6. The Origin Of Life And Microbial Evolution

Question 1

Describe the early earth’s atmosphere. 6

Answer 1

1. Methane, co2, ammonia and nitrogen
2. Reducing conditions, no oxygen, the atmosphere was anaerobic
3. For the first 0.5billion years, the earth was 100 degrees+ so no surface water
4. Water condensed to form oceans as Earth cooled
5. Sedimentary rocks formed when particles settled at bottom of ocean and were compressed
6. Water sating comes form the artist sedimentary rocks

Question 2

What do we know about the origin of life? 5

Answer 2

1. Sedimentary rocks, therefore water, are 3860million years old
2. Earliest life forms were microbial
3. Fossils found in rocks 3500million years old
4. Relatively short interval before life began
5. Early life included filamentous bacteria, one fossil is about 3800million years old

Question 3

Describe the abiotic formation of biological molecules in the early earth. 6

Answer 3

1. Biologically important molecules can be formed in reducing atmosphere
2. First biological molecules formed chemically, so were not life
3. High energy input required. Energy came from uv radiation (no ozone) and lightening (residual heat and water condensation). Also, meteorite strikes
4. Molecules formed include sugars, amino acids, nucleotides and fatty acids
5. In the 1950s, muller and clrey reproduced this in lab conditions
6. He used chemical elements present in water and produced these molecules using uv radiation

Question 4

Describe the role of meteor strikes in the early earth. 3

Answer 4

1. Provided energy - lots of them T the time
2. Not obvious now due to oceans, forests and erosion
3. Meteor strikes still very obvious on the moon so we know they happened

Question 5

Describe the formation of macromolecules in the early earth. 6

Answer 5

1. Monomers became polymers through condensation
2. Polymers react by condensation to form more complex molecules
3. Organic molecules splashed into hot, dry surfaces catalysed condensation and polymer formation eg. Amino acids into protenoids
4. Molecules land on montmorillonite clay, which absorbs organic molecules eg rna and catalysts polymerisation
5. Macromolecules washed back into oceans
6. Gradual accumulation, creating the primordial soup

Question 6

Describe the RNA world. 5

Answer 6

1. During prebiotic synthesis period, early rna was created
2. Some rna molecules act like enzymes, like ribozymes
3. Can self replicate but inefficiently, many errors in copies
4. Purely a chemical reaction
5. Rna life may have preceded cellular life

Question 7

Describe early cell formation as life began to develop. 6

Answer 7

1. In water, phospholipids spontaneously arrange themselves into bilayer vesicles
2. Proteins embedded in lipid bilayer and other molecules eg, ribozymes, with self replicating rna trapped in aqueous centre
3. RNA make lots of variations of themselves through mutation, leading to evolution
4. RNA became the template for proteins and proteins became more catalytically specific enzymes
5. Different protein types with different functions
6. Gradual change, as some protein enzymes are at still complexed with rna eg telomerase, an ancient enzyme

Question 8

How did early cells develop into modern cells? 6

Answer 8

1. Change from rna to dna., as dna becomes template and rna becomes intermediate
2. DNA polymerase has greater fidelity than rna polymerase, as it self replicates more efficiently
3. All templates for all proteins drawn together in one place, the dna chromosome
4. Can selectively transcribe what is needed
5. Regulation of protein synthesis begins in response to environment, saves energy
6. Greater efficiency and fidelity of genetic replication allows greater evolutionary fitness

Question 9

Describe the metabolism of primitive cells. 3

Answer 9

1. Energy needed to maintain and replicate the cell
2. Pre-Cyanobacteria, no oxygen so no aerobic respiration
3. Iron sulphide and hydrogen sulphide are abundant and chemically react:
   FeS + H2S -> FeS2 + H2 and, in the presence of water, e-

Question 10

Describe the energy mechanisms of early cells. 6

Answer 10

1. Primitive hydrogenase catalyses production of e- and hydroxyl ions from the equation
   FeS+H2S -> FeS2 + H2 and, in presence of water, e-
2. This removes 2e- from H, which reduce elemental sulphur to hydrogen sulphide, which leaves the cell by diffusion
3. Protons, H+, accumulate outside cell
4. They flow into cell via primitive ATPase and catalyse phosphorylation of ADP to ATP
5. ATP allows reactions to occur - energy
6. Works with only two proteins and lost of substrate, which we know was available

Question 11

Describe the discovery and habitat of thermophilic microbes. 6

Answer 11

1. Isolated in early seventies from hotel volcanic water springs in Yellowstone and other places
2. Not bacteria
3. Initially names archaebacteria (ancient bacteria), now known as archaea.
4. Not just surviving but thriving, 10^6 to 10^7 cells per ml
5. Found in many host habitats eg hydrothermal vents, 2-3 miles down
6. Caused by volcanic gases being pushed through gaps in Ocean floor. Minerals condense, forming chimneys and gaps are found at tectonic plate boundaries

Question 12

What are hydrothermal vents? 6

Answer 12

1. Ecosystem not dependent on sunlight, there isn’t any
2. Harsh conditions, H2S, CO, 250 degrees + heat surrounding area, creating a temperature gradient
3. Archaea as primary producers, they are food source for filter feeders, which are eaten by higher animals
4. Variety of life, microbial, primitive Protozoa and higher life eg crabs
5. Use h2s and fes energ sources
6. Thought to be the closest thing to first life on Earth fur to ribosomal sequencing, as used in the tree of life

Question 13

What is a chronometer and how was it found for the tree of life? 6

Answer 13

1. In 1970s, carl woes wanted to find evolutionary relationships between organisms
2. Chronometer is a universally found molecule that changes over evolution
3. To be used to compare evolution so DNA sequence should change at rate constant to evolutionary distance
4. Chose dna that encodes ribosome
5. Ribosomes are in every living cell, Including viruses
6. Certain parts are totally conserved, other arts tolerate quite a lot of change.

Question 14

How was the tree of life put together? 6

Answer 14

1. Can design primers for conserved region and non conserved region and compare sequences
2. All organisms compared against each other to find evolutionary indices = differences in bases/counted bases
3. Can use this to make a tree
4. Corrected values to account for mutate once and then back again
5. Two organisms with most differences (so greatest evolutionary indice) are least related
6. Only had sequencing and computing ability power by 1990s to do on a grand scale

Question 15

Describe the tree of life. 5

Answer 15

1. The earliest organisms are bacteria and archaea at bottom
2. Korarchaeota are archaea, closest to LUCA
3. Archaea at bottom are all ancient thermophiles
4. Some of the most ancient are found around hydrothermal vents, similar to conditions on ancient earth
5. Presumed LUCA was thermophilic, one theory on how it produced three domains is that LUCA split into bacteria and another group, then the other group split into archaea and eukaryotes

Question 16

Describe the phospholipid layers and other traits in archaea. 5

Answer 16

1. Archaea have a phospholipid monolayer which is more difficult to melt
2. Archaea have one circular chromosome
3. No peptidoglycan or membrane sterols
4. 70s ribosomes
5. Methionine initiates protein synthesis, like eukaryotes. I’m bacteria, this is N-formylmethionine

Question 17

Describe the early earth. 4

Answer 17

1. Formed 4600 million years ago
2. Was initially inhospitable
3. No surface water, all in atmosphere
4. Earth began to cool. Leading to formation of a temperate crust and water condensation