Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 4. Emergence of life

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1 Chapter 4 Emergence of life

2 major transitions of life One of the first was a change from inorganic chemicals to organic compounds Figure 4.2 Emergence of life

3 Inorganic to organic evolution (4 billion years ago) FIGURE 4.3 Life in Test Tubes, The Miller-Urey Experiment

4 The transition on earth to organic evolution occurred about 4 billion years ago The earliest microorganisms were heterotrophs Heterotrophs they did not directly manufactured ingredients needed for their own maintenance and duplication, but instead subsisted on organic chemicals available in their environment

5 Cell-Prokaryotic, Heterotrophs (3.5 billion years ago) Oldest fossils of microorganisms are found in rocks 3.5 billion years ago in Western Australia FIGURE 4.4 Bacterial cell, generalized

6 Characteristics of early microorganisms Prokaryotic Absence of organelles Heterotrophs Reproduce asexually

7 Cell-prokaryotic, autotrophs (2.7 billion years ago) The earth was not born with atmospheric O 2 Rocks about 2.7 billion years old indicate that free O 2 has already begun to accumulate in the atmosphere. Photosynthesis was well established Photosynthesizing prokaryotic cells were autotrophs Autotroph: an organism that synthesize compounds sufficient to sustain its own cellular metabolism. The early photosynthetic prokaryotes that generate O2 as a by-product were cyanobacteria

8 Cell s prokaryotes to Eukaryotes (2 billion years ago) Chemical traces unique to eukaryotic cells are found in rocks, 2.1 billion years of age. Characteristics of eukaryotic cells The cellular DNA is enclosed by the nucleus The cell contains numerous organelles, dedicated to particular function Mitochondria Central vacuole Chloroplast Cell wall Eukaryotic cells can reproduce asexually or sexually What are the advantages of sexual reproduction?

9 FIGURE Eukaryotic cells, generalized from an animal and plant

10 Multicellularity After binary fission cells may remain in contact with each other producing a complex of joined cells Multicellular organisms take advantage of cell specialization

11 Major transition of life and consequences Ozone O3 is a derivative of O2, circles the earth high above in the atmosphere like a shield O3 filters out much of the incoming UV radiation

12 Pollutant The first prokaryotic cells to evolve did so in the absence of O 2. Later, photosynthesis was established, and O 2 began to accumulate in the atmosphere O 2 became a pollutant to the first anaerobic prokaryotes, Why? Cells and multicellular organisms that evolved later in the presence of O 2, they became dependent on O 2

13 Other transitions of life Origin of sex The origin of multicelluar organisms The origin of social groups and cooperative effort The origin of consciousness

14 Endosymbiosis: The view that eukaryotic cells evolved from partnership with different prokaryotic organisms How origin of eukaryotes happened? What are the evidences that mitochondria and chloroplasts evolved from free living prokaryotes? FIGURE 4.7 Origin of eukaryotes

15 Chemical coding from genotype to phenotype-genes A gene: a section of the DNA that codes for a particular protein through the mrna intermediary it transcribes Gene expression: When the gene becomes active, its coding sequence is decoded and its message is translated into a particular product

16 What are the differences between transcription and translation in prokaryotes and eukaryotes? FIGURE 4.11 Transcription and translation in prokaryotes and eukaryotes

17 Sources of genetic material in the cell? Nuclear DNA Chloroplast DNA Mitochondrial DNA

18 What is life Two features distinguish life from non-life: replication & metabolism The task of replication falls to DNA and the task of metabolism falls to enzymes The biologists assume that the earliest living organism was molecular in size and DNA-like in character

19 An RNA world If the RNA had the initial ability to replicate and act as an enzyme, then Initial life may have been RNA

20 An RNA world If the RNA had the initial ability to replicate and act as an enzyme, then Initial life may have been RNA A protein world Proteins may represent the initial step to life: RNA molecules are too restricted but proteins are varied. Without the enzymatic action of protein, nothing could replicate & energy would not be processed fast enough to sustain early life Some biologists think that the RNA based life has evolved separately from the protein based life.