Various structural features contribute to the success of prokaryotes
External Structures The cell wall Is one of the most important features of nearly all prokaryotes Is covered by a sticky capsule Colorized TEM 70,000 Capsule Figure 16.10A
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Some prokaryotes Stick to their substrate with pili Pili
Colorized TEM 16,000 Pili Figure 16.10B
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Motility Many bacteria and archaea
Are equipped with flagella, which enable them to move Flagellum Plasma membrane Cell wall Rotary movement of each flagellum Colorized TEM 14,000 Figure 16.10C
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Reproduction and Adaptation
Prokaryotes Have the potential to reproduce quickly in favorable environments Binary fission Most produce a new generation in 1- 3 hours Some can reproduce every 20 minutes!
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Some prokaryotes can withstand harsh conditions
By forming endospores Thick, protective coating Dehydrates and becomes dormant It has the capacity to survive harsh conditions Some endospores remain dormant for centuries TEM 34,000 Endospore Figure 16.10D
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Internal Organization
Some prokaryotic cells Have specialized membranes that perform metabolic functions Aerobic, photosynthesis & anaerobic Aerobic cyanobacteria Respiratory membrane Thylakoid membrane TEM 45,000 TEM 6,000 Figure 16.10E
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16.11 Prokaryotes obtain nourishment in a variety of ways
As a group Prokaryotes exhibit much more nutritional diversity than eukaryotes Autotrophs Photoautotrophs Chemoautotrophs Heterotrophs Photoheterotrophs Chemoheterotrophs
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Types of Nutrition Autotrophs make their own organic compounds from inorganic sources Photoautotrophs harness sunlight for energy and use CO2 for carbon Chemoautotrophs obtain energy from inorganic chemicals instead of sunlight H2S; S; Fe containing compounds
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Most prokaryotes are Heterotrophs (other feeders) they obtain their carbon atoms from organic compounds Photoheterotrophs can obtain energy from sunlight Chemoheterotrophs are so diverse that almost any organic molecule can serve as food for some species Figure 16.11A
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Nutritional classification of organisms
Table 16.11
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Metabolic Cooperation
In some prokaryotes The cyanobacteria has genes for photosynthesis and for nitrogen fixation (N2 → NH3+), but the O2 production inactivates the nitrogen fixing enzyme To combat this they form colonies in which most cells photosynthesize, while others fix nitrogen LM 650 Photosynthetic cells Nitrogen-fixing cells Colorized SEM 2,8000 Figure 16.11B
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Metabolic cooperation occurs in surface-coating colonies called biofilms
Colorized SEM 13,000
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16.12 Archaea thrive in extreme environments and in other habitats
Archaea are common in Salt lakes, acidic hot springs, deep-sea hydrothermal vents Figure 16.12A, B
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Extreme Halophiles Thrive in very salty places Great Salt Lakes
Dead Sea
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Extreme Thermophiles Heat loving
Some live neat deep ocean vents where temperatures reach up to 100°C Some thrive in acid
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Methanogens Aerobic environments and give off methane
They can be found in digestive tracts of cows, human and swamps.
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16.13 Bacteria include a diverse assemblage of prokaryotes
Domain Bacteria is currently divided into nine groups, five of which are considered subgroups. Proteobacteria Chlamydias Spirochetes LM 13,000 Colorized TEM 5,000 Figure 16.13A, B
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Subgroups cont., Gram-positive bacteria
Cell walls have thick layer of peptidoglycan which stains purple. Cyanobacteria, which photosynthesize in a plantlike way Colorized SEM 2,800 LM 650 Photosynthetic cells Nitrogen-fixing cells Colorized SEM 2,8000 Figure 16.13C, D
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CONNECTION 16.14 Some bacteria cause disease
Pathogenic bacteria cause disease by producing exotoxins or endotoxins Gram negative species are generally more threatening than gram positive . The lipids on the outer membranes are often toxic. SEM 12,000 Spirochete that causes Lyme disease “Bull’s-eye”rash Tick that carries the Lyme disease bacterium SEM 2,800 Figure 16.14A, B
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Pathogenic bacteria cause about half of all human diseases
2 million die from TB each year 2 million dies from diarrheal causing pathogens such as: cholera Samonella campylobacter.
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Exotoxins secreted by bacterial cells and include some of the most potent poisons known, such as Botulinum toxin Endotoxins are part of the outer membrane of the cell wall of Gram-negative bacteria. Properly refer to as lipopolysaccharide complex pathogens such as Escherichia coli, Salmonella, Shigella, Pseudomonas, Neisseria, Haemophilus influenzae, Bordetella pertussis and Vibrio cholerae.
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Preventing Bacterial Disease
Sanitation Water treatment systems Sewage systems Antibiotics Education Lyme Disease Transmitted by ticks that attach to dear and mice Disease leads to debilitating arthritis, heart disease and nervous disorders Classic signs are the red-bulls eye target rash Using insect repellent and wear light colored clothing may help reduce contact with tics
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Compare and contrast Exotoxins and Endotoxins
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CONNECTION 16.15 Bacteria can be used as biological weapons
Bacteria, such as the species that causes anthrax Can be used as biological weapons Figure 16.15
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Use of Bacteria as a weapon
Anthrax spores mailed to Congress in resulted in the death of 5 people and illness to 18 others. During the middle ages, armies hurled individuals killed by bubonic plague at the enemy. Early settlers in South and North America gave the native American people items that purposely were contaminated with infectious bacteria often wiping out whole tribes.
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Why is Bacillus Anthracis an effective bioweapon?
It is easy to obtain Spore forming bacterium that lives in the soil of agricultural regions Easy to grow in the lab Form deadly endospores that are resistant to extreme conditions and can be stored for long periods. Easy to disperse
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CONNECTION 16.16 Prokaryotes help recycle chemicals and clean up the environment All of life depends on the cycling of chemical elements between organisms and the nonliving parts of our environment. Rhizobium live in the nodules of legumes Convert large amounts of nitrogen gas to nitrates in the soil. Cyanobacteria Contribute to aquatic environmnets Release oxygen to the atmosphere Convert nitrogen gas to ammonium
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Bioremediation The use of organisms to clean up pollution
Prokaryotes are decomposers in Sewage treatment and can clean up oil spills and toxic mine wastes Liquid wastes Outflow Rotating spray arm Rock bed coated with aerobic bacteria and fungi
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PROTISTS 16.17 The eukaryotic cell probably originated as a community of prokaryotes Eukaryotic cells Evolved from prokaryotic cells more than 2 billion years ago
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The nucleus and endomembrane system
Probably evolved from infoldings of the plasma membrane
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Mitochondria and chloroplasts
Probably evolved from aerobic and photosynthetic endosymbionts, respectively
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A model of the origin of eukaryotes
Cytoplasm Ancestral prokaryote Plasma membrane Endoplasmic reticulum Nucleus Nuclear envelope Cell with nucleus and endomembrane system Membrane infolding Aerobic heterotrophic prokaryote Ancestral host cell Endosymbiosis Mitochondrion Chloroplast Photosynthetic eukaryotic cell Photosynthetic prokaryote Some cells A model of the origin of eukaryotes Figure 16.17
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16.18 Protists are an extremely diverse assortment of eukaryotes
Are mostly unicellular eukaryotes Molecular systematics Is exploring eukaryotic phylogeny LM 275 Figure 16.18
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16.19 A tentative phylogeny of eukaryotes includes multiple clades of protists
The taxonomy of protists Is a work in progress Diplomonads Euglenozoans Dinoflagellates Apicomplexans Ciliates Water molds Diatoms Brown algae Amoebas Plasmodial slime molds Cellular slime molds Fungi Choanoflagellates Animals Red algae Green algae Closest algal relatives of plants Plants Alveolates Stramenopila Amoebozoa Ancestral eukaryote Figure 16.19
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16.20 Diplomonads and euglenozoans include some flagellated parasites
The parasitic Giardia Is a diplomonad with highly reduced mitochondria Colorized SEM 4,000 Figure 16.20A
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Euglenozoans Include trypanosomes and Euglena Figure 16.20B, C
Colorized SEM 1,300 Figure 16.20B, C
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16.21 Alveolates have sacs beneath the plasma membrane and include dinoflagellates, apicomplexans, and ciliates Dinoflagellates Are unicellular algae SEM 2,300 Figure 16.21A
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Apicomplexans are parasites Such as Plasmodium, which causes malaria
Red blood cell Apex TEM 26,000 Figure 16.21B
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Cilliates Use cilia to move and feed Cilia Macronucleus Figure 16.21C
LM 60 Figure 16.21C
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16.22 Stramenopiles are named for their “hairy” flagella and include the water molds, diatoms, and brown algae This clade includes Fungus-like water molds Figure 16.22A
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Photosynthetic, unicellular diatoms
LM 400 Figure 16.22B
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Brown algae, large complex seaweeds
Figure 16.22C
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16.23 Amoebozoans have pseudopodia and include amoebas and slime molds
Move and feed by means of pseudopodia LM 185 Figure 16.23A
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A plasmodial slime mold is a multinucleate plasmodium
That forms reproductive structures under adverse conditions Figure 16.23B
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Cellular slime molds Have unicellular and multicellular stages 45
Slug-like aggregate 45 LM 1,000 15 Amoeboid cells Reproductive structure Figure 16.23C
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16.24 Red algae and green algae are the closest relatives of land plants
Contribute to coral reefs Figure 16.24A
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Green algae May be unicellular, colonial, or multicellular
Chlamydomonas Volvox colonies LM 80 LM 1,200 Figure 16.24B
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The life cycles of many algae
Involve the alternation of haploid gametophyte and diploid sporophyte generations Mitosis Male gametophyte Gametes Spores Meiosis Fusion of gametes Female gametophyte Zygote Sporophyte Haploid (n) Diploid (2n) Key Figure 16.24C
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16.25 Multicellularity evolved several times in eukaryotes
Multicellularity evolved in several different lineages Probably by specialization of the cells of colonial protists Unicellular protist Colony Early multicellular organism with specialized, interdepen- dent cells Later organism that produces gametes Food- synthesizing cells Locomotor cells Somatic cells Gamete 1 2 3 Figure 16.25
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Multicellular life arose over a billion years ago
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