Biology 111 Lake Tahoe Community College

Biology 111 Lake Tahoe Community College

Winter Quarter Instructor: Sue Kloss

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Chapter 15 – Bio 111

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Read portion National Geographic re: origin of earth and/or lives of a cell

I. Bioterrorism – Anthrax 2001 (Fig. 15.1)

A. Plague infested bodies hurled into enemy ranks in middle ages

B. US Pledged in 1969 to end bioterror research

C. Most bacteria are beneficial or neutral to humans and to all life, and life probably began w/

bacteria

II. Early earth and the origin of life (Fig. 15.2) – life needed the build up of O2

A.  (Fig. 15.3) Life began on a young earth

1.  3 billion yrs ago- earth bristles w/volcanoes, poisonous atmosphere;

2.  greenish mats of prokaryotes line shore

3.  O2 released from prokaryotes will change atmosphere forever

4.  Formation and breakup of Pangaea will have huge influence on diversity and distribution of life

5.  Homo sapiens will alter the land air and sea, also

6.  It is thought that the universe is expanding, the result of a giant explosion 10 – 20 billion years ago

7.  The earth probably started as a swirling mass of dust that condensed

8.  The core of earth is molten material, and there are layers of varying density

9.  The outermost layer is the thin, solid crust of the earth

10.  Early atmosphere of earth was composed of CO, CO2, N2 and H20, w/ possibly some methane and ammonia

11.  First seas may have formed when earth cooled enough for water to condense as rain

12.  Lightning, volcanic activity and UV radiation made early earth a pretty different place

13.  In this environment, life began

14.  Stromatolites are the fossilized mats of prokaryotes

B.  Stanley Miller’s experiments

1.  1953 Miller showed that amino acids and other organic molecules could have been formed on lifeless earth

2.  Oparin and Haldane proposed that O2 (corrosive – disrupts chemical bonds by extracting electrons) in atmosphere prevents spontaneous formation of organic molecules

3.  Early earth’s atmosphere would have added electrons, encouraging formation of chemical bonds

4.  Miller showed this was possible in the laboratory

C.  How did life originate?

1.  people used to think that life spontaneously arose, up till mid 19th century, eg flies came from rotting meat

2.  In 1862 Louis Pasteur confirmed that all life comes from preexisting life – no spontaneous generation.

3.  Did not address where life comes from

4.  We think that life began in prokaryotic form about 3.6 billion yrs ago – 4 Stages

5.  Stage 1 - aynthesis and accumulation of small organic molecules would have been a first step in formation of life

6.  2nd stage, formation of polymers would have preceded formation of life

7.  3rd stage - Origin of mechanism of polymer replication would have had to occur – ribozymes and RNA “genes” (Fig. 15.5)

8.  4th stage - Finally, aggregates of polymers must have had to have different chemical characteristics from surroundings – precells (Fig. 15.6 and 15.7)

D.  The first polymers may have been formed on hot rocks or clay

1.  after small organic molecules formed, the next step would have been polymerization – long chains of small organic molecules to form one long molecule

2.  polymers are formed by dehydration synthesis – a process that links two monomers (small molecules) together in a process that results in formation of water – thus dehydration synth.

3.  Normally, enzymes facilitate, but this can also be accomplished in lab settings where water is vaporized and the monomers are concentrated; some spontaneously bond

4.  Clay particles have electrically charged sites for binding monomers, so this could have spontaneously occurred on clay surfaces.

E.  The first genetic materials may have been RNA, which in lab settings has been known to spontaneously assemble

1. this process could occur a number of times, resulting in replication of genetic information

F.  Molecular cooperatives enclosed by membranes

1.  Life requires a great number of complex organic molecules and the molecules must interact and cooperate in precise ways

2.  If RNA served as a recipe for binding together amino acids, which could then be linked by Zinc, or some other metal that may have served as a catalyst, then the resulting protein could have been an enzyme that helped RNA replicate- reciprocal molecular cooperation

3. this process could occur a number of times, resulting in replication of genetic information

5.  Experiments have shown that in aqueous environment, certain organic molecules self (including lipids and proteins) assemble into spheres filled w/fluid; these have a semipermeable membrane

6.  these are cell-like, but not truly living.

7.  if these were likely to grow and replicate more efficiently than other collections of coops, they would have been favored by natural selection

8.  Scientists are fairly certain the first cells were prokaryotes

II. Prokaryotes

A. Prokaryotes have inhabited earth for billions of years

1. Fossil record shows that prokaryotes were abundant 3.5 bya

2. evolved alone on earth for next 1.5 billion yrs

3. outnumber all eukaryotes

4. more prokaryotes in your mouth than all people who ever lived

5.  prokaryotes thrive in habitats not suitable for any eukaryotes - extremes of heat, cold,

acidity, saline, alkaline

6.  tiny - 1- 10 um; most eukaryotes 10 - 100 um. Numerous can fit on head of a pin (fig.

15.8)

7.  Some cause serious illness (bubonic plague killed 25% of human pop in 1300’s), STD,

food poisoning

8. most are benign or beneficial - intestinal forms provide us with vitamins; mouth bacteria

prevent yeast from growing there

9. essential as decomposers; recycle organic compounds

10. important in food chain for this reason

B. Archaea and bacteria are 2 main branches of prokaryotic evolution

1. fundamentally different cellular organization than eukaryotes

a. lack membranes around nucleus and membranous organelles

2. 2 domains represented by prokaryotes

a. Archaea

b. bacteria

3. differences btn these 2

a. nucleotide sequences in RNA are different

4. sequences in eukaryotes more closely match archaea

5.  some genes of archaea are closer to bacteria, some closer to eukarya. Some are unique to archaea

6. cell walls of bacteria have peptidoglycan - sugars linked by short polypeptides

7. archaea not inhibited by antibiotics, bacteria are

C. Bacteria come in a variety of shapes (Fig. 15.10)

1. cocci - spheres

a. staphylococcus - cluster of cocci

b. streptococcus - chain of cocci

2. bacilli - rod shaped

a. diplobacilli

b. streptobacilli

3. curved or spiral - spirochete

a. some of these may be comma - shaped

b. helical- corkscrew

c. if very short and rigid, called spirilla

D. Prokaryotes obtain nourishment in a variety of ways (fig. 15.11)

1. autotrophs - self-feeders

a. photoautotrophs - use sun energy to make food - eg cyanobacteria do Ps

b. chemoautotrophs - obtain energy from inorganic chemicals

2. most prokaryotes are heterotrophs - other feeders

3.  most bacteria obtain nutrition the same way humans do - obtain both energy and carbon

from organic compounds

E. Archaea thrive in extreme environments - and in the ocean

1. thrive where no other organisms can survive

2. extreme halophiles - salt lovers - fig. 15.9

3. extreme thermophiles - - may live in water above the boiling pt. of water at sea level

a. many acidic hot pools in Yellowstone have archaea

4.  methanogens - live in swamps, anaerobic muds; intestines - gas is the result of metabolism

5. many live in the ocean, not in extreme areas, below 150 m

6. one of the most abundant cell types in oceans

F. Diverse structural features help prokaryotes thrive almost everywhere

1. flagella - unique structural features

a. lacks microtubules, made of protein

b. (Fig. 15.12) has rotating rings that give it a propeller movement

c.  allows bacteria to move from less favorable environments, toward more favorable

ones

2. May have pilli

a. help bacteria stick to each other and to surfaces

b. special pilli are involved in bacteria reproduction - sex pilli

3. may withstand harsh conditions as an endospore - e.g. anthrax

a.  endospore is a cell inside a cell. If outer cell disintegrates, endospore waits till

harsh conditions are over and then absorbs water, resumes growth (Fig. 15.13)

b. may remain dormant for centuries

c. some are incredibly resistant - labs use autoclaves - heat water to 250 F

d. bacteria that causes botulism is killed this way

d.  some bacteria produce actinomycetes - filaments meant to bridge unhospitable

gaps in environment - streptomycin is drug produced by one of these (Fig 15.11)

4. Some bacteria cause disease

a. exotoxins - toxic proteins secreted by bacteria - Staphylococcus aureus - “skin

sloughing” and toxic shock

b. endotoxins - toxins components of cell walls - salmonella, typhoid fever

c. lyme disease cause by bacteria - no cure after a month

5. prokaryotes can recycle chemicals and clean environment

a. breakdown of organic wastes in septic/sewage tment plants Fig. 15.16.and 15.17

b. oil pollution

c. old mining sites - bacteria consume acidic wastes and metals

III. Protists

A. the first eukaryotic cells probably originated as a community of prokaryotes

1. fossil record shows eukaryotes evolved from prokaryotes 2 billion years ago

2. Fig. 15.18 - membrane infolding allowed endomembrane system to develop

3.  endosymbiosis - first mitochondria and chloroplasts - much more energy

available

4. perhaps smaller cells were indigestible

5. some euks have chloroplasts, all have mitochondria, probably evolved first

6. both types of organelles have DNA, RNA and ribosomes

7. larger cell supplies molecules and organic ions

8. also helps explain why mitochondria and chloroplasts both have 2 outer membranes, if engulfed by larger cell originally

B.  Protists - unicellular eukaryotes and their close multicellular relatives - probably represent

multiple kingdoms

C. Mitochondria and chloroplasts are similar to prokaryotes in many ways-

1. contain DNA, RNA and ribosomes

2. replicate own DNA, reproduce in cells; process resembles binary fission

D. Protists are mostly unicellular eukaryotes

1. Algae - synthesize own food: Ps

2. protozoans - eat bacteria, other protists, or organic matter

3. colonial or multicellular eukaryotes

E. Apparently, first protists arose from prokaryotes, rest of life descended from them

F. Protist Diversity: protozoans, slime molds, multicellular algae, unicellular algae (fig. 15.19)

1. protozoans - ingest food, aquatic environment

a. eat bacteria or other protozoans, or absorb nutrients

1). flagellates- move by one or more flagella. most nonparasitic

a). giardia - human intestine; most like eukaryotic cells

b). trypanosoma - sleeping sickness

2). amoebas and forams -absence of permanent locomotor organelles.

a). feed by pseudopod engulfing prey - becomes food vacuole

b). move by oozing, any shape

c. forams have pseudopods and almost all marine; CaCO3

3). apicomplexans - all parasitic

a). one end contains complex of organelles specialized for penetrating host cells

b). plasmodium, spread by mosquito, feeds on red blood cells- malaria

4). ciliates - use cilia to move and eat; aquatic

a). Paramecium

b). Stentor

b. highly diverse

2. cellular slime molds - both unicellular and multicellular life stages

a. Dictyostelium: (fig 15.21)

1). amoeboid stage when food (bacteria) is plentiful

2). colony - swarm together, slug like, secreting slime.

3). develop into reproductive structure

b. nothing in common with true molds or fungi

3. plasmodial slime molds - found in moist, decaying matter (Fig. 15.20)

a. plasmodium (different from malaria-causing species)- single mass of cytoplasm, undivided by membranes, contain many nuclei

b. weblike form increases surface area for resource acquisition

c. when resources are scarce, organism stops growing and differentiates into reproductive structures

4. algae- (Fig. 15.22) most are photosynthesizing protists; like plants in that they synthesize

own food

a. have chlorophyll a

b. some heterotrophic protists are considered algae bc they share many features

1). dinoflagellates -

a). freshwater or marine unicellular algae

b). spinning movement - 2 flagella

c). cause red tide

2). diatoms - marine and freshwater

a). unicellular, Psing algae- cell wall contains silica - mineral that makes glass

b). cell wall- two halves like a box and lid

c). important in food chain

d). store food in oil, which makes them buoyant, near sunlight

e). massive accumulations in sediments- diatomaceous earth

used as filter or abrasive

3). green algae

a). chlamydomonas - freshwater lakes and ponds

b). Volvox - daughter colonies

c). cellulose, starch and chloroplasts suggest they are ancestors to plants

5. Seaweeds - multicellular marine algae that lack true stems, leaves, roots and vascular structures (Fig. 15.23)

a. brown algae - brown or olive colored- related to diatoms; e.g. kelp

b. red algae - important in reef building

c. green algae - Ulva- sea lettuce. Alternation of generations - alternation of generations - alternation of haploid and diploid forms of the organism (Fig. 16.26C)

1). sporophyte - diploid stage

2). gametophyte - haploid stage

6. Multicellular life may have evolved from colonial protists, and evolved over hundreds of millions of years (fig 15.24)

Ch. 15 Homework Questions/Lesson Objectives

1.  Describe the conditions under which the first life likely formed and the nature of those first living organisms

2.  Describe the timing and likely events that led to first life on earth

3.  Describe the experiments of Stanley Miller and their significance in understanding how life might have first evolved

4.  Explain the potential role of clay particles in life on earth

5.  Describe the roles of RNA in evolution of early life

6.  Describe how the first cooperative of molecules enclosed in membranes may have originated

7.  Describe the history and diverse roles of prokaryotes

8.  Compare the characteristics of Arachaea and Bacteria

9.  Compare diff’t shapes of bacteria

10.  Describe structures and functions of prokaryotic features

11.  Explain what causes bacterial “blooms”

12.  Describe some diseases associated with bacteria

13.  Describe and explain significance of Kochs Postulates

14.  Describe positive uses of prokaryotes to humans

15.  Explain how first eukaryotic cells likely originated as community of prokaryotes

16.  Describe different types of protists. Explain why biologists think they belong to 5 kingdoms

17.  Describe characteristics of 4 most common groups of protozoa

18.  Describe and compare cellular slime molds and plasmodial slime molds

19. Describe the characteristics of algae, including sea weeds. Compare dinoflagellates, diatoms and green algae