Brief history of life on Earth

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Lawrence Benson
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4 Billion Years ago: First animals and plants (Fossil evidence indicates that modern humans originated in Africa about 200,000 years ago)

1 Brief history of life on Earth 4.6 Billion Years ago: Earth forms 3.6 Billion Years ago : First life on the planet (Prokaryotes = Bacteria) 2.8 Billion Years ago : First eukaryotic life (also microbial algae/protozoa) 0.4 Billion Years ago: First animals and plants (Fossil evidence indicates that modern humans originated in Africa about 200,000 years ago) Fossilized stromatolite * Stromatolites - layered rock-like structures formed in shallow water by the trapping/binding/cementation of sedimentary grains by microbes; Represent the most ancient records of life on Earth. 1

Two types of Cellular Organization Eukaryotic cells DNA surrounded by a membrane/envelope =>cell nucleus Prokaryotic cells DNA not surrounded

2 Two types of Cellular Organization Eukaryotic cells DNA surrounded by a membrane/envelope =>cell nucleus Prokaryotic cells DNA not surrounded by an envelope Prokaryotic Structure Relatively simple structure: DNA, ribosomes, cell membrane, cell wall, plus a few other parts (not shown) 2

Eukaryotic Structure By comparison, euks are much more complex, containing

membranes EUK Eukaryotes have energy organelles (mitochondria / chloroplasts), an

3 Eukaryotic Structure By comparison, euks are much more complex, containing specialized organelles to perform particular functions Prokaryotes and eukaryotes: universal vs. distinct structures Universal: Both have DNA, ribosomes (to make proteins), and cell membranes EUK Eukaryotes have energy organelles (mitochondria / chloroplasts), an endomembrane system (ER/GOLGI) to package and sort materials, cytoskeleton (fibers that move materials around and help with cell division), and a nuclear membrane PROK 3

4 How did we get from prok to euk??? Lynn Margulis Endosymbiotic theory Euks came from proks ingesting other proks, but instead of digesting them they began to use them as organelles Evidence shows that mitochondria and chloroplasts have bacterial origins TAXONOMY Biology attempts to catalog organisms 1. Aristotle: described 500 plants and animals 2. Linnaeus: described 1000 s of plants and animals, devised the binomial system (Genus/Species), part of the hierarchal system of nomenclature 3. Whittaker: 5 Kingdom system (Animals/Plants/Fungi/Protista/Bacteria) 4. Woese: 3 Domain System 4

Nomenclature gives scientific names to organisms Linnaeus Binomial system:

homo sapiens) His groupings were based upon shared physical characteristics.

5 Nomenclature gives scientific names to organisms Linnaeus Binomial system: everything has two names based on genus and species (e.g. homo sapiens) His groupings were based upon shared physical characteristics. Quoted as saying GOD CREATES, LINNAEUS NAMES Whittaker s Five Kingdom System 1. Animals 2. Plants 3. Fungi 4. Protists (algae/protozoa/ + lower fungi ) 5. Monera (prokaryotes) Note that 4 out of 5 are eukaryotic organisms, only 1/5 prokaryotic 5

The three-domain system places the Monera in separate lineages Classification is based on differences in ribosomal RNA (and/or the DNA genes that encode these RNAs) Carl Woese Recall that all life

6 The three-domain system places the Monera in separate lineages Classification is based on differences in ribosomal RNA (and/or the DNA genes that encode these RNAs) Carl Woese Recall that all life forms have ribosomes, so by comparing how similar the ribosomes are to each other we can see how closely they are related to one another Comparison of rrna genes from diverse organisms Note that certain regions of the sequences vary from each other, so that the more similar they are, the more closely related are the organisms (more differences = more distant relationship) 6

Relationship between diverse organisms based on sequences of rrna genes Organisms A and B have only 2 differences between them, whereas both A+B have 6 differences from C: thus it is inferred that

7 Relationship between diverse organisms based on sequences of rrna genes Organisms A and B have only 2 differences between them, whereas both A+B have 6 differences from C: thus it is inferred that A+B should be closer together on a family tree than either should be to organism C (note that X is the universal ancestor of all three other organisms) Three Domain System THE THREE DOMAINS ARE: EUBACTERIA, ARCHAE, and EURKARYA (thus 2/3 PROKS and 1/3 EUKS) 7

COMPARISON Eubacteria OF Eubacteria Archae Eukaryotes THIS HIGHLIGHTS THE DIFFERENCES BETWEEN THE 3 DOMAINS Source: S. Finkel, 2002 Eubacterial vs.

8 COMPARISON Eubacteria OF Eubacteria Archae Eukaryotes THIS HIGHLIGHTS THE DIFFERENCES BETWEEN THE 3 DOMAINS Source: S. Finkel, 2002 Eubacterial vs. Archaeal cytoplasmic membranes ARCHAE cell membrane is much stronger with more molecules and tighter bonding than EUBACTERIA -- this helps them to survive extreme environments 8

9 Bacteria: Shapes and Arrangements Bacilli Cylinder shape Can be singles or form chains Examples: E. coli, Shigella, Salmonella, Anthrax, etc. 9

at each end; Spirochetes are thin and flexable, with an internal flagella called

10 Cocci CUBE OF 8 = Sarcina Examples: Staph infections, Strep throat bacteria, etc. Spirals and other shapes Spirilla are thick and rigid, with a single flagellum at each end; Spirochetes are thin and flexable, with an internal flagella called an axial filament that rotates beneath the cell wall (moves like a cork screw ) 10

Bacteria: Structure From the outside to the inside of the cell Bacterial flagella Provide motility Rotate (clockwise/countercwise) Embedded in cell wall,

11 Bacteria: Structure From the outside to the inside of the cell Bacterial flagella Provide motility Rotate (clockwise/countercwise) Embedded in cell wall, extend out from there Allow bacteria to move toward nutrients, or away from repellants (e.g. antibiotics, white blood cells) this is called chemotaxis 11

12 Structure of bacterial flagella Basal body = motor embedded in the cell wall and membrane; Rotates, which then drives the external filament Bacterial motion mediated by flagella If the flagella rotate counterclockwise, the bacterium moves in a straight path ( run ) if they rotate clockwise, the bacterium will tend to stay in place ( tumble ) 12

13 Chemotaxis For example: If bacteria encounter food, the organisms stay around the same area (see A above). However, if food is sensed somewhere nearby, they ll move toward it (see B ). Movement of Shigella within and between cells Note that these organisms invade intestinal cells and then move from one cell to another, causing water loss = extreme diarrhea 13

fibers Help bacteria to attach to surfaces (e.g.

14 TYPES OF FLAGELLA Monotrichous: one flagellum at one end Amphitrichous: flagella at both ends Lophotrichous: two or more flagella clustered at one end only Peritrichous: many flagella all around the cell Pili Protein fibers Help bacteria to attach to surfaces (e.g. urethra in Urinary tract infections) Special pili (conjugation pili) are used for bacteria intercourse where they move DNA between cells Enhance ability to cause disease 14

15 Binding of pili to host cells Note that the tips of pili contain proteins that dock down and lock on to receptor molecules on host cell surfaces Glycocalyx Sticky, sugary layer around cells Not all bacteria have it, but the ones that do are more dangerous! Attachment is easier (sticky) Retain water, so they don t dry out Repel the white blood cells of the immune system as WBCs are keyed to look for foreign proteins so these sugars help hide the cell 15

16 Two types: Cell wall 1. Gram-positive: thick layer of peptidoglycan (surrounds cells and protects them); also contains teichoic acid; Retains the primary (purple) gram stain in spite of gram alcohol (destaining) treatment. 2. Gram negative: thin layer of peptidoglycan, lose the gram stain when gram alcohol (destainer) is applied. ** Also have an extra membrane outside the cell wall called LPS (lipopolysaccharide) layer contains endotoxin, an internal poison that makes these cells dangerous (re: septic shock) Structure of Gram-positive cell envelope Note the thick peptidoglycan and the Teichoic acid that binds together the cell wall components 16

This part contains endotoxin Cell envelope of Gram-Positive vs.

17 Structure of gram-negative cell envelope Note the thin peptidoglycan sandwiched between two membranes, as well as the lack of teichoic acid This part contains endotoxin Cell envelope of Gram-Positive vs. Gram-Negative Bacteria Hint: Make sure you can compare and contrast these two for an exam! 17

18 Structure of E. coli peptidoglycan Synthesis of peptidoglycan 18

nutrients, exports waste, site of ATP production in bacs Chemical composition: 40% phospholipids 60% embedded

19 b-lactam antibiotics Prevent new cell walls from being formed so bacs burst apart (below)! Cell membrane Permeability barrier (cellular materials separate from environment); imports specific nutrients, exports waste, site of ATP production in bacs Chemical composition: 40% phospholipids 60% embedded proteins Both move (Fluid mosaic model) Action of disinfectants/drugs: alcohols dissolve this layer; some Anti-biotics poke holes in it 19

Cytoplasm Is the center of biochemical activity Structures within the cytosol --Ribosomes --Inclusion bodies: store nutrients (Phosphate/Sulfur/Glycogen) --DNA: two forms A.

Plasmids = molecules of DNA separate from chromosome that can carry genes for toxins or antibiotic resistance Spores Are designed for dormancy Spore formation: when nutrients

20 Cytoplasm Is the center of biochemical activity Structures within the cytosol --Ribosomes --Inclusion bodies: store nutrients (Phosphate/Sulfur/Glycogen) --DNA: two forms A. Chromosome(s) B. Plasmids = molecules of DNA separate from chromosome that can carry genes for toxins or antibiotic resistance Spores Are designed for dormancy Spore formation: when nutrients are limited Chemical composition: chromosome + small amount of cytoplasm surrounded by thick layers of peptidoglycan Resistance: little water so heat resistant; Dipicolinic Acid stabilizes the DNA Can survive alcohol, boiling water, etc for many years Many Pathogenic bacteria form spores including Anthrax, Botulism, and Tetanus bacteria 20

21 Bacterial Spore Formation When nutrients are available, the spore will germinate back to a normal cell again 21

MORPHOLOGY: the study of form and structure

MICROBIOLOGY CHAPTER 3 Bacteria Morphology 3:1 Bacteria Structure and Function MORPHOLOGY: the study of form and structure Structure of Bacteria 1. PROKARYOTIC no membrane bound nucleus nor other organelles