Presentation is loading. Please wait.

Presentation is loading. Please wait.

Origins of Life and Other Revolutions

Similar presentations


Presentation on theme: "Origins of Life and Other Revolutions"— Presentation transcript:

1 Origins of Life and Other Revolutions

2 Key Events in Evolution of Life on Earth
Origins of life Oxygen revolution Eukaryotes (Endosymbiogenesis) Multicellularity Cambrian Explosion Major Habitat Transitions Invasion of land

3 Key Events in Evolution of Life on Earth
1.2 bya: First multicellular eukaryotes 535–525 mya: Cambrian explosion (great increase in diversity of animal forms) 500 mya: Colonization of land by fungi, plants and animals 2.1 bya: First eukaryotes (single-celled) 3.5 billion years ago (bya): First prokaryotes (single-celled) 500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 Present Millions of years ago (mya)

4 Outline Origins of life Evolution of Eukaryotes Evolution of Animals
Major Habitat Transitions

5 Outline Origins of life Evolution of Eukaryotes Evolution of Animals
Major Habitat Transitions

6 EUKARYA BACTERIA ARCHAEA Fig. 26-21 Land plants Dinoflagellates
Green algae Forams Ciliates Diatoms Red algae Amoebas Cellular slime molds Euglena Trypanosomes Animals Leishmania Fungi Sulfolobus Green nonsulfur bacteria Thermophiles (Mitochondrion) Figure The three domains of life Spirochetes Halophiles Chlamydia COMMON ANCESTOR OF ALL LIFE Green sulfur bacteria BACTERIA Methanobacterium Cyanobacteria ARCHAEA (Plastids, including chloroplasts)

7 The 3 Domains of Life Eukarya
Phylogenetic relationships based on 18S rRNA sequences, showing clade separation of bacteria, archaea, and eukaryotes.

8 Origins of Life (Herron & Freeman, Chapter 17)
4/14/2017 The Earth was formed ~4.6 billion years ago Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

9 What were the earliest life forms?
Prokaryotes are the earliest life forms we know of, but what might have preceded them?

10 Protobionts 20 µm Fig. 25-3 Glucose-phosphate Glucose-phosphate Phosphatase Starch Amylase Phosphate Maltose Figure 25.3 Laboratory versions of protobionts (a) Simple reproduction by liposomes Maltose (b) Simple metabolism Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Protobionts exhibit simple reproduction and metabolism and maintain an internal chemical environment

11 Protobionts Replication and metabolism are key properties of life
Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water

12 Self-Replicating RNA and the Dawn of Natural Selection
The early genetic material might have formed an “RNA world” The first genetic material was probably RNA, not DNA Early life forms might have consisted of protobionts with RNA as the genetic code Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection

13 RNA World RNA can both serve as the genetic code (hereditary material) and also perform enzymatic functions (ribozymes) RNA molecules called ribozymes have been found to catalyze many different reactions For example, ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA Natural selection in the laboratory has produced ribozymes capable of self-replication (Herron& Freeman written prior to this discovery)http://www.rsc.org/chemistryworld/News/2009/January/ asp

14 Self-Replicating RNA and the Dawn of Natural Selection
Ribozymes (= RNA enzyme or catalytic RNA) RNA that can catalyze chemical reactions. Many natural ribozymes catalyze either the breaking or synthesis of phosphoester bonds in DNA or RNA. Such capacity would enable the capacity to self replicate and propagate life. The functional part of the ribosome, the molecular machine that translates RNA into proteins, is fundamentally a ribozyme

15 Figure 17.2a The ribozyme from Tetrahymena thermophila
(a) The primary nucleotide sequence, which is the genotype of this catalytic RNA. This RNA is an intron (an intervening sequence between two genes) that separates two regions of the Tetrahymena genome that code for ribosomal RNA (rRNA) genes. Tom Cech and colleagues found that this sequence has the catalytic capability to splice itself out from between the two adjacent rRNAs after they have been transcribed (Kruger et al. 1982). The sequence shown here is a 413-nucleotide version, shortened from the naturally occurring form by the use of a restriction enzyme. A secondary structure of this molecule is formed when nucleotides base pair with each other as the molecule folds back upon itself during transcription from DNA. Note that in RNA, uridine (U) replaces thymidine (T), and that three types of base pairs are common: A-U, G-U, and G-C. The secondary structure shown here is drawn such that no RNA strands cross each other and, as such, does not accurately reflect how the molecule folds further into a tertiary (three-dimensional) structure.

16 Figure 17.2b The ribozyme from Tetrahymena thermophila
(b) A cartoon of the catalysis performed by the Tetrahymena ribozyme in vitro, which is its phenotype. A short oligonucleotide substrate (orange) binds to the 5' end of the ribozyme (red) through complementary base pairing (green ticks). In the presence of a divalent cation, such as Mg2+, the ribozyme catalyzes the breakage of a phosphoester bond in the substrate and the ligation of the 3' fragment to its own 3' end. This "pick-up-the-tail" event can be used to discriminate catalytically active mutant sequences from less active or inactive mutants during in vitro evolution experiments (see Figure 17.4).

17 RNA World RNA can both serve as the genetic code and also perform enzymatic functions (ribozymes) But, can RNA self replicate? If so, it would have all components to be considered “life”

18 Figure 17.6 Test-tube selection scheme for identifying ribozymes that can synthesize RNA
See text for explanation. After Bartel and Szostak (1993).

19 Figure 17.8a A ribozyme that can catalyze template-based RNA synthesis.
(a) Shows a schematic diagram of a ribozyme evolved in the lab by Wendy Johnston and colleagues (2001). The RNA of which the ribozyme is made is represented by green, black, magenta, and blue lines. The RNA sequence shown in red is the template that the researchers challenged their ribozyme to copy. The sequence in orange is a primer, complementary to the beginning of the template, which gives the ribozyme a place to start. The primer is also radioactively labeled (asterisk), which allowed the researchers to detect it, and any longer strands built from it, in an electrophoresis gel. (b) Shows the full sequence of the template. The nucleotides that extend beyond the primer are numbered. (c) Shows an electrophoresis gel revealing the products that the ribozyme had made after various lengths of time. By the end of 24 hours, the ribozyme had made complete copies of the template, 14 base pairs longer than the primer. From Johnston et al. (2001).

20 Synthetic Life Humans can now create synthetic life, by constructing a genome on the computer, synthesizing the DNA and injecting the genetic code into a cell

21 The First Single-Celled Organisms
Prokaryotes Billions of years ago 4 3 2 1 The First Single-Celled Organisms The oldest known fossils are stromatolites, rock-like structures composed of many layers of bacteria and sediment Stromatolites date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago

22 Stromatolites The oldest known fossils are of cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old

23 Prokaryotes Prokaryote: No internal membranes, organelles, nucleus
Bacteria + Archaea, not a Eukaryote Not a coherent category Archaea and Bacteria are not closer to each other than to Eukaryotes

24 EUKARYA BACTERIA ARCHAEA Land plants Dinoflagellates Green algae
Forams Ciliates Diatoms Red algae Amoebas Cellular slime molds Euglena Trypanosomes Animals Leishmania Fungi Sulfolobus Green nonsulfur bacteria Thermophiles (Mitochondrion) Figure The three domains of life Spirochetes Halophiles Chlamydia COMMON ANCESTOR OF ALL LIFE Green sulfur bacteria BACTERIA Methanobacterium Cyanobacteria ARCHAEA (Plastids, including chloroplasts)

25 Figure 17.18 An estimate of the phylogeny of all living organisms
This tree is based on the analysis of nucleotide sequences of small-subunit rRNAs. The photos show E. coli representing the Bacteria, Methanococcus jannaschii representing the Archaea, and an ant and an aphid representing the Eucarya. From Woese (1996).

26 Incredible Metabolic Diversity
Some can use inorganic chemicals as the electron donor in the redox reaction of making ATP (respiration) (animals use organic carbon, food, as the electron donor) Eukaryotes can use only oxygen as the terminal electron acceptor when making ATP in the electron transport chain (aerobic respiration) Prokaryotes can use NO3-, NO2-2, SO4-2, etc. (anaerobic respiration) Some are photosynthetic Some can fix nitrogen, converting atmospheric N2  NH3

27 Outline Origins of life Evolution of Eukaryotes Evolution of Animals
Major Habitat Transitions

28 Oxygen Revolution “Oxygen revolution” from 2.7 to 2.2 billion yrs ago
Atmospheric oxygen Billions of years ago 4 3 2 1 Oxygen Revolution “Oxygen revolution” from 2.7 to 2.2 billion yrs ago O2 in the atmosphere was generated by photosynthetic activity of cyanobacteria Cyanobacteria were the first organisms to use H2O (instead of H2S or other compounds) as a source of electrons and hydrogen for fixing CO2 Photosynthesis: 6 CO2 + 6 H2O + photons → C6H12O6 + 6 O2

29 Oxygen Revolution O2 allows the production of more energy and more efficient metabolism C6H12O O2 → 6 CO H2O, ΔG = kJ per mole of C6H12O6 Aerobic metabolism: 36 ATP molecules per glucose Anaerobic metabolism: 2 ATP molecules per glucose Aerobic and anaerobic metabolism share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. However, Oxygen is also Toxic Oxygen is highly toxic to many species Electrons that escape from the electron transport chain can bind to oxygen and produce reactive oxygen species Reactive oxygen species (H2O2, O2−) can damage DNA and other molecules

30 Evolutionary History dictates type of Metabolism
The fact that much of prokaryotic life evolved BEFORE the oxygen revolution is reflected in the diverse forms of anaerobic metabolism Most bacteria do not require oxygen, and for many it is toxic Most bacteria use other molecules as the terminal electron acceptor when making ATP The fact eukaryotic life evolved AFTER the oxygen revolution is reflected in the fact that all eukaryotes use aerobic metabolism They use oxygen as the terminal electron acceptor in energy production

31 Lynn Margulis Endosymbiotic Theory Wrote the seminal paper “The Origin of Mitosing Eukaryotic Cells” 1966 Certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts. Mitochondria developed from proteobacteria (in particular, Rickettsiales or close relatives) and chloroplasts from cyanobacteria Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (in being circular in shape, its size, and DNA composition)

32 Covered in Chapter 15, Freeman and Herron
Figure 25.9 A model of the origin of eukaryotes through serial endosymbiosis Probably Archaea The organelles (mitochondria and chloroplasts) greatly aid in energy production in eukaryotes.

33 Given the evolutionary history of endosymbiosis (or endosymbiogenesis) leading to eukaryotes, eukaryotes will inevitably share traits with both archaea and bacteria Table 27.2

34 Outline Origins of life Evolution of Eukaryotes Evolution of Animals
Major Habitat Transitions

35 230 mya: Permian Extinction
4/14/2017 65 mya: Cretaceous Extinction (dinosaurs go extinct) 230 mya: Permian Extinction 570 mya: Cambrian Explosion

36 (3) Origins of Animal Phyla Cambrian Explosion (570 MYA)
4/14/2017 (3) Origins of Animal Phyla Cambrian Explosion (570 MYA) Burgess Shale

37 Radiations: Extinctions???? Cambrian Explosion
4/14/2017 (1) Precambrian-Paleozoic (570 MYA) Boundary Cambrian Explosion Radiations: Evolution of hard body parts Diversification of body forms Radiation of Invertebrates Extinctions????

38 4/14/2017

39 4/14/2017

40 4/14/2017 What is an Animal?

41 What is an Animal? Multicellular (metazoan)
4/14/2017 What is an Animal? Multicellular (metazoan) Heterotrophic (eat, not photo or chemosynthetic) Eukaryote No Cell Walls, have collagen Nervous tissue, muscle tissue Particular Life History-developmental patterns (this lecture)

42 Origins of Multicellularity
4/14/2017 Origins of Multicellularity It is thought that metazoans arose from Colonial flagellate protists Oxygen Revolution: allow higher metabolic rate larger body size powered motion

43 Cells of sponges are similar to flagellate protists
4/14/2017 Cells of sponges are similar to flagellate protists

44 Doushantuo formation Southern China
4/14/2017 Doushantuo formation Southern China 570 million years ago Clusters of cells (embryos?) Sponges Fossilized metazoan embryo at the 256 cell stage

45 4/14/2017 Burgess Shale Fossils Marrella Aysheaia Canadia Hallucigenea

46 4/14/2017 WHY?

47 (higher energy, larger animals possible)
4/14/2017 Ecological arms race? Increase in oxygen? (higher energy, larger animals possible)

48 4/14/2017 The Paleozoic Sea

49 4/14/2017 When?

50 4/14/2017 Are Genetic Distances and fossil record roughly congruent?

51 Was the Cambrian Explosion an Explosion?
4/14/2017 Was the Cambrian Explosion an Explosion? Geology: YES Sudden Appearance of Animal Fossils Genetics: NO DNA Divergences Predate Cambrian

52 Precambrian Annelida Arthropoda Mollusca Agnatha Gnathostomata
4/14/2017 Annelida Mollusca Agnatha Million Years Ago Arthropoda Echinodermata Gnathostomata 200 Cambrian 600 Based on phylogeny of animals based on DNA sequence data, the radiation of animals predates the geological record of the Cambrian Explosion 800 1000 Precambrian 1200 Wray et al. 1996 1400

53 Fossil Record vs Molecular Clock
4/14/2017 Fossil Record vs Molecular Clock Molecular clock and fossil record are not always congruent Fossil record is incomplete, and soft bodied species are usually not preserved Mutation rates can vary among species (depending on generation time, replication error, mismatch repair) But they provide complementary information Fossil record contains extinct species, while molecular data is based on extant taxa Major events in fossil record could be used to calibrate the molecular clock

54 Fossil Record vs Molecular Clock
4/14/2017 Fossil Record vs Molecular Clock So it’s highly likely that the divergence of animal lineages (phyla) was more gradual than the fossil record would suggest and that the time of divergence happened earlier

55 Evolution of Animal Body Plans
4/14/2017 Evolution of Animal Body Plans True Tissues Tissue Layers (Diplo vs Triploblasts) Body Symmetry Evolution of body cavity (Coelom) Evolution of Development

56 4/14/2017 Cambrian Explosion

57 Of course, evolution continued after the Cambrian Explosion
4/14/2017 Of course, evolution continued after the Cambrian Explosion But major body plans evolved within a short period of time

58 How could this happen? (genetic mechanism?)
4/14/2017 How could this happen? (genetic mechanism?)

59 4/14/2017 Genetic Mechanisms? We talked about how selection and drift could result in speciation The formation of novel body plans calls for changes (mutation, selection, drift) at loci that cause fundamental morphological changes

60 The Evolution of Development (Freeman& Herron, Chapter 19)
The tremendous increase in diversity during the Cambrian explosion appears to have been caused by evolution of developmental genes Changes in developmental genes can result in radically new morphological forms Developmental genes control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult

61 Changes in a few regulatory genes could have big impacts
4/14/2017 Changes in a few regulatory genes could have big impacts Most new features of multicellular organisms arise when preexisting cell types appear at new locations or new times in the embryo. Changes in the specification of cell fates is a major mechanism for the evolution of different organismal forms.

62 Example of Evolution Developmental Genes that could result in radically new body forms
Hox genes are a class of homeotic genes that provide positional information during development If Hox genes are expressed in the wrong location, body parts can be produced in the wrong location For example, in crustaceans, a swimming appendage can be produced in a segment instead of a feeding appendage

63 Mutations in a Hox gene causing legs to grow out of the head
In this case, the identity of one head segment has been changed to that of a thoracic segment. Figure 19.2b Homeotic mutants in Drosophila (b) Mutations in the antp gene can produce adult flies with legs growing from the head. In this case, the identity of one head segment has been changed to that of a thoracic segment.

64 Hox Clusters Gene family formed by gene duplication events
4/14/2017 Hox Clusters Gene family formed by gene duplication events Hox genes, usually found clustered next to each other along animal chromosomes Hox gene products are regulatory proteins that bind to DNA and control the transcription of other genes

65 Figure 19.1 Hox genes in Drosophila
In these diagrams,T1-T3 and A1-A8 indicate the three thoracic and eight abdominal segments, respectively. The int, mx, and 1a regions of the embryo form head structures. The bottom part of the figure shows the relative locations of genes in the HOM cluster. Each gene is color coded to indicate where it is expressed. Expression of pb, for example, influences the identity of cells that make the proboscis or mouthparts of the fly; both are shaded green. From Gerhart and Kirschner (1997).

66 4/14/2017

67 Christiane Nüsslein-Volhard and Sean Carroll
4/14/2017 Christiane Nüsslein-Volhard and Sean Carroll

68 4/14/2017 Hox Clusters Hox genes specify the developmental fate of individual regions within the body (modules), and usually the genes are activated and expressed in the body in the same order as their position in the cluster These genes regulate timing and location of gene expression during development

69 4/14/2017 Example: Hox Genes

70 Figure 19.3 Hox genes from various animal phyla
The boxes on the right represent homeotic loci that have been found in each of the taxa on the tree. Genes that are thought to be homologous are lined up vertically; the vertical white lines group genes that are clearly homologous. Modified from Valentine et al. (1996), de Rosa et al. (1999), and Hoegg and Meyer (2005).

71 Evolution of Hox clusters
4/14/2017 Evolution of Hox clusters HOX-clusters undergo essential rearrangements in evolution of main taxa Duplication, deletion, divergence of the genes lead to differentiation in body plans Other regulatory genes/gene families are also important

72 Animal body plans 4/14/2017

73 Evolutionary changes in Hox Genes
New morphological forms likely come from gene duplication events that produce new developmental genes A possible mechanism for the evolution of six- legged insects from a many-legged crustacean ancestor has been demonstrated in lab experiments Specific changes in the Ubx gene have been identified that can “turn off” leg development

74 Hox gene 6 Hox gene 7 Hox gene 8 Ubx About 400 mya Drosophila Artemia
Figure Origin of the insect body plan Drosophila Artemia

75 Figure 19.4 The arthropod radiation
Note the diversity of form and function in the segments and limbs of these representative taxa. Onychophorans are the closest living relative of arthropods.

76 Differences in Hox gene expression distinguish the various arthropod segmentation patterns
Figure 19.5 Differences in Hox gene expression distinguish the various arthropod segmentation patterns The Hox cluster for all arthropods is similar, represented by the color-coded boxes on the left. The evolutionary tree shows the relationships between some of the major arthropod groups and the Onychophora. The diagrams on the right show where the various Hox genes are expressed in representatives of these taxa. Appendages such as antennae, mouthparts, wings, and legs are shown for some segments. Each unique body plan is associated with a unique pattern of Hox gene expression. From Knoll and Carroll (1999).

77 Evolution of Vertebrates (Phylum Chordata)
Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes Two duplications of Hox genes are thought to have occurred in the vertebrate lineage These duplications may have been important in the evolution of new vertebrate characteristics

78 Polyploidization is probably the single most important mechanism for the evolution of major lineages and for speciation in plants Multiple rounds of polyploidization might have occurred during the early evolution of vertebrates

79 Hypothetical vertebrate ancestor (invertebrate)
with a single Hox cluster First Hox duplication Hypothetical early vertebrates (jawless) with two Hox clusters Second Hox duplication Figure Hox mutations and the origin of vertebrates Vertebrates (with jaws) with four Hox clusters

80 Outline Origins of life Evolution of Eukaryotes Evolution of Animals
Major Habitat Transitions

81 Habitat Transitions Freshwater invasions Invasion of Land
Key innovations with the invasion of land

82 Geological record of timing of terrestrial invasions

83 Example of extraordinary environmental change:
Transitions between Saltwater  Freshwater and Water  Land Constitute Major Evolutionary Transitions in the History of Life So a striking example of an extraordinary environmental change: are Transitions between major habitat boundaries such as the invasion from saltwater  freshwater habitats, and the invasion from aquatic habitats  onto land These major habitat transitions Constitute Major Evolutionary Transitions in the History of Life

84 Sea Fresh Land Protista X X Porifera X X Cnideria X X Ctenophora X Platyhelminthes X X X Nemertea X X X Rotifera X X Gastrotricha X X Kinorhyncha X Nematoda X X Nematomorpha X X Entoprocta X X Annelida X X X Mollusca X X X Phoronida X Bryozoa X X Brachiopoda X Sipunculida X Echiuroida X Priapulida X Tardigrada X X Onychophora X Arthropoda X X X Echinodermata X Chaetognatha X Pogonophora X Hemichordata X Chordata X X X Life evolved in the sea, and freshwater and terrestrial habitats impose profound physiological challenges for most taxa (Hutchinson 1957; Lee & Bell 1999) Of ~40 Animal Phyla, only 16 invaded fresh water, and only 7 invaded land As you all know, Life evolved in the sea, and freshwater and terrestrial habitats impose profound physiological challenges for most taxa The bulk of animal diversity is in the sea, and of the ~40 Animal Phyla, only 16 have been able to invade fresh water, and only 7 have been able to invade land

85 Habitat Invasions Sea Fresh water Soil Land Protista X X X
4/14/2017 Sea Fresh water Soil Land Protista X X X Porifera X X Cnideria X X Ctenophora X Platyhelminthes X X X X Nemertea X X X Rotifera X X X Gastrotricha X X Kinorhyncha X Nematoda X X X Nematomorpha X X Entoprocta X X Annelida X X X X Mollusca X X X X Phoronida X Habitat Invasions

86 Habitat Invasions Sea Fresh water Soil Land Bryozoa X X Brachiopoda X
4/14/2017 Sea Fresh water Soil Land Bryozoa X X Brachiopoda X Sipunculida X Echiuroida X Priapulida X Tardigrada X X X Onychophora X X Arthropoda X X X X Echinodermata X Chaetognatha X Pogonophora X Hemichordata X Chordata X X X X Habitat Invasions

87 4/14/2017 Osmoregulation The regulation of water and ions poses among the greatest challenges for surviving in different habitats. Marine habitats pose the least challenge, while terrestrial habitats pose the most. In terrestrial habitats must seek both water and ions (food). In Freshwater habitats, ions are limiting while water is not.

88 The invasion of land occurred relatively recently (late in the history of life on earth)

89 The Colonization of Land
Precambrian: colonization of land by bacteria Late Ordovician–Late Devonian: Terrestrial ecosystems of plants, fungi, arthropods and eventually vertebrates Late Silurian: vascular plants Devonian: evidence of interactions among groups (fungal-plant symbiosis, arthropod herbivory) Late Devonian: Two major megaclades that were major participants in the Cambrian explosion appear on land The lophotrochozoans: gastropod and bivalve mollusks, oligochaete annelids, rotifers, etc. The ecdysozoans: arthropods, nematodes, etc. Invasion of land by crustaceans  origin of insects (Hexapods) Early Carboniferous: radiation of tetrapods (vertebrates with 4 legs)

90 Major Transitions of the Paleozoic

91 The invasion of land by crustaceans (terrestrial crustaceans = insects)

92 Questions What are some of the key biological revolutions that occurred during the history of life on earth, and how did they come about? Why is it hypothesized that early life on earth was in the form of RNA? How did the Oxygen Revolution come about? What are the implications of a high oxygen atmosphere for organismal physiology? How were Eukaryotes created? What are animals? About when did animals evolve? Is there congruence between fossil estimates versus molecular clock estimates of the timing? How did animals diversify (Cambrian Explosion)? Where did life evolve (land, sea)? About when did organisms begin to live on land? What are some challenges of living on land (relative to the sea)?

93 Which of the following is MOST likely to be true regarding evolutionary relationships among the major domains of life? (A) Bacteria and Archaea are both grouped into the category of “Prokaryotes” because they are more closely related to each other than to Eukaryotes (B) Archaea are ancestral to all other forms of Life (C) The Oxygen Revolution defines the emergence of life on Earth (D) Eukaryotes arose from a symbiotic relationship among prokaryotes (E) Eukaryotes evolved from Prokaryotes through Horizontal Gene Transfer

94 2. Which of the following is Least likely to be true regarding Prokaryotic Metabolism and the Oxygen Revolution? The oxygen revolution led to the proliferation of diverse types of prokaryotic metabolism (B) The oxygen revolution enabled the preponderance of more efficient metabolism that could produce more ATP per unit glucose (C) The oxygen revolution altered the atmosphere of the Earth (D) The oxygen revolution created an inhospitable habitat for many classes of prokaryotes that use molecules other than oxygen as their terminal electronic acceptor for energy production (E) The oxygen revolution was caused as a byproduct of photosynthetic activity of cyanobacteria

95 3. Which of the following does NOT make RNA a good candidate for early life on earth? (a) RNA could act as an enzyme (b) RNA could serve as the genetic code (c) RNA is much more stable than DNA in our current atmosphere (d) RNA can catalyze chemical reactions that break or synthesize phosphodiester bonds in RNA or DNA (e) Recent studies suggest that RNA is capable of self replication

96 4. Which is the following is NOT a consequence of the Oxygen Revolution? (a) The ability of organisms to metabolically produce more ATP by using oxygen as the terminal electron acceptor during respiration (b) Eukaryotes, which evolved after the Oxygen Revolution, all use aerobic metabolism (c) The transformation of the earth's atmosphere ~2.5 billion years ago from one that was chemically reducing to one that is oxidizing (d) The heightened risk of DNA and cellular damage in organisms through oxygen free radicals (e) The proliferation of bacteria that use oxygen as the terminal electron acceptor during respiration, such that nearly all bacterial species are aerobic

97 Answers 1D 2A 3C 4E


Download ppt "Origins of Life and Other Revolutions"

Similar presentations


Ads by Google