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Genetics and evolution > Origin of life! > Flashcards

Origin of life! Flashcards

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1
Q

How old is the universe?

A

13.7BY

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2
Q

What does Jupiter support?

A

Asteroid belt

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3
Q

Where did the earth water come from?

A

Late heavy bombardment - rocks, minerals dissolved (meteorites transfer minerals between planets and comets transfer water and dissolved minerals, as they are made of ice)

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4
Q

Describe the environment of the Hadean Eon

A

Smoggy Toxic environment
Dust/Ash in atmosphere
Anaerobic

Surface mostly acidic water
Violent – 30m+ tides
Sea regularly boils/churns

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5
Q

Approximately how long ago did life originate on earth?

A

3.8BYA

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6
Q

What are the 6 theories for the origin of life?

A

Panspermia
Clay minerals
Volcanoes
Ice
Primordial soup
Deep sea vents

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7
Q

What is the Panspermia hypothesis?

A

Life exists throughout the universe and can be distributed via space dust, meteoroids, asteroids, comets, or even spacecraft

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8
Q

What discovery supports the Panspermia hypothesis? Why is this thought to be wrong?

A

Uracil and nicotinic acid discovered on a non-terrestrial asteroid - however, these compounds could have formed spontaneously.
Additionally this doesn’t explain the origins of life as it would have had to emerged elsewhere.

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9
Q

What is the mineral clay hypothesis?

A

Life may have originated from self-replicating molecular structures on mineral surfaces, particularly clays.
The clays form a mold which can concentrate chemicals for reaction.

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10
Q

Describe the primordial soup theory

A

Key elements reacted with a spark of life from a high energy source such as lightning to form the basic compounds for life such as:
Amino acids
Carbon-based
Nucleic acids

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11
Q

What experiments support the primordial soup theory?

A

Miller-Urey experiments showed that it was possible to spontaneously produce amino acids by applying high energy to concentrated components

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12
Q

What’s wrong with the primordial soup theory?

A

Unlikely to happen spontaneously
Cannot create enough complexity as compounds need to also replicate
Lightning as the energy source could create, but could also destroy-potentially a catalyst should be used instead
The compound locations were likely very dilute due to planet wide ocean- compounds need to be concentrated for reactions to happen

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13
Q

What gradients do you need to drive reactions?

A

Proton gradients
All life is based on redox reactions (of hydrogen and oxygen- making water an essential component of life)

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14
Q

What are black smokers? Describe them.

A

Deep-sea hydrothermal vents found along mid-ocean ridges, where superheated, mineral-rich (including iron pyrites Fe-S), acidic water is expelled at high pressures from the Earth’s crust.

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15
Q

Why might life have originated around hydrothermal vents?

A

They are rich in chemical energy, minerals, and biodiversity, high temperatures provide energy for reactions.

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16
Q

What is the basis of energy production in black smokers?

A

H2S (Hydrogen sulfide) can react with O2 (oxygen) to release energy. However, these vents are oxygen-poor. So H2S might react with Fe to form an acidic environment with iron pyrites as catalysts.

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17
Q

How might life have originated in alkaline hydrothermal vents?

A

The proton gradient between the alkaline vent fluid and the acidic ocean water could drive reactions essential for life, such as the synthesis of organic molecules and the fixation of carbon dioxide

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18
Q

What is LUCA?

A

Last universal common ancestor
A genetic and biochemical community of organisms, rather than a single being or species

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19
Q

What was the very early atmosphere abundant in?

A

Hydrogen which can react with carbon, oxygen and nitrogen to form methane, water and ammonia - key aspects of life

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20
Q

List the 4 geological eons of earth in order - latest to earliest

A

Hadean
Archean
Proterozoic
Paleozoic- begins with the Cambrian

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21
Q

What important events occurred in the hadean eon? Give the approx year

A

Hadean eon = 4.55-3.8 bya
4.55 BYA the earth was formed
4.1-3.8 BYA the late heavy bombardment
3.8 BYA life emerges

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22
Q

List the 4 important events of the archean eon and the approximate year

A

3.8-2.5 bya
3.8 bya life emerges
3.5 bya oxygen producing life emerges
3.2 bya photosythesis
2.5 bya oxygen crisis
ARCH = ARCHAEAN = more sophisticated life than prokaryotes

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23
Q

List the 4 important events of the Proterozoic eon and the approximate eon

A

2.5 bya-0.5bya
2.5 bya oxygen crisis +snowball earth
1.8 bya eukaryotes emerge
1.2 bya chloroplasts emerge
0.5 bya multicellular life emerges
Pro = PROKARYOTES

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24
Q

Why is it predicted that life started 3.8bya?

A

This is the earliest identified carbon deposit in rock, with the earliest fossils identified between 3.5-3.77 bya

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25
What is the most supported theory for the origins of life?
Deep sea alkali vents
26
What was a major limitation of the Miller-Urey experiments?
They were meant to simulate the conditions of the early atmosphere but this was inaccurate. In their 1953 experiment, Miller and Urey used a reducing atmosphere composed mainly of methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water vapor (H₂O). However, later research suggested that the early Earth's atmosphere was composed more of carbon dioxide (CO₂), nitrogen (N₂), and water vapor, with only small amounts of hydrogen. This discrepancy means that the types and amounts of organic molecules produced in their experiment—such as amino acids—might not reflect what actually formed on early Earth
27
What is the significance of acidic oceans on the early earth?
There is a high concentration of hydrogen atoms which are useful for generating proton gradients (used for driving chemical reactions-produces reducing potential)
28
How is an alkali vent formed?
Serpentinization: Movement of tectonic plates causes mantle (which is made up of molten magma) to be exposed. When this comes into contact with sea water, water and minerals are incorporated into the magma in pockets of steam The pockets circulate and come back to the surface and this forms the alkali vent as the steam is released along with minerals.
29
What are natural flow reactors and why are they useful?
Small chambers inside the alkali vent that can concentrate compounds and act like bioreactors. Also provides a fe-s catalyst and heat to increase the rate of reactions. They are alkaline on the inside and the ocean on the outside is acidic so there can be electrochemical gradients set up for releasing energy.
30
How are the characteristics of LUCA predicted?
If there are themes across all the domains of life, it is likely that these were present in LUCA. e.g. presence of membranes, use of ATP for energy, presence of Nucleic Acids for storing genetic information, and basic metabolism.
31
Proteins are needed to transcribe and translate DNA but DNA is needed to encode the proteins in the first place so which came first?
RNA RNA could be used instead of proteins to catalyse reactions and is also replicative and so it is likely that this came first before DNA and proteins.
32
What are the advantages of having DNA over RNA?
It's more stable It can be longer and store more information It is easier to replicate as it has a template strand It is the hereditary molecule of all life
33
What is the evidence for RNA coming before DNA despite the advantages of DNA?
DNA replication is not conserved (bacteria and archaea have different replication enzymes, so these groups must have diverged). DNA can't catalyse reactions like RNA. RNA could form in alkali vents
34
Why can RNA act as a catalyst?
Because it is single stranded, it can fold up on itself and bind to itself and other structures e.g. tRNA can bind to amino acids.
35
What does the first and second base of a codon tell you about the amino acid?
1st base is used to specify the precursor of the amino acid (C-alpha ketoglutarate, A- Oxaloacetate, U- Pyruvate) 2nd base is used to determine whether the amino acid is hydrophobic (U) or hydrophilic (A)
36
How did RNA develop in function over time?
RNA gets spontaneously produced Becomes longer It becomes structural and catalytic Structural elements and proteins start to be added in to form riboproteins Eventually, proteins take over the role of catalysis
37
How might RNA have helped catalyse the creation of peptide bonds between amino acids in hydrothermal vents?
The first base binds the nitrogen of the amino group of the first amino acid to the carboxyl group of the second amino acid. The second base binds to the R group. The third base binds to the carboxyl end and helps form a bond with the amino group of the next amino acid.
38
What are the origins of DNA?
It's easy to derive deoxyribose from ribose (just remove an oxygen) and thymine from uracil (just add a methyl group). RNA can also form double strands like DNA. DNA takes over as the storage molecule.
39
How do you synthesise carbon based compounds from scratch? When would this be needed and in which organisms?
If you use the Krebs cycle backwards you can input ATP (or less complex acetyl thioesters), H+ and CO2 to create carbon compounds. This requires heat and Fe-S. Done in nutrient poor areas Done in bacteria and archaea found in deep sea vents
40
What are the products when you react acetyl thioester with carbon dioxide or a phosphate?
CO2 - makes pyruvic acid which is a precursor for amino acids PO3 - makes acetyl phosphate which is an alternative to ATP (albeit not as good). To make this more sustainable ATP synthase would need to evolve.
41
How do you go from LUCA in a rock bioreactor to a free living structure?
Need to develop a membrane to keep reactions concentrated and become independent. Membranes were unlikely to be lipid but similar. Developed as internal linings in alkali vents and then developed into external coverings.
42
How was oxygen produced on earth before the great oxygenation event?
Photolysis - uses UV light to split water, forming hydrogen and oxygen.
43
Why have Mars and Venus lost their water?
Photolysis used up all of their water. Hydrogen has low density and was lost to space. Oxygen has higher density and reacted with other elements in the air to make CO2 or the crust to make iron oxides (hence why mars is red)
44
Why has earth not lost its oceans to photolysis like Mars and Venus have?
If the rate of oxygen formation is greater than the rate of incorporation of oxygen into the air or crust, then it accumulates in the atmosphere. Oxygen can then can replenish water by reacting back with hydrogen. Photosynthetic life provides this rapid oxygen production which is not present on Mars or Venus.
45
Describe the type of organisms in the Archaean and Proterozoic eons and how this relates to atmospheric composition
In the Archean eon the main form of life was methanogens - shown by drop in CO2 and rise in CH4 levels. In the Proterozoic the CH4 levels dropped and O2 levels rose showing that whilst there were still methanogens, there was also oxygenesis.
46
What is the evidence for the great oxygenation event?
Rock isotope composition Increase in iron oxides (the great rusting event). There is a time lag between oxygen being found in rock and the great oxygenation event because the oxygen is incorporated before it accumulates in the atmosphere.
47
What were the causes of the great oxygenation event?
1. Oxygen producing life forms (as a toxic by-product) 2. Reduction in the activity of the Earth - less reactive compounds were released into the atmosphere to can react with oxygen to remove it. 3. Oxygen from photosynthesis (cyanobacteria-first fossils 2.7 bya and stromatolites 3.5 bya )
48
Why are anoxygenic photosynthetic bacteria purple?
Blue light is very energetic but dangerous (UV). Red light is not very energetic so not very useful for photosynthesis. Both red and blue are reflected making the bacteria appear purple.
49
Why are cyanobacteria green?
They were in competition with the anoxygenic purple photosynthetic bacteria (which evolved first) and so the most light available to use was blue and red. So, they evolved to be able to utilise this.
50
How did the great oxygenation event lead to a mass extinction event?
Oxygen was toxic to the anaerobes
51
How did the great oxygenation event lead to an ice age 'snowball earth'?
Methane levels sharply dropped when it reacted with oxygen to form CO2. CO2 is a less potent greenhouse gas than methane. Less potent greenhouse gases = cooling effect.
52
What is required to fix carbon from CO2 into carbohydrates?
- A reducing power eg. NADPH - Energy e.g. ATP - A catalyst e.g. RuBISCO - A precursor to add CO2 to.
53
what is the likely development of photosystems
Despite having different roles, both photosystems are really similar (both have similar structure, both use pigments to capture light, both allow for protons to move to form a proton gradient). Both photosystems are also highly conserved so it is likely that they evolved early and originated from the same protein (photosystem 1 because photosystem two wasnt needed in purple bacteria which used sulfur as an electron source rather than water)) and then diverged in function, producing photosystem 2, so that water is used to replenish electrons. both photosystems then came together in cyanobacteria for modern photosynthesis (p2 helped p1 to do its job with less useful blue and red light).
54
What are planetessimals?
Little planets
55
What are protoplanets?
Moon-sized planets
56
what pigment is mainly used by photosynthetic bacteria
haem and bacteriochlorophyll
57
why is there variation between chloroplasts and cyanobacteria
selective loss (by mutation and deletion) and selective fusion (by duplication and rearrangement) of genes and structures
58
why did photosynthesis evolve
because in order to become independent from vents you have to set up your own proton gradients to harness energy.
59
why is manganese used in the manganese cluster
can exist in many valency states so it can react easily and absorb high energy electrons to prevent UV damage. manganese crystal structures can also be found in vents.
60
what are semi autonomous organelles
mitochondria and chloroplasts they have their own circular genome, transcription and translation machinery, self-replicating by binary fission, distinct biogenesis, distinct function.
61
where are semiautonomous proteins synthesised
some of their genes moved to the nuclear chromosomes so some protein is translated in the cytoplasm and moved into the organelle. they also have have their own transcription and translation machinery to synthesise proteins from their own genome within the organelle.
62
what is the theory in which semiautonomous may have originally been prokaryotes and which prokaryotes might chloroplasts and mitochondria have been
endosymbiosis theory chloroplasts-cyanobacteria mitochondria- alpha proteobacterium
63
describe the steps of endosymbiosis
1. free living prokaryotic cell is engulfed by a 'eukaryotic cell' 2. the engulfed cell is retained 3. there is compartmentalisation of function 4. there are genes transferred to the nucleus 5. there are systems of protein/metabolite import/export
64
what cam first mitochondria or chloroplasts?
mitochondria because they are present in all eukaryotes whereas chloroplasts are only present in plants and algae
65
what is the shopping bag model
instead of one endosymbiosis event occurring, many events occurred and transferred genes to the nucleus each time until the cell was able to retain the new cell and full endosymbiosis supported.
66
what circumstantial evidence is there for endosymbiosis
-size -double membrane with components similar to prokaryote membranes -circular genome -prokaryotic enzymes and -complexes eg. ribosomes and -tRNA -prokaryotic codons -multiple endosymbioses to form organelles with numerous membranes.
67
what proteins transport proteins synthesised in the cytoplasm into the chloroplast and mitochondria
TOC/TIC in chloroplasts (TOC is also a prokaryote export channel) TOM/TIM in Mitochondria
68
what molecular evidence is there for endosymbiosis
-ox-phos complexes are similar to prokaryotes -photosynthetic mechanisms in cyanobacteria are similar to chloroplasts - nuclear genes affecting organelles are homologous to cyanobacteria and other prokaryotes. -similar division proteins and mechanisms such as FtsZ, MinD, MinE (all used for formation of contractile ring). These are nuclear genes that effect only chloroplasts and are homologous to those found in cyanobacteria-showing gene transfer to nucleus.
69
what other organelles may have come about due to endosymbiosis
golgi, ER, Peroxisomes, Nucleus
70
what is the obligatory endosymbiosis stage in the development of the nucleus
methanogenic bacterium feeds protomitochondrion and vice versa. host feeds itself. then compartmentalisation and gene transfer.
71
what is the proto-eukaryotic stage of endosymbiosis in the development of the nucleus
loss of independence. methanogen bacteria becomes nucleus with most DNA and mitochondrion provides energy (each takes on a distinct metabolic role)
72
what led to multicellular life
colonial organisms becoming more specialised, eg volvox
73
What is the Earths protoplanet companion called?
Thea
74
What did the late heavy bombardment do?
Sterilises Earth Water falls to Earth Meteroites fall Made hydrogen abundant and gave a molteen centre
74
What is a semi-autonomous organelle?
Organelles within eukaryotic cells that possess their own DNA and ribosomes, allowing them to independently replicate and produce some of their own proteins
75
What does the endosymbiosis theory assume mitochondria came from?
a-proteobacteria
76
What does the endosymbiosis theory assume chloroplasts come from?
Cyanobacteria
77
What is the endosymbiosis theory?
It proposes that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells and developed a mutualistic relationship
78
What is the molecular evidence for the endosymbiosis theory?
Similarity of OxPhos and photosynthesis proteins to bacterial proteins Nuclear genes homologous to bacterial genes Plant nuclear FtsZ gene affecting chloroplast division
79
What is the function of the FtsZ gene?
It controls division in chloroplasts (originally bacterial cell division gene), and its knockout prevents chloroplast replication
80
How does endosymbiosis relate to multicellularity?
Colonial organisms like Volvox show intermediate forms of symbiosis leading to cellular specialization and eventually multicellular life
81
What is the oxygen evolving centre?
A manganese-containing cluster in Photosystem II that splits water to release oxygen and provide electrons
82
What was the effect of increasing oxygen on methane?
O₂ reacted with CH₄ (a potent greenhouse gas), producing CO₂ (a weaker greenhouse gas), causing a significant drop in global temperature

Genetics and evolution (16 decks)

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