Module 1 - Origin + Energy-Generating Systems Flashcards

1
Q

What are the three main types of evidence for the earliest life on Earth?

A

So-called microfossils in ancient rocks
Stable isotope analysis of carbon
Fossilised stromatolites

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2
Q

Name the two scientists who first proposed the Primordial Soup hypothesis

A

Haldane and Oparin

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3
Q

What three main factors made the early atmosphere inhospitable to life?

A

High temperatures (over 100C)
Lack of liquid water
High levels of UV radiation

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4
Q

What is a key criticism of the Urey-Miller experiment?

A

The gases used did not accurately mimic the gases in the early atmosphere

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5
Q

Why are hydrothermal vents now considered a plausible location for the first formation of life? (3 Reasons)

A

There is an abundance of consistent chemical energy sources
These environments were protected from the (likely) very hostile conditions on the surface
The potential for mineral compartmentalisation in these structures

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6
Q

Three reasons why RNA is preferred over DNA as the hypothetical initial replicating polymer?

A

RNA is single-stranded and more able to fold
RNAs are known to self-replicate
RNAs can have inherent enzymatic activity

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7
Q

Name the 5 main “Steps/Stages” of the development of the RNA World

A
  1. Pre-biotic synthesis of RNA and proteins
  2. RNAs able to self-replicate
  3. Lipid-bound vesicles form, containing RNAs (cellular life)
  4. Proteins take over some catalytic functions
  5. (More stable) DNA evolves as the coding polymer from RNA
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8
Q

Name the four gases mainly present in the early atmosphere, the one key missing gas and whether the conditions were reducing or oxidising

A

Methane, CO2, Ammonia, Nitrogen; NO OXYGEN; reducing conditions

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9
Q

Describe the most likely metabolism mechanism of the first cells

A

A primitive membrane-bound hydrogenase enzyme spans the cell membrane;
Hydrogen acts as an electron donor, Elemental Sulphur as an electron acceptor;
A proton gradient is produced to drive ATP Synthesis via a primitive ATPase

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10
Q

When did the first eukaryotic cells probably appear?

A

Approx 1.5-2 bya

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11
Q

How are alignments used in modern phylogenetics?

A

Alignments are hypotheses as to how sequences have diverged over time (since a last common ancestor);
An algorithm can minimise mismatches by adding gaps - the more gaps required the more distantly related

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12
Q

Are the actual evolutionary distances generally greater or smaller than those calculated from alignment

A

GREATER (i.e. more distant)

The corrected distance must take into account REVERSIONS and MULTIPLE MUTATIONS AT THE SAME SITE

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13
Q

Name the four factors that make a gene/sequence useful for phylogenetics

A
  1. Gene present in all organisms of interest
  2. Not laterally transferred
  3. An appropriate level of sequence conservation/divergence
  4. Large enough to contain a record of the historical information
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14
Q

Which gene is generally the most useful for phylogenetics and why?

A

16s rRNA:
1. it contains both VERY CONSERVED and VERY DIVERSE regions (conserved regions make alignment easier, diverse regions allow closely related species to be distinguished)
2. It is part of the core translation machinery - so it has been conserved in ALL BACTERIAL SPECIES with a preserved function

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15
Q

What did Carl Woese propose based on RNA sequencing?

A

That there may be a third domain of life besides prokaryotes and eukaryotes (ARCHAEA)

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16
Q

Name and define the two types of chemotrophs

A

Chemoorganotrophs - use organic chemicals e.g. glucose as an energy source

Chemolithotrophs - use inorganic chemicals e.g., hydrogen, Fe2+ etc

17
Q

Why (chemically speaking) is anaerobic respiration less efficient than aerobic respiration?

A

Oxygen is at the bottom of the “electron tower,” so it is most efficient to use oxygen as the final electron acceptor

18
Q

Name some other chemicals which can act as alternative electron acceptors instead of oxygen

A

Nitrogen and sulphur, carbon dioxide, iron compounds

19
Q

How do fermentation and respiration fundamentally differ in their mechanisms of ATP synthesis?

A

Fermentation: SUBSTRATE LEVEL PHOSPHORYLATION (ATP directly synthesised from energy-rich intermediate)

Respiration: OXIDATIVE PHOSPHORYLATION (ATP produced from proton motive force, via electron transport)

20
Q

Describe how redox balance is involved in fermentation

A

Electrons must be removed onto NAD+ to form NADH (reduced form)

21
Q

What happens in fermentation to allow NAD+ to be recycled (if no electron acceptor is present)

A

The electrons are used to reduce organic compounds to fermentation products (e.g., alcohols/acids) which are excreted from the cell

22
Q

Name the 5 bacterial phyla containing photosynthetic species

A

Chlorobi (Green sulfur), Chloroflexi, Cyanobacteria, Proteobacteria, Firmicutes

23
Q

What is the difference between oxygenic and anoxygenic phototrophs?

A

Oxygenic: reducing power comes from water (resulting in O2 production)
Anoxygenic: reducing power comes from a variety of chemicals (e.g., H2S)

Therefore not all photosynthesis produces oxygen!

24
Q

Name 3 specific “things(?)” that are thought to have been essential to the formation of the first living cells

A

Montmorillite clay; liposomes; Self-Replicating RNAs

25
Q

Name 2 conditions in the early atmosphere which may have been essential for the formation of life, and why?

A

UV radiation; Lightning Strikes
(they have been shown to catalyse condensation reactions when in reducing conditions -> may have led to formation of first organic compounds)